Good evening everybody and welcome to tonight's members webinar. My name is Bruce Stevenson and I have the honour and pleasure of chairing tonight's webinar. I don't think we have any new members on tonight, so, not too much housekeeping.

Just a little reminder that if you have any questions, if you just pop them into the Q&A box, we will deal with those at the end and we do also have A poll question later on, but we will deal with that when it happens. So for those of you that joined us last week, welcome back. I'm sure you thoroughly enjoyed last week's session as much as I did.

For those of you that were not with us last week, just a reminder that part one of Maria's talk is available on our website, and I would encourage you to go back and have a look at that. Not only because of the fact that some of tonight refers back to that, but also for the fact that it was an absolutely amazing presentation. So for the, those people that weren't with us, Maria has been a lecturer on the subject of veterinary anatomy since May 2000.

She worked at ICBAS teaching clinical and systematic anatomies. In 2011, Maria moved to Sydney, where she finished her PhD and worked at USYD and later to the US at UPenn. She's now living in Germany and has never lost touch with the clinical practise of veterinary medicine.

She understands the importance of a good anatomical background for any veterinarian. And as a teacher and speaker, she does not merely focus on the anatomy itself, but rather addresses the functions and clinical importance of certain anatomical structures. Maria, welcome back to the webinar vet, and it's over to you.

Thank you, Bruce. Very nice of you. So, I'll just remind you again what this is about.

So applied or clinical anatomy is about using anatomical knowledge to better understand medical diagnostic and surgical procedures. Again, I like to emphasise that I am an anatomist and not an ophthalmologist, and so I will be focusing on some common eye diseases and issues as we explore anatomical features on the eye. So, In last week's session, we had covered the eyeball itself and the optical nerve.

And this, this week we will be looking into the adnexa of the eye. So last week's session would not be complete if I would not continue by addressing all of these additional components of, of the eye. So we'll be looking into the extrinsic muscles.

So we had last week, we were looking into intrinsic muscles. The intrinsic muscles are the ones within the the eyeball itself, and we were looking at the ciliary muscles and the muscles on the iris. So both of those are One is responsible for the accommodation of the lens, while the muscles on the iris are then responsible for the size of the pupil.

We will be looking now at the extrinsic muscles, which means the, the muscles which are attaching on the outer side of the eyeball and who are, which are responsible for moving the eyeball in different directions. These muscles are here located. Some of them have been sectioned.

They protect the, the vessels and the, the blood vessels and the optic nerve which are coursing here and deep to the, to these muscles, and all of these structures are then covered by orbital fascia. We will be looking into all of these one by one. We will be also addressing the eyelids, so upper and lower eyelid, and the third eyelid, and the respective conjunctiva, which is on the Inner side of these of these eyelids and then we will address the lacrymolaparatus where we will look at the glands producing the tear.

And then the whole system, responsible for the drainage of this of this tear film and sending it over to, to the nas. OK, so let's go one by one. I will start by explaining that the orbit is a cone-shaped cavity located medial to this arc, so we have the zygomatic arch here.

And so it's a conic shape, as we kind of see here. So this is the eyeball and some of it's adexa and it's, as you can see, there's a base of the cone and then it kind of moves caudally or posteriorly, and there's it's apex here located at the, at close to the orbital fissure. So the base of the The base of this cone is located here, where we have the orbital rim or margin here.

And then, as I said, so it's, it continues, stretching towards the orbital feature and, and, close to the of the canal. So here we see the structures through a dissection, again, the eyeball, the lachrymal gland, some of the extrinsic muscles, and then here would be then these these small openings here on the. On the apex of this cone-shaped structure.

OK. So, we have several groups of extrinsic muscles. We're looking into.

22 different groups here and we'll look at, at an additional muscle that does not exist in the, humans and is responsible for retracting the, the eye bulb. So, there are 4, straight muscles, they're called, Their names are relating to the area where they insert on the sclera. So there will be a dorsal straight muscle, there will be a lateral straight muscle, there will be a ventral here straight muscle, and then a medial one.

And as the name suggests, so they're very straight, they're very long. They're not too thick, they're rather thin and flat. The name for them in, in, in, in Latin would be then the rectus rectus dorsalis, rectus lateralis, rectus ventralis, and rectus mealis.

No, we will look into the action of each one of these. There are two additional ones here. This is another group.

These are the oblique muscles. So this is the dorsal oblique. The dorsal oblique is the same like the just like the straight muscles.

It originates close to the orbital fissure as well, and then it runs along on a dorsal position, dorsal and medial position. But it runs through a little cartilage here on a dorsal medial position on the orbital margin, and then curves around this, this trochlea, that's the how it's called, the little trochleum. It curves around it to then insert under the dorsal rectus muscle.

