Eye Optics & Vision | Talah Namour | HNS 242

Assalamu allayikum everyone. Uh I am Talmur and I'm going to give you the eye today. Um we're going to discuss basically the anatomy of the eye and uh cover the physiology lectures. Uh the physiology lectures are a bit challenging even for me but inshallah we're going to go over them together and make it as easy as possible. So let's start. First of all, our eyes are the organs that we see with. Okay. And they Are located into in these two um sockets or the the the sockets that are found in our skull. TMA. Uh these

sockets are made up of a bunch of bones. As you can guys see, we have like so many different colors which are basically different bones. Um and these sockets are placed in a way where they kind of look like a pyramid. You can see that. So basically we have this is basically where the eyes are and then we have like a like a roof a floor medial And a lateral wall and they all basically converge into an apex tam. Um and they are kind of slanted in a way that is subhan allah perfect just for

our vision tam. So this is basically the uh different bones that make up our um like eye socket. Okay. So we have the frontal, we have the sppheninoid, we have the ethmoid, um zygomatic, magillary, palatine and lacrium. So all of these bones come Together to give us our orbit. Um and these basically are then divided into a superior wall, medial, the floor and then the lateral. And we can kind of see what makes up each wall. So basically for the superior wall, the frontal bone and the sppheninoid are the two bones that ma mainly make

up the superior wall. And why is that important? Because if we have any fracture in these bones, then you're probably more susceptible to brain Injury cuz we know uh above our frontal bone we have the frontal lobe of our brain. Right? So this is just like clinical um importance for these walls or for these like bones specifically. And then we have the zygomatic, the palletine and the magillary. They come all together to form the floor of the orbit. And any damage to the floor would cause the eye and basically all of the contents of the

eye, the socket to herniate or fall down into our magilary Sinus. Cuz right in here we have the magillary sinus which is basically pretty sure you guys covered that sinuses are just like airfield spaces in our bones. So the eye would herniate and go down or the contents of the eyeball uh and the socket would just go down there. And then we have the medial wall which is made up of the ethmoid and the lacrimal bone. And then we have the lateral which is made up of the Sppheninoid and the zygomatic. Last but not least

we have the apex which is basically done by the optic canal. And in the optic canal what goes out there is basically the optic nerve tam. So that's about it for the uh what is it called? the bones that make up the like orbit and then we're going to go talk about what do we have inside this orbit. So inside the orbit we have multiple structures like the extraocular muscles that help uh help move our eyes. We have The nerves that enervate the eyes the muscle and everything that is in there. All right. Uh we

have blood vessels that will provide blood. we have um orbital fat because if you think of it the eye is a very squishy um organ. It can be easily damaged and the bone is just hard. So we would need something to cushion and take away the the the hardness of the bone and that's usually done by the orbital fat and all above that we have the Eyelids that you guys have. So basically the eyelids are the outermost um like let's say part of the orbit that kind of like covers everything that's just behind. We're going

to talk more about the extraocular muscles. So I'm not going to talk about them here. But for the nerves we have multiple nerves in here. It's just literally um so they're all they all have to do with the eye. Optic is for vision and then we have the oculo motor uh which Basically helps in the movement of the extraocular muscles. We have the tlear which which does the same. We have the triinal which has nothing to do directly with the movement of the eye but it it passes through there and I think it has to

do with the um parasympathetic and sympathetic innervation. I'm not sure though. And we have the abusent. All right. Um then for the blood vessels we have the artery and the vein. So the athalmic artery is there to supply uh The eye and all the structures and the muscles and then we have the superior and inferior athalmic veins just to drain drain it out. All right. Perfect. Now there's a very important um basically openings in the like Okay. So, as you guys can see here, wait, let me see if I can. Okay, so I want to

draw one second. Okay, so can you see this area right here? So, this is basically a fissure in the bone. So, it's like a space that allows for the Entry and the exit of uh very essential nerves and like other structures. All right. So we have the superior fissure and then we have the inferior and then we have basically the optic canal. Okay, which is kind of easy but yeah and the optic canal from the name it only has basically the optic um what is it called? The optic nerve to mom. So again we have

the optic canal that has basically the optic nerve and the Opthalmic artery. That's important. So optic canal has optic nerve and opthalmic artery. And then and it's just really easy to to to like kind of find. It's just literally a small circle into the bone. Then we have the superior orbital fissure and inferior orbital fissure. And from what you can see right here, oh I can just draw from here. Never mind. Okay. So superior orbital fissure is all of this. All right. And it has all of these structures. So it Has the lacrimal nerve. It

has the frontal nerve. It has the nasociliary nerve and abducent. It has what else? The inferior division of the ocular motor nerve. So we have basically lacriml. Um nasocillary. So it kind of and if you guys think of it, it kind of like works. So nasocillary has to do with the nose. Lacrimmal has to do with basically the lacermal duct or the like the tears. So they're all structures that are right Here. So lacriml, nasocillary and then the frontal cuz we basically have the frontal bone right here. So it would have the frontal nerve, right?

Um abducent nerve because it has to do with the movement of the eye and we have the tlear which also has to do with the movement of the eye and then the inferior division of the ocular motor. So basically all of the nerves that have to do with extraocular eye movement. So uh inferior uh what is it called? Inferior division of ocular motor tlear abduent and then we have just the nasocillary lacermal and that's it and the frontal cuz and the frontal like we have the frontal bone right here so all of these are found

in the superior orbital fissure all right and um apart from the uh from the nerves we have one vein which is the superior opthalmic vein and it's kind of easy because superior fissure will have the superior opthalmic vein okay so again what do we Have in the superior orbital fissure the lacriml, the nasocillary, tlear, abdu and oculo motor, frontal and then we have the superior opthalamic vein. Come on. And then moving on to the inferior orbital fissure. Inferior orbital fissure right here is going to have the zygomatic nerve. It's going to have the infraorbital nerve

and it's going to have the inferior opthalmic vein. So everything that's kind of down. So we know that basically Um so we said we have the frontal bone here. So we have the frontal nerve. What what what bone do we have in here? We have the zygomatic. So we're going to have the zygomatic nerve. All right. So zygomatic nerve uh inferior opthalmic vein because it's the inferior fissure and infraorbital uh nerve and it's just the orbit and it's kind of inferior. So infraorbital nerve. Okay. I'm just trying to kind of do um association. So you

could memorize them. Okay, these Contents are really important for um your OSP. They're really important for um any injuries that they might like the questions. They might be like, "Oh, the superior orbital fisher like yell, what are the contents?" I'm pretty sure you're going to get like an asky question about this cuz I remember we had such an asky question. All right, perfect. So these are um everything in here. So we have a pneummonic for the nerves that pass Through the superior orbital fissure. And basically the pneummonic is live frankly to see absolutely no insult.

So live is for lacriml. Remember raal frankly is for frontal cuz lacriml is for the eye the tears. Frontal is up. So frontal. And then we have to c absolutely. So t is for um tlear. S is for basically a division of the ocular motor. A is for abducence. So those three are for the movement of extraocular muscles. And then we have no For the nasocillary and insult is for the inferior division of the ocular motor nerve. So basically we have both divisions in here and the other one we did not but ocular motor nerve

superior and inferior is going to be there. Is this clear? I think it's clear. So this is just like a fast summary that I did from SHBT uh that can kind of just come on just revise everything for you. So optic canal optic nerve and opthalmic artery. So pbital fissure the lift frankly to see no um what is it called no insult. So again lacrim uh frontal tlear uh superior division of ocular motor abducent and then nosilary and inferior uh division. All right. Um, you can just like you can just memorize it as ocular motor

superior and inferior in my opinion. I don't know why they're just saying that but whatever. Then we have the inferior orbital fissure that has basically the zygomatic branch of Maxillary nerve or the zygomatic nerve. Okay. And it has the infraorbital vessels. Okay. Um, nasol lacrimal canal drains the whatever these are not important. All right. Now we talked about the walls and we said the walls are important. Why? Because we have different kinds of orbital fractures right? So for the different types of orbital fractures right here um we have something called orbital rim fracture and the

rim is anything around the edges Of the orbit. All right. So this is basically an orbital rim fracture. It can happen either here. Usually it happens in the sutures or the outer edges of the bony orbit. Um that's why it's called the rum. Okay. And then we have something called a blowout fracture. And for a blowout fracture from the name blow out, so something's going to go out of its own place. So we're going to have things herniating from the orbit into basically nearby Structures. So, as we mentioned earlier, if the floor of the orbit

was uh damaged, we're going to have the contents herniating down into the um maxillary sinus. If they go basically up, they might go to the ethmoidal or the frontal depending on the place of the uh fracture. And now any exactly any any like wherever it goes it could bleed as well to any basically blood fractures they affect the med wall causing them to go To the maxillary as we just mentioned that complications. So basically uh when we have these fractures what what happen can basically we can have herniation like we can see here. So the

floor is gone everything is going all the way down into the magillary sinus. Okay. Or basically um we can have because of let's say um so because of the edema and the inflammation we can have exothalamus because the intra the incre the intraocular pressure is just going to Increase and this is going to cause the basically the eye to protrude and you can guys see this clearly in here and I'm pretty sure you took exoplamus before and ender repro uh thyroid disease we have exothalamus if there is any injury Y to the eye. It might

cause exoplan to mom. It's just basically protrusion of the eye. Now the opthalmic artery honestly I'm just going to go over this really quickly. Just know it's a branch of the Internal kurateed. It goes through the optic canal as we mentioned earlier and then it goes into um what is it called? It goes all the way around the optic nerve. Okay. Um and then uh what does it do? It basically supplies blood to the orbital content. So it's just the only artery there. Um and it has multiple branches and I'm not sure how what are

they expecting from you. Uh best I think you Have to know the different branches. Okay. Tam this is everything about artery. Nothing much to say. Inferior epalmic vein. Come on. I drain the orbital contents. It pass through the superior orbital fissure. We mentioned that before. What does it do? It drains into the civerous sinus. And the cavernous sinus is really important. Why is the cvernous sinus important? Because the civerous sinus is close to the brain. So if you have any infection There, it can cause really really serious uh complications. Um those are not important in

my opinion. Moving on into the extraocular muscles. Okay. Elevator palpibbrous superiors. Okay. Or LPS. Now the levator palp superioras you can literally see it right here. Um so basically what does it do from its position? You could tell that it Literally elevates the eyelid leo. Okay. So it elevated upward. What is it interervated by? It's elevated by the ocular motor nerve. So you have to keep in mind if we have oculum motor pulsy what's going to happen the elevation of the eyelid is gone. That's why we would have tossis. So basically the eyelid would be

kind of down. Come on. Superior tarsel muscle is kind of it's like a smooth muscle component. All right in here and basically it helps in the Elevation of the eyelid as you could see. And it's innervated by the sympathetic nervous system. Okay. And why is that important? That's a very very very important uh uh like uh detail. Okay. Um, sympathetic nervous system when it's dysfunctional like in her syndrome, we have a damage to the sympathetic trunk. What happens is we're going to have partialtosis. And why do we have this partial protosis? It's Because of the

um damage to the sympathetic nervous system that supplies the superior tarsel plate. Tim, is this clear? Yes. Okay. Okay. Now, uh let's go into the rest of the extracular muscles. So, how many extracular muscles do we have? We have six. Come on. And I like this image cuz it kind of gives everything. It gives you the different Okay, wait. Let me just remove this. Um, okay. So it Gives you the different muscles. So we have superior oblique. Oh my god, what did I do? Okay, can you see my screen? Wait, can you see my screen?

