So, hello everyone and welcome to another webinar. As I was talking to the host just before the recording, I know we're all going through rather difficult and challenging times, and I wish you and yours best of health, and I'll try to take your mind off COVID-19 for one. By talking about the applied anatomy of the fundus and making sense of ophthalmoscopy, an ophthalmoscopic examination is something that we need to do in any patient that presents for blindness or in any patient that presents with a systemic disease that may have funduscopic and retinal manifestations such as a cat with systemic hypertension or dog infected with some of the infectious organisms, that's when you really need to do your ophthalmoscopic exam and in this talk, I'll try to take you through the anatomy of the fundus, some normal variations.

Some abnormalities, some techniques just to help you in this very important diagnostic technique and prepare you for my next webinar in October when we talk about acute blindness. Obviously, you will not be able to diagnose patients presenting with acute blindness if you are not doing an ophthalmoscopic examination. As always, I have no relevant financial relationship to disclose, but I do want to acknowledge the sources of some of the slides I'll be showing David Maxs from UC Davis for the concept of slides 6 through 18 about building a funders.

The late Keith Barnett who lent me some of these slides and a textbook I've co-authored with David Maggs, Stutter's fundamentals. Many of the pictures I'll be showing are from this textbook. Right, so we're talking about the funders, but first we need to define what is a fundus.

It's a word we often use, but people are not always sure of the exact meaning. The strict definition is that it is everything that we see through an almoscope. So here we have a picture of a fundus.

This is what you would see if you look through the pupil of a cat with the ophthalmoscope and you are seeing here the optic disc and blood vessels and the tapetum, this is the subalbinotic animal, so you're seeing, seeing choroidal blood vessels in other patients. This would be the non-tapital area and this is really what Comprises a fundus, even though there are a few more tissues here that we'll touch on in a minute that are there and are an important part of the fundus, but we are not quite seeing them. But in order to understand really what we are seeing in the picture I just screened, we need to begin at the very basic and elementary level of the anatomy of the eye and that's represented by this simple diagram.

It always helps to think of the eye as a globe consisting of three layers. The outermost layer shown here in blue is the connective tissue of the eye, the cornea, the transparent cornea in the front, and the sclera, the non-transparent posterior continuation of the cornea. Then in yellow we have an intermediate layer, the UVR consisting of the iris and ciliary body that we not be talking about today, and the choroid, the blood supply of the outer retina, we'll certainly be talking about it today and then the innermost layer of this globe shown here in red is the retina, .

You could philosophise for a minute and say that really the retina is the reason we have an eye, this wonderful tissue that captures light and forms an image. If we didn't have a retina, there would be no reason to have an eye. So, If we are doing ophthalmoscopy, looking at the fundus you place yourself here in front of the cornea holding an ophthalmoscope and you're looking through the cornea and through the interior chamber and through the lens and you are seeing the retina as the innermost tissue of the posterior part of the eye.

Behind the retina, we know we have the choroid which We sometimes see and behind the choroid, we have the outermost layer, the sclera. OK? So keep these three layers and their order in the back of your mind, retina is the innermost layer of the fundus, choroid in yellow is the intermediate layer, and the sclera is the outermost layer of the fundus.

However, as I said, there are a few more tissues intermingled with these three primary tissues, and they are shown here histologically. So again, starting this time from the outside going in, we have the sclera here. Then we have the choroid shown here in yellow and shown as this vascular tissue here.

This is followed by the tepium, we haven't mentioned it yet, but we are going to be talking about the tepitium, the wonderful reflective layer of the eye, followed by a single epithelial layer shown here, which is the RPE or retin pigment epithelium. And finally, we have what's called the sensory retina, again, the tissue that captures light and transduces it into a neuronal signal, the innermost tissue shown here in red and shown here histologically. And there are a few more structures besides what you're seeing here of thermoscopically, histologically, excuse me, when you're looking at almoscopically, as we said, you're also seeing the retinal blood vessels and you are seeing the optic nerve head.

So I know there is a lot to take in, so let's go through them once again slowly, from the outside in. We have the sclera showing here in blue, shown here histologically. The next layer, the choroid, the vascular supply of the retina, shown here in yellow, shown here as this vascular tissue, followed by the reflective tepium.

Followed by a single epithelial layer, the retinal pigment epithelium. Followed by the sensory retina shown here in red, shown here histologically, the innermost layer of the fundus. So really the question is how do we get from this histological picture to this clinical or ophthalmoscopic picture that we are seeing?

