Hi everyone, and welcome to this webinar on ocular dilemmas in equine pre-purchase examination. I'm Rhea Cholder, a board eligible veterinary ophthalmologist with a particular interest in equine ophthalmology. And I hope that by the end of this session you'll feel a bit more confident, not only recognising but also interpreting the ocular findings that you might encounter when performing the eye exam part of a pre-purchase examination.
So we're gonna start off by looking at some of the limitations of the pre-purchase exam when it comes to the eyes specifically. Then I'll spend a little bit of time covering what I think is the best approach to getting the most out of the eye exam part, although I'm not going to dwell on that bit too much because. I imagine most of you have already attended the relevant CPD vetting courses that cover that, so yeah, we'll go through that just in brief detail.
We'll then go through some abnormal findings that you might come across, followed by some variations of normal er that can sometimes catch people out. So here are our aims for today. So ideally be able to perform a systematic ocular examination for a pre-purchase examination.
Recognise common normal variants, identify lesions that might influence a purchase decision. And also know when to refer to an ophthalmologist for a specialist opinion. And as we go through these conditions, I'm going to show you quite a few photos, and with each photo you're going to see this kind of traffic light system, so either a green, amber or red circle in the corner.
And this isn't a, it's not kind of like a rigid scoring system per se, but rather a bit of a guide to help you think about just how significant a finding is in the context of a pre-purchase exam. So green for me means that the finding is generally considered an incidental abnormality or a variation of completely normal. So it's something that you might want to document if it's an incidental abnormality, but in most cases it's unlikely to affect er the horse's vision, welfare, or intended use and therefore, you know, unlikely for you to advise against purchase based on this finding alone.
The amber, . Kind of means that the significance depends a little bit more on the individual case, so you'll need to interpret the finding alongside things like the horse's history, age, intended use, and any other ocular abnormalities er you've identified. So these ones will require your clinical judgement, and sometimes further investigation or a referral might be appropriate.
And then the red, that's for more more important findings that might raise a a bit of concern in your mind, so things that have the potential to be, for example, progressive or painful, vision threatening, all kind of require some form of ongoing treatment, . You know, they don't automatically mean that the horse shouldn't be purchased, but they do warrant a discussion with the prospective purchaser about the potential implications on that horse's intended use. But remember that no, no single abnormality that we, we discuss should ever kind of be interpreted in isolation.
This, a vetting is about assessing the whole horse, and these collars are just a bit of a guide to help prioritise your level of concern, I guess. So as you guys know, There are lots of limitations to a pre-purchase exam. It's a single day assessment of the horse's health and soundness at that time on that day, which does limit how much you can tell the owner about the state of the horse's overall eye health.
And it's not a pass or fail. Our role is to assess and communicate our findings that could represent a risk for the horse's intended use, so that the prospective purchaser can make an informed decision, and ultimately it's, it's the purchaser who decides whether they're comfortable with that level of risk that you have identified during the examination. Now the good thing about eyes is that they're really easy to examine on the whole, so you can just look straight at them and straight inside them with the naked eye, unlike, you know, the heart, the lungs, you know, joints, so you can assess them pretty easily.
And with very little equipment. And there's also no dynamic component to the eye exam, so I actually think it's one of the easier parts of a vetting, because there's less, there's less inference and it's less subjective as long as you know what looks normal and what doesn't. The eyes also are pretty good at showing evidence of having had acute injury, previous injury before.
And thankfully there are two, usually, and so if there is an abnormality in one and you're not 100% sure if it's just a variation of normal, or, you know, an incidental finding, you should in theory have a control eye to compare to, which is priceless. You're also not expected to quantify vision in a horse, so. You know, there's no kind of, oh, he's 5/10 visual or, you know, 6/10 blind or whatever.
It's a yes or a no visual or blind slash severely impaired. So again, easier than assessing lameness, for example, in my opinion. Having said that, I do appreciate that there are a few things about the eye exam that can be quite daunting, so it does require you to be comfortable using, a direct ophthalmoscope, which is usually the only piece of equipment you'll actually have for examining the eyes during the vetting and.
If you're not comfortable using a direct ophthalmoscope, it's gonna be really hard for you to do a good job at bettings because in order to look at the fundus at the back of the eye, you need to know what to do with a direct ophthalmoscope. And I don't have time to go through. How to perform direct ophthalmoscopy in this webinar, but the, I did do a webinar a couple of years ago on just that, so if you are a bit unsure or you're just starting out doing vettings, it might be worth giving that a watch.