Yeah. Okay. Okay. Okay, perfect. All right. So basically, okay, so these are this is like an amazing photo cuz I uh because basically Um it has all of the different muscles, the six extracular muscles. It shows you how we can clinically test them and the muscle actions. So we have basically superior rectus, we have medial rectus, lateral and inferior and then we have a superior oblique and an inferior oblique. Okay. And basically the the function is just yeah you could think of it by yourself. So basically superior oblique if we contract it it what what

will it do? Sorry not the oblique sorry The superior rectus this straight one. So if I retract it up or contract it what happens is basically we're going to have elevation right cuz it's just elevating it so easy. So uh inferior rectus opposite so it's going to depress it um superior rectus elevate inferior rectus uh depress and then we have medial okay this is not medial this is lateral that's medial medial and then lateral Okay so because the nose is right here so medial is going to cause so when you contract it it's it will

cause the eye to look into to the nose. So this is basically adduction. So you're adducting it. So the eye is being adducted towards the nose. And then the lateral rectus is going to do the opposite thing which is basically abduction. So look the superior rectus elevate inferior rectus depress. And then left or later sorry not left lateral rectus is going to Cause abduction. and the medial rectus is going to cause adduction. Okay, is this clear? I think it's clear. And then we're going to have the superior oblique and the uh basically inferior oblique. So

basically oblique is going to take it in the other way. So look at the wait, let me just erase everything so it's clear. So let's look at the superior oblique. Now what will the superior oblique do? So the superior oblique is Attached right here. So if it pulls, it's kind of going to cause the eye to kind of depress but look down. Do you get what I mean? So basically superior oblique is going to cause the eye to look downwards like this. Cuz when you push to that way, the eye is going to so it's

like a bowl like a like a ball. Okay? And then when you push it like this, so let's say the pupil is here, it's going to look down. So it's kind of um it's called in Into because basically you're going to look into the basically um how can I say it into origin like the eye is going to look down and into the nose. Okay? Cuz this is the superior oblique. You're pulling it like this. It's going to look down to uh inferior oblique is going to do the opposite. So basically the inferior oblique is

attached right here. And if you pull it like this, the eye is going to look up like this. So it's going to Look extortion. So it's going to look to the side and up. So again, inferior oblique extortion, superior oblique in torsion. How do we clinically test this? Or like if you want to know if basically a nerve is affected, how do we test this with the etch? So what you do is uh you sit I think you guys took this in pro. You sit across the patient same level and you ask the patient to

follow your finger and you do an ach and you look at their Eye movement. So yeah, you look from up down like if if everything is working fine. So basically if we go up what are we testing elevation so we're testing superior superior rectus right and if we ask them to look like on that side look so basically this so kind of we have it how do I say okay it's kind of exorted up so this is the inferior oblique and then when we go down so it's like an we go down this is the

superior rectus. Uh, sorry, superior oblique. Why? Cuz you're looking in the nose. So, let me let me just show you something just so I don't I think I confused you a little bit. Let me show you. Basically, this is your nose. Okay. When we're doing the when we go up, so I'm going up. What's happening is the eye is looking up and towards the nose. This is extortion. So, this right here. So I'm looking like here. This is extortion. So this is my inferior oblique. So the obliques are usually the opposite. So Inferior oblique, we're

looking up towards the nose. Superior oblique, we're looking down towards the nose. Okay? So this is in this is extorion and this is in like in out in out. All right. And then the sub after I do this, we're gonna go basically to to this the nose side the the side of the nose. So this is a duction. This is the medial rectus. And then we're going to complete and go all the way to the Other side. So this is my arch. And then I'm going to go all the way to the other side. This

side in here I'm checking the lateral rectus. Then I go up just up and down like normally. So superior rectus and inferior rectus. Come on. clear other than the movements what's important is basically annervation you can memorize two that are important and then the rest you would know they're all by oculum motor so uh basically we all know I think the S4 L6 so SO4 LR6 so SO4 means so is by the tcular nerve or the nerve number four and LR6 is basically lateral rectus and it's basically number six. So basically we have the superior

oblique number four tam this is stlear and then the lateral rectus this is number six. Um so now that we have the superior oblique and lateral rectus gone everything else is by the ocular motor which is number three. Tama is that Clear? So just just literally memorize S uh SO4 LR6 that's basically how I know it. So SO4 superior oblique tlear uh LR6 lateral rectus um abusent okay and then ocul motor is everything else. So if we have the tlear nerve if the tlear nerve is basically injured how would the patient present? So the patient

would present with So how would the patient present? Let me show you. Um let's see. I think of it together. So what would Happen is this is basically wait nerve SO4. So this is the superior oblique. Okay. Wait, never mind. This is the superior oblique. All right. So what happens is this is no longer functioning. So it's not going to contract. So what happens? Everything else is going to overpower it. So the inferior oblique is going to overpower it. So what would happen? So the tlear nerve usually what does it help doing? It happen it

helps in insion. So it Helps us basically look down and if so basically down and in. All right. So if the tlear nerve is gone what will happen? The patient will present with an eye that's up and out. So basically it's looking up and like kind of out. Come on. This is basically the inferior oblique is not going to be overpowered. Um nothing is going to balance it out. So it's just going to take the full power and it will cause the eye to go um basically in sorry up and out. Come on. This is

for tular nerve uh policy. Abducent. Basically abducent what do we what does it do? It basically causes abduction by the lateral rectus. So how do we abduct? Basically abduction is just our eye moving away from the nose. So looking to the side. So what happens is since we can't look to the side, the eye the medial rectus is gone. Sorry, the lateral rectus is gone. So the medial rectus is going to be the stronger part that's going to take over And it's going to cause the eye to be adducted. So basically the eye is going

to be somewhere here. Oculum motor any other thing is going to cause oculum motor. So this is basically the poly. So what we're going to have we're going to have a dipopia which is basically double vision lateral squint. You can see the lateral squint right here. It's kind of the lateral rectus is overpowered. So it's kind of like taking It to the side. Why? Because lateral rectus is supplied by um I can't see. Wait, let me uh lateral rectus is supplied by can I say inferior is up and out and is down and then yes

you can say that sorry I just saw your question okay so basically um the ocul motor nerve oh sorry yeah so if we have ocular motor nerve lesion we're going to have the eye we have a lateral squint and dipopia why lateral Rectus is unopposed and it's acting and it's kind of pushing it to the side. Come on. We're going to havetosis. Why? Because of LPS that we mentioned earlier. We're going to have pupil dilation and light reflex loss because basically the constrictor pupil inside the eye is um innervated by ocular motor. And that's it

for ocular motor. And these are the very obvious signs. you can't move the eye upward downward like like superior rectus is gone Inferior rectus is gone um medial rectus is gone you get me so yeah but these are the things that are so obvious it's going to be the the thetosis because of the LPS the lateral squint the dopia and all of these things moving on to troial nerve tlear nerve just what we said we just talked about it so basically Usually the tlear nerve allows us to look down and in. So what happens? It's

going to look basically it's going to look up and out. So it's Looking better. Come on. Um I don't care about these. Now abducent is going to cause a media squint. Why? Because we said in an abduent what happens is that the medial rectus overpowers it. So it's going to to kind of uh so the lateral rectus is gone. So, it's going the medial rectus is going to be the stronger person in here. It's going to push it into the nose. The moment we're going to have this medial squint. Uh, is everything Clear up until

now? So, what is this? So, basically, it's a bit hard, but it's kind of So, okay, let's look. So basically the eye lateral rectus overpowering. Okay. So lateral rectus overpowering. What is that? So which nerve? Three, four or six? Three. Perfect. Yes, it's ocular motor policy. Now what about this? So it's basically we have a media squint. So the medial practice is overpowering. Six has gone bad. Perfect. The decent. Okay. Everything is okay up until now. I think. Yeah. Okay. Perfect. Let's complete now. We're going to talk about basically the eye itself. So let's look

at the eye. You can see this is our beautiful eye. We have eyelids. We have eyelashes. We have basically the limbbus or like this is The area around our lens. Um we have the pupil, the iris, the scara. So what is the scara? The scara is basically the white area right here. And you can see that it has a little bit of blood vessels like into it, right? And then we have the medial and the lateral canthus which is basically these openings right here. Um basically allowed for the movement of the tears. So again here

we have one is the scara which is the white thing. Two is the cornea, three is the Iris and four is the pupil. So there is a lot of like misconception the pupils are basically I don't know if it's like wide but and I always thought you know the pupil is the colored part but actually the iris is the colored part and the pupil is just the black part. Okay. And the cornea is basically the the bulging out of the so basically if you look at someone's eye like closely you could see basically a very

clear area that's going Up and that's the cornea. So our eyelids what are the eyelids made up from? So the eyelids basically have the skin subcutaneous um ignore the loss subcutaneous connective tissue voluntary muscle teracial layer and the conductiva. So basically this is the skin and then underneath it we have basically the subcutaneous connective tissue. Then we have voluntary muscles. What are the voluntary muscles in our eyelids? Basically the ones we talked the veter uh the LPS the veter palpoius um we have the torso facial layer the torso facial layer is somewhere in here and

then we have our conjunctiva right um so this is come on a more um so this is basically more like anatomy of the eyelid so we have the skin right here and then we're going to have the I'm sorry wait one Okay. So, basically we're going to have the skin right here and then beneath the Skin we're going to have the orbiculus orbicularis oculi muscle. So, this is another um voluntary muscle. We're going to have the superior toarsel plate. we're going to have sebaceous glands and um below the sebaceous glands eventually we're going to have

the conjunctiva. All right. So these are the orbicularis oculi. Orbicularis oculi are basically the u levator p is supplied by sympathetic right? No levator p uh is supplied by oculo motor but the superior Toarsel um superior toel we talked about it. Wait one second. Let me show you. So the superior, okay, look in here. The superior toarsel plate, okay, or the superior toarsel muscle is the one that's supplied by the sympathetic nervous system. And it's kind of part of the levator paler superiors. But elevator is mainly inervated by ocul motor. Okay, is this clear? Okay,