How do all these tissues that I just come together to form this ophthalmoscopic image, I call this building a fundus. So let's put these tissues that I've just listed one on top of the other and end up with the classic funduscopic presentation that we are all familiar with. So to be in the fundus, we start with the outermost layer, the sclera, shown here histologically shown here in blue.

The sclera, as I said, is really just a connective tissue that was non-transparent connective tissue, posterior continuation of the cornea. So here it is in. Front of you, this pinkish yellowish boring connective tissue with a hole in the middle for the optic nerve to come through.

You also see this hole depicted here in this diagram. On top of this sclera, we have the choroid. So here we are placing the choroidal blood vessels on top of this sclera.

So we have the sclera. Shown here in blue, the overlying choroid showing here in yellow, and that's how it would look in a diagram, and this is what it looks like in a fundoscopic appearance of an albino cat. So you can see the yellowish, sclera peeking through.

Here and here and here quite a lot of yellowish scleral tissue. You see the broad choroidal blood vessels, radial blood vessels converging on the optic disc. It may be a bit challenging at first, but I think you can tell them apart from the retinal blood vessels such as this vein or even this artery here, you see that the choroidal blood vessels are much broader and they are of lighter shade than the retinal blood vessels.

So these here are the choroidal vessels in an animal and here they are shown in this diagram. Our next two tissues are the tepitum and the RPE, so we place the tepitum and the RPE on top of the choroid and now we no longer see the underlying choroid and sclera. Instead we are seeing the tepitum here.

And on top of the tepium. Or in front of the tepium, if you look at it histologically, we have the RPE. This is the pigmented RPE.

However, there is also non-pigmented RPE overlying the teal area. I'll get back to this point in a few slides, but basically all of the posterior part of the globe is covered by RPE some of it is pigmented, which is why we have the non-typetal area. Some of it is non-pigmented in the tepiid area, allowing us to see the tepium.

OK. And again, this is what it would look like in a live animal. So we have the non-tepitum, the dark pigmented RPE here at the bottom.

Again, we have an optic nerve head in both pictures and we have a very reflective tepitum dorsally. The next and final layer we have to place on top of the tapetum and RPE is the retina. And here we've done just that.

And note that actually the only visible part of the retina is the retinal blood vessels. OK. This picture is very similar to this one.

I've placed the retina, but actually you're not seeing much of the retina. It is a transparent tissue or mostly transparent, I'd say it's more like wax paper, not totally transparent or like sarin wrap. Plastic wrap, you do see a bit of difference in the sheen of the tepi between this picture and this picture and the shin of the non-tepitium, but basically the only visible part of the retina is the blood vessels that you are seeing here.

So now we have placed all these tissues, one on top of the other. We've started with the sclera, went onto the choroid. Placed on top of it, the tapetum and the RPE placed the retina and we have come up with this fundoscopic picture we have just built ourselves a fundus.

So if we take a closer look at the retina, which, as I said, is really as far as I'm concerned, the most important part of the eye. It's not just the most important part of the eye, it's really, I think the most exquisite tissue in the body. The retina is only 250 microns thick.

That's a quarter of a millimetre thick, 3 human hairs. If we were sitting in a classroom, I'd now ask each of you to pluck out a hair, look at it, and think of three hairs placed next to each other. That's a thickness of your retina, this amazing.

Tissue that gives us this amazing sense of sight and vision. You're seeing your computer screen, you're looking at the room around you, the whole world you are seeing through this tissue which is just 0.25 of a millimetre thick and If you want to hear more about the vision in our patients, please go back to the webinar I gave in May about vision in animals, really an exquisite sense made possible by a quarter of a millimetre, tissue.

As I said, it is transparent, mostly, and we only see the retina when they're are changes, retinal changes due to disease. We'll touch on that in a minute. As I said, in most cases, the only visible part of the retina is the retinal blood vessels.

So taking a closer look at the retina, we can divide it physio histologically it's divided as you can see here into 10 layers, but physiologically we are looking at 3 layers. Going from the outside in and you'll note that I've flipped my pictures now 90 degrees, so turn this 190 degrees, turn this 190 degrees clockwise, and you get these pictures here. So once again we have here the sclera as the outermost tissue in blue, then we have the choroid, the blood supply shown here in yellow.

