Every so often I study Otis’s eyes. Sometimes one is running, or a bit gunky, so I take a long look. And I see these dark bubbles above and below his pupil.
I noticed them first a couple of years ago but didn’t worry too much, and forgot to enquire as to what they were. Anyway, the last couple of weeks I’ve been aware of their presence. Not that they’ve grown or changed, but I was curious as to what they were. As he had conjunctivitis eighteen months ago and the vet checked his eyes last summer I was pretty certain there wasn’t a long term problem. Or that anything was amiss anyway.
In an attempt to find out if these bubbles are normal I’ve been looking at other horses and noticed that some do have the bubbles, perhaps smaller than Otis’s.
Finally yesterday I managed to sit down and do the one thing you shouldn’t do, Google the bubbles. I’m not a hypochondriac and pretty sure Otis’s eyesight is fine, so I looked up the anatomy of the eye.
These dark bubbles, often likened to ruffled curtains, are called Corpora Nigra. They don’t affect eyesight, and all horses have them to a degree, but their role is to shield the eye from bright sunlight.
You can, I read, get cysts on the corpora nigra, which can affect eyesight. But they are easily treated with laser surgery. Symptoms of corpora cysts are increased spookiness, particularly when going