Perfect. Um, let's go back. Okay, so the arvicularis oculi is basically the one that's around our eye and it closes the eyelids. All right. And it's enervated by the facial nerve. So if we have facial nerve pulsy, what happens? The eyes stay open. Okay? If we have ocul motor pulsy, our eyes are going the eyelids going to go down. We're going to have ptosis. Okay. Is this clear? But the tarso facial layer uh Tarso facial layer basically they're ligaments. They anchor the eyelids. They separate the layers um and they kind of give some strength to

the eyelids. So we have basically the superior tarsus. We have the inferior tarsus and these are connected by the palpibbral ligament. We have a lateral and a medial palpibbral ligament. So they kind of are just there to uh strengthen our eyelid. They're there to uh anchor the eyelid and separate the different layers because we Have multiple layers. All right. And basically where we have the glands in the tarsoicial layer. Um so these glands are called either the tarscel glands or the miobian mibomian mi it's such a hard word mioian glands tama. So these mibomian glands

basically they're embedded into the tarsel um tarso facial layer and if we have an inflammation in the edge of these and these meomian glands they're there just to kind of Lubricate the eye to help in the secretion of tears. um they're just glands that help in like lubrication of the eye inflammation in the edge of the eyelid and inflammation in these glands where this is called a sty. Okay. But if we have a blockage, all right, if we have a blockage of muscle in a bigger gland like the lacriml gland or basically something that's rather

embedded inside the eyelid itself, this Is what we call a calaz calazion or a cyst tma um and it will look something like that. So you see the sty is a bit at the edge. Okay. And it's just inflammation. But blockage is called calazion which basically orazio I don't know but like Dr. Silhou has it in a very very specific way. I'm trying to like which is basically it's a cyst because there's blockage. It's called a cyst. Okay. So aai is just an Inflammation. Calazion or I don't know how to chilazone. Uh it's just a

cyst and it's just a blockage. Okay. So inflammation sty blockage chilazioin or calazioin and a cyst. Okay. Perfect. Now we have the conjunctiva which is the most inner layer of the eyelids. Okay. So again we we went through all of them. We went through the skin. We went through the um subcutaneous fat or like the soft connective tissue. Then we went through The uh muscles which is the orbiculus oculi and the LPS the one that's the four um and then we had the okay the tosso facial ligament and um what is it called the mibomian

glands and now we have the conjunctiva. Now the conjunctiva it covers this clara which is this white area. it attaches uh to the scara cornea junction. So basically analiscla cornea that's where the conductiva is and uh basically um it Kind of like folds upon each other that's why we kind of have superior and inferior furnaces uh foresies and we can see them like wait let me show you here okay so right here you can see how it kind of closes upon itself. So we have this is the palpibbral conductiva and this is the the blue

one is basically the bulber conductiva and they kind of like you see how like they kind of close upon each other and because they close upon each other we have a Superior forex and an inferior forex them and it kind of just protects the eye. So basically if we have any object that goes into here it can either end up in here and that's when you kind of feel like itchy and like you kind of like you know um try to remove it. So it end up it's end up probably either in the superior and

then for next um we have three different layers. We have the ocular, we have the forial and we have the peltebral. So Basically the ocular is just the one that's the bulber or like the one on the cornea. Okay. And then we have the palpibbral which is basically the one that is on the sides and the forial is just the fornices. Okay. So as we can see here palpibbral is the one that's like basically right let me just erase cuz it's too hectag. Okay so the palpibbral is just the one that's like kind of underneath

the eyelid. And then we have the bulber or the corneal or the Ocular which is the one that's on the corneal. And then the forial is just the foreseees that is formed because again it's like holding upon each other. Clear. I think it is clear. Um okay. H we're going to talk about the lacrimal apparatus. So the lacrimal apparatus is basically the thing that causes the tears. Um it's made up of lacrimmal glands, ducts, caniculi, sack, nasol lacrimal duct. We have anterior and supra orbital. Uh So prolateral orbit. So we like wait let me show

you right here. So in here we have the okay let's look at this. This is the lacrimal sac sack as like a bag. So lacrimal sack and then it gives out the canal canaliculi. So basically canaliculi are very tiny um basically tubes that will open up into the eye. Uh, and this is the puncta where basically you could see the puncta in your like if you look take your eyelid like down you could see like two white Openings and these are the puncta. Um, and then this sack is going to go down into a nasal

lacer duct. Okay. Um, I don't care about this. Um, this is basically the lacriml duck. This is the um lock. Wait, let me just double check something. So, sorry. This is a better image. I kind of like this more. Yeah. So, this is the lacrimal gland. It's the one that's like created Stuff. And this is the lacrimal sack, the the caliculi, the dacrimal duct, and so on. Alo, I think it's clear. So, uh this is the enervation. So, what is it invated by? It's enervated by the lacrimal branch of the opthalmic nerve and It's duct

obviously it's going to be lacriml branch of what opthalmic why is it the opthalmic nerve nerve is the one that's the closest in here like it's close to the eye sothalmic nerve okay so opthalmic nerve Is the nerve eye okay so it it will give off lacriml or lacrimmation the parasympathetic comes from the facial nerve and that's why if we have facial nerve pulsy what would happen. We're going uh to not be able to secrete a tear. We're not be we're not going to be able to um have tear formation or sympathetic is by post

gangalionic from the superior cervical gangalion. Guys, this is just memorization tier drainage uh pathway. So basically you see this puncta that I was talking about like if you open your eyes you can literally see them. uh they will go into the canaliculi into the neglocal sack and that then they will go through the duct into the inferior miatus in the nasal cavity and that's why when we cry we sniffle a lot basically they're going to go from the puncta okay so basically lacriml gland okay wait let me show you make it more clear we have

the lacrial glandal gland Will cause the tears to form these tears are going to go through the lacrimal ducts and now multip So they're going to go find the punctum. Okay. From the puncture they're going to go into the canaliculi into the sack. From the sack they're going to go all the way down into the nasol lacrimal duct and it's called nasol lacriml. So feed nasal. So it will go into the inferior miatus and that's why we sniffle a Lot. Hello. Babies. Sometimes they have issues with their nasol lacrimal duct. No. they can have nasolacrimal

duct obstruction and this is called dacro stenosis. Okay. Um dacro stenosis can be really bad or they need to usually get like they need to like kind of open it up using so basically what they do is they kind of go through the puncture and through the thing with a probe and try to like just ease their way into it. high in kids but adults they usually do A surgery where they kind of like create a whole new opening for the basically drainage tama. Uh dacrocyitis is basically the inflammation of the lacrimal gland because cyitis

is just an inflammation. Dacro is everything that has to do with the lacriml. Cyitis is just the cyst itself inflamed and you can see it right here. So basically this is lacriml duct or lacriml cyst inflamed. So I think everything is clear up until now. What do you guys think? Any questions? It's clear. Moving on. Let's move on. Um, okay. Now we're going to talk. Yeah, sure. What's your question? I have a question. Does the lacrimal part of the opthalmic join the parasympathetic part of the lacrimmation thing? Yeah, that's the question. Does it join with

V1? It does. It's part of V1. Yeah, I mean method from like the facial nerve. Does it join with V1 to have you and you start tearing up? There was something in the lectures it goes or joins it. Like honestly, I have no idea. I haven't that idea. I'm not going to tell you something. I can look up into it and like answer you later. But um I'm not sure. Oh, it's just too complicated. Also, no. Yeah. like like just and for me like if I am like in your place and I'm studying for it

I would literally study and know lacriml duct lacriml branch I mean nerve that's the general you know like the very general because I don't think they would it's too detailed yeah it's detailed and like I would for nerves and like pathways and all of these things I would I think they would go into other like other more important nerves you know like facial nerve malan Or they love the different branch the facial nerve. Got you. Thank you. Do you do you hear like a lot of sounds behind me or is it okay? No, that's okay.

It's okay. Um, okay. Now, we're going to talk about the eyeball itself. Okay. We've been talking about everything around the eye. We talking about the eye socket. Now, we're going to talk about the eyeball itself. So, I don't know why The images are not clear. It's kind of pissing me off, but it's okay. we can deal with that. So first of all the very first layer is basically this clear layer right here and it's called the cornea. So from the cornea we in we're going in cornea then we have the interior chamber and you can

see it in here. So basically the interior chamber is what kind of gives us the like the the curve of the eye. So basically if You look at your friend's eye you could see that it's curved. This is basically the cornea and the interior chamber. Lent chamber basically has a humor the mom and this aus humor is basically as we said another thing that kind of like bulges out bulges it out it's um it provides all of these structures like you know the nutrients it needs and so on and then we have this is the

antior chamber bad interior chamber we have this and this this is the iris and then We have our pupil right here um and then at the back we have the posterior chamber chamber the mom and then we have the lens. So again cornea um interior chamber we have the iris pupil posterior chamber and the lens behind the lens we have the vrus chamber. Okay. And this virtuous chamber right here, it's basically just a chamber that has a lot of virtuous humor, which is basically what literally makes the shape of our Eyeball. We have a lot

of other things like the cellular bodies, the um what is it called? The retina, the choroid, the scara. But we're going to talk about all of these. Don't worry. Hello. I'm pretty sure Dr. talks about this cuz na in fifth year she made us like summarize all of these things and like just literally um what is it called not summarize u repeat after her. So basically the cornea it has five layers what are the five layers Epithelium bowman layer stroma the membrane and then the endthelium. Okay um this was not in the lecture by the

