Hello, everyone. Thank you for joining today's webinar. Maria is going to talk about the anatomy of the eye.

This is a part one of a series, so don't, don't miss part two next Thursday. If you have questions, please place them in the Q&A box, and at the end of the presentation, we will give 10 minutes to answer, to answer your questions. Maria Moonz has been a lecturer on the subject of veterinary anatomy since May of 2000.

She worked at ICBAS teaching clinical anatomy and systematic anatomies. She moved to Sydney in 200. 11, finished her PhD and worked at the University of Sydney.

Later, she also worked at the University of Pennsylvania in the USA. She is now living in Germany. Maria has never lost touch with the clinical practise of veterinary medicine.

She owns a small animal clinic in Portugal and practises surgeries in a clinic in Germany. She understands the importance of a good anatomical background for any veterinary clinician, surgeon. As a teacher and a speaker, she does not merely focus on the anatomy itself, but rather addresses the functions and clinical importance of certain anatomical structures.

So, Maria, thank you so much for being with us this evening. Over to you please for your presentation. Thank you so much, Phil.

So, I just got the picture here, so you would know who is on the other side of the, of the screen. But, yeah. So, as FO was already mentioning, so I am an anatomist.

My main subject has been always, the applied anatomy or the clinical anatomy, which consists on using an anatomical knowledge to better understand medical diagnostic and surgical procedures. So I am not an ophthalmologist. I'm not a specialist.

I've been teaching, veterinary anatomy for over 15 years. And so, in this presentation, I will be focusing only on some simple and common eye, diseases or issues as we explore, anatomical features on the eye. So, Mhm.

All right. So, In this session, we will be looking at the anatomy of the eye, apply the anatomy of the eye. And the eye is the organ of vision.

It's It's responsible for acquiring light stimuli and then transforming it into a sort of electrical, electrical signal, which is then conveyed to the brain. The eye, consists of various parts. So the eyeball itself here.

And the optic nerve coming emerging from it, then we will have extrinsic muscles or extraocular muscles which rotate the eye, make it move, and the fascia that surround these muscles. Then we will be looking also at the eyelids, the 3rd eyelid as well, and the conjunctiva. And at the end, we will also be looking at the lyramolaparatus, so the production of tears and its drainage.

So, in this first session, I am only focusing on the first two, so we will be looking into the eyeball itself and the optic nerve, and this will be enough for 1 hour, believe me. So, The eyeball, I think it's better understood, and I, I, and, and I, I always describe it as, it's like it would be a fruit. So it would be, something with a soft core.

So within. Here in the core in the, the centre, we would have several chambers with fluids, liquids or gels here in this, in the centre, while the, the shell, the outer shell is quite hard. And this shell is actually made of three concentric layers or tunics, also called tunics, which we will look into.

So that will be the fibrous layer, the outer layer, then the vascular layer in between, the one here in, in the dark colour, and then the inner layer which is the nervous layer also called like that. So let's go then one by one. So the fibrous layer here is, has two different components.

It has the sclera here occupying 3, the 34, posterior 3/4 of, of the eyeball and the cornea. In the anterior position. Then the next layer here will be in, in pink here in in this colour, we will have the choroid, covering the inner part of the sclera, then the ciliary body and the iris in more anterior position.

And then the last layer or inner layer will be then the retina itself. So here we see it in yellow, and that's the, the last layer. And then beneath these layers, as I said, there will be chambers with fluids or jelly substances, OK?

So, here we go. So, the fibrous layer, the fibrous layer is responsible for the shape and for the protection of the eyeball. It's made of the dense collaginous fibres.

The sclera, as I said, is most, covers most of it on the, on the posterior side. It, It serves for the insertion of those muscles that I've showed in the on the first slide. So this would be the extrinsic muscles attaching to the scleum.

And then, as you can see here in this picture, we see that the sclera is a bit thinner in its anterior part and as we move here to the posterior part, we see that it's much thicker. The sclera also has fenestrations and at this point here in a ventral ventral posterior position. It has fenestrations, to let, so vessels, arteries, and, and nerve, and sorry, arteries and veins to come through, but also the, the axons from nerve cells from the retina, which also come through.