Another challenge with eyes is there is just a huge amount of variation in normal eyes and until you've seen a lot of them, or, you know, you've gone on lots of ophthalmology CPD. It's actually really easy to mistake normal for abnormal or the other way around, and I was certainly guilty of doing this when I wasn't super familiar with eyes. There are also issues with the conditions in which you're expected to examine these eyes during vetting, so, You're often in a dark, well, sometimes not a dark stable or a barn, but there's kind of windows, there's doors, there's lots of noise, the horse isn't sedated, the owner might not be very good at holding them.
Which makes it really challenging, and you are a little bit, at the mercy of, the environment in which you're performing the, the vetting. And then on top of that, we also don't routinely dilate the pupils for a vetting, and That makes examining the lens and the fundus at the back of the eye really, really challenging. So even You know, experienced vets would struggle to get a really good look at the lens and the fundus without dilating the pupil, but, this is pretty much what you're expected to do, which is, which is a pretty big ask.
So how likely are you to actually find a significant eye problem during a vetting? Well, There's a fair few studies out there that have looked at different groups of apparently healthy horses to see how common ocular abnormalities are. And around 5 to 10% of horses were found to have an eye abnormality in these papers that was considered significant enough that it could potentially affect vision.
So, you know, it's pretty low. However, these studies did just look at quite specific populations of horses, so particular breeds or age groups, so, take it with a bit of a pinch of salt. However, these studies also were performed on the whole by ophthalmologists or, you know, people with extensive ophthalmology training and using things like slit lamps and dilating the pupil.
So I think in general practise using just a direct ophthalmoscope and without dilating the pupil. The chances of you detecting a significant ocular abnormality are going to be a fair bit lower than that. So where do we start?
So, number one, assess the horse from afar. And I think this is a step that's really easy to overlook. A lot of people sit, and kind of straight in with their direct ophthalmoscope, to have a close look.
But if you do that, it's surprisingly easy to miss some subtle but significant abnormalities, so before you do get up close, just stop, you know, there's no rush, take a few seconds to just stand back and watch the horse, ideally from kind of outside the stable, and you can do this whilst you're having, you know, the bit of kind of chit chit chat with the with the owner. And just have a look to see. You know, does the horse's behaviour seem a bit unusual?
Are they unusually spooky? Is it favouring one eye or trying to look out of one eye more than the other? And then once that's, once you've done that and you're kind of in the stable with the horse and it's got its head collar on and restrained.
Just stand in front of the horse, you know, from a bit of a distance and compare the two eyes, for any symmetry, any asymmetry before you start kind of touching the horse. So Are the upper eyelash angles the same, are the pupil sizes the same? Is there more kind of discharge from one eye, does the tapetal reflection look the same in both eyes, all those types of things.
And these small asymmetries, if they are present, can be pretty useful clues and help direct the rest of your examination. So for example, if you had a horse with mild unilateral posterior uveitis, for example, it may look almost normal if you examine each eye individually and kind of separate from each other. But when you compare them side by side from kind of standing in front of the horse and going to and fro, you might notice that one eye, for example, has a little bit more tearing or a lower eyelash angle or a smaller pupil, and you know, none of those changes are dramatic on their own, but together can be enough to tell you that something isn't quite right.
And taking those extra few seconds to stand back, and compare both eyes before you start the close-up exam can make a huge difference to what you pick up. For example, if you went straight in and examined this eye close up without looking from afar, you might think, yep, this looks fine, er, the horse is comfortable, you know, there's no discharge, the cornea looks nice and clear. The Iris looks OK, nothing really stands out.
But then if you take a step back and use your ophthalmoscope to illuminate both eyes in turn from a distance, some really important differences become obvious, so you can see in this eye on the left . That the vitreous, which is this bit here, is a different colour to the other side, and that's suggestive of something called vitritis, which is a classic sign of posterior equine recurrent uveitis. The iris is also darker, which again can indicate chronic uveitis.
The next step is to assess vision and perform a kind of basic neurophthalmic examination to assess your cranial nerves, so you want to check the menace response, pupillary light reflex, and the palpebral reflex in both eyes. And if you identify any deficits, they're likely to be clinically significant and they will warrant further investigation. So, for example, a horse has an absolute menace menace response on one side, but a normal PLR and normal popebral.