This is one of them. The other one, the other oblique muscle is the, is the ventral oblique. It's, it is actually an exception to all these muscles because it does not originate here on the posterior position, but rather here anterior on the medial position in the close to the orbital ranges from the, the pelotine bone.

So it runs . And, and, passes here over the medial, sorry, the ventral rectus and then inserts here very close to the insertion of the lateral straight muscle or rectus lateralis. OK?

So this is the exception to the rule. It does not, it does not insert close to the orbital fissure, but rather on the medial position here, close to the orbital rim. OK.

So, let me just move you through a few videos before I run you through the, through the next The next muscle. So these are the actions of these muscles. So we will see here the action of The dorsal straight muscle and the ventral straight muscle.

So, what we see here is the contraction of the dorsal straight muscle will pull. The eyeball and rotate it dorsally. While the ventral one does the opposite.

So we have this movement with the eyeball rotating ventrally with the ventral straight muscle. So these are quite easy to understand. Let's look at the lateral and medial, we also have videos for those.

But here we have the lateral straight muscle. The medial is not visible, but it, it's located right here. And I know that this is the lateral and this is the medial because I see the trochlear here.

So this cartilage, which is then on the medial dorsal position to the eyeball. And again, we see the lateral straight muscle contracting and pulling, so the, the eyeball will move laterally. Well, the medial does the opposite.

So the medial rectus or medial straight muscles will do the opposite movement. Mhm. Then we will have.

The obliques, and let's look at the action on the obliques. So, as I said, we have the dorsal oblique coming on a dorsal medial position and then inserting here under. So the tendon inserts under the dorsal straight muscle.

And so, actually, the video starts with the ventral moving. I think it starts with the ventral oblique moving the eye. Let's see how that goes.

Yeah, so that's it. So the ventral oblique is pulling here. It's rotating the eyeball clockwise.

That's what we are doing here. Yeah. And then this is the opposite movement with the dorsal oblique pulling it, .

Medly, but on a dorsal position and then we will have the counterclockwise rotation. OK, make it run again. Ventralloli?

The dorsal like contracting. OK. So this is rather weird to look at them working one by one.

You have to understand that these muscles do not work alone. They work with and you know and with, with other of these extrinsic muscles. And also these rotations are are are not possible without some of these straight muscles working at the same time.

Also, these rotations are also not clearly visible because the pupil is is round in a dog, so we actually do not see this rotation taking place. We will look into into some diagrams of cats where the, where the pupil is then contracted and and in a vertical position, so the slit like contracted pupil, then we will see that these rotations taking place and . Neurological, deficits.

But let me just go through the next the next muscle. So we've seen the straight muscles, we've seen the oblique muscles, and we're now looking into another muscle here which is then the retractor of the eyeball of the bulbus. So the retractor is actually one muscle, but it's divided in in In 4 different vesicles, and then it inserts in a more caudal position.

So if you look here, these are the straight muscles, the straight muscles attached here very on the sclera but very close to the limbus, to the, so we've seen what the limbus was, what's this area. Between the cornea and the sclera. So they come really, really very far and anteriorly on the sclera to, to insert on it.

This is the ventral straight muscle attaching very, anteriorly on the sclera. And then you see here the number 14. So number 14 is the retractor of the boss.

Here's the 14 and here's another part of number 14 of the retractor and you see that it inserts in a rather caudal or posterior position here on the sclera. So what it does, Well, it works, the 4 fascicles work at once and as one, and then they, as the name says, they will retract the bulles. This is an exaggerated movement.

The pull is not so, so hard, but this is what happens with the movement with the, with the retractor. This muscle does not exist in humankind. It does only exist.

In animals. OK. So, in fact, we have these 3 axes, and so we've seen these movements with the medial and the, and the lateral rectus.

We've seen this movement with the dorsal and the ventral rectus. We've seen this movement with the obliques working one by one, counterclockwise or or the clock clockwise, and this is the movement from the retractor of the bulbus. OK, so this is the interesting part of all of this is looking at the innervation of the, of these muscles.

So, it's not too complicated if we understand that the oculomotor nerve is actually the most important nerve responsible for, for innervating all of these muscles. So if we think about it, here's, Pair 3, so that's the ocular motor, cranial nerve 3. So it's responsible for the dorsal rectus, the ventral rectus, the medial rectus, and also for the ventral oblique.

So there are two muscles here, which are the exceptions to the rule. One of them is the dorsal oblique, and this is innervated by cranial nerve 4, that's the trochlear. That's a rochlear nerve.

And of course the name comes from the trochleaa where the, the, the muscle is, is running through or passing through. So trochlear nerve innervates solely this, dorsal oblique muscle. Then we have the lateral labrus muscle innervated solely by one cranial nerve and that's the, the 6th.