So this area will be called the area crebiform. And that's where, as I said, these vessels and nerves come, come through to, to then emerge from the, the eye bone. OK.

So here we have another image now, in the frontal view. So we see that the sclera is actually what they call the white part of the eye. Here we are looking into the visible part of the sclera.

Most of it is not visible, and this part which is visible is covered by conjunctiva. We also see this line here. Which is the line separating the sclera from the cornea.

And this line here is the corneal corneal scleral junction or also called the the limbus, yeah. The cornea itself is then covering this area. Of course, we are not able to see it in this picture because it's a transparent structure.

So we're actually seeing through the cornea and we're able to see the iris here in the back and the the central opening of the iris, which is the, the pupil. But in this lateral view, We're actually able to see the, the cornea itself. So.

The cornea is transparent. There we can see again, through it, we can see the, the, the iris. So as you can tell from the slide before, you see that the cornea actually bulges forward.

It does not follow the same curvature as the, as the sclera. It bulges forward to be able to refract the light. So, which means that these light rays will be then.

Conveyed to to one single point which will be going through the, the pupil and then just reaching deeper parts of the, of the eyeball. So we will call it the fundus of the eye. So, let's look into the cornea then on more on detail.

So we see here that the cornea is actually a rather thick structure. Here's, for instance, a microscopic view of the, of an eyeball and so you see that it's a rather thick structure. Here we see the lens and this is the iris and the, this is the, the limbus, and here at this point, we start seeing the, the sclera.

So these are the, again, we're just looking at the, at the cornea itself. What we're looking at is, the outer layer is an epithelium. Then we have a very minimal line here, which is then the bowman layer right beneath the epithelium.

Then we have the substanciaropria, which is the thicker part of the, the cornea itself. Then we have a short membrane here, a very thin membrane called the decimate membrane, and after that, we will have another layer of epithelium. So, that's what we have here.

So we have epithelium, then a thin layer, the bowman, then all of this is substanciaropria, and then we will have a decimate and the inner epithelium. So what I can tell about the cornea is that For this structure to be completely transparent, it does not contain any, blood vessels. So there are no blood vessels throughout the whole cornea.

There, however, several nerves, nerve terminations here in, in the different layers of the cornea. So it's a highly sensitive, structure, but it does not have any, sort of blood vessels running through it or it would would lose its transparency. So these, these cells here, these fibres, these collageinous fibres that we see here are arranged in such a way that they're actually in a lamellar architecture to let, to, to keep that structure completely transparent.

It's it's, it's architecture that actually makes it completely transparent. So, if it's not actually vascularized, how does the cornea then get its nourishment, its blood supply? Well, it actually has 3 sources, so we will have little capillaries coming from the limbus itself and reaching the periphery of the cornea and so these little vessels are able to To, supply the periphery of, of these layers here.

Then we have 2 more Two more substances. Here we have the, the precorneal tear film. So the, the tear is completely spread with the eyelids, covering this, this area and, and with the blinking movements.

They will spread the tear over the whole surface of the, of the cornea. And so, so the tear itself, so the tear film, let's say, will, by diffusion, then cross some of these layers of the, of the cornea and, and nourish it. This is from the surface, from the inner side of the cornea, we have another fluid and that's called the aqueous humour.

And this aqueous humour is also able to nourish the, the cornea from the, from the inner side. So through the fusion again, we will see that some molecules are able to, to, to, to cross some of these layers and then nourish these, these, The this part of the inner side of the cornea. OK, so that was the limbos, the little capillaries, then the, the precorneal tear film, and the aqueous humour on the inner side.

That's how the cornea gets its nourishment. So, looking into the applied anatomy here, what we see here is a corneal ulcer. So there's an injury here in the, in the cornea.

This one seems to be quite deep, actually, because it seems to me like it would be more decimeto cell. So when we pass all of these layers, epithelium, bowman, and then most of this substantialropria reaching, one of the final layers, which is the decimet membrane. And when we're reaching it, we're very close to having actually A disaster happening which when this decimate membrane is destroyed, then all this fluid, this aqueous humour fluid would flow out and we would lose this eye.

