Scrubs, Stethoscopes, and Scalpels- The Life of a Vet Student: Ophthalmology

I love ophthalmology. Which I never thought I would say. I used to think eyeballs were gross. Now I think they're cool. Maybe this is part of what they were talking about in first year on how passionate and crazy teachers can convert you. Or maybe it's because Sydney's eyes have been horrible for the past 3 years and it's part of my daily routine to stare at and play with eyes now. Either way, I love it.

Midori, my green iguana. I love her eyes =]

Jack, my bearded dragon. I love how orange his iris is.

Today I had my introductory lab to ophthalmology, where we went over all the basic diagnostic tests and got to test them out ourselves. I can't wait until I have my ophthalmology rotation in 2 weeks... 2 afternoons shadowing vets looking at eyeballs is going to be awesome.

What's cool about these tests too is that some of them can be done at home, if you know how to do them. I've tried them on my lizards, but I don't think the reflexes are the same as in cats and dogs. Two of the tests we did we do so often in veterinary medicine that I forget they're ophthalmic tests... and that would be the menace and palpebral reflex. For the menace response, you cover up one eye on your dog, and then move your hand towards their eyeball, and they should blink. It's like the flinch response that people have. And then in one test, you've already tested two nerves- the optic nerve (the ability to see) and the facial nerve (the ability to blink). For the palpebral reflex, you gently tap at the corner or the eye, and the dog should blink. We use this all the time in anesthesia to make sure the patient is deep enough, because if they are properly sedated they won't have the palpebral reflex, but they will if they're light. And again, this is testing two nerves- the trigeminal nerve (sensation on the face) and the facial nerve (the ability to blink). Another ophthalmic test is another one people can do, and that we do do on a regular basis- tracking. As in, can my dog see this object and follow it. In clinics we use cotton balls, because we know that the dog isn't smelling it or hearing it, and if they follow it they definitely have to see it. And all you have to do is wave it around, drop it on the ground, ect. and watch the dog's eyes or head follow it. And with that, you know the dog can see, and if their eyeballs moved, you've tested the oculomotor nerve and abducens nerve, both of which control eyeball movement.

Then we get into the fun stuff. We did a Schirmer Tear Test to measure tear production, a fluorescein test to look at the cornea, and we did direct and indirect ophthalmoscopy to look at the back of the eye (fundus). We also got to use tonometry to test the pressure of the eye.

For the Schirmer Tear Test, you take a test strip and stick it in the eye, essentially causing irritation to cause tear production. And it does pretty much what the name implies- it's a tear test, so we want to know that a dog can produce adequate tear film. Tear film is what provides nutrition to the cornea, and if you don't have enough there are a whole bunch of problems that go along with that. The test strip has a line of blue dye that wicks up with the tears so you can read it. Normal production in a dog is over 15.

With the fluorescein stain we are looking to see if there is an ulceration in the cornea. The fluorescein dye is this bright, neon green dye that sticks to the stroma of the cornea, which is the layer under the epithelial (top) layer. If there is a corneal ulcer, the epithelium is usually gone, and so the dye sticks to the exposed stroma. So you just have to take a drop and place it in the eye, and then you shine your light into the eyeball, and if there is any fluorescein uptake you will see bright, neon green. If you don't see anything, there is no stromal exposure and probably no ulcer. Which is good.

Sydney after her fluorescein stain- you can still see all the bright green dye around her eye. But no ulcers, yay!

Direct ophthalmoscopy is what they do to you at the doctor's office, where they get that instrument and shine a light right in your eyes. Animal eyes are so much cooler than primate eyes though. Using this we can see the optic nerve and all of the blood vessels in the fundus of the eye. Indirect ophthalmoscopy provides the same end result, but you can look at the whole fundus at once, whereas with direct it is much more magnified and you can only see a small area at a time. That can be fun, because you can look around and find the optic nerve, and then the dog moves it's eyes or head and you get to start over. You don't have that problem with the indirect method, because you're able to see the entire fundus at once.

What you would see with indirect ophthalmology... the little circle in the center is where the optic nerve comes in, known as the optic disc. All the little red squiggly lines are blood vessels. The darker part is the choroid, and the top, lighter part is the tapetum. The tapetum is what makes some animals' eyes seem to glow when you shine a light in them ("eye shine")

Tonometry is my favorite test, just because I think it's cool. Tonometry is a test to measure pressure in the eye, which is most important with glaucoma. We have two different ways to measure pressure. One method uses a little round pin, which shoots out and bounces off of the cornea. The instrument measures the speed with which it returned and gives you a reading based off of that. The other method uses a tonopen, where you press directly on the cornea. You need topical anesthetic in the eye for this one, but then you just push the little probe onto the cornea, and you see the cornea indent a little bit, and you just keep doing that until it beeps at you and you get your reading. Normal pressure in a dog is between 10-20. With glaucoma, the readings are much much higher, like in the 40's and 50's. I really want a tonopen because they're small enough that you can use them on exotics. The only problem is they're like $3000... but since my lizard has such horrible eye problems, I think it could be a good investment in the future. But first I'd have to find out what normal pressure in a lizard eye is.

There is a whole lot more with eyeballs that I could get into, but I won't. At least, not until I have my ophthalmology rotation.