That's the abducent nerve. So, 11 nerve for the dorsal oblique muscle and one nerve for the lateral rectus and so we have them all covered, as I said, most of them are innervated by the ocular motor nerve. The, the retractorboy, which is not here represented on this diagram.

Parts of it, so the medial parts are innervated by the oculomotor motor nerve, while the lateral parts are innervated by the abducent nerve. OK, but let's then, let's then try to understand what's going on here with these, with these cats. So what we see here is that there's a, a divergence strabismus or a lateral strabismus.

So, The eyeballs or the, the pupils, let's say that are. Are here on located on, on the, on the lateral side, more peripheral. So what we, we understand from this picture is that the medial rectus is not really working.

But the lateral is pulling hard, right? So, what is going on here is that usually we have a balance between forces from the medial rectus and the lateral rectus and the pupil stays in the middle. But if this one stops working, what happens is that the counteraction from this one will always pull towards To the lateral position and so the pupil will, the eyeball will rotate to the, to a lateral position.

So this is what's happening bilaterally. And so what we have here is the damage on the ocular motor nerve. So if, if it's, it does not have to necessarily be a neurological deficit, but most likely what we see is here the ocular motor is.

Damaged. Maybe other parts of the brain are damaged as well. It can be normally, it's a central, central nervous system issue.

So this is what's happening here. We have ocular motor oculomotor nerve deficits. This is the opposite situation where you have a convergence trabismus.

So what we have here is that the medial rectus is really pulling hard and we do not have a counteraction from the lateral rectus muscle. So what we have here is an issue with the, the innervation, so we're talking about the abducent nerve is not working properly on both sides here. And this cat, so the ola motor is working, but the abducent is not.

Looking at these pictures here, so we have, more or less the same situation here, a divergence, so we have the same situation as, as this cat here. Again, we have an issue with the ocular motor. So the abducent is still working and pulling right there with the, with its like.

Muscle. In this situation, we have this cat, convergence trabismus, so lateral straight muscle is, is paralysed and we have an issue, a deficit from the abducent nerve and the ocular motor is, is working. What we have here is then something unusual, and that is a lesion of the trochlear nerve.

So what happens here is that this pool is and it not existing, is not working, and so what will happen is that the dorsal part of the is relaxed, so this muscle is paralysed and relaxed. So this top part of the pupil will move laterally and there will be a pull here on the ventral oblique, which is not being compensated by the dorsal oblique, and we have this sort of this sort of, situation with, with the obliques, being the dorsal oblique not working, so a lesion or a deficit on the cranial nerve, 4th or trochlear nerve. And again, this situation is visible in a cat when we have this sort of pupil, most likely if we have a round pupil and a, and a dog, we would be unable to, to diagnose this situation.

Moving on, all of these structures, so the eyeball itself, all the nerves and, and blood vessels, the optic nerve inclusive, and then, all of these muscles that I've been talking about, they're all protected and covered by a thick, collaginous, . Layer, that's called the periobita. The periorbital covers all these structures and, and it goes along the per the periosteum of of the of these bones here lining the the the orbit.

And it finishes off at the orbital rim, and here it attaches to the to the bones themselves. So what we have here again is the orbits and, and, the structures are not there, but here I just wanted to show you that the orbital rim orbital margin here is nearly all made of bones, except for this, this little edge here where we have a ligament, and that's the orbital ligament. So it's soft tissue, not a bony structure.

And just showing you that because this, at this point, Beneath these orbital ligament, we will have the, the lacrimal gland located. So the lacrimal gland is located on a dorsal dorsolateral position, when we relating to the, to the eyeball. So periorbita is the outermost fascia that we have here covering all of these structures.

We have two more thinner fascias beneath the periorbita. One is the superficial muscular fascia. This one covers the elevator of the upper eyelid and the lachrymal gland itself, while the deep muscular fascia will cover all other All these extrinsic muscles that I've been talking about, all the straight muscles, obliques, and the retractor and the eyeball itself.

They're not as important. These, between these layers, between these fascia, we will have fat tissue. And what happens is that when the animal is extremely cachetic and and has lost a lot of weight, you will see a sunken eyeball because of all this fat that has disappeared, and then you will see these sunken eyes.

Moving on then to the eyelids now, what we see here. Is the we're looking into the upper and lower eyelids. They meet at the lateral cantus and the medial cantus.

These, eyelids are covered by, skin on the outer surface and on the inner inner surface, they both have conjunctiva. So looking at a transverse cut through through both of them, what we see here is that here's the skin as an outer layer, there's an intermediate layer here with muscles and and glands and fibrous tissue, and then here we have the contrativa again as mucous membrane on the inner as an inner layer. So these muscles here, there, there's there's more than one muscle.