Anyway, it's not the case here. It has not reached that point yet. And what we see is that These new vessels are trying to, to reach this injured area and, and of course bring inflammatory response to, to this area.

These neo vessels, and in this case, what we see is fluid, edoema, through the layers of the, of the cornea in between these, these layers that we've, we've just mentioned. And so, in, in both situations, what we see is that the cornea is losing its transparency and so the, the vision is impaired in both, in both cases. So, here are more examples of some corneal ulcers.

Here we have again the edoema. This is a traumatic A traumatic corneal ulcer. Here you see also the conjunctiva and, and the, the scle itself are very congested and hyperemic.

In this case, the the ulcer was rather superficial, so we actually use some fluoroa to, so a special dye to, to see how large the, the corneal ulcer was. And you can see here that in, in many of these situations, it's a very painful, issue because again what we said, the cornea is extremely innervated and so it's, it creates this, sort of laphro spasm and epipherum because the eye is under pain, the animal is in pain. So, moving on, we have the next layer, and that's the vascular layer, also called the ua.

This layer is responsible for the blood supply of more than one structure. For instance, it, it supplies the The cornea and the retina itself. It's also responsible for suspending and regulating the shape of the lens here, and then for regulating also the size of the pupil.

With the iris and then producing the aqueous humour, so this fluid that I was saying is right behind the cornea, between the cornea and the lens. It occupies this space here. It's made up of three components, so we will have the choroid.

The choroid is, as we said before, covering the The inner part of the sclera, then we have its two anterior parts, the ciliary ciliary body and the iris itself. And so, Let's start with the corra then. So, the choroid is a highly vascularized, structure and highly pigmented also.

Actually, both the choroid here in, in the dark colour and the retina have pigment. And what does it serve? What's its purpose?

So what happens is when the light is, is running through all of these transparent, fluids and structures that we have here in the front and reaches the, the fundus of the eye, we don't want this light to, to be reflected and And runs through the through the retina several times. So it will run once and then be immediately absorbed by these pigments either in the retina or in the choroid. And that's why the fundus of the eye is highly pigmented.

We don't want a reflection of this, of these light rays. So, if, if this would happen, it would, it would create 2nd and 3rd and 4th readings from the retina and this would be creating a blurred vision. Here's the fungus of the eye, what we can see with the ophthalmoscope, and we can actually see, here, the dark, part of the choroid, here the dark part of the ho, so highly pigmented, but then we see this.

So, and both on the dog and the cat here, and these are other species, but I'm mainly focusing on the dogs and cats today. We have one special region of the, of the choroid. It's a moon-shaped area in the choroid, which has, special, crystalline, rods, which reflect the light.

So this is the only area that does not, that is, is reflecting light and it can have different colours. So depending on the species, as you see here, cats and dogs have different light colour. But this can also change in, in breeds and also by age, so, with the ageing, the, the colour can also have some changes.

But it's usually in these yellow, green, or bluish colour. When you hit the, the, the light with the ophthalmoscope, you can see that when you flash the lights and when you have the flashlights in your car, you can also see these, these reflective, reflective area of the choroid. So this area is called the tepitum lucidum.

So, either you use this this Latin name or you can also say that this is the capital area. So this is the non-capital area, the dark, the dark pigmented area, and the area which is reflecting light is then called the capital area or tepium lucidum. Oh, sorry, OK.

So, this is all about, actually we can move on. This is all about the coro. Let's move them to the the the components.

So the ciliary body is, is then anterior. It's continuing the The, the choroid now on a more anterior position. So it's continuous to it.

Right here you can see it's continuous to the with the choroid, that's right there. And so, it has different parts. One of them is these ciliary processes, so these are like finger.

For projections of collaginous fibres again, which run towards or, or are directed towards the, the lens itself. From them, from the tips of these finger, like processes or ciliary processes, you see that there are some fibres, the sonular fibres, which actually then extend from these, the tips of these ciliary processes and attach to the lens itself. So to the, to these two poles.

Of the, of the of the lens. So if we look at this picture right here, what we see is that we have the iris here in the front with the pupil in the centre. Which is right here, right?

So this is iris here on this side, and right behind it, then we will have the ciliary body, so posterior to it. So that's what we see here. This is a little cut on the, on the iris, and we can see that the ciliary body is right behind it.