That should tell you that the eye is detecting light, you know, the retina is working, but the horse isn't consciously seeing with that eye, so then you should start looking for causes of blindness, such as a cataract. Likewise, if you had an absent or reduced PLR compared to the other eye, that can indicate either a neurological problem but also potentially a structural disease within the eye that's actually preventing the iris from moving normally. Once you've assessed the vision, and the neurophthalmic reflex, you can move on to examining the ocular structures themselves and.
This bit is actually pretty quick if everything is normal, but the biggest tip I can give you with with this bit is to be systematic. So try and examine the eyes the same way every single time you do a vetting and stick to a routine that works for you. That way you'll develop a bit of a muscle memory and you're far less likely to miss something.
So I like to start on the outside of the eye and then work my way in, but you could do the opposite or you could do something else entirely, so long as you have a system and you do it the same each time. It's amazing how easy it is to miss things like little eyelid masses, for example, if you don't have a set routine. Especially, I think when you're starting out, if you're a bit stressed about it, or, or you're rushing or you're tired or all of those things, .
You're more likely to miss things if you don't have that muscle memory. So I do the adnexa first, so eyelids, eyelid margins, move in, conjunctiva, third eyelid, and then cornea, iris, lens, fundus. And now I'll go through each of these in turn, just looking at some of the more common abnormalities you might come across and more importantly, which ones are likely to be significant in the context of a pre-purchase.
And it's worth me mentioning that, You're unlikely to come across really really obvious and severe eye disease, that hasn't already kind of been identified, so. You know things like a huge ulcer or a perforated cornea, you know, glaucoma, for example, they're all things that. You know are important, but these are things that are going to have been really readily apparent clinically and will have hopefully already been diagnosed and then disclosed to the prospective purchaser, so I'm not going to spend any time covering those really extreme obvious abnormalities because I think you'll, that won't be a dilemma for you.
But instead I'll focus on the more subtle findings that are maybe easily overlooked. So first, the adnexa, this are, this is, basically the accessory structures around the eyes, so the eyelids, the eyelid margins, the eyelashes, etc. So get your light source.
And this can be done in a in bright light, you know, you don't have to kind of close all the doors, etc. When you're examining the annexa, but you do need a light source. And examine the eyelids all the way around.
And try to ask yourself whether the margins are sitting nicely against the eyeball or whether there's any kind of rolling in or rolling out, so that's entropion or ectropion, both of which can predispose to chronic irritation, recurrent infections, ulcers, etc. And then whilst you're kind of looking around the eyelids, you also want to be checking for any eyelid margin defects, so notches or areas of scarring. Small notches, pretty common in horses, likely insignificant, so long as there's not any associated hairs rubbing.
Against the cornea, but larger lid defects can basically disrupt the normal spreading of the tear film across the eye, which does increase the risk of corneal irritation and and ulceration, etc. So this horse, for example, has obviously had some kind of lower eyelid laceration medially in the past and as a result it's got this scarring and this defect. Now this, it's not too bad actually because of the third eyelid being in this region, that's kind of protecting the cornea where this laceration was.
So this is less serious than a margin defect that would be lateral, for example, but still abnormal, needs noting. I'll put it as an amber because it, I think the significance of this depends a little bit on how that eyelid moves, when the horse tries to blink, and whether there's any evidence or history of this causing, an issue in the past. You're also going to be looking for any eyelid bumps, swellings, lesions on the eyelid that might look near plastics, so sarcoids, for example, are probably one of the more common, but other, tumours like squamous cell carcinoma as well.
And these are important because they might enlarge over time, they might require removal or laser treatment, so these, yeah, you always want to document these. So for example, this is a horse with multiple areas of kind of scabbing and ulceration on the eyelids which you know, not uncommon, especially in horses with this kind of depigmented skin. And these might be kind of pre-cancerous kind of actinic changes, or these might already be, you know, squamous cell carcinomas, so.
I put this as a red because If this is a squamous cell carcinoma, which you're only going to know if it's biopsied, we all know that these can be pretty locally aggressive, they can be expensive to treat and they can recur even if they are treated, so, yeah. Pretty important that the owner is aware of these, er, the prospective owner. Finally, pretty uncommon, but some horses, particularly Frisians weirdly, have, can get this condition called dystoiasis, which is when they have little extra eyelashes emerging from the eyelid margin that can then rub against the cornea and cause kind of chronic irritation.