This is the main one, the orbicularis oculi. The orbicularissoli is like a sphincter muscle. It goes all around the pal palpal fissure.

The palpable fissuring is is the opening between the, the two eyelids. So this orbicularis oli muscle goes all around here and just like a sphincter muscle, it just closes the . Closes the eyes, so it closes the palpable palpable fissure.

We have an additional muscle here represented on the upper eyelid, that's the levator palps superureus. It's, it lifts, lifts the, the upper eyelid. Between these muscles, we can see fibrous tissue, so that's the tarsus.

And here, as a, on a deeper layer here we see some Some glands, these are important glands. These are called the torsal glands. They secrete through small canonically small ducts.

They have little pores here opening on the, on the margins of each, eyelid, so both, upper eyelid and lower eyelid have little openings here where these tarsal glands secrete. An oily substance that will be responsible, well, it will be part of the tear itself. I will explain that later on.

Still on the other side of the. Outer side of the outer layer of each of these lids, we see these cilia or eyelashes, so these additional hairs which are protecting the, the eyeball itself. Mhm.

So, so looking at the applied anatomy here, so what we see is that in some cases, in some breeds, there's a tendency for situations like this where we have, well, sharppes are, are here represented already. Where, mostly the lower eyelid suffers, suffers an inversion, so it rolls inwards and so these cilia, these eyelashes and the and the skin itself, gets in contact with the surface of the, of the cornea. So it's, it's creating injuries to the cornea and of course extreme pain because the cornea is so sensitive as we, as we've seen last week.

So there are numerous possibilities here as possible sur surgeries to to repair this problem. This is a temporary solution. And this is only for animals that have not, that have not completely outgrown, so they're not, adults yet, and so, these are just temporary solutions, while these are just the, the final and definitive solutions where part of the skin is removed and there are, as I said, different options according to the, the type of entropion.

We here we have the opposite situation where the eyelid itself is kind of sagging away from. From the eyeball itself, so it's not in touch with the eyeball. And what happens is that when this happens, there's more as a tendency for the dry eyes to, to develop because the, the tear film is not 100% distributed over the, the, the surface of the cornea.

And again, there are different methods to, to solve this, this problem, surgically. This is another situation, we're talking now about facial deficits or facial paralysis. We're looking here at the menace response.

So we're testing here, so we're moving the, the hand very fast towards the, the eye. And we're actually testing if the, we're testing two cranial nerves at the same time with this, with the menace response. So we're testing if the animal is able to see, so we're testing the optic nerve.

But at the same time, when the animal closes its eye, we're testing the facial nerves. So the this orbicularis oculi, this muscle I've told you that that is occupies a large part of the. Of the intermediate layer of upper and lower eyelid should be closing this this palpable fissure, closing the eye once this threat is, is, so this, this response is, is active.

So we could, by this we're testing, as I said, two nerves, the optic nerve or the and the facial nerve. We can actually also touch the medial canus, for instance. We do that quite a lot when we are testing.

Palpable reflexes in anaesthesia to see how, how how deep the, the anaesthesia, how far we, we're going. And so, we are touching, the edges or the borders or usually it's the medial canus and so we're actually in this case, Not testing the optic nerve, of course, but testing the trigeminal nerve, which is the, the one responsible for the sensory pathways, bringing the sensory information to the brain. So that's the sensory information coming the brain going through the trigeminal nerve and the facial nerve now responding, so the motor pathway, again, contracting the orbicularis oly and closing, closing the eye.

That's the palpable reflex. In these two pictures here. We have chronic facial paralysis, so these muscles have not been working for, for quite a while, and so we see facial asymmetry.

So this side is absolutely healthy, absolutely no issue, and we here we see that the left side of this cocker spaniel is the muscles are relaxed, they're not contracting, they're not moving, they're paralysed and so we see here already on. The temporal area that this muscles atrophied. Also these, you can see that they're atrophied and, and the whole lip is, is drooping, the eye as well, and the ear.

Also, the same situation here with this Labrador. Again, and as symmetry with the face. The palpal fissure is different on left and right, and again, the cheeks, the, the frontal and temporal area, and the, the ear are, drooping.

Yeah, so that's facial paralysis. Moving on to the 3rd eyelid itself. So the 3rd eyelid is usually not visible.

It becomes visible when, when we have, for instance, damage on the cornea, as a, as a protective measure, this, this eyelid, can protrude and become visible. When the animal is sleeping or very sleepy, we can also, kind of see part at least of this third eyelid. This turtle lid, as I said, it's located in, it's, it has a semi-lunar, shape, sort of a triangular shape.

Usually this visible border is pigmented. And it's located here in the medial angle, so it's under, under the both upper and lower eyelids. So it's being pulled normally by, by a smooth muscle that retracts it and pulls it and keeps it kind of hidden behind these all of these eyelids and the medial angle.