And it's, and we have about 80 to 100 of these ciliary processes extending all the way, and then with these ennular fibres attaching to the, the periphery of the, the lens. So this goes all around the. This goes all around the, the lens, and so this is a suspensory system, so it suspends the, the lens right here in the centre.

Another important component here is the ciliary muscles. So, the, at the base of the ciliary, processes, we have the muscles here. The ciliary muscles are smooth muscles, so they will act by influence of the parasympathetic and sympathetic, nervous system.

And so, what will happen is that when the ciliary, muscles contract, they will pull on the, on the ciliary processes, but of course, directly over to the cellular fibrils, and this will put tension on the, on the lens. This will change the shape of the lens, and so we better see it in on a video here. So here we have the, the lens itself so that you, you just see how it's, how it looks like.

So you see that the core of the lens is, is thicker. It's more dense, and this is the, the nucleus of the lens, and you see that it has, it has the, the poles here and then here you have the posterior surface being a bit more convex than the anterior one. This lens is made up of collaginous fibres, and just like the, the cornea, they're again organised in such a way that they're like lamellas and it's completely transparent.

And here we have, a picture of the zonular fibres, attaching directly to the, to the lens, attaching to the capsule of the lens because it, it does have a capsule on the outside and so these are the fibres attached to, to this, attached to this capsule. So, let's look into that video again and I will show you what I'm talking about here. I'll just make it bigger here.

And so what we see then, we're looking from, from the fundus of the eye, and we're looking through, this is the, the lens are looking through and in front of the lens, we have the iris in blue there, and the pupil here. This opening will be the pupil. And so we see that these are then the ciliary processes with the with the cellular fibres extending to the, to the outer side of the lens, yeah.

So what we see here is that we will see a pull on the, on the ciliary muscle. This will be the sympathetic action. So the, the, the nerves, the parasympathetic nerves will contract the muscles.

This will, this will change the pull on the, on the zonal fibres and we will see that this will happen. So. This is what happens.

It concentrates, the nucleus gets thicker and actually The vision focuses on near objects, and as the muscle relaxes, then We will have, sorry, we will have. As the muscle relaxes, we will have then a lens which is a bit more flat. And so the, sorry, this is what I had here.

Oh, I cannot stop it. I will stop it now. So when we have it relaxed, the muscle is relaxed and then the lens is completely flat, then we see that a distant object is being focused and not near objects.

So what happens here? Is, the so-called accommodation. So the ability of the animal to focus on near objects or distant objects is the accommodation of the lens.

And this is again by influence of this muscle, the smooth muscle, and either we have sympathetic innervation or action, and we have a focus on near objects or we have, we have sympathetic action with the relaxation of the, of the ciliary muscles, and then we have a focus on distant objects. Coming back. OK.

I think that was it. I hope you understood this. So just about the lens here, we have two different pictures here.

So this is an absolutely normal situation, physiological situation. We have the lens through ageing, the, the fibres will just, dehydrate as as the animal ages, and so this is happening, so it's losing its transparency and becoming a bit. A bit wider, let's say.

But this is a physiological process, whereas this situation here, we have a cataract and this is a pathological situation, OK? I'm not going over through details with the cataracts because that would, that would take us another hour. So, let's go through the 3rd component, which is the iris then.

So the iris lays directly over the, the lens. It lays here, anterior to the lens and to the ciliary body. So I, I think of it as a flat donut with a central opening right here.

Which is the pupil, as you said. So, just like the ciliary body, the iris is full of muscles and, And also, it's And also it, it has, it has a lot of pigments. So depending on the amount of pigment, we will have different colours of the eyes.

If we will have more pigment, it will be a darker colour. If we have lighter. Or, or less pigment then we will have lighter colours.

It also depends on the, the, the amount of collaginous fibres, how dense they are. So the iris is a muscular structure, as I was saying. There are two important muscles in it.

One is the dilator muscle of the pupil right here, and this one here right around the pupil, which is the sphincter muscle of the pupil. So the sphincter muscle of the pupils, just like any, any sphincter muscle, when it contracts, it reduces the size of the pupil. As you can see it here, it's circ, it's a circular arrangement around it and when it contracts, it just closes the, the pupil.