On their own, if there's only kind of one or two and, they're not particularly thick or spiky, they're probably fine and clinically insignificant. But if there's a lot of them, or if there's a few really thick kind of clusters, then they can be clinically significant. And they can be pretty difficult to spot, which you can probably see from this photo.
I've circled two of them, but there are actually a couple more on that lower lid medially. But yeah, if this horse had You know, zero history of anything, you know, conjunctivitis, discharge, then I wouldn't be worried about those. But yeah, if there was a horse with a lot of them that kept getting recurrent discharge, recurrent conjunctivitis, then that would obviously raise a little bit more of a concern, but they are treatable, so they can be treated with cryotherapy or electrolysis, but again that's money, .
So yeah, definitely should be discussed. Then once you've assessed the eyelids and eyelid margins, move in and look at the third eyelid and conjunctiva, so. The third eyelid is at rest.
It's usually pretty kind of tucked away, so what I tend to try and do is . Push the eyeball back a little bit, so through the upper lid just with my thumb or one of my fingers, just gently push the eyeball back, and what that will do is it will make the third eyelid just passively protrude, and it'll allow you to assess more of it, . And the main thing we're looking for on third eyelids is squamous cell carcinomas, pretty much.
So, yeah, it doesn't take long to protrude the 3rd eyelid and it's pretty well tolerated, so worth doing. The cornea is usually pretty straightforward to examine also because it's obviously at the front and abnormalities are pretty visible to the naked eye. The challenge is more just deciding whether what you found is, is significant, so just start by looking at the cornea, again, this doesn't necessarily have to be in a darkened stable.
Small Focal areas of cloudiness or opacity are usually scars, so just fibrosis, assuming that is comfortable, this is. And they're pretty common in horses if you actually start looking because, you know, horses just like to stick their heads in spiky things and they're usually the result of a healed ulcer. So a small scar with no sign of ocular discomfort is just an incidental finding, and I wouldn't be worried about it.
So focal scars like this, . Note it down, but nothing to worry about. One thing that you should pay close attention to with the cornea is whether there are any blood vessels growing on the cornea, so that's called corneal neovascularisation.
And If that's present, it's basically telling you that the eye is responding to something, so there's some form of ongoing or recurrent insult, and the cornea is trying to respond to that. And one of the more common causes of that in horses is something called immune mediated keratitis or IMMK. And this is clinically significant because Although many cases of IMMK respond quite well, to eye drops, so steroids, for example, some cases do eventually become refractory to treatment and require, surgical intervention, which is, in the form of something called a carotectomy or cyclosporine implants, and neither of those are cheap and.
The surgery can cause scarring as well, which then may affect vision. And active IMMK can cause a little bit of discomfort, can require, you know, long periods of medication. And with that, you know, you've got withdrawal periods as well if you're using things like steroids and your horse competes at FBI events, so .
Yeah, one to watch out for, and this is an example of IMMK and You know this could potentially have gone unnoticed I guess by the seller, but when you have a really close look, you can probably appreciate that there's a bit of a haze to the cornea. There's blood vessels growing on it, yeah, and this one would be where I would definitely recommend that this horse is assessed by an ophthalmologist so that they can do a slit lamp exam, characterise the disease a bit further and discuss treatment options. Moving on to the iris, so this is probably one of the more common places to find abnormalities, .
And I do find that this part of the exam is easier when you're in a dark and stable, so. Try and just block off as many windows, doors, etc. And What that will do is it will just reduce any reflections that can hide potentially some subtle changes inside the eye.
One of the more common findings you'll come across with the iris are a granular erytica cysts. So these are usually found on the dorsal pupillary margin, but they can, they can also occur eventually, but most are dorsal and they are kind of smooth round, cysts basically arising from the edge of the pupil. And small ones are.
Generally considered an incidental finding, although they do in theory have the potential to get bigger, I guess, but, small ones I'm not so worried about. Large cysts, and they can get pretty big, . Can potentially affect vision because they occupy a big, proportion of the people, they can also be quite mobile sometimes, so, And they can kind of bob around inside the eye when the horse is moving, which can contribute to, spooking behaviour when the horse is being ridden.