way this was in the physiology lecture but I included it right here because I'm pretty sure Dr. Salwa loves this. Okay. Um, next. So, this is basically what I've just mentioned. Interior chamber, it's between the cornea and the iris. Posterior chamber is between the iris and the lens. Uh, the pupil is the Central opening. Acuous humor, it's um basically the acuous humor starts so it's produced in the posterior chamber, but then it goes all the way into the interior chamber. Tam um so basically let's go through here. So in here we have basically the cellular

body and the cellar body is what basically secretes this uh acuous humor. It starts from here and then it goes all the way into the interior chamber. Come on. Uh why is it important? It's important because we Have the cornea is avascular. What does avascular mean? It has no supply from blood like blood vessels. So it's avascular and um that's why it kind of needs nourishment and it needs a lot of like you know everything that would keep it vital. A lens it sits between the interior and posterior segments. It's transparent by convex. It's a

disc blah blah blah. It's attached to celary muscles and why are the cer muscles Important? sorry, celary muscles because basically later on we're going to talk about accommodation which allows us to look at things in nearby and away. Okay. It plays with the shape of the lens. Um yeah, exactly accommodation. Then we have the vetrus chamber and the vetrus humor. So basically it's the very like the thug at the at the back of the eye and it's basically all made up of like um a liquid which is basically the just humor which is kind of

gelatinous like It's like a gelatin um and as I mentioned it helps maintain the eye shape. So that's what gives us our eyeball shape. Now we mentioned the cornea and we mentioned the lens. So basically in the uh sorry yeah we mentioned the lens and we mentioned the uh basically the anterior chamber posterior chamber and everything. So is a opacities in the lens or basically we have let's say calcification or any problem in the lens It would show up as this guy having a cataract. Okay. Um and in here to cataract has many different reasons

and diabetes can cause cataracts like you know like so many different things can cause cataracts but all you have to know is that if we have opacities in the lens it is a cataract. Uh next is basically uh we talked about the acus humor right we said acus humor is made in the posterior chamber it goes into the interior chamber disruption Production or in the reabsorption because basically what happens acus humor is going to be like produced by it's going to be produced by all of these different um bodies they're going to produce all of

that best what happens is and is a problem in either production over production problem in reabsorption. So basically let's say there's a clogged um because basically we have like a whole Uh way of like drainage. If this drainage was blocked, what happens is and know uh we're going to have something called gluccom. And a gluccom is just basically um the eye is basically the acuous humor is just like piling up, piling up, piling up and it's causing the eye to become really hard and it's really painful. We have to open angle close angle and I'm

pretty sure you guys went over this in the clinical uh this is Nothing for me to say. the layers of the eye. Um, come on, let's look together. So, what we're we're saying about the layers of the eye, we finished basically listen everything that's out like from the outside. Now, from let's say kind of from the back or from the inside. What we have is we have an outer fibrous layer which is basically the scara. It goes all the way from in from yani backward all the way into the Front. And that's the basically the

white area that you see. And then we have the cornea. We talked about that. And after the scara we have the koid or the vascular layer. Now the koid from the name it has basically the choid plexus. It has all of the vascular like everything that provides the blood. It's it's basically continuous with the silary body and we said body what does it do? It releases the acuous humor. And then we have retina. Now the Retina is the basically neural layer. It is the place where we have all of the different kinds of cells that

helps us see blah blah blah. We're going to talk about all of this. Body again, we said it's basically zonular fibers. They attached to the lens. They form the suspensary ligament which hold the lens in the place. Okay. Um, okay. Wait. This is the celary muscle. Okay. Okay. Wait. This is celery muscle. So, The muscle, okay, is basically the one that's attached to the lens. They cause the lens either to come like that and to kind of con constrict or relax. So it's either going to become more round or it's going to become like this.

And this is for accommodation. We're going to talk about it later. Physiology. Um wait body is the thing that releases the accuracy humor. But let me check Something. Um we we can talk about this later. Okay, iris. It's basically this is the iris. Now, the iris is made up of some circular muscles and radial muscles. The circular muscles and the radial muscles are the things that would cause the pupil either to constrict or contract. Sorry, constrict or dilate. Contract or dilate. Constrict or dilate. Circular muscles. Okay, if you Look at it, circular are going to

cause basically the mus the the pupil to constrict. and a circular are. So basically this is the pupil. Okay. Now the circular are kind of like just making it smaller. Okay. So when they contract they're just going to make it smaller while radial. Okay. If you see the radial muscles they're right here. They kind of push pupil which kind of dilates the pupil. So circular constricts radial dilates. One is basically um what is it called? One of them. So the circular muscles circular muscles which cause constriction is enervated by the parasympathetic because basically the parasympathetic

your feed and what is it called? Rest and feed and rest something rest and something. It's basically for resting and you're not it's not fight or flight. Okay. So because you're resting, you don't need a lot of light to go into your your eyes to kind of see what's going on. So it's just like you chilling. So the eyelid is basically uh sorry, the pupil is basically constricted. The iris works to construct the pupil and the works for accommodation. Yep. So basically iris is there. So the iris has the circular and the radial muscles which

are the ones that would either Constrict or um they would constrict or uh dilate the pupil. Hello celary muscles they're attached to the lens. Now the lens is there for accommodation. So the lens is the thing that would accommodate and know can I see well can I see like a closed object or a far object properly while iris which is surrounding the pupil it has basically circular and radial muscles. Is that clear? Clear. Perfect. So okay so what is it called? Let me see. Okay. Um, okay. So, so we were saying and know circular muscles

they constrict. Why? Cuz basically rest and feed or whatever. I forgot there was something called rest and see it was like something best berated muscles they do the opposite. They dilate. It's in flight or fight. It's sympathetic. So basically, if I'm running away from a bear, from a bear, I Have to like like literally see everything properly. So I need the most amount of light to go into my eyes so I can see everything. Rest and digest. Okay, thank you so much. Cuz my brain was like, what was the other word? Anyways, so yeah, for

parasympathetic rest and digest, sympathetic um what is it called? Uh flight or fight. So in flight or fight, what would happen? Dilation. So dilation rad if you look at the way they look you could see it Literally circular they when they con when they contract they're going to cause the pupil to constrict but rad when they contract because they're like straight lines they're going to pull the pupil. I hope it's clear and I hope the people are not noisy around. Anyways now we're going to go to the retina. Okay. So, retina retina is the neural

layer. By neural layer, I mean basically have all of the rods, the cones, um all of the Cells and then we have basically the choid bada, but then we have the scara. This is just like the vision and everything. Basically at the end we're going to have basically the optic nerve. So basically everything is going to go merge all together into the optic nerve and it will go leave and basically in here the point where basically optic nerve is going to leave it's called the optic disc and the blind spot. Basically the spot where we

see Nothing or blind spot retina is the innermost layer of the eye. Mentioned that uh retinal layers outer pigmented layer. Okay. And we have the inner neural layer. So basically this is important because now when we talk about the vision it it's something that we have to keep in mind. So we have an outer pigmented layer. And why is it important? So we have in here is the outer pigmented layer that's attached to the chorid. So we said Inclin so this pigmented layer is attached to the chorid and then the inner neural layer basically has

a photo receptors. pigmented layer is important because when light hits the retina, okay, so we have bunch of lights hitting the retina, we need something to like kind of absorb extra light. So, y when you look at the light, okay, we have millions and billions of rays going inside. So, they're going to hit the photo receptors, but at the same time, They're going to hit everywhere else. So we need something that's going to absorb the extra absorb all of the extra light and kind of focus important light into the photo receptors. So this is why

we have a pigmented layer and then the optic disc as we said it's the area where we exit the optic nerve. So optic nerve this is the optic and the central retinal artery branches are literally originally there and I'm pretty sure in the clinical You've seen a bunch of photos of the optic disc or a bunch of photos of central retinal artery with a kind of hemorrhage how would it look like blah blah blah then we have uh the optic disc is called the blind spot why is it called the blind spot because basically we

literally have no photo receptors there we see nothing there it's just literally basically the place where the optic nerve leaves. Um then we have the macula it's just I don't know it's Basically the central depression where we have the phobia. The phobia is really important because it's the area where we have the maximum quality of the f photo. Why? Because it's the place where we have the most cones. We're going to talk about this later on. So it's the thinnest region of the retina and has highest visual acity and sensitivity. Hello. This is just a

revision of the different layers of the eye. So this is The fibrous or the scara and then it becomes the cornea in here. Then we have the koid mcelary body um what is it called? Iris and then we have last but not least. Now to the horrible part of all of this which is the physiology. Anatomy is easy. Anatomy is super easy and I'm pretty sure Dr. and repeated it like a bunch of times. We're going to go into physiology, which is literally physics. Like I'm like revising these things. I'm like, this is physics. Um,

wait, what's the after pigmented layer absorbs extra light to concentrate the light path? Yep. Is this a question or are you like reminding me? Um, question. Yeah. So, basically outer pigmented layer, what does it do? it kind of uh like a a bunch of light rays. So we have the the like basically okay imagine these are the cones and the rods and This is the u basically the the pigmented area. So the light is going to hit everywhere everywhere ever every ever. So any excess is going to be absorbed by the pigmented area which basically

has melanin which is like the dark the dark color which is going to just like literally absorb the extra will other ones whatever is absorbed whatever hits the cones and the rods are going to be like kind of um like processed by the cones and the Rods clear. Perfect. Now we're going to talk about vision. Do you want to take a prayer break? Yeah, if you guys want to take a prayer break, I don't mind like five minutes. Okay, perfect. Yeah, let's take a 5 minute prayer break. Um, one second. Let me pause the recording.

Okay, so now we're going to discuss vision. Come on. So, what is vision? Basically, it's our ability to see. And you might think, I know it's just simple. You look at something and you see it. But Subhan Allah, the way we see things is crazy. Now, first of all, uh we human beings cannot see everything. Uh the ability by everything I mean like we cannot detect all kinds of wavelengths or all kinds of lights. So, we can Literally the visible light is everything we see from here. like it's literally from the magenta into the like

like orange. I don't know what color is that but you know like this is everything this is the only spectrum that we can see mom um and basically we we this is this is these are basically the wavelengths that we can detect best the visual perception is different basically it's basically what we can interret from everything we're saying to Mom and we have different kinds of visions we have phototopic vision which is basically the daytime vision we have color vision which is basically the normal color vision Scottopic vision which is basically night vision. We have

misopic vision which is twilight vision. Uh ashi is basically phototopic and scotopic. Scottopic is at night. Phototopic is daytime. Color vision usually comes with daytime. Nighttime you don't have any color and you when You when you're at night and you're trying to like go through your room you literally see everything is like shades of black. So mom um in here it's kind of the same thing. We measure light in or the light intensity of what or whatever we can see in logarithmic scale. Okay. Because basically um like okay we can't detect a lot of light

but basically it sensitivity is really really really like High um and that's why we kind of like see it through logarithmic scale. Um something that's really important the zero in here that doesn't mean we cannot see anything or basically it's complete u uh complete darkness. No, but it's rather just very like minimal light. Okay. You go moon gazing or like stargazing. It's just literally like you barely can see anything. You just literally see dots in the sky. Um and Then again skotopic is basically very low light or night vision. So basically it's powered by rods.