We have the RP. Is that I mentioned and the photoreceptors, the rods and the cones that I mentioned in my vision talk back in May, and these are the cells that actually capture the incoming light, the incoming photons, and transduce the energy of the photons to a neuronal signal. So this is the outer retina and again it's outer cause it's facing the choroid and the sclera.

So RPE and photoreceptors as the outer retina where vision is really initiated, then we have several intermediate layers of neurons to begin the processing of the visual signal. And the innermost layer of the retina composed of ganglion cells shown here and their axons, each ganglion cell has an axon and the convergence of all of these axons at the optic nerve head is the beginning of. Cranial nerve to or the optic nerve.

So again, on the outermost aspect of the retina, we have the photoreceptors and again it's outer cause it's facing the choroid. The innermost aspect facing the vitreous is the ganglion cells and here would be the vitreous. And actually, at this point some of you are telling yourselves, gosh, this retina doesn't make sense.

It doesn't make sense the way it's laid out. It doesn't make sense because It's inverted. What do I mean by inverted?

As I said, here is a vitreous, here is the lens, here is a cornea. So light comes from up here, goes through the entire eye, goes through the entire retina, is absorbed by the photoreceptors where the neuronal signal is initiated, and then this signal is transmitted this way. Into the inner retina, processed in the mid retina, transmitted to the inner retina to the ganglion cell axons which again exit the eye this way.

This is totally wrong. It doesn't make sense. It would be so much more logical if the retina was upside down if the photoreceptors were here and then light would strike them.

As the first rein layer, the signal would be processed and transmitted this way and then the axons of the ganglion cells would actually go out this way. So makes much more sense having a one way flow rather than having light coming here, the signal going here, then the axons going this way, this is inverted, . By the way, the upside down retina or the correct orientation would be the eye of the octopuses.

Octopuses have a much more logical retina, or their retina makes much more sense than ours. So why is the retina inverted? The retina is really inverted because of the blood supply of the retina.

The blood supply of the retina really has two components to it. It's a dual blood supply. We have the retinal blood vessels that we always see ophthalmoscopically when we look at the fundus.

These blood vessels are Laying lying over the inner retina, they are here and they penetrate into the mid retina, but we also have the choroid that I mentioned earlier, I said it's a vascular layer supplying the outer retina, supplying the Photoreceptors. And this is really the reason why the retina is inverted because of these photoreceptors. I said earlier that retina is an exquisite tissue giving us this wonderful sense of vision.

And it is also the most metabolically active tissue in the body. And not only is it the most metabolically active tissue in the body, it is also the tissue in the body that's most exposed to light and radiation, because really if you think about it, the eye, the entire purpose of the eye is to focus light on the retina. And I take you back to when you were little kids, and you'd go outside on a sunny day, and you'd hold the magnifying glass in one hand, and then you'd get a bunch of dry leaves or, or some paper on the pavement and you would hold the magnifying glass, and it would focus the Sunlight onto the leaves and if you wait long enough, eventually smoke would start coming out of the pile of leaves and it could catch fire, OK, because the magnifying glass.

Focused or concentrated the energy of the sun on that pile of leaves. Well, think about it, your eye does the same. Your eye takes all the incoming light and focuses it on this retina, on the photoreceptors on this 1/4 of a millimetre tissue.

So and it does it 12 hours a day. So by all rights it means, you know, there should be the retina should be on fire. There should be smoke coming out of your ears because It's exposed to so much focused sunlight, and the only reason you don't have smoke coming out of your ears is because of the choroid, sort of a private blood supply or private air conditioning unit for these for.

Receptors, so a cooling unit for the photoreceptors and blood supply for very metabolic the active tissue and that's why the retina is inverted so these photoreceptors could have their own private blood supply. So again, we're talking about a dual blood supply. We have the arteries and vein on the retinal surface, those that we are seeing with an ophthalmoscope and as I said, they penetrate all the way to the mid retina, the outer retina, the photoreceptors, the rods and the cones, they are supplied by the choroid and that's the nature of the dual blood supply of the retina.

So taking a closer look at the retin blood vessels that we're seeing moscopically because this after all is a talk about the fundus. As I said, they supply the inner and mid retina and as in every other tissue and every other organ, they're divided into veins and arteries. The veins are The larger vessels and we usually see 3 or 4 of them.