So this one, for example, actually on the ventral border. Nice little small one. I wouldn't be worried too much about this.
This one obviously a little bit larger, it's off to the side, which I guess is a good thing, . But yeah, a bit of a question mark with this one, I guess I'd want to know. How quickly it's popped up.
And also if it's fixed or bobbing around quite a lot. If it was fixed and had been like this for years, I probably wouldn't be too worried about it. This horse, however, obviously this granuloridica is huge, almost completely filling the pupil and the visual axis, so more concerning, will definitely be affecting this horse's vision, especially, in bright light when the pupil is constricted.
So this one is a, is a red, but. Having said that, granuloritica cysts are quite easy to treat. So, laser ablation, for example, which can be done standing, can get rid of these quite nicely, but again, kind of like the testicia, you know, it's important that the prospective purchaser knows that treatment would likely be needed, .
Because, you know, we don't wanna be necessarily putting owners off buying a horse with this, for example, it's to make sure that they just have the information they need to make an informed decision. Personally, I mean, I would rather buy a horse with this than one with, you know, a, a 1/10 lameness that we don't quite know what's causing it or, you know, a really subtle, grade one heart murmur, you know, that has a much more uncertain prognosis. So even though this has got a red.
Just because it's currently obstructing the horse, the horse's vision. It's a condition with a good treatment option, so, certainly not a hopeless finding. Next is something called iris hypoplasia, which is pretty cool and it's something you'll usually see in horses with kind of blue eyes, and walled eyes, and more often on the upper part of the iris, although it can occur on the lower part too.
And it looks like kind of darker or slightly raised or bowed looking patches on the iris, but what you're actually seeing is an area where the iris tissue is really thin, so it's hypoplastic. And if you shine your light source through the pupil using retro illumination, which is when you look in the dark and shine a light at the eye to get that petal reflex. You'll often be able to see the tapetal reflex through these thin areas which kind of confirms your diagnosis as well.
And for the vast majority of horses, this is simply a variation of normal, incidental finding, won't cause any pain or affect vision. However, There are cases where you can get quite severe iris hypoplasia. And that's when they do, it does become a little bit more significant because when the hyperplasia is really, extensive, the pupil, the iris, sorry, doesn't have enough tissue, to dilate.
So the horses basically have a really, really small pupil all the time, and that can interfere with vision. So, most cases of this would be a green for me, but, and you can reassure the purchaser, nothing to worry about, but. If the iris changes are really extensive and the pupil or the pupil's shape is noticeably abnormal compared to the other eye, remember we've got another eye to compare to, it's worth thinking about whether this actually could have an impact on the function of the eye, so.
This is an area of iris hyperplasia, dorsally, . Relatively mild, I guess, it is bulging forward a little bit, but presuming this pupil fully dilates in a darkened stable, then this wouldn't be an issue for me. Whereas this horse, we have much larger areas of hypoplasia, both on the top and the bottom of the iris and.
If you look how small this horse's pupil is, it's absolutely tiny. So, and this was the case in dark light and in bright light, so this would pose an issue for vision, which is why it's a red for me. Melanomas as well on the iris, pretty common, tend to look like patches of dark brown or black within the iris, sometimes kind of a bit bulgy.
Most of these are actually, not super exciting and very slow growing. And I mean, I've known horses that can be kind of symptom-free for, you know, years, if not, you know, for their whole life, with an iris melanoma. Whereas in some, they get quite big and they start to push against the cornea.
Or cause uveitis, or even secondary glaucoma, so. Small ones like this little one up here. Not very exciting, I would note it, but, move on.
Obviously this is pretty big and you're unlikely to be presented with one like this, I think, but I just wanted to show you what an advanced melanoma looks like and. It's obviously pretty evident in this horse with a really pale iris, but it might actually not be as evident if this horse had a dark brown iris. This also has a couple of, eyelid melanomas, as you can see, so yeah, this would be a red for me.
This melanoma is probably pushing up against the cornea, . And yeah, this would be a bit of a red flag for this eye. The iris is also part of the uvea, and the uvea can tell you a lot about whether there's been previous inflammation inside the eye, so uveitis, particularly equine recurrent uveitis, so ERU, which.