Unlike the other two, so this one is, covered both on the outer layer and the inner layer, we have conjunctiva. And it has a cartilage to support it. So it's a T-shaped cartilage that sustains.

The the third eyelid, and at the base of this tea we have a lachrymal gland. So it's the laryal gland or the gland of the third eyelid. This gland is able to produce about 30%.

Of the the the film itself. So, again, looking at the applied anatomy, this is what people usually call the cherry eye. And here, I hope this diagrams are clear enough for you to understand.

So, here, simply we're looking at the cartilage itself with a T shape, you know. So again, the T shape and then we see that the gland is here located then at the base of this T. And now we're looking at the 3rd eyelid here.

So this is the transversal sagittal section of the eyeball, and we see here the 3rd eyelid touching it, touching the, the eyeball itself, and then hiding here behind the, the lower eyelid and hiding here, and the, the, the gland of the third eyelid is really deep, deep down here. So in this first picture, we have an inverted eyelid, so the, the border of the this margin, it kind of reflects, deflects itself and then inverts and and can and can just stay like this and sometimes it's not even clear that it that it's, it's taking place. Because it's minimal, the opposite situation can happen, so where we have an inflexion outwards.

So this is, this can also happen. But what we see here with this cherry eye is this situation where we have the third eyelid completely folding itself, where the, the gland itself moves up. So it moves on a, in a position between between the third eyelid and the eyeball, and it just goes, so superficially and outwards.

So, In the past, people, and when I started to work, people still did this. They just cut this gland off and removed it completely. Meanwhile, this technique is no longer it's no longer done because they because the scientists have done, made it clear that this, this, third gland is actually, this gland of the third eyelid is actually important for, as I said, 30% of the production of the tear film, so it's better to keep it.

So this is a technique to reduce and, and put tension on, and on that, on the conjunctiva and over that gland, so that, that That there's no chance that the, the cartilage is able to, to fold itself and, and that the situation is happening again. Yeah. Looking at something else, there was a person asking me about Horner's syndrome last week.

Hope, Jana's still there. So Horner's syndrome is, of course, a combination then of Different, different signs here. We have, what we have in general with Horner's syndrome is that the sympathetic innervation to the, to the eye is missing.

So here we have again the diagram I showed last week. These are the sympathetic nerves, these are the parasympathetic as the green, the green lines here, and here's the sympathetic pathways. So we have, and the sympathetic.

Nervous system, we have two main nerves. One is pre-synaptic before the synapse, and then this is the post-synaptic or second, . The neuron.

So what happens, it can happen, so the lesion can happen on this postsynaptic neuron or the presynaptic. It doesn't matter. What, what does happen to the eye is what we see here.

Which is, so this pupil is contracted. As we've seen last week, the parasympathetic, action on the eye works on the sphincter muscle of the, of the pupil, and so it contracts the pupil. So when the sympathetic innervation is failing, as I said here, the parasympathetic will have no antagonistic, action and so the the parasympathetic will.

Will prevail and we'll see here the a contracted pupil. The other situation we see here is that the palpable fissure is smaller, so it's narrower. We see also that the eye is somehow retracted, and then we see this, we see a protrusion of the third eyelid.

So some scientists say that these two situations, the narrower palpable fissure and the protrusion of the third eye eyelet take place because there's an ophthalmus because the bulbus is retracted caudally because the retrac boy is, is pulling it back. Others are saying that the optosis, for instance, is happening is taking place because there are smaller muscles, on the eyelids, that are, smooth muscles and then they're under sympathetic innervation and when they are also not working then, so this takes place. The orbicularis oli is, is stronger and there's a optosis taking place.

The protrusion of the third eyelid is more visible in cats because here we have smooth muscle and pulling this, this third eyelid, and, and this is why it's normally more visible in cats than in dogs and dogs, this, this retraction of the third eyelid is not so much from this muscle, not, not taking, not this one is not so important due to this, to this muscle. What else? Mm, OK, so, what I wanted to say with this image here is that most of these situations of Horner syndrome are taking place because, so it's they are opathic situations, so unexplained, but some do take place here at Timpanabula.

Because part of these fibres run through the bulla or close to it, ventrally to it. And so when we have an otitis media, so when we have really an otitis externum moving in into otitis media and we have the tympanic bula affected, these fibres can be affected and then we could see this taking place. So on Horner's syndrome taking place right at the on the same side as where we would diagnose an otitis medium.

So, since we were looking at the eyelids and the conjuncti already, let's go and try to understand this now with the conjunctiva and the different parts of it. So we've seen that the inner layer of the of both the lower lid. And the upper eyelid have conjunctiva, that's called the pulpro conjunctiva.