So this would be a vein, this would be a vein, this would be a vein. Not that they cross in a dog, they cross the surface of a disc, sometimes forming a Venus circle. The arteries are greater in number.

We are seeing about 1520 arteries. They are much narrower in diameter. They are brighter in colour and they start at the rim at the edge of the.

Discs. See, this one is an artery. This one is an artery.

So is this one and this one and this one, note that they start and here is another one. They start at the edge of the optic disc. They don't cross its surface like the veins do.

When we are looking at the fundus, we are naturally drawn to the veins cause, they are the larger vessels, larger diameter, but actually you should train yourself to look out for the arteries cause they are the first. To disappear in retinal diseases and especially in retinal degeneration. So this would be a normal fundus and again we've got 4 prominent veins here and then we've got the smaller arteries starting at the edge of the disc.

This is an eye with, I'd say an intermediate stage of retinal atrophy. You'll notice that the veins are still here. They're narrower than they used to be, but what's striking is that the arteries have almost completely disappeared.

You can just see faint. Shadows of former arteries here, here and here, but they are mostly gone, so train your and here in advanced stage while both the veins and the arteries are gone. But for early detection of retinal atrophy, train yourself to look for the arteries rather than for the veins.

Besides attenuation, we can see all sorts of other pathologies in, blood vessels. Really the eye once again is a wonderful organ in that it is the only organ where you can see blood vessels in a non-invasive manner just by taking an ophthalmoscope. Every other tissue in the body, you need to cut open to look at its blood supply.

The retina you can look at its blood supply just with an ophthalmoscope. And here you can see that obviously there is something wrong with the colour of these blood vessels. The veins are no longer red, they are cream colour and this is indeed this is a case of hyperlipidemia and you can see how lippemic the blood is turned, case of polythemia and you can see how dark and congested the blood vessel.

Cells are, and here you can see how tortuous they've become in cases of systemic hypertension. So yes, you can see signs of systemic diseases that affect the vascular supply or in the blood vessels. You can see them noninvasively with your ophthalmoscope and obviously you can see lots of haemorrhage in the retina, USM.

In the beginning to systemic hypertension, which is what we have here on top, infectious diseases, which is what we have here. Sometimes we have pre-retinal haemorrhage, so different clinical presentations of the haemorrhage depending on where it's originating, but again a very non-invasive and easy tool to see vascular disease in the retina. So we've spoken about the retina vasculature.

The other structure I I want to talk about is the optic nerve head. The optic nerve head or the optic disc really constitutes the convergence of all of the axons of all of the retinal ganglion cells. Here is a diagram showing again the outer retina, the mid retina, and the inner retina with the ganglion cells and you can see that each ganglion.

Cell has one axon relaying the visual signal to the cortex. All of these axons come together, they converge here you can see them histologically. So here are the ganglion cells and here is the nerve fibre layer or the axonal layer and you can see it increases as we approach the optic nerve head because there is a great increasing number of the confluence of all of the axons of all of these ganglion cells in this area.

They do a 90 degree turn and Exit the eye through the hole in the sclera that I showed you earlier in those diagrams, and that's the optic nerve, cranial nerve too. So really the optic nerve head represents the beginning of cranial nerve two confluence of all of the axons from all of the ganglion cells spread throughout the retina converging on this one point. Sometimes you may see that the optic nerve head or the optic disc is located in the total area, sometimes it's located in the non-typetal area.

It doesn't change in location. The location of the optic disc is actually fixed. It is fixed by the, the coordinates, if you will, the topographical coordinates are fixed by the hole in the sclera and The hole in the orbital bone through which the optic nerve must pass to get to the brain.

The difference between this picture here and this picture here is that this dog has a large tepitum and therefore all of the disc is located in the tepium. This dog has a small tepium and therefore all of the disc is in the non-tepitum, but again, topographically speaking, if I was looking at coordinates, they are in identical location. Another normal variation in the appearance of an optic disc is that sometimes you will see it surrounded by a ring, which may be dark as shown in the left here, it may be hyperreflective and incomplete.

Such as your show seeing in the picture on the right, and there is usually a dark spot in the centre of the disc. You'll see it in many of the pictures that I've shown, I just been pointed out before, that's also a common variation. Another common variation, normal variation in the optic disc of a dog is the myelination.

The optic nerve of a dog is coated by myelin. At the level of the optic nerve head and that is really what give, what gives the optic nerve head both its colour and its shape. Notice that in a normal dog, it is pink and circular to triangular.