And so this muscle acts under parasympathetic, . Action, no. Whereas the dilator muscle of the pupil is, its fibres are arranged radially.

You see they're running from the pupil towards the periphery of the, of the iris. And so when it contracts, it contracts as a whole. And so it opens, it opens the, the pupil wide, you know.

In this case, so we're looking here in, in this example, A, we're looking at the human eye or the, the dog's eye, but we actually have other species that have a different arrangement for the sphincter muscle. The dilator muscle continues to have the same arrangement in every single animal, but the sphincter muscle actually is different. So, in this case, we're looking into the one from, from a horse, also a goat would look like this.

Where the fibres are not in circle, in a circular arrangement, but rather have some fibres extending to, to the poles here. So the, the medial and the lateral pole, and so, When it contracts, it closes, but it it has this oval shape. That's what we see here, right?

Whereas in the cat, with these, fibres of the sphincter muscle will be going up vertically here, up and down, and so when they close, it shows this slip like shape of the, of the, of the pupil when it's contracted. OK, so let's look into this little video. And we see here.

The shape of the muscle. So here we have the sphincter muscle again and then the dilator muscle of the, of the, of the pupil, and so we see it on the action. So sphincter closing and dilator opening.

Yeah. This is a rather simple one. I have another video.

More interesting than this one. OK. So, And this cat, what we have is different sizes of pupils.

As symmetric, size. So, of course, what we could have here is that one eye has some eye drops, adrenaline, or, some sympathetic mimetic, drops that will, drugs, which will, would create the situation. But, it could be also a neurological, damage.

So what we have here is diagram where you can actually understand what's, what's going on. So we have in green, we have parasympathetic fibres running with the oculomotor nerve. And here we have sympathetic fibres and, and, and purple, and they come directly from the cranial cervical ganglion.

So both are running into the, sorry. Into the eyeball, and they will affect both iris and ciliary body. So let's look into that.

So what we have here, I will show you again how this situation happens with the, with the, with the pupil changing its size according to these two muscles in the iris and we'll start by looking into it. In a bright environment. Yeah.

So this is a pupillary reflex. So we have a bright light coming directly to the iris and, and there's a directly very sympathetic response, and the pupil closes. And why does it do that?

To protect the, the retina. So, to reduce the amount of light because this would be excessive. To reduce the amount of light to the, to the retina, to the, to the fundus of the eye, and protect it.

While in darker environments, we would want this, we would want to have a dilated pupil, so we would get as much information as possible in, in a darker place. Yeah. And that's it.

I thought this was Much, much nicer as a video. So yeah, so, this was just anatomical explanation of this happens with a pupillary reflex. Again, this is sympathetic innervation happening here.

So what we could have in this case is a damage to one side, so only one of these, in this case, the, the left, oculomotor nerve could be damaged and you would have, So this, this dilated pupil in, in constantly, so this an isochoa could be a sign of damage to that ocular motor nerve to this parasympathetic fibres which are running with it. OK. So, after we've seen the, the lens and the ciliary body and the iris and the cornea itself, now we're looking into the inside at this aqueous humour because I've said that this vascular layer is also responsible for producing this aqueous humour.

So, we actually see that the iris here is dividing this space between the cornea and the lens into two chambers. So we have an anterior chamber, which is a space between the iris and the cornea right here. So this is the anterior chamber.

And there's a much smaller chamber between the iris and the lens. I mean, it, you can see it more here and right there. That will be the posterior chamber.

But they communicate with each other through the pupil, yeah. So, the aqueous humour is produced by the The ciliary body by the epithelium here. These cells secrete IQs humour than this fluid into the posterior chamber.

This fluid, this aqueous humour will then flow through the pupil towards the anterior chamber, and from there, it reaches this iridocorneal angle, so the angle between the iris and the cornea, where it reaches venous sinuses and goes into the, into the venous system. To the blood circulation. So here we have it as a video.

Here we see it coming from the ciliary body, posterior chamber, pupil, anterior chamber, and then spreading, spreading, spreading and reaching the iridocorneal angle. And then it will be drained right there. OK.