It's the leading cause of blindness in horses and one of the first things you might notice in a horse with ERU is that er there's a change in the colour of the iris, so more often than not it becomes darker, sometimes it becomes lighter, but the vast majority get a darkened iris. And you also want to look for something called synechia, which are little adhesions that form inside the eye, after, a bout of uveitis, and they most commonly occur between the iris and the lens. And if you see those, they're a pretty good clue that the horse has had previous uveitis, and even if the eye looks quiet on the day of the vetting.
So hopefully you can appreciate here how the iris looks kind of velvety and is this diffuse really dark brown colour which is not normal. We also have an abnormally shaped pupil called dyscoria and that's due to all of these little adhesions that you can see here around the iris, so they're the posterior synechia that I mentioned. So what all of these things tell you about this horse is that it's either had a a single really bad bout of uveitis from something like blunt trauma or this is an ERUI.
Either way, this is one that I would want to have a full, ophthalmic assessment of with it's pupil dilated, assess the lens, assess the back of the eye, so that the owner can make an informed decision. Another one, as you can see, diffusely darkened iris here, you've got posterior synechia. Causing dyscoria, abnormally shaped people, all changes consistent with previous uveitis, it's also got little, little cataracts, .
And this also has vitritus, which is inflammation of the vitreous, or the jelly at the back of the eye, so that's why that reflection looks kind of like this murky pond water colour. So yeah, this horse looks like it's got active disease rather than just a chronic historic disease. And the reason we're so bothered about ERU as ophthalmologists is that as I previously mentioned, it is the leading cause of blindness in horses worldwide and it's not just a condition that goes away, it's progressive, it's painful, so even if a horse looks comfortable on the day of the vetting.
But it's got signs that it's previously had uveitis. There's no guarantee that it won't have another flare-up of uveitis in the future. And it's just a nightmare of a disease to manage, so the flare-ups often require really intensive treatment, frequent vet checks, prolonged periods of work or out of competition, you know, again if they're competing, we've got all the withdrawal periods to consider, so.
If you do find evidence suggesting previous or active ERU during a pre-purchase, yeah, send this horse to an ophthalmologist, get them to give the pro prospective purchaser, their opinion so that they fully understand what they're getting themselves into. There are also quite a few normal variations of the iris, just like there are in people. So horses can have a bit of a a a range of iris colours, so pictures of lighter bits, dark bits, white spots, really, really beautiful, so yeah, don't be caught out by these.
Moving on to the lens, so the most common abnormality you're likely to come across is cataracts. And these can vary hugely in size and shape, so they might just be a teeny tiny little speck within the lens that has no effect on vision, or they could. Involve, you know, the, the whole of the lens, resulting in complete blindness.
And if the horse did have a complete cataract, you would hopefully have detected that previously when you were doing a neurophthalmic assessment because it would have been an absent menace response and also when you did your distant examination, you would have noticed that there was no petal reflection on that side. But when it comes to examining the lens close up, again similar with the iris, I find that this is much easier if you're in as dark a stable as possible. You want to hold your light source, whether that's just your direct or a pent torch by your temple.
And then I find if you crouch down slightly, just so that you're below the level of the horse's eye, so you're looking up to the horse's eye and you shine a light straight towards the pupil, at about farm's distance away. You want to try and get that foetal reflection, so, . If you're struggling to see this, to be a reflection like in this photo, just.
Change your positioning a little bit, crouch down a little bit more, change your angle and it can make a big difference, so. You're basically looking for something that is blocking that tapetal reflection. So This is an example of a cataract that is being illuminated from behind like that previous picture.
I think they've tweaked with the settings on this, it's all very dark, but you can probably appreciate how that little cataract is, is blocking that tapetal reflection from you. And another one, so this is being illuminated directly, so that's why it's looking white rather than black. And this is called a nuclear cataract, because it's just affecting the middle of the lens.
And another cataract here which Would be a bit harder to see compared to the previous two, especially if the pupil wasn't dilated fully as it is here in this picture. Now you probably noticed that for all three of those cataracts, I had a red, traffic light for these. And the reason is Personally, I think that any cataract seen during abetting warrants at least offering the prospective purchaser to get the horse examined by an ophthalmologist and.
The reason being is that any cataract has the potential to progress, get bigger, affect vision. Now there are some that are more and less likely than others to progress, but. Realistically, without a slit lamp examination, without dilating the pupil, it's really hard to assess and localise er a cataract and the extent of it.