In shape and you can see that here this is actually a dog with lots of myelination. You can see the original optic nerve head here in pink and then some extra myelination giving it a triangular shape. So this is the myelin coat.

On the left, you have a dog with no myelination, and therefore its optic nerve is round and it is more grey in colour, . And this again would be a normal variation depending on the amount of myelination. Sometimes, however, it is taken to an extreme, as I said here.

You have a smaller and paler looking optic nerve because of lack of myelination, that would be normal. This is already abnormal. This is way too small and way too pale and not compared to the right eye.

Now we are looking at the case of hypoplasia or a smaller than normal optic nerve. Sometimes we can see extra myelination on the surface of the retina. So here you can see it very nicely in this picture.

You can see the optic nerve with the myelin sheath here in the centre, but you The myelination starts at the level of the optic nerve axons as they converge on the optic nerve and that's why we're seeing these pinkish, whitish tufts, myelin coating the axons of the optic nerve head. And this is a picture of a human or a primate fundus and showing very nicely the myelination. You can see the medulated fibres as they are converging on the optic disc of this primate.

So this would be normal variation, extramyelination. Here is some more extramyelination for you again, pinkish tuft converging on the optic disc. This may look like extramyelination, like another pinkish tuft, but actually you see that it's more white than pinkish and actually you can see that it's obscuring the view of this blood vessel here.

This is an optic nerve glioma. This is neoplasia or tumour of the optic nerve. So this would be normal, this would be abnormal.

The only way to distinguish and know that this is normal or not is if you've looked at enough eyes, that would be the most important message of my talk here today. Another two nerves are showing normal and abnormal. So here we have a normal optic nerve looking optic nerve.

And the things for you to notice are number one, how focused the disc margin is, it's very well defined, very sharp, and how well we can see the blood vessels on the surface of the disc, again veins crossing the disc, arteries stopping at the rib. You can see them very clearly on the surface of the disc. Here, the borders of the disc are definitely blurry.

They're not as sharp as this one, and you can see that it's very hard to see the blood vessels on the surface of the disc. They're very sharp and well visualised. Here, very blurry here.

This is a normal dog on the right. This is a case of optical neuritis on the left. Again, you have to see enough dogs to appreciate that and I will be talking about optic neuritis in my next webinar in October when we talk about acute blindness in our patients.

And The final tissue that I want to talk about, after covering the optic nervehead and vasculature and sensory retina, I want to talk about the next tis of the final tissue. I want to talk about the epitum, that wonderful reflective layer that gives The eyes of our patients there, . Shine at night.

This is a picture given to me by a colleague in Brazil and for those of you trying to figure out what it is, it's actually a pond full of alligators or caymans more precisely, and you can see the typical reflection of these caymans here. So count the number of dots, divide by 2, and you can figure out how many alligators are in this pond. So why do our patients have an epitan besides the need for wonderful eye shine?

. They have a epitium in order to increase their sensitivity or at nighttime in order to increase their nighttime vision. This is explained by this cartoon here and we will start with a picture on the left showing 3 photons coming into the retina. This one is absorbed by this photoreceptor, this one is absorbed by this photoreceptor.

The 3rd 1 went through the entire retina and wasn't absorbed at all. It is scattered here in the rectum pigment epithelium. Now daytime when there is enough photons entering the eye, this is not such a terrible tragedy if this photon was not absorbed.

However, at nighttime, if this photon wasn't absorbed, it represents a terrible waste, you know, there are only a few photons entering your eye at nighttime, and each one that is not absorbed is really not seen and therefore it is wasted, you are seeing less well at night. And therefore, God or evolution, depending on what you believe in, said, gosh, this is a terrible waste. Let's help these animals see at night by putting a reflective mirror behind the retina.

And this is what the tepitium is. The tepitium is a reflective mirror located in the choroid, so that now this third photon that wasn't absorbed in the retina through its first pass is striking the tapeto, is striking the mirror, bounces back onto the retina, and now it's absorbed here. It's also depicted here, striking the Caitum and bouncing back.

So we have just doubled the probability that this photon will be absorbed and indeed it has been absorbed. Now it is being seen and being visualised, . As with everything else in nature or evolution, there is a price to be paid.

The presence of the epitium increases your nighttime sensitivity. The patient has just been able to, see this photon. However, note that the photon has, is not absorbed in its original trajectory.