And we've seen the bulbur conjunctiva and when we were talking about the sclera, and I said that the visible part of the sclera was covered by bulbur. Conjunctiva. So this is actually one single structure that folds itself and continues one way or the other.

So the palpable conjunctiva folds itself in in the back, and that's where this angle where it turns from palpable conjunctiva and it starts covering parts of the sclera as bulbar conjunctiva, we call the the angle itself, we call the conjunctival fora. Here we have 2, where we have the 3rd eyelid, we have the palpable conjunctiva and the forex here, and another 4ex here because there are 2 there are 2 deflections here of the of the conjunctiva. There's an additional information here, which I did not put on the diagram because I thought that there would be too much information here.

This space, this potential space between the palpable conjunctiva and the bulbar conjunctiva is called the conjunctible sac. So all this space here between the two and reaching out to the conjunctible, conjunctible forex. All of this is the conjunctible sack.

And why am I talking about this? Because when we look at the the lacrimal glands, what we see is that they secrete. The tears over to this, in this area, the, the conjunctible sac right here, and both of these down here.

And then with the blinking movements, what we see is that the tear film which has been lodged here, deposited here in this, in this conjunctive sac, will be then spread over the surface of the cornea. No. So conjunctivitis, so the conjunctivitis can as an inflammation or infection of the, of the conjunctiva.

It can take place due to diff for different reasons, so it can be allergic, for instance. Or foreign bodies, for instance, can lodge themselves into these, into these conjunctable sacks and and be difficult to to be removed. Or we can have a situation like this where we have kerato KCS or Crato conche devita ica where The lack of or the lack of reduction on the production of tear will will create will create an issue over the cornea and on the conjunctiva itself.

In either of these situations, what we see normally is bileferospasm, so signs of pain with high shyness, shyness, lethargy and altered behaviour. Sometimes we see an elevated third eyelid, so kind of this protective measure to protect the, the the cornea and the conjunctiva itself. Here we see serious edoema here on the conjuncti itself.

This is the bulbar conjunctiva here. And we see epio the some, some. Some higher amount of, of tear production.

The lachrymal apparatus. So the lachrymallaparatus is all about the production of tears and drainage then of these tears and and mucus that is lodged on the over the surface of the eye bone. So we have here, as I've mentioned a few of these glands again.

So we have the lacrimal glands, and as, as I've said, it's located dorso laterally to the eyeball itself, under that, beneath that orbital ligament that I've mentioned. This lachrymal gland. Secretes then, about 70% of the tear.

The gland of the third eyelid secretes about 30% of the of the tear film. Both of these secrete what we call the watery layer of the of the tear film. So the, the tear film is actually has three components.

One is the watery part, which is the, the, the largest part of it. Then we have a superficial layer on the tear film, which is an oily, which has an, she is the oily part, it's superficial to the watery part, and we still have glycoproteins circulating in between. So, both the lachrymal gland and the gland of the third eyelid, as I said, they produce mostly this watery part, the main part of the, of the tear.

While these torsal glands that I had mentioned here, located on the upper and lower eyelid, the dorsal glands produce the oily. Which means this, superficial layer which is covering the water. And why, why is it, why is it so important to have this oily, layer because it actually avoids the tear or the, the watery part from dripping.

Directly out of the eye, over the, over the skin. And it's it's keeping the, it's avoiding the evaporation of the watery part, and it keeps it within, so it keeps it within the, the palpable fissure. So the conjunctiva itself is somehow also important in, in not in the production of tear, but as, as as production of mucus and, and so that it keeps the moisture as well over the surface of the cornea.

So the tear film is produced by all of these glands, as we said, and then it is spread through the surface of the cornea by the blinking movements of both the upper and lower eyelids. And and then it must be drained. So this the film has has washed the, the surface of the cornea, so it's, it's kind of washes all the foreign bodies that were on the surface.

It has, it has been responsible for protecting the, the cornea and keeping it transparent, but also to to to nourish part of the superficial layers of the cornea as we've seen last week. The eyelids by blinking and by closing, they're not only spreading the tear film over the surface of the of the eyeball, but they're also protecting the eye from excessive light. So they're protecting the retina.

So let's look into the drainage system now of the electromal apparatus. So we have, we start with the electromal punctum. These are little openings right here.

They're on the medial border or the medial edge of the of the margins of both upper and lower eyelids. So we have one on each side. These little openings then continue with two small cannalicullis, so these little thing, these two cannali coli are here then subcutaneous, of course, they're not visible.

They're both under the skin, the medial ankle, and they converge to the larymal sac, a small deposit here, which is excavated on the lacrimal bone. From here, The, the tears and the, the mucus drained from the surface of the eyeball will continue through this long nasolacrimal duct. So this nasolacrimal duct is actually running within a canal in the lacrimal bone and then the maxilla itself.