Star rods are the um stars in scottopic vision and uh usually it enables near darkness or night mod like vision again we said another's no color phtopic vision is basically uh done by cones and they allow daytime and uh color um color vision and it allows basically a lot of detail and we can see that all of these Things in well lit environments and stomach misopic as we mentioned it's basically a blend of both. Um it's we said it's twilight so basically it's when there is a bit of light but it's dark you get me

like in dawn or at dusk or in dim lighting. Um so that's it. And if you can see in here so this is basically the the spectrum. So phototopic is usually cones. Uh scotopic is rods and this is dark and this is light. And now if we Look at the sun we're going to have retinal damage because this is just because the retina is over stimulated. We have the intensity is so so so high that basically it can cause retinal damage. Now visual adaptation to light. Basically, you know how when you go from a room

that is poorly lit into a room that is like well lit. So, we're going to have kind of a change in between the cells that are like dominant in action. So, let's look in here. Here it's the opposite. If you go from a room of highlight into a room with low light, what happens is at the beginning the cones are more sensitive. the phones are like over over like working and they're like trying to help in like um you know stimulating the image that we see and then once we go into a room that's really

dark there's going to be kind of a a shift from the cones to the rods and then the rods are going to take over. So Yeah and this is what we call dark adaptation and light adaptation. Now dark adaptation um we're going to talk about what happens exactly in dark adaptation. In dark adaptation the mom where again we have the uh rods are more predominant. Basically the retina is going to increase the sensitivity of the rods by specific things. First of all our pupils are going to dilate. So our pupils dilate to allow like so

basically When you're in dark or like a low low dim wait low lit or a dim lighted room what happens is you barely have any rays of light. So the pupils are going to dilate so it can allow anything to go in like literally anything like like any ray of light any like like photon just to like go in and so we can see it. So that's what happens. First of all, this the pupil is going to dilate. Second of all, we're going to have synaptic changes in the retinal neurons. We're Going to talk about

these later on like not very later on like in a bit. We're going to talk about these. So, we're going to have synaptic changes and we're going to have redopsin regeneration. So, what is rodopsin? Redopsin is uh basically a pigment. Come on. This pigment is uh important in this pigment is important in night vision. So redopsin is basically opsson plus retina. Okay. So we have like kind of in our in our retina we have like two Things called retinyl and opsin. So retinyl and opsin when they bind together and this happens usually when it's dark

we're going to have redopsin. So adoptsin is going to regenerate and this is going to cause basically um improved night vision. Mom, so we have three things for dark adaptation. Pupil dilation, neuronal, retinal neuronic changes and then redoption regeneration. Mom, I think it's pretty clear personally talking. Uh, and then okay. And then this is basically uh what is it called? Uh this is basically a graph that shows the distribution of the cones and the rods in the retina. So we talked uh like a bit ago about the retina and then how it has the photo

receptor which is basically the rods and the cones. Now the abundance of cones is the greatest wear at the phobia. Remember how we said like literally 5 minutes ago the phobia Has is the place or it's kind of like a place literally a dip. Okay. And this dip we have the highest concentration of cones and this is where we have the highest visual acuity and it causes the clearest image to be produced. So if you look at the distribution this is the cones they're the highest at the phobia. Come on. Uh and the rods they're

basically higher at the periphery. So basically the rods are like kind of everywhere around but They're found all over but they are kind of just scattered all over but the cones are concentrated in the phobia. And this kind of explains why um in the darkam you don't really when you you kind of see objects clearly when you're not looking at it. And I think you can like just literally turn off the lights and try to like look at an object and you can I think you can see everything around more clearly than the object Itself.

And it takes time to kind of like you know see the object clearly and this is subhan Allah. Um yeah and this is just again showing you the phobia. So the phobia is just like a dip in the retina and this dip is just like really really concentrated with cones uh which are the ones that are like supposed to give us the color vision the the daylight well lit area. This is what we usually see the mom and you can see it's kind of a dip and it allows the light to Directly go to the

cone. And you can see how we have gangalian cells in here and everything, but in here in the fia specifically, it's just a dip that allows the light directly to go into the cones. Hello. Now, this is the where things get really spicy. Um, honestly, this part is crazy. Like, I know for me, like it took me some time to kind of remember all of these things. Uh, I don't I didn't even study all of this for step one. like I had to like do a Lot of refreshing. Let's talk about this. Okay, so this

is the retina. This is the different layers of the retina. You can see the pigment epithelium. Remember how earlier we said you know we have pigmented epithelium and then we have the basically photo receptors going out of it. So the pigmented epithelium has basically melanosomes. These melanosomes as we mentioned earlier what do they do? they kind of absorb all of the let's say The the excess rays the the the scattered rays just to kind of focus the light into the cones and the rods. Uh we have so here's the photo receptors and then we have

basically basically I'm not sure if you have to know the layers but I remember Dr. cared about them. I'm not sure if I don't know I didn't go through your clinical to know 100% what you should know and what you what you shouldn't know but for me what I care about is you Understand rods and cones they're in the photo receptor outer segment the mom then we have in the plexififor layer we have the bipolar cells basically um connecting with the cone okay and the horizontal cell the mom so we have a horizontal cell attaching

to most of them the horizontal cell you can think have heard like a a finetuner. It kind of like fine-tunes everything. A lot of things are going to happen. Horizontal cell is just there to Fine-tune everything later on. Um and then we have basically in the inner nuclear layer. So anything okay anything that has nuclear layer has cell bodies. So you see what's after nuclear layer has the cell bodies of the cones and the rods. Inner nuclear layer has the cell bodies of the bipolar cell. And then we have the plexopform. inner plexopform. It's basically

when the place where the bipolar is like kind of uh synapsing with the uh ganglen Cells and then we have the ganglion cell layer. I forot we can we can memorize them together now. So again pigment epithelium and then we have the photo receptor segment. I don't care outer or inner photo receptor segment and then we have the outer nuclear layer. Why is it the outer? Because we have an inner nuclear layer. So outer nuclear layer first outer plexififor layer. So the nucleus the area where they signapse and then we have the inner nuclear layer

and Then the inner plexififor layer where basically and then the gang layer it's easy to memorize. I don't know if you have to memorize it but I kind of like do you get the way I'm trying to make you memorize it or am I confusing you? Okay, perfect. But then very fun thing all the gangalian cells they're going to join together. All of the nerves from the gang they're going to join together form A bundle of nerve which is basically the optic nerve. Okay. So let's go layer by layer and understand how do we see

things. Come on. First of all we're going to go to the rods and cone. Higher rods and cone. So these are the rods and cones. We have again they are on the pigmented layer. This pigmented layer they absorb the stray light and they kind of reduce the reflection. They kind of just optimize the light to reach the rods and the and Then we have something um okay then we have something that's really important here. Basically how do rods and cones understand light or the process is called transduction. transduction can sound scary. Um, but it's easy.

What you have to understand the the fundamental thing to understand in here is that basically um it's funny the the cells themselves the rods and the cones they are always deolarized when there is no Light when we have no light nothing no stimuli basically we're talking about photo receptors what is basically the stimulus the stimulus has to be photons or they're light. So we don't have any stimulus. We don't have light. The cells are depolarized. And why are they deolarized? Because remember the retinol and the opsin that we talked about? We have retinol. We have

opsin. So they're binded together. So when they bind together, what do they do? They kind of Cause the cell to release glutamate. So the cgmp is going to be really high. Sodium channels. So cgmp levels are really high. sodium channels are open. Um the cell is depolarized and glutamate is literally being fired like fired fired fired fired. This is in case of no light. So think of it like that no light glutamate is high the cell is depolarized. Once the light shine into so once we bring a light and we shine it into here what

happens is this retinyl And opson they're going to break up. So the retina is going to move the optin is going to move. Retina is going to change its shape. Well, this is going to cause the glutamate or like the cgmp to like drop. So cgmp gone. CGMP is gone. Sodium channels will close. Sodium channels are closing. The cell is hyperpolarized. Cell is hyperpolarized. This means there's no glutamate being Released. Hello. This is the transduction. This is the basics of transduction. Hello. What I want you to understand is no. Basically in in rods, okay, in

rods, okay, uh when basically in rods, let's talk about the cones. cones. When light is shine on the cone, that's when it's going to kind of activate the bipolar cell. So, light is shined on it. CGMP is Low. CGMP is low. Sodium channels are closed. The cell is hyperpolarized. Glutamate decreases. That's when it's going to activate the bipolar cell. So, that's when it's going to cause kind of a graded potential. That's when that's when it's going to cause something. This is when the stimulus happens. Is this idea clear? Great. Perfect. Okay. This is like the

basis of everything. So, we have three cones. We have not Specifically three. Yeah. Three cones. We have the red, the green, and the blue. These are basically they're wavelength anorizers. So basically the blue color is literally just a wavelength. The red is a wavelength. The the the blue is a the green is a wavelength and then basically um different pigments pigments is just basically I don't know like different wavelengths coming all together you know like Light wavelength but like it's such an interesting thing to to think of you know and basically any white light we

see is basically all these three colors together. Any black color we see is none of these colors I think or something like that or uh none of them stimulated. Yeah, I think something like this. Okay. Uh basically is different in these cones Cuz basically we have three different options and these the three different options each are like kind of um related to a color you know like the red has let's say let's call it red opsson the green has a green option the blue has blue that's not the actual name but see you get me

but this is how like miss and the cones kind of detect the color this is not really important you just have to know on the three cones They're wavelength analyzers and that's how they detect the con the colors. So are we okay up until now? Is it clear? So basically when when does the the cell kind of send a stimulus when it's depolarized will hyperpolarized? Hyperpolarized. Perfect. When it's hyperpolarized. Hyperpolarized means it's not secretting a lot of glutamate means the cgmp is Low. It means that basically um what is it called? The sodium channels are