It was supposed to be absorbed by this photoreceptor. Instead, it is absorbed here. It means that the epitium also scatters light and therefore reduces the visual acuity of our patient.

There is a price to be paid for everything. However, As I said, overlying the epitium, we have the retinal pigment epithelium. We have in fact the retinal pigment epithelium, if you remember, overlying all of the choroid including the epiinal area.

And that presents a problem because retinal pigment epithelium, as the name implies, is epithelium that contains pigment. If, and if there is pigment in the retinal pigment epithelium, why the light won't be able to reach the underlying epitium. And therefore, again, God or nature in their whatever you believe in, realise that in order for light to reach the tepitium, the overlying retinal pigment epithelium should be non-pigmented.

OK, so it's a bit of a funny name. We have here non-pigmented retinal pigment epithelium in order for the light to reach the underlying epitium and that's depicted here in these two histological pictures. On the right, you have a non-typetal area.

So we have the sclera here, we have the choroid here, we have the retinal pigment epithelium here, and we have the photoreceptors here. On the left, we have a tilized area. So again, choroid tepitum.

RPE and photoreceptors and note the difference in the amount of pigmentation of the RPE in the picture here and the picture here. Here there is no underlying tittum. Therefore, the RPE is heavily pigmented.

This characterises this location. That's why the non-typetium is very dark because the overlying RPE is heavily pigmented. Here the RPE is overlying with the pit.

Therefore, it is poorly pigmented or hardly pigmented at all, and that's why this RPE is overlying this tapium here and allows the light to reach the non the tapeal area, excuse me. The Titan. Changes in reflectivity depending on the thickness of the retina.

So if we have retinal thinning due to retinal atrophy. Then the tepium becomes more reflective because there is less retina between the incoming light and the tepium. So if the retina is atrophied, you can see that the reflect tepium becomes hyperreflected, more light is reflected back, and that's depicted in these two pictures of a dog with a.

Green tepium. This is normal reflection, but if the retina is atrophied, and we've already seen this picture of an atrophied retina with no blood vessels whatsoever, then the tepium becomes hyperreflective simply because the overlying retina has become thinner. On the other hand, the tepium may also become hyporeflective instead of hyperreflective, and that's in cases of edoema.

If there is fluid in the retina here, then the underlying tepitum will become hyporeflective and here are two pictures from a dog fundus. It's the same dog as you can see by the pattern of the blood vessels. Where we were able to catch retinal inflammation, which you can see here by the blurry edges of this lesion by the hyporeflective edges of these lesions, and here the same lesion is hyper reflective as the disease progressed, the retina has atrophied.

The epitium is what gives, the eye of our patients, some of its greatest variation in colour, in pigment content, size, etc. Let me go through them quickly. Most epitium would be, blue or green.

And yellow, orange, these are the most common colours. However, we can get great epitomes such as what you are seeing here. We can have variation in the amount of pigment, as I said, over the.

The the RPE overlying the pi is usually non-pigmented, but this would all be normal variations of overlying RPE that contains different amounts of pigments, so it's not totally non-pigmented RPE. There are differences in the size of the tepium, as I mentioned earlier, here you see a dog with a very small tepium. Here is a dog with hardly no typitium, and the size of the tepium is actually linked to the size of or associated with the size of the dog.

Big dogs have large tepitium area, small dogs have small tepits, so this may be a Chihuahua or a Yorkshire terrier. This is definitely a small breed dog. The transition area between the non-tepitum and the tepium may be.

Sharp as you are seeing in both of these pictures, or it may be more of a gradual transition or border area and that's been associated with the length of the hair coat. So dogs with long hair coat would have more of a gradual transition such as you were seeing here. Dogs with a short hair coat would have more of a sharp border such as you are seeing here.

And another variation has to do with age. Our patients are born with no tepitum. And this is a fondest picture of a very, very young dog just several days old.

Then the area of the future tepium becomes blue, and that's a dog that's approximately 6 to 8 weeks of age, and the definitive adult epitium would only develop at 4 to 6 months of age, so age is another source of variation. And the final source of variation as I hinted before, has to do with the amount of pigmentation that you are seeing in the RPE shown here histologically. So patients, and I'm talking many.