So this aqueous humour because it's being constantly produced and constantly drained, it needs to be in balance. So, if for some reason, the alcorneal angle is impaired by some sort of disease or, or inherited or whatever, so what will happen is that you will have a constant production of the Of the, of the fluid, and then it, it just builds up into the, into the, into these chambers and it has no way to, to come out for some reason or in a very, in a small, a small percentage, does get drained, but not all of it. So what we have is a failure in maintaining the pressure within the eye.

It just keeps increasing and increasing this intraocular pressure. And so, so we have what we, we say, a glaucoma. And the glaucoma could be an inherited problem.

It could be secondary to, trauma or different diseases. It can be an acute situation, it can be a chronic situation. And so, what we have as findings is that there's pain and altered behaviour.

Usually the vision is impaired, but also there's, it's a painful situation, therefore, the animal behaves, . Abnormally. In these pictures, we see some of these signs, so we see the epicleral and the conjunction and the conjunctival.

And conjunctable hyperremium. We also see that the pupil is completely dilated, and why is that? Because, of course, the fluid in here is pushing this pupil also to, to dilate, to open, it's pushing it, to the sides, to the periphery, so it's, that's why most of the times, you will have a dilated pupil.

You will have both almas, which means that you have this, this bulging of the, of the cornea even more accentuated. Then you can have this situation here, which, where you have a luxation of the lens, and how does this take place because the, the pressure is so high here that these cellular fibres start getting destroyed. Because there's too much pressure on the lens being pushed, posteriorly, that either you get a partial damage and destruction of them and you have a subluxation or you have a complete complete destruction of, of all of these, of these fibres, zonnular fibres, and then the, the lens is completely luxated.

And, in this case, when there's a complete luxation, the vitreous body, which is the, the, the, then the jelly substance that lays here behind the, the gel comes in contact with this, this fluid, the aqueous humour, and so, All of a sudden, you lose the nourishment that the AQS humour was giving the, the cornea, the retina itself was is also lacking some proper nourishment and all of a sudden, the cornea is also damaged and the retina is also damaged and we can reach total blindness with, with a situation like this. So, we're reaching the inner layer then? Which is the retina itself.

It's also called the nervous layer, which is then responsible for the vision itself. So the retina is made up of different parts according to its location. So, what we have here is this retina that is covering now the inner part of the choroid is called the optic retina or neural retina, whereas this one here covering the ciliary body and the iris will be then the ciliary and iriddic part of the retina.

What you see here in this picture right away is that these two are much thinner, so the uric and the ciliary parts of the retina are much thinner than this one here covering the choroid, so the optical. So this means that these two parts here in the, in the covering the iris and ciliary body are do not contain any nerve cells, so they're not able to, to To convert the, the light stimulus into, into any, any sort of electrical stimuli, so they're called the blind retina, and this one will be the one covering the cord will be the part responsible for actually interpreting that visual stimulus and, and converting it into, into electrical signal. Mm.

Yeah. So, we're looking now at histology, but only the optic part. So the parts which I said were covering the iris and the ciliary body are extremely thin and they do not contain these nerve cells.

So we're only looking at the optical part of, of the retina here. So, here we have a first layer of pigmental cells. They lay directly over the choroid.

OK, so the choroid would be here, right on the bottom. Then we have a first layer of the retina. On the inner side of the choroid, and this first layer is only, it's only made up of pigmented cells.

So, again, to, to be able to absorb light and avoid it to be reflected and scattered and create blurred vision. This, Now we see then 3 different layers. As we come more and more deeper and deeper into the, into the, into the centre, to the centre of the, of the eyeball.

So this first layer are photoreceptors. There, there are rods and cones. These are responsible for interpreting black and white, images, while the cones are responsible for some colour, the fragmentation.

These, the stimulus is then, conveyed to the next. To layer of neurons, these will be the bipolar neurons. At this point, then the, the image or the visual stimulus is then already transformed into electrical signal, which was then conveyed to multipolar neurons which Which nerve cells are here, but the axons are then here running altogether, and they're going to meet at one single point.

So, what we have here, let's say, would be then the vitreous body. Yeah, so this would be choroid here on the outside, and then going all the way in, and this would be the inner part of the retina. So, I will show you other pictures, maybe to understand it a little bit better.