So, you know, even specialists can't always tell people how likely a cataract is to progress, but. I think when that's coming from a specialist, people are much more likely to, to kind of be OK with that than if their GP vet is telling them. So, yeah, don't be kind of strong-armed into hanging your hat on whether you think a cataract is likely to progress or not unless you are super, super familiar with eyes because it's, it's not easy to predict.
Another thing with the lens that you will definitely come across, especially if you're vetting older horses, is something called nuclear sclerosis. So this is a completely normal age-related change where the centre or the nucleus of the lens becomes denser over time. And it gives the lens a slightly cloudy, bluish appearance when you're just looking at the eye in normal light and often people mistake these for, for cataracts, but it's not a cataract, and it doesn't usually affect vision.
So this image is a pretty good example and this is being illuminated just directly, so with a, with a pen torch for example from the front. And you can see this kind of central slightly hazy and iridescent area, which is the nucleus of the lens and . The way that we know that this is nuclear sclerosis rather than a cataract is that we will still get that bright to petal reflection through this, if we, retro illuminate.
And also we'll be able to look straight through this when we come to our fundus exam which is next, whereas if this was a cataract, it would kind of block our view to the back of the eye, so. If you see a bit of cloudiness in the centre of the lens in an older horse, but the eye is visual, you've got a good pedo reflex, you can see the fundus, don't panic, it's just gonna be normal age related nuclear sclerosis. Finally, we will move on to the fundus or the back of the eye.
Again, this is the bit that you need the place to be as dark as possible. Doing this in a brightly lit stable is super, super hard, so don't even try it. .
The first abnormality you might come across from time to time is something called an RPE or retinal pigment epithelium coloboma, which is also known as a window defect. And these are pretty small, well defined, usually circular, depigmented areas just next to or close to the optic nerve heads, so this is an example and. Coloboma basically means a piece of tissue that's missing, so in this case, the, the retinal pigment epithelium or RPE is absent, which is allowing you to see the underlying structures, which is why it looks lighter.
Than the kind of surrounding non-topetal fundus here. And we don't really know what causes these, but what we do know is they don't tend to affect vision and they're not progressive, so if you come across one of these, not something to be concerned about, just document it and move on. Another similar one here and they are this kind of often this kind of bilobed appearance, not always but often, so again, nothing to worry about.
And one here as well, right next to the optic head. Next, butterfly lesions, which most of you have probably heard of. They're sometimes also referred to as peripapillary chorioretinopathy or peripapillary chorioretinal scars.
And these look like butterfly wings, hence the name, kind of areas of hypopigmentation or pigmentary disturbance on either side of the optic nerve head. And it can just be one wing or it can be two. And these are a bit of a grey area in terms of what they mean.
So they can be seen in horses with ERU. But they can also be found completely incidentally in horses with no history of eye disease whatsoever. So on their own, their clinical significance is a little uncertain, hence the amber light.
In general, if you found one of these and a horse had no history of previous episodes of kind of ocular pain, discharge, or, you know, actually diagnosed uveitis, and the rest of the eye looks totally pristine, then they're likely just an incidental finding. And one thing I was always taught to look for with these is try and look at the little fine retinal blood vessels around the optic nerve head when these are present and if you can still clearly see those little blood vessels around the optic nerve head, that's more reassuring to me. So, these ones here are much more visible here and you can kind of see them here but not quite as nicely.
But yeah, this not worry me too much, it was otherwise perfect. But on the other hand, if you see them and there is, you know, the iris is a bit darker than normal, there's a teeny little area of posterior synechia or the retinal blood vessels around the optic nerve head look pretty weedy, then I'd be more concerned. Proliferative optic neuropathy is a condition seen mainly in older horses, so, you know, you might, you will see it if you're especially vetting horses kind of 15 years plus, and these appear as little small cream coloured pieces of tissue protruding from the optic nerve head.
And again, as is often the way, we don't know what causes these, but they are considered an incidental age-related finding, so. Unless the lesion is really big and kind of obscuring the optic nerve head, it's not really thought to have any significant effect on vision, so all good, note it down, move on. Senile retinopathy again is something in older horses, hence the name and it is considered an incidental finding and it looks like kind of the best way I can describe it is these black cracks in the in the retina, often near the optic nerve head or at the junction between the tapetal and non-tapetal fundus, which is the dark bit and the kind of bright reflective bit.