closed. Perfect. Hello. Let's go to the next step. So these are basically the cones. Hello. There's there is light. What happens is they're hyperpolarized. Less glutamate. So less glutamate we have bipolar cells. Bipolar cells. So basically from the word bipolar bipolar the the cells is bipolar. So we have basically something Called an on center and an off center. No like decreased amount of glutamate the on center is going to fire. So on center is going to be depolarized. So less glutamate means the on center of the bipolar cell is going to be activated. It's going

to be depolarized and it's going to send a graded presumption. Hello. Is this clear? So in bipolar it's kind of the opposite. When the cell is Depolarized it's going to send a stimulus. And how is it? How is it like depolarized? Why basically my confict glutamate? Was this clear? It's opposite for both. What do you mean for both? Like bipolar. The other one the other cell. H you mean with the the rod? Yep. Yes. If the rod is hyperpolarized, it sends. If by if bipolar cell is depolarized, it sends. Yeah. Okay. Okay. So, basically we're

doing the one. So, what is it called? Wait, sorry. Less glutamate. The bipolar cell is depolarized. It secretes basically it causes greatest potential secretes whatever chemical. So, we finished photo receptors. We finished bipolar cells. Now we're going to go to the gangalian cells because we said you know it's three Levels gangalian cells we have basically this is a gangalian cell we have something called on center off surround off center on surround it's like it's like a circle literally the circle is in here so you see basically the on center off surround so basically is a

muscle it's on and it punch so if this the light comes into the center this means you know the the light is on so it increases firing off center and if the light is on The surrounding it will decrease the firing. So on center of surround think of it like that if the light is on the center it increases if the light is off oh sorry is on the surrounding it decreases it's on when it's on center so on and on increases on and off decreases do you get what I mean and a light I

put it on the center and basically where where am I the wait let me I kind of confused you Guys, wait. So, basically I'm talking about This scenario number one. Hello. We have an uncenter of surrounding cell and I have an a light. Wait, sorry. I have light. Light on. Yep. When on center. Light on center. Only center. Come on. So if the light is on the center and it's an on center, so basically what will happen? The firing is going to increase. Yep. If the light is on surrounding and it's off as surrounding, it

will decrease. You Know what I'm trying to say is know light is on center or or surrounding light on. Okay, light is on and we have basically on center off surrounding. So think of it like that. If the light is on the center, it's going to increase but is a light on off surround. Y is a light is on the surrounding but surrounding says off so it's going to decrease. Y is on and on increase on and off decrease. Do you get what I'm trying to say? Okay, let me let me elaborate. So, wait. I

have I have a question. Method. Yanni. Are we talking about K? There's one part that's an on. Well, there's another part that's an off. If the light on the on part, it increases. But the light light is on the off part, it decreases the stimulus. Yeah. It's two it's two places exactly functions. Let me show you. Yeah. Let me draw the circle and try to to explain. So I'm trying to say as and know I need like a Wait, what did I do? Do you still see me? Yeah, you're good. You're good. Okay, let's add

an empty paper to explain it. Let's present. Come on. So what I'm trying to say is we have a a cell called on center. Okay. This is and then off surround Light. Okay. So if the light comes onto the center. Okay. So on center it's called on center. So the stimulus is going to increase. Hello. Yes. If this light goes to the surrounding without touching the center or the surrounding is off. So basically we're going to have an un the surrounding but the surrounding is off. So what will it do? Ah felt I got it.

I understand This. It's clear. Okay. Is it clear? It is clear. I guess this is the thing. Two types. So another one is called off center on surround. So it's just the opposite. So basically light on center only. So this is an on center cell. So if the light is on the center only then it will fire rapidly. But if the light is on the off center it's going to decrease the firing. Do you get me? Okay. A light on surround. Okay. So is a a light is on the surround only and it's not touching.

So basically on off it won't fire. But if the light wait light on okay and it's off surrounding wait there's something uh stupid in here. Never mind image. There's something wrong. It's there. It's there. Exactly. Basically, do you see my camera or no? Okay. So, basically we have two cells is on and the light goes into it then it will increase. But as a light does not go into the middle and goes to the surrounding it's going to decrease firing. The light goes a little bit on the center and then a little bit on the

surrounding. Come on. This is going to cause basically weak firing is center and the surrounding stimulated at the same time. The response is going to be weak because you Have to have it centered on one area. You get me? Why is this important? Because the gangalian cells are the cells that are going to kind of detect the contrast and the edges. You get me? So it's the thing that's going to kind of give us finalizing the contrast with edges of the of the photos and everything. You get me? Or whatever we see. And basically what

gangalian cells command do they kind of change graded potentials Into action potentials. Hello. So now we had graded potentials. Now we have action potentials. So y let's go through what's happening. Let's go again through whatever happened. So first of all light is shined into the cone. What will happen? The cone is going to be hyperpolarized. Why? Because the retinyl and the opsin they left each other. CGMP levels dropped. Sodium channels closed. And because sodium channels closed it's hyperpolarized. So the glutamate Decreased. Glutamate decre decreased what would happen bipolar cell the unbipolar cell is going to

be activated okay bipolar cell that's on it's going to kind of fire more and more into the gangalian cell and then the gangalian cell if it if it mine drops onto the on let's say it's on center okay and off surrounding and the light goes into the on center then the the firing is going to decrease and vice versa. You get me? By then all of these are going to become eventually an action potential that goes through the optic nerve. Is that clear? For rods what happen is kind of the opposite. Okay. So a lot

of glutamate what happens is the off is going to be activated. And because the off is going to be activated, everything will change. You get me? So in I have a question. Yes. We were talking mechanism previously was About the cones. Yeah. The same thing applies to the rods and know basically when when we have more glutamate. Okay. Basically they get depolarized when they when it's dark. So the rods will get depolarized when it's dark. So when it's dark, we're going to have more glutamate. Glutamate is going to uh act on the off center bipolar

cell. So it's going to kind of like change the pathway into the Off center. So we go into the off center. Okay. Off center. Off center on surround. Okay. Off center. So light is not in the in the basically center. So it will decrease the firing contrast contrast in like dim light is really really low. Do you get me? So in hypothetically speaking on center off surround is for the cones and off center on surround is for the rods. It's clear. Yeah. Okay. H we have two gangalian cells. Kaman. So we have magnosellular cells which

are basically large and they're specifically for motion. So M and M motion location and depth parvocellular cells they're smaller in size and they're there to kind of see the fine any fine details the process color the shape you know for texture is like really teeny tiny things. So magnellular the big ones are there for motion for location for depth and so on. cellular Is there just for the fine details the color the shape you get me just know that let's revise all of this so basically this is how it starts so the light goes into

the center let's say it's depolized so the glutamate decreases so the bipolar cell muscle is not is activated it will increase the firing on the uncenter. You get me? Increased firing to the optic nerve. So we see edges properly. The contrast Is better and so on. So mom is it clear? So this is basically it. It's clear. Okay. Next. Um let's go on. So in the visual pathway basically this is basically what we this is literally what we said photo receptors which is the bipolar cell into the gangalian cell and then they're going to go

to the optic nerve optic kayazm optic tract and then they're going to go to the phalamus into the LG End which is basically lateral geniculate nucleus in the lateral geniculate nucleus this is the place where perception happens in a way so what happens is everything that we got is going to come into the lateral general nucleus lateral geniculate nucleus the it's kind of a relay station us the phalamus I'm pretty sure you guys remember from neuro is the is a relay station to every kind of thing like Um emotions for movement for um I don't

know sensory everything to mom so what happens is and know everything is going to relay there so the parvisellar and the magnosellular pathways are all going to relay there and everything from the retin to the cortex everything is going to go there. So all of the information that we have about everything that we're trying to see will end up relaying in the lateral geniculate nucleus in the Phalamus and then what happens is basically this is this is everything that comes from the eye but a lot of things that are in the brain will come and

relay there. Okay. So what happens is it's kind of really wild but what we see is 10 to 20% of basically stimulus into the retina and 80 to 90% basically our brain trying to rationalize what we're saying. So basically I'm looking at this water bottle okay 10 to 20% is just the Different colors and everything from my eye and the rest the rest of the image is just my brain saying oh this is a water bottle so it probably looks like this. You get me? But this kind of modulation and trying to create uh photo

all of these signals that will do that all relay in the lateral geniculate body things from the the cortico spinal cortico pontine cortico bulber fibers this water bottle the way it feels the Way it everything you know how do I reach to it all of these signals every signal related to the thing will relayulate uh nucleus. Is everything clear up until now? I think it is and then after this. Okay. Where did I go? Sorry. Um do you see my screen? Everything is okay. It's fine. Just wait. I can see the screen or I can

see you. Why can I not see both? Maybe it's from your side. Yeah, it is. Um Oh, wait. Never mind. It works, I think. Yay. Okay. We finished from the phalamus. We're going to go to the actual brain. Where will it go? It will go to the We have basically two places. We have the vententral stream and the dorsal stream. Both of them are in the occipital lobe. Okay. Sorry. No, I don't mean that. But No, wait. We have basically sorry vententral stream and dorsal stream vententral with dorsal they're going to start they were they'll

go from okay the phalamus to the occipital and then they're going to end in different areas. Okay. So you see this is the uh what is it called? This is the uh lateral geniculate nucleus and the phalamus. It will go will relay into the occipital lobe and then it's going to go Through pathways. V1, V2, V3. I don't I don't think you guys have to know the V things but just know where will it end up. Okay, ventral stream basically it's called what pathway or it's basically the object recognition system. So it kind of tells

you what you're looking at. So I'm looking at a water bottle. So my basically the vententral stream is kind of telling me tala you're looking at a water bottle. So how does that help? It's it's basically this pathway Specifically is there to kind of recognize the shape to identify the thing to store muscle and this this visual memory. So later on when I look at the same bottle I'll remember oh it's this bottle you know for this is the vententral pathway or the what pathway or it's basically object recognition system. This pathway ends up in

the inferior temporal lo. That's what you need to know. I don't think you need to know V1, V2, V4 graduated. It doesn't matter. Okay, just know and know ventral vententral pathway. It's the what pathway. It helps us like kind of understand the object. What object are we looking at? And it's it relays in the inferior temporal lobe. It helps in recognizing a shape object. It's identifying things and basically storing the memory for later on. And then we have the dorsal stream. A dorsal stream is basically the where. So it's basically the motion and action. So

