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Learn from the Pupil

It’s always scary. You walk into the barn and right away sense that something is wrong. The horse that is usually at his door is way back in the stall. As soon as you enter the stall he comes over, seeking comfort and relief. Even in the dim light you can see that one eye is shut tight. There are tears running down his cheek. You speak softly and very gently try to pry his eyelids open, but he won’t let you. You know he’s in pain, and you are in a panic.

Veterinarians get calls like this quite often. All we know from your phone call is that you have a horse with a painful eye. It could be anything from conjunctivitis to a punctured eyeball. As you know, eyes are sensitive, and many things can cause the kind of pain that will make a horse keep his eye shut. As a veterinarian I ask myself: Should I cancel another call to get to your farm right now, or can it wait a bit when I will be a half hour closer to you?

My tendency in most cases is to give you some first aid measures over the phone which will enable us both to better assess the situation within a couple of hours. The first thing I would probably tell you is to give your horse a systemic anti-inflammatory medicine. Banamine or Butazolidin (Bute) are quick acting and very effective. The homeopathic remedy, Arnica, is also helpful. Next I advise cold water soaks. Throw some ice cubes into a pail and then some cold water. Make a pad of a folded hand towel and dip it into the water. Wring out the excess and very gently place the pad over the horse’s eye. He will probably flinch at first, but once he feels the coolness, it will be welcome. Hold the pad gently on the shut eye for a few minutes, then wet it again and reapply. Keep this going for about an hour, and in most cases the eye will begin to open for you.

Before going further we need a quick anatomy lesson. The colored part of the eye is the iris. The iris is muscle. Its opening or closing lets more or less light into the inner eye. The pupil isn’t really a structure; it is the dark opening that is regulated by the iris. Think of it as the doorway to the inner eye. When the iris constricts as in bright sunlight, the pupil is smaller. In the dark the iris pulls back and the pupil gets larger.

You can evaluate the overall seriousness of most eye conditions by checking the relative size of the pupil. Nothing tells more about the overall health and condition of an eye than the diameter of that pupil.
Severe eye inflammations cause a spasm of the iris and make it constrict even more than it does in bright sunlight. It constricts so much that pupil is hardly visible at all. All you can see is the colored iris with the pupil as a tiny dot in the middle. Compare one eye to the other. If the painful eye has a small pupil as compared to the other side, it means a serious problem. This is important information for your vet and his or her decision as to how soon to see your horse.

Tonight, after dark, take a strong flashlight out to the barn and look at some horses’ eyes. Watch the pupil constrict as you shine the light directly into the eye. Compare both sides. Having done this you will be in a good position to let the pupil be your teacher should you ever have an equine eye problem.


– David A. Jefferson, D.V.M.

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