And this is a pretty mild photo, mild case, but it can be quite extensive and. As long as that is visual, these are also of no concern. And then finally we have bullet hole retinopathy or bullet hole chorioretinopathy, also known as focal chorioretinopathy, or just bullet holes.
And these appear as small round, areas of what we call pigment clumping, so little dark, spots with a lighter ring around them. That are usually present in the non-petal fundus, or, kind of just around the optic nerve head. And there's a few theories as to what causes these.
There's some schools of thought which think that these are related to EHV one infection, or inflammation of the choroidal blood vessels, but as it stands at the minute, there's no definitive proof as to what causes these. And Also these are generally considered an incidental finding, again in the absence of any other clinical signs. And then, you know, there's one study that found that these were actually present in up to about 20% of a population of normal horses that were studied, so they're they're not uncommon, especially if you really go looking for them.
And you might read or hear in some CPD that if there's a lot of them, . Then they might affect vision. But As far as I'm aware, that is still not to be proven.
There was a study published in 2014 that looked at horses with absolutely hundreds of these, and they did an electroretinogram, which was basically assessing the, function of the retina. And they found that they didn't affect retinal function at all. So, personally, I still consider these an incidental finding, even if there's quite a lot of them.
And now some variations of normal in the fundus that you're likely to come across, and again there are quite a few, so it's not abnormal for horses to have these kind of hazy rays coming out of the optic nerve head. So, this is just myelin, which is normal, so we call this peripapillary myelination. And again you can kind of probably appreciate the haziness on this one as well, and this is, this is actually a really nice photo to appreciate those retinal vessels that I was mentioning earlier.
And different coat colours will also often cause variations of normal within the fundus, so this horse had this big blaze, almost like a white face and. It has almost this corresponding streak or kind of blaze in its fundus as well where there's no pigment, there's no tapetum sorry in this streak here, which means that the underlying choroid and the blood vessels can be seen, and this is totally normal. And this is kind of the same thing but affecting a much larger area of the fundus, so this horse has hardly any tapeum, and everything looks kind of very pinky, yellowy, so this horse will probably be colour dilute and.
This type of fundus can catch some people out. I've done a second opinion on one like this, and the vet who was quite experienced, thought that these were, retinal haemorrhages because he just looked at the back of the eye and it was just all red, but yeah, it's just a beautiful, normal, subalbinotic fundus. So in summary, when performing the ophthalmic exam, or we're vetting.
Be systematic, examine every I'd say, every time, and don't rush. Document every abnormality, even incidental findings, I would document them. When in doubt, don't guess, you're not there to guess, there is always the option to recommend examination by a specialist ophthalmologist.
If that's declined, fine, but you've done your job. And remember the purpose of a pre-purchase. Your role is not to pass or fail the horse, it's to identify abnormalities, explain their likely significance, or refer to someone who can.
And then just to finish, I just wanted to put some things into perspective as well, so. Losing vision in an eye or even a horse losing an eye altogether isn't necessarily the end of a horse's athletic career, so, plenty of horses go on to perform at very high levels even with one functional eye, so. Adventure to Cannon in the middle here, had his, right eye removed because of ERU.
Still went on to win Pitstead with one eye, for example. Wren's Breath on the left, successful racehorse with one eye. Patch on the right, .
One eye ran in the Kentucky Derby with one eye, so. While having an eye that is visually impaired or having to have one removed is not ideal, it doesn't automatically mean a horse can't have a successful ridden career. That said, It does come down to the individual horse and what the purchaser wants to do with it, so temperate temperament, and just personality of the horse plays a huge role and, you know, a calm, sensible, mature horse may adapt amazingly to Losing an eye or losing vision in an eye, whereas, you know, a really highly strung, naturally spooky horse may become more reactive if that happens and they lose an eye, which would obviously have safety.
Safety implications, but it's not for you to decide. I just wanted to put it into perspective because, you know, you can't chop off a lame leg, but you can chop out, a defective eye and the horse can be totally fine, if it has that done. So, Yeah, hopefully after that you'll feel a little bit more confident tackling the ocular exam of a PPE and the reality is that most horses will have completely normalised and you won't have to worry about this, but by following the same systematic routine every time, you're much less likely to miss something important.
So yeah, thank you very much for listening.