Where is this object? Where is it going? Um so basically the bottle is beside me. So how do I know the bottle is beside me? Through the dorsal stream. The where. So um the wear or the dorsal stream it's for motion detection. It's for knowing where the things are and for guiding the eye movements and hand movements. So basically because I know the bottle is on my side. If I want to take the bottle I know how to go. You get me? It's just Like something it's like because you know our brain is just like

multiple circuits all working together. Um what else? And it ends in the parietital loop. Come up. So the what is in the what is in the uh temporal lobe. That's the the where is in the dorsome. Okay. I think that's all you need to know for these. Um I'll just tell you what I understood And what I think is important because this is crazy. We have in the visual cortex we have different kinds of cells. We have something called simple cell. A simple cell is basically a cell that detects a straight line. Okay. So a

straight line a straight array of of light. So I can see this this light. This is my simple cell acting. And then we have something called complex cell. So complex cell is able to see a straight line moving. So if the line is Moving, okay, a straight line is moving uh that's what a complex cell would see. So a simple cell is just going to detect the light. A complex cell is going to detect the light the the the line with the motion. Hello. And then we have the hyper complex cell which which is going

to detect the line its edge and its motion. So it's just like they build it up. Simple. I'm just going to see a line. Complex, I'm gonna see a line in Movement. Hyper complex, I'm going to see it in like kind of a 3D and I'll see the edges and I'll see the motion and I'll see the line. You get me? But these cells are there in the visual cortex and they help us kind of create the the the like the full image. How do they do that? I don't think you guys need to know

cuz that's crazy. Is that clear? Okay, moving on to the last part of this which is basically the optics. This is a This is the easy part. I felt like it's really easy. So, refraction. Refraction is just something we took in physics. Okay, it's basically a light. When I put this, okay, this pencil in this water looks like it's broken or it's bending. Why? Because basically the speed the speed of light in air is different than the speed of light in water. But it's going to cause this image to look distorted and that's what we

call refraction. Why does it why Does refraction happen? Because we have something called refractive index. What is the refractive index? It's basically the bending of light as it changes mediums. Hello. Basic physics. Literally physics. So basically we used to take and we used to like graph these I don't know if you remember but we had to like have like like a normal line and then if basically the thing is going from lighter to denser it's going to bend towards the Line but if it's going from denser to lighter it's going away from the line these

things are physics I don't think you really need to know this uh this is basically the visible spectrum of light for us we're talking about this Again, not important for now. Types of lenses. This is important cuz if someone wears glasses, you have to know understand the types of lenses. Uh because different lenses um address different problems. So spherical lenses And we have cylindrical lenses. Spherical lenses are the most common lenses and these are the lenses that are uh commonly used in glasses. We have two different kinds. We have convex and concave. Now convex is

converging lenses. So basically what it does is it tries to get all the light together to converge into one point. Come on. And basically these lights these uh this is the convex and then we have a concave Lens. Okay, which is kind of uh it causes basically the the light to go like they're together and they she kind of wants them to disperse away. So diverging lines. So they they curve inward and then they spread apart. Come on. Convex and concave is used to kind of focus the light into a point. Okay. Either into or

outside the basically we're we're going to talk about this more in details. But the idea is we're trying to focus the light to Kind of address myopia and uh what is it called? What was the other one? nearsightedness and farsightedness. I forgot the other one, but we're going to talk about it. Okay, hyperopia. Hyperopia. Okay, so we're going to So, one of them is used for myopia and the other is used for hyperopia. Okay, we're going to talk about these more details in the next slides. And then we have something called cylindrical slides. Now, these

are not as y commonly used as The spherical uh but they are important for aigmatism. Okay. A stigmatism is basically people that see, you know, when sometimes you look at the light and then it looks blurry like blurry and stuff. Um, this is a stigmatism. Okay. Um, okay. Now, exactly. So, what do they do? They kind of focus the light. So, basically, we have a lot of lights and they focused into one line. So this is what a stigmatism the main problem is and we Have multiple lines on different axises. So this cylindrical lens is

going to kind of converge them all into one line so you can see properly and this is how what will fix the blurriness and make the whole image clear. So that's all you need to know. And the two types of lenses we have spherical cylindrical I don't know why I can't say that word spherical and a concave and convex. One of them is used to for myopia and the other is used for Hyperopia or cylindrical is used for aigmatism. We're going to talk about this command. Moving on. So shyen um this is a wait this

is a concave I think. Yeah. Yeah. So this is basically converging lens and this is a diverging lens. Converging it's kind of converging all of the lights into one point. Hello diverging is kind of like dispersing the lights all over. Um and there's something that's really important that We used to take in physics and it's even important for us in our like this vision. It's basically the focal length. Now the focal length is basically from the lens up until the point where all the lights are converging and that's usually where the image is created. Okay.

Um, just keep in mind the focal length lens power and prescription. I'm pretty sure um I don't know if you if you guys wear glasses and I don't wear glasses But everyone in my family does. If you have anyone in your family who wears glasses and you just look at the prescription, it's so weird cuz it just has plus minus weird things. I don't know. So lens power. Why does it have the plus and the minus? We're going to talk about this now. So the lens power is basically how strong the lens is in bending

the light because the whole problem is in the light bending. So usually the power is Calculated by one over the focal length. So focal length is 1 meter. So the power is one diop diopter diopter because it's an op like optical thing. Okay. A diopter is a 1 meter. So one over one it's one diopter. 1 / 0.5 it's going to be two 1 / 0.1 m it's going to be 10. So what we need to identify basically what do they what optimmetrists try to do is they try to identify the lens focal length. Hello

to kind of correct the focal length or kind of like correct it With the the the convex or the concave um glasses or whatever. Okay. So they calculate this focal length and they use this formula here. Power equals 1 / focal length to figure out the diopter that is needed. Okay. Or the power that is needed lens like to correct the vision convex. Okay. The one that brings the light rays together. Basically the converging which is this one. The convex. It's used for farsightedness. So basically if a person Cannot see farsightedness um what do they

do? They usually they usually what is it called? They they give them convex lenses to bring the light rays together so they can focus. Come on. Is that clear? Is that clear? Okay. So, convex again it's used okay for farsightedness. Does anyone know what does farsightedness Mean? Asan farsightedness means they can see what is far away but they can't see what's closed. Um and this is what basically in other words it's hyper opium. So they can clearly see Masalan 10 m away or like 100 m away but they cannot see very closely and this basically

happens Kaman and when people get older um in a way they kind of and you know how my mother she she she recently started wearing just glasses because she Can't see the clothes by okay but far like anything that's far away she can easily see so this is what we call hyperopia Okay. And uh we give them convex convex here converging lenses to fix that cuz in a way we want to converge the light converge these things at a place where they can see the close stuff. Do you get me? And the sign is power

because we're converting them. We're bringing them all together. So we're adding things Together. On the other hand, nearsighted, they can see the closed things, but they can't see the far away things. What do we do? We give them concave or diverging lenses. So, they're going to spread everything out. So, the the far away is kind of clear. Okay? And because we're kind of diverging or like causing the rays to go apart away from each other, it's negative. This is used for myopia or Nearsightedness. H these are so like I don't know I don't useless. So

basically this is the object and then we have four refractive surfaces where it goes through. So basically when light goes through it goes through air which is this is the normal but then it goes through the corneium and then it goes through the acuous humor and then the lens and then the vituous. So it has different so each each thing has different density. Okay. So all of these have different densities and you can see that. So it goes through four refractive surfaces. Most of the refraction occurs at the corneium. Okay, which is interesting cuz you

you can look at the figures and you could see that the lens has the highest refractive index. The why is it why is it the most why is it the most at the cornea not at the lens? Because basically if you think of it the difference between The air and the cornea is 38. Hello 38. And then it goes inside the difference between the acuous humor and the lens is not that much. It's just like literally 7. So which is stronger 38 with a 7. I keep 38. So technically speaking actually this is not 7

that's 07. You can see why I I went into medicine because physics and math both of them suck. Anyways, so uh what is it called? Most refraction where will it occur between Cornea and the and the air. What has the most refractive index? It's the lens. Is that clear? Because I don't if if locker brings this image and he's like yellow where does most refraction occur and someone just chooses the lens just because it has the highest refractive index and like oh high refractive index the most refraction occurs there it does have the most refractive

index but compared to the accuracy humor the difference is Really low you get me the refraction is not going to be as strong as the refraction between the air and the cornea is that clear. I hope it is. Oh, wait. I forgot to say something in here. Now, since we have all of these refractive surfaces and the light is going through all of this journey, people decided like scientists decided and know the refractive power of everything is 59 diameters. So, it's Basically one over something that eventually equal 59. What is this something? I don't know

and I don't want to know. Come on, but I'm trying to revise the power thing with you guys. Oh, yeah. It's here. It's 1 over 17. Sorry, I just hate physics in math. So, the reduced eye schematic model, they're kind of just saying and know, okay, we have four refractive surfaces, but you know what? Let's just say one one strength or one whatever. Okay, which is basically the 59 diopters. And how did they calculated that? They just calculated the um the length focal length. Is it called focal length? Yeah, the focal length. They calculated the

focal length from the uh one second from the lens to the phobia. This is the focal length because basically if you think of it, all every all the light is going to go through the lens and then it's going to eventually converge in the fobia. So this is the Focal length uh and it was 17 mm. So one over 17 mm equals 59. Okay. Plus plus another thing that is kind of come on extra they went and they kind of got the diop diopters of each and everything posterior surface of the cornea will they added

them all together. Come on they ended up equal 59. So say I guess um let me just double check if 1 over 17 is actually 59. Imagine if it's not like one divided by oh no it Is. Anyways this is all just um hello we have something called the visual angle. And why did I do this? Because I want to show you something that is really really okay. So visual angle what is the visual angle? It's basically the angle that uh that is formed with the basically lens okay the corneium actually it's the lens but

ignore it okay so let's imagine this is here so it's basically the Angle the the okay so basically the end and the start of an object so basically this is the the har so you see this pen so the end of the pen and the start of the pen What I wanted to show you and that's the reason why I'm trying to the the vidual angle changes with distance. So if it's really close, you see how the angle increased. If it's really far, you see how the angle decreased. If it's really big, you see how