But what I wanted to show you here is actually what happens to these axons. So as these As these axons come over here to the retina, they come to one single point. They, they concentrate in one single point here.

Which is called the optic disc, and where these fenestrations from the sclera are, they want to come out from the eyeball. They will go through this, these fenestrations of the creepiform area in the sclera, and they will come, emerge out of the, of the eyeball to then create the optic nerve itself. So as they, they all come from all parts of the retina, they come to one single point to, to emerge out of them, to leave the, the eyeball, and out here, you, you're then calling this the, the optic nerve itself.

The optic nerve is then protected by sheets of myelin and then it's moving on to to the brain. So, Again, this optic disc is a blind spot. There are no photoreceptors here.

There are no nerve cells. It's just fibres, exons moving out. So this is also a blind spot on the retina.

And here, as we said, that was the parts covering the, the ciliary body and the the iris, and this would be blind parts of the retina itself. Another important thing here is this, is this line here. What I'm trying to demonstrate here is how the light is crossing all these structures and reaching this one specific point here.

If you do a straight line, you see that this is a point of maximal optical resolution. It's called the macula, and in the macula, you have the highest concentration of photoreceptors and your nervous cells. So it's a little depression on the On the retina because it's a direct point across the Across the the eye.

So I have it here again as a little video. So we see the light has to travel through all of these transparent structures. I don't have here the cornea, but the cornea would be here in the front.

It would be completely transparent as we've said. Then we would have the aqueous humour right here. Again, this fluid which is flowing in these chambers, which is completely transparent.

It would cross then now the the lens, again, a transparent Structure. Here we have the vitreous body, a jelly substance that that is here between the, the lens and the retina, and then the light reaches the macula. To be then either absorbed or reflected by the tapetum lucidum.

Depends on which area of the chore it's it's hitting. Mhm. OK.

Here is what we have again. So, here I show you exactly what, what I was trying to explain with the layers. So in the back, we have the choroid with all its pigments right there.

And in this case, we have the tepitum lucidum, which is an extra, an extra layer on the, on the choroid. It's not all over, as I said, it's a special area of the, of the choroid that has this tepitum lucidum. And here we would have the pigmented cells of the, of the retina, right, right above the, the On the inner side of the choroid, and then the nerve cells going one after the other, the photoreceptors, and the neurons, and another set of neurons.

In this case, because we have a tepitum lucidum and where the tepitum lucidum is present in the choroid, we do not have pigmented cells. On the retina, because what would happen, of course, is that when the light is coming through, it would be absorbed by these pigmented cells and do not, would not reach the choroid. So, in these areas where we have the tepitaro, these cells are here, but they have no pigments.

They have have no melanin. Yeah, so they are just normal cells, not pigmented, and the light comes through, it is reflected by the pita lucidum, and then it will run again and it will be, will be read over and over again by the retina. Just to enhance the vision in dark places, as I said.

In this case, We have retinal detachment. The retinal detachment is a disorder that takes place, . With, not between the, it's not a detachment between the retina and the choroids.

So this is a normal eye, let's say, and this is the one with the detachment. You can see that the retina is here, all folded up. And here is the, the optic disc where all the axons are, are coming out to, to continue as the optic nerve, yeah.

So, what happens here is not that, not that the retina is coming away from the choroid itself. What's happening is that These, these two layers are detached from the retina. So, there's a detachment from There's a detachment here between the neural neural cells and this layer of the pigmented cells.

So the break, the detachment would be right here on this line. And this is because they have different embryonic origins, and that's why there's a detachment between this layer and the next one, the, the photoreceptors. So the ocular fundus or the fundus of the eye may be observed then with the ophthalmoscope.

In this case, there's a, well, somebody is observing this, this cat, and actually we see that the pupil is Absolutely normal, so he, he probably cannot see much through there. Usually, you apply, apply eye drops to dilate that pupil, so these will be sympatic or memetic drugs to To, make that pupil then dilated so that he could really see the full the full fundus. So in the fundus of the eye, we're able to see different structures, we're able to see the optic disc.