And then it finishes off here, and the nares normally ventral to the ailer fold or the ventral nasal meatus. It's not so easy to find the opening, but it is possible to identify it with proper lighting. Here we're analysing, the production of, tears, so we're doing the Shermer test and within one minute, this, strip should read about 18 to 22 millimetres, so that's how, how much it should spread, so the, the amount of, of tear should reach these values.

Here we have a little dog, with tear stains. This can be happening for different reasons. The lacrymal puncta could be blocked for some reason, and then we have excess tears running down the the face.

These larymal puncta can be cannulated, and so they, they both can be found here on, as I said, on the medial edge of the upper and lower eyelids. They then can be cannulated and And unblocked, here we can see, a test, so we can analyse if, if the system is the the drainage system is working or not by simply putting a drop of fluorosoine on the surface of the eyeball, and we see if the If the mesolacrimal duct and the whole drainage system is working and that the fluoroine then shows up here and at the nares. With these two pictures of inoculations, I just wanted to show you that There are 2 different, at least 2 different, surgical ways of proceeding and for the nucleation.

Here we have a transconjunctival and here we have a lateral innucleation, independently of which technique is technique is is used. You will see that in both, in both techniques we the the muscles are being severed here very close to the sclera, so most of the muscles are being kept. Inside the orbiter they are left behind and we are trying only to remove the eyeball itself and nothing else.

So not the muscles should be mostly left in the orbit along with the fascia, along with the fat, along with All the vessels and, and nerves in the back. So not to have a, a very big depression and, and when, well, when, when the procedure is done and postoperatively, that it's not so aesthetically you know, shocking for, for the people. But one thing that I wanted to mention with these inequations is that people have to make sure that the upper and lower eyelids are removed, and also the third eyelid has to be removed, and of course the, the lachrymal gland as well.

So the whole system producing t film has to be removed, the dorsal glands, the The, the, the lacrimal gland from the third light lid and the lacrimal gland itself are all being removed, so there are no, there's no accumulation of, of tear, after the inoculation is, is performed. And I think that was it for today. I hope you have enjoyed it.

I do not have a poll question, but I do have some suggestions, and I would appreciate if you would, try to help me figure out what would be interesting for you guys rather than me just pushing topics, which might not interest too many people. So, thank you. See you next time.

Thanks, Maria. Thank you very much for that. So folks, we are going to do a slightly different poll question to what you are used to, in that it's not a question to ask you what is the correct answer, as far as part of the presentation.

But Kyle is going to start the, poll for us now. Simply click on the subject that you would, best like to hear us get Maria back to talk to us about. Now, there's a lot to read on this and the poll question obviously can scroll down so that you can choose what you want.

Please do not be too worried about this. You'll see question A is write your own suggestions. You are welcome to pop those into the Q&A box because those are kept, after this presentation.

Or what you can do if you think of something later on, simply just email in to the office. And, Dawn or Kyle or one of the other fantastic team that we have in the office will be able to pick those up. And, we are always looking for topics and subjects.

Some of you that have been on with me before, know that I like to, remind everybody that the webinar vet is our channel. It is not here for anybody else but us. So the subjects, the topics, the talks that you, we want to hear is what we are brought by the fantastic team of the webinar vet.

And this is why this variation on the poll question that Maria has brought up to us and the emails, if you want to later on, to send into the office, it really does help us to know what topics people are wanting to hear. So while that runs in the background, and Kyle will monitor that. Maria, thank you very much for a very, very insightful, talk this evening.

And I have to say that, there was a couple of, let's call them nervous moments for me in the beginning when you were talking about all the cranial nerves, and it had flashbacks to anatomy, in the beginning of my University days, and I, I could feel the sweat starting to run down my back as I remembered. Professor LeRoux, I even remember his name 35 years later, asking me what nerves did what. So, thank you for those memories.

Maybe not such fond memories, but lovely memories. It's always easier when we're listening to somebody like you. You know, spouted, and you go, well, of course it is.

And, and I was sitting here with my fingers running through the pneumonics of how I remembered all the cranial nerves and everything. So, that was lovely. Thank you.

I, I think we, at the end, when you were talking about nucleations, for, for those of us that have surgical biases and that, we always dread an innucleation. Not so much because the surgery is very, precise and delicate, but because we might leave a little bit of gland behind and, you know, you get, post-op check and it all looks great, and then a week or three later, they come back and the eye is all swollen and your heart just sinks because you, you, you may or may not have left some of that land behind. But, once you know the anatomy, as I said in your bio, you know, you yourself are a great advocate of this.