the angle increased. If It's really small, you see how the angle decreased. So yeah, visual angle is basically the angle between the object and basic any two points that two points and the lens two points are basically just the the top and the bottom of the the object and where it lands. Is this clear? And you have to know that the visual angle differs size distance and these things clear. Anyways, I hope it's clear. Why is the visual angle important? Actually, never mind. Okay. Hello. We have something that we um Okay. So we we were

talking about glasses before we kind of go and be like okay you need glasses. What do we need to determine? We need to determine visual acquity. What is v visual acquity? Visual equity is basically the Sharpness of the vision or the resolving power. I have to make sure that this person's vision is 10 out of 10 like perfect. Okay. How do we do this? It's basically the ability to see two points as separate. Basically just the same idea and to see the top and the bottom. So the visual activity how do we test it? We

tested was something called the Snellan chart. And I'm pretty sure everyone who got their driving license, everyone who goes to the like optim uh Opthalmologist just for a checkup, they always go and check the Snell and charts. This is the Snellon chart. The E, the four, the all of these things. The Snellan chart, what does it depend on? It depends on so basically it depends on the distance the patient is standing from this chart over the distance where a normal person would see it when we say six out of six. So what do when you

when you see like Um like basically the results that that of a person after going to the opthalmologist and six out of six what does that mean? This means a normal vision. This means a normal you were able to see the letter from six meters that you were supposed to see at 6 mters. Do you get me any? A person with perfect vision is usually sees this e at 6 m and you were able to see it at 6 m. So perfect. Your vision is perfect cuz in you are supposed to see it at 6

m. So six out of six is perfect. But six out of 60 y 6 m six you saw something at 6 m that a normal person sees out of 60 m. This means your vision is so poor. Mom six out of five means you see better than everyone cuz six you're seeing at 6 m what person at 5 meters is able to see. Do you get what I mean? So the denominator is usually what you're Supposed to see it like the the the Norman that chair I can see it I'm supposed to see it from

60 m away and I am 60 m away. So I'm 60 out of 60. So perfect. As long as denominator decreases and the denominator increases this means poor vision. The opposite means amazing vision. Okay. Equal means normal vision. Is this clear? I think we lost our soldiers. I'm okay. Hello. Let's see here. Basically, if we are trying to kind of put everyone in a chart where we're like these people are normal, these people are fine. So the normal is 6 out of six. Hello. If we saw 6 out of 12. So basically half let's say

half of the hey. What do we put this in? Which category? We put it in mild impairment. Any a little bit you know like they cannot see the the the letters In the sign that is hanged in the street. Not bad. You know, six over 18 rates increasing. The the gap is higher and higher. So six out of 12 is like half you know 6 out of 18 is like 1/3. This is basically moderate impairment. So basically it's getting more the patient is having more difficulty in looking at things that are really far. Once it

reaches six out of 60, this is really bad. This is really Really bad and very poor vision. Imagine someone is only able to see something six meters close to it but a normal human being can see it from this is the per the person trying to see the object but this object is visible to a normal person. This is the normal. This is the abnormal. He has to be so close to see the thing. So six out of 60 severe impairment. Blindness is usually three out of 60. So if you cannot see the objects 3

m Uh like from 3 m from the object compared to a person that can see it from 60 that's you're blind. Okay. Legal blindness. Okay. For people who you know they need to kind of get like an eligibility for like whatever cause it's basically 20 out of 200. Um, this is for this total blindness is basically they cannot see any lights. Like literally no light is detected. Nothing. Hello. Some people they're kind of okay. They don't know How to read the e. They're illiterate. Um, or if the durometer is more it means the eyesight is

bad. If the difference between the denominator and the nominator is really really high, that's bad. If the nominator is low and the denominator is really high, it's really bad. Yeah. But if the denominator is high and the denominator is really low, that means amazing. If they're equal, yeah, it's ratio based. So basically denominator is basically a Normal a normal person is supposed to see it from this number and denominator decreased that means oh my god like the the gap is crazy. Okay so is uh as we said some people are illiterate they can't read they

can't count. So what we do we do oh they're not even able to to tell it you know. So what do we do? We do we can put them fingers ask them to like tell us how many fingers are there. We can try to do Uh hand motion. This is specifically for command patients that cannot even like talk to us, you know, like let's say they're through they have a stroke or they have anything. So that's are the things that we could do. Uh then we can try to see light perception through the pupils and

everything. If there was no light perception, they're totally blind. We have something called refractive error. Okay. uh refractive error is basically errors due to Whatever cause. Sometimes it's due to the spherical and it's something called spherical aberration. So the sphere itself has an issue. It's causing the the the rays are not converging into one point. So usually the converging lenses they allow them everything to converge into one point. The lens has I don't know like something it's either the shape is wrong. um had this can be not only in like glasses lenses in our own

lenses. Um so they they can't converge At one point and this is going to cause a blurred or unclear image. We have something called chromatic aberration. It has to do chromatic means colors. So it has to do with the colors. So basically what happens is that the eye is not able to kind of understand the different wavelengths of different colors all at one time because they bend at different angles. So what happens is the color of the image is not Going to be really clear. It's going to be blurry and the color is going to

be like not blurry. you know this is what we call chromatic aberration. Um it's just chromatic has to do with the the colors. So basically the wavelength it the different colors in the different wavelengths have like they bend at a different places. So that's why we kind of have the color unclear. Defraction is I think it's just Basic physics. They're straight. They go through a very long like small area but they bend and spread out. Well this just reduces the sharpness of the image. So basically if you know if you see these things it's going

to be sharp but if you see the others it's not going to be as sharp on these things refractive errors they're basically come on clinically like clinically significant these are basically the hyperopia and the Myopia hyperopia is farsightedness so basically they cannot see the far they cannot see sorry the closed objects why because you see the eyeball it's really short but the the image is converging outside the eyeball. It's converging outside and he basically where does usually the image converge? It converges in the phobia. Why? Because we said the phobia has the most porny uh

cones. It has the most cones honest visual acquity will happen. So it's converging outside. Hello. But this is what hyperopia this is the cause of hyperopia. How do we correct it? We give them converging uh lenses which is basically the convex. So we add plus so we kind of increase and we add more distance for the high so it can kind of you know like converge into the right place. Myopia is the other way around. So basically the eyeball is too long and basically the lights are converging way farther than the phobia. And what Happens

is we give them diverging. So kind of like you see how like they don't directly convert like they don't directly converge they kind of get dispersed and then they go into the lens and then they get diverted like converted together do you get what I mean we kind of want to decrease the distance where they they we want them to directly converge away from the lens we want them to diverge and then converge Converge why because the eyeball is too long do you get the concept Okay, perfect. So again, converging, we want them to converge

at an earlier time because the eyeball is too short. In diverging, we want them to diverge a bit and then converge at the lens because the eyeball is too long. Huh? So hyperopia hyperopia or farsightedness is fixed by converging or convex lenses and usually with prescription it is a plus sign. Myopia is the opposite Nearsightedness eyeball is too long. So we fix it by diverging. We want to diverge them a little bit and then they will they will converge at the lens and this is basically concave or minus and this is as stigmatism. We mentioned

it. And what happens is we have an irregularity or the surface or curvature of the cornea uh multiple points one vision is distorted. So that's why we put cylindrical lenses and they help in kind Of fixing the curvature and focusing the light all into the retina. Next sorry okay now let's I think this is the last thing. Accommodation. Yeah. What is accommodation? We talked about this. Accommodation is basically it has to do with the lens. So accommodation is our ability to see something far away and close enough. So remember how we said and uh basically

we our lens okay it has Celarior muscles attached to it. Muscles they'll either make the lens fat or thin. Fat or thin. Come on. When the object is far, okay, when the object is really far, okay, we don't really care if if the lens is basically the light has enough time to kind of converge. This is if an object is really far. So what will happen if the object is far? If the object is far, what will happen? The lens is going to be fluff. Come on. And wait. So when we're talking about flat, what

will happen? The sior muscles are going to contract. They're going to contract because it's really far. We want the the thing to to pass normally through the lens. We want the if the object is near, we want the lens to become fat. So the celary muscles are going to Relax and this is how the lens is going to change. So what happens is the idea is if we're bringing something that's far closer or or something that's close farther if it's far the lens is going to be thin cuz we don't need a lot of refractive

power. That's the idea. When we when we kind of make it fatter, we increasing the refractive power. Do you get me? Near is fat, far as flat. Oh my god, it rhymes. Yeah. Near is fat and far as Flat. True. Why is the farther flat? Cuz again, it has, you see, like in here, we have enough time for the the the the lens to for the thing to go through it and then convert. But near point, it doesn't have a lot of time. So, it has to go through like a like a really like dense

thing and like it has to have like a stronger refractive like power so it could like refract. Is that clear? I like the pneummonic near as fat and far as Flat. And for the lens to be fat, it has to be relaxed. The celery muscles have to relax. So if the object is near the serial muscles are relaxed if the object is far the serial muscles are contracted to kind of pull the lens all together I think it's easy accommodation is one of the easiest things ever now this is something that uh basically accommodation rate

is uh decreasing as age goes on why because the elasticity of the eye of the tissues everything in There is going decrease and because of that we have something called prisbiopsia. Prisbiopsia is kind of prisbiopia sorry or pris the idea is and know basically this is kind of like far far uh sightedness but it happens due to old age do you get me that's basically hyperopia but because of old age that's why we have we call it presbiopia cuz like the ethology or the cause of the far-sightedness is Different than hyperopia you at me. Yeah.

Press biopia is just caused by old age. Basically, the lens is going to get a bit less elastic. It's going to get the muscles are going to get less elastic. Everything is just going to like but because of that it's going to cause the hyperopia. But hyperopia can be caused because of basically the eyeball like being too too small and stuff. Is this clear? So how do we how do we how do we fix Breast myopia? What kind of lens? Okay. Blush. It's basically Okay, let's Okay, this is the last slide file. Let's go up

to Okay, basically it's not going to be concave. It's going to be convex because we want to converge it. Why? You see focal point is way better. We want the focal point to be closer in here. So, we want it to basically converge earlier. You get me? So, it's going to be a convex. Yeah. Yeah. It's just like hyper opio. It's literally just hyperopia. Any press biopia is hyperopia, but it's just a different name because the ethology is different cuz it's caused by old age and that's it. Anyways, thank you so much for attending. I

really appreciate it. I hope I helped in some way. I hope it I made it easier. And that's All. Please scan the code. Thank you. I really appreciate it. You're welcome. Um,