About dogs here, but also cats, in fact, that have a dark hair coat and a dark iris, extensive pigmentation in these tissues would also have extensive pigmentation in the RPE and therefore the non-type area would be very black and dark. Patients with less pigmentation, with a tan iris and a brown hair coat will have hypopigmented RPE in the non-titted area and therefore it will not be as dark as these ones. See that here we are actually unable to see the retinal blood vessels.

We are starting to see them here. And if the patient is albinotic or subalbinotic, why there is no pigment whatsoever in the RPE and we are starting to see the red reflection of the choroidal blood vessels. Here, if we take a close look, we can actually see the choroidal blood vessels again the radial thick.

Why, blood vessels that you are seeing more clearly here, we call this a tigroid petum, it really resembles the stripes on a tiger. So in animals that are totally albinotic, this is the view that you may be seeing, with the choroidal. Blood vessels here and it will be underlying sclera and sometimes it may be a focal presentation such as in this horse, but again you're seeing the underlying sclera and the broad choroidal blood vessels.

So really, this would be a classic fundus of an albinotic animal. It looks Like a mess, but hopefully by now you can recognise the components. We are seeing the optic disc here, we are seeing retinal veins crossing the surface of the disc.

We are seeing retinal arteries here and here and here and here at the edge of the disc and then with the dashed. Arrows, we are seeing the broad choroidal vessels here, here, here and here. As I said, train yourself to look out for the arteries.

They are the important ones and hopefully by now you can pick them out even in this picture. Which means really that when an owner presents with this dog and they're saying, oh gosh, my dog has a haemorrhage in the left eye. Well, by now you can Take a look and realise no, this is not a haemorrhage.

You can see that this is an albinotic eye because it has a blue iris and therefore we are seeing the red reflection of the choroidal blood vessels through the pupil here just like back in the old days when we had . Cameras with film and a flash in them. You take a picture of a person of, of a blonde person with a blue iris and their pupils would light up in red.

Same thing, you are seeing the choroidal reflection in an albinotic eye. This is a non-albinotic eye with a normal peal reflection. So that's a quick, not a quick, a detailed view of a canine fundus and now that you know what the fundus is built like, I'll take you through, quickly through some other fundus.

So this would be a normal feline fundus. The striking thing that you can see is that there are far fewer arteries, than they were in a dog. Number 2, you can see that just like the retinal.

Arteries of a dog, the veins here also stop at the rims, so with the cat, both the arteries and the veins stop at the edge or the rim of the optic disc. And the other notable thing about the feline fundus is not the optic disc, it is non-myelinated, therefore it is round and pale just like the. Atrophied canine disc that I showed you earlier, which has lost all its myelination, and optic disc of the cat is non-myelinated.

The myelination of the feline optic nerve starts in a more posterior aspect and therefore, excuse me, this would be a classic optic nerve head of a cat, round, pale with blood vessels stopping at the rim. Fewer colour variations in a dog. Here we see the two most common ones, yellow and blue, and just like a dog, we can see variations due to varying amount of pigments.

So again a pigmented eye with a reflection and albinotic eye with a red reflection due to the presence of choroidal blood vessels and the reflection from the choroid. These are the fungus of three ruminant species. The oval, the disc of a cow is oval, that of a sheep is more kidney shaped, and it is more round in a goat.

Note that in all three species, the non Pitum is more grey in colour rather than black and note, especially in a cow, but also in the goat here actually in all of them, you can see that the arteries and veins are paired. They run together and they branch beautifully at 90 degree angle. This is the fungust of the horse.

The optic disc is oval, pink, and in invariably in the non-typetum, it looks like an egg lying on its side, in the non-type area. You don't see blood. Vessels unless you take a very close look and start seeing them here, there is actually a fair number of them.

There's about 50 or 60 of them emerging from the edge of the optic disc, but they run for a very short distance, so really no blood supply from inner retinal blood vessels to the inner retina. All of the blood supply or nearly all of the blood supply is choroidal. Here are some lab animals, you can see a rabbit, you can see a mouse, neither one of them has an epitome, but what you're seeing very nicely here is the prominent optic nerve axons of the rabbit.

The rabbit has blood vessels only going at 3 o'clock and 9 o'clock in the mouse, you can see it radiating like rays of the beautiful, sun. Non-mammals to pictures on the left, a bird on the right, an alligator, you can see that the fundus is non-vascularized in these animals and usually non-tapitalized and in both cases you're not seeing the optic disc because it's hidden by a vascularized structure. It's the peon in the case of a bird.