It's not only Knowing the anatomy for the anatomy, it's the functionality of it. Yeah, that's true. Actually, no, just coming back to your, to your, to your flashback.

That's exactly my, my first, my first suggestion there is B, which is two sessions about cranial nerves and about neurological exam and, and lesions. I have a lot of fun with cranial nerves. I, I actually enjoy them very much.

It's, it's playing with them in the end. Yeah, and it, it's, they are so important, you know, and they are terrifying to students and, and I think to clinicians alike, you know, when you get that case and you got to Start, doing neurological exams, you get this, this flashback and you, you've got to kind of think about what you're doing. But they are very, very important.

So, hopefully, we get a lot of, a lot of requests for that one because that would certainly be one that I would want. We do have some questions coming in, Maria. And, one of them which is very interesting is, what is the evolutionary purpose of the oblique muscles?

The evolutionary. Oh, I wouldn't know with, with evolution, how, how that they, as I said, they don't work by themselves. They work in conjunction with, with the other extrinsic muscles.

You do not see them working independently, they move together with, with all the others. So also even the the retractor bulbus is a muscle that does not work by itself. It works together with all the others.

So, It's, it's difficult to say exactly where, where it stands to, to, to, for the need to rotate the, the, the bulb in a clockwise or counterclockwise because it, it's, it's a machine that works together with several others and It's difficult to say where exactly there's a need for a counterclockwise or clockwise rotation when you, you're looking up or looking down, but this has to do most likely with, as I said, this slit-like, pupil, so with the movements of the, of the pupil itself. Yeah. Well, you know, we, we know that in, in humans, it's stimulated by the excessive consumption of alcohol as well.

So, in animals that, that probably doesn't really hold true there. So, anonymous, we can't give you an answer to that one. Greg has come up with quite a few, interesting questions, and he wants to know why are golden retrievers prone to Horner syndrome?

And, again, this is most likely in an idiopathic, condition in most, in most breeds. It's, there, there are several studies trying to understand how, they are damaged. In cats, as I said, this is, most of the times taking place with, with the bulletin pannika because it's, it's a larger compartment in cats.

And, and so there's a stronger relation to, to the sympathetic, innervation. But in, in the different breeds, some say it can be hereditary, but there, there's so many studies and they haven't still figured out because there's 3. There's the central part of the nervous system, so the, the autonomic nervous system or, or sympathetic nervous system still runs centrally, and then it has these two.

These two, neurons, the presynnatic and, and, post-synaptic neurons. So it has such a long chain before it gets there because it goes all the way to the thorax before it actually runs back to the, to the head and to the eye. So it, it's such a long pathway.

I still, I think it's, it's still taking years before they figure out why some, some breeds are more prone or less prone to, to get it. It'll keep some grad students busy for a few years to come. Arthur has, he's also been taken back like me.

He says, brilliant revision takes me back to the anatomy dissections and sharing one cadaver between four of us. Welcome back to the memories, Arthur. One more question because we're running out of time also comes in from Greg and it's a very, very interesting one.

Do chameleons have more extrinsic muscles? Comedians. Yeah.

I, I told you he's got some interesting questions. I have to read them all. More extrinsic, I know that the humankind does not have a retractor, retractor of the bulbus.

That's, that's one thing I do know. And I do know that there are some people who are able to control some of the, the muscles here on, so. Let's say the retractable was it pulls back, right?

And then there are some muscles within the, the eyelids which are keeping the eye, in, I mean, protracted as a forward, no. So what happens is that what, and these people, they're able to have some control over those muscles on the pulpyre, and they can, they kind of do this exothalus, so they push it, push the, the bulbos out of the eye, which, which is extremely horrifying to watch. But but I know that some people are able to do that.

If comedian, I think with comedians will not so much the, the muscles of the eyes, they use more the facial. The facial muscles and that's, that's more with the facial, facial nerve, not so much the. Yeah, and I think with the, with the extrinsic eyes.

I think those people that can sort of push their eyes out like that are when they learn to control it, it's quite freaky. And once again, you know, the rest of us just get it induced by excessive alcohol. So it's all good, it's all good.

Maria, we've come to the end of tonight's session. It's been absolutely fabulous listening to you. And just a reminder for those of you that The first part of it.

You certainly can go back onto the website and go and have a look at part one. The information is absolutely fantastic. And Maria, it is my absolute pleasure and honour to be able to thank you for your time and the team will feed back to you on those poll results and we look forward to sharing your company on the webinar vet in the future.

Thank you so much, Bruce. It was a pleasure today. Thanks, Maria, and thanks to everybody for attending tonight.

We really appreciate it. To Kyle in the background, my controller. Thank you for all your help and to our new member of the team, Amelia, welcome to the webinar vet.

And from myself, Bruce Stevenson, it's good night. Good night.