So the, again, the, this spot where All the nerves are running out, to form the optic nerve on the outside. And, through this, through this optic disc, along with this optic disc, we will have then the retinal vessels also, as we said, crossing this creviform area and, and either running into the, the, the, the eye as arteries or emerging out from it as little veins. And the other thing we see is that the beta lucid, so the reflective area of the choroid.

So, here we have it. So these are two dogs, which are quite different from what we see here in a cat. So, you see here by the size of the, of the optic disc, again, what we said is the, the convergence of the, of all the the exons from the optical retina.

And then we see that the vessels are also coming and confluent to this, to this optic disc because they're emerging in the same spot out of the, in and out of the, of the eyeball. So they have this sort of radiation, so one is, dorsal and then one lateral one medial. This is the normal arrangement in, in dogs, and this is the cat, a much smaller, .

A much smaller optic disc. Also, you don't see this venous trunk coming around the optic disc like you, you see it here coming around it and the cat this is not typical, so you see the, the vessels not as ramified as the, the, the dogs and the smaller optic disc. OK.

I don't know if we still have time for a little poll question. So this is a little poll question for all of you. Hope you have fun.

The point was to, to choose the false statement, not to choose the right one. And I don't know if, if people just, chose the first one because it was the correct thing, and it is correct. The to absorb scattered and reflected light is absolutely correct, but also the others are correct.

So to prevent the light from striking the retina for a second time is absolutely correct. To avoid blurred vision is also 100% correct. So the false statement is that It has nothing to do with protection of the optic nerve, yeah, so it's, it says the, the pigments are not, are not involved with any of that.

I don't know if we still have a few more questions from the audience. I'm happy to, Yes, thank you. Thank you, Maria, for an excellent presentation.

I just want to, remember that to the audience that this is a part one of a two-part series, so we look forward to seeing you in part two next. Thursday, we have two questions for you. The first one, Greg is asking, can administration of alpha lipoic acid help prevent or reduce cataract formation in diabetic dogs?

OK. Again, I'm not an ophthalmologist. I'm an anatomist.

So, the question is regarding, let me see if I can still go back. When did I speak about the cataracts? It was right here.

So Greg was, was asking if the application of uronic acid. Would, would solve a problem with the, with the lens. Prevent or reduce cataract formation, yes.

I'm, I'm not a specialist again on any of this. The, the thing is that it depends on the cause for the, for the cataract. It can have different different origins and I wouldn't say that the, the auronic acid would, would help, in, in all cases.

So, I cannot, I can, I can, would not be able to answer such a question. And that's why I did not go any further with cataracts because as I said, it, it would give me another hour of of of presentation because cataracts can have so many, so many different shapes and origins and Difficult. OK, we have another one.

Says if you know how photons of light get transmitted into electrical signals to the optic nerve, can this be digitised? You mean in the retina, when we have the retina right here? When we have the transmission here of the, of the information between, between these two cells, I'm not sure I understood the question if it, how could it be digitised.

I don't know. Can you repeat the question again? Yes, of course, if you know how photos of light get transmitted into electrical signals to the optic nerve.

OK. So, I understand. Again, this is, this is physiology.

It's not it's not my, my field again. But I do know that what, what seems to happen at this point is that these photo. These, these first layers, these rods and cones are able to, decompose the light and then, some sort, create some sort of a chemical.

So transform it into, into a chemical, substance, and this one will then be transferred to these other, neurons who, which will then, transform it into a, into an electrical stimuli. How this takes place, this is something for the physiologists or, or for chemists, it's again, not my field, I'm sorry. Mm, OK.

Thank you. So we have our last question and it's from Ian and it says in Horner's syndrome, is this due to an excess of sympathetic or a certain lack of parasympathetic nervous input? This is from who is asking this?

Ian, Ian. So, Ian, I invite you to come to my next session because I will talk about Horner syndrome in my next session. Because this involves not only, not only the, the, the eyeball and the, and the pupil itself, but also the eyelids, and therefore, I will be speaking about it next week.

So I have images and I will, I will run you through it. Perfect. Thank you very much, Maria.

And thank you for this amazing presentation again and see you next Thursday, everyone. Bye. Thank you.

Thank you, Theo.