This velvet-like structure, pigmented structure covering the optic disc of a bird, and here is a conus papillaris, as the name implies, it's a cone, protruding into the vitreous cavity of an alligator. As my teacher in Florida used to say, think of how close I have to be to the alligator to actually take this picture. And finally, humans, this is you and me on the left, we have no epitum but so we can't see as well at night as our patients, but we do possess a fovea and macula shown as this dark spot here shown histologically as this pit here.

This is an area with a great concentration of cones giving us a Very high acuity vision. Only primates are the only mammalian species that have amacula. Therefore, primates have the highest acuity of all mammalian species.

However, raptors would have two fovea. You can see one here and one here and that is one reason why raptors have such a very high acuity vision. So that's a look at the fundus.

Now let's talk briefly in the remaining time about how we look at the fundus, we do it through ophthalmoscopy, thermoscopy should only be conducted in a darkened room following dilation of the pupil and therefore what I usually do when a patient comes in is before even talking, starting to take the history, I quickly check Schirmer tear test, tear production, pupillary lyric. Reflex and intraocular pressure and then I give them a drop of tropekamide in order to dilate the pupil. As you know, tropekomide is parasympathylytic, it can affect tear production, it can affect PLR and can close the angle and elevate IOP.

So 3 things to check before giving tropekomide, put a drop of tropekomide and now you have 15 minutes to take the history, conduct the physical examination. Examine the anterior portion of the eye and by after 15 minutes, you can check the lens and the fundus using an ophthalmoscope, all sorts of ophthalmoscopes out there, divided into two main categories. This is the indirect ophthalmoscope and it's called indirect cause I'm looking at the fundus indirectly through a handheld lens.

The advantages are that it provides a very large viewing field and therefore I can very rapidly get a glimpse of the entire fundus, the tepium non-tapetum blood vessels, optic nerve. I can see it all in 2 seconds. I'm using both of my eyes, so I have binocular vision and depth vision, and I feel safe cause I'm standing at arm's length away from the patient.

The disadvantages are that because I'm looking through a lens, the image is inverted. There is low magnification, which is the consequence of having a large field. If you're seeing a large field, you're not seeing it in great detail and the price, this should be about $1500 US dollars.

A cheap alternative to the indirect is just take your trans illuminator, take a handheld lens, stand at the full arms extension from the patient and you'd get a pretty good fun this image of the patient. The other type of almoscope is a directive thermoscope, handheld almoscope. The disadvantages of this one are the advantages of the direct and vice versa.

So we have a small viewing field with the direct ophthalmoscope, which means that the examination is much lengthier, takes you a long time to see everything that you want to see. You're using just one eye to look at it, so no depth perception, and I'm standing close to the animals which in the case of an aggressive cat or dog can make me nervous. However, we do get an upright image, we get large magnification, so you can see every lesion in great detail.

It is much cheaper because really you only have to buy the ophthalmoscope itself. The handle is the same one that you're using for your transilluminator and your otoscope, so 3 instruments can go on the same handle, very cost effective, and it's got some extra features like philtres and grids. We don't have time to go.

Into that and an advantage, sorry, compromise between the direct and indirect is the recently introduced monocular indirect that you're seeing here, but really it all comes down to magnification versus viewing field. So as you can see here the direct great magnification, look at the detail. Of the optic disc, but very small fields.

So I'd have to spend a lot of time if I want to examine the periphery of the funders. The indirect is the exact opposite, mm small magnification, but look how quickly I can examine the entire fundus with this large viewing field and the monocular indirect somewhere in between. And my final slide and maybe the most important one is please practise ophthalmoscopy on every patient that comes into your clinic, not just on your ophthalmic patient, not just on your blind patients.

Practise it on every patient that comes into your clinic because #1, the technique is complex and it takes time to master it, and number 2. As I've just shown you in the past hour, there is lots and lots of variation and normal variations and you have to learn to recognise normal variation. You are able to diagnose pathology and the only way you'll train yourself to recognise normal variations and to master the technique is if you practise ophthalmoscopy on each and every patient that comes into your clinic, whether it's for vaccination, dermatological problem, or ophthalmic problem.

Practise your ophthalmoscopy and then you'll be ready for my upcoming talk in October about blindness in our patients. Thank you very much and I'll be glad to take any questions that you will mail our host at the webinar vet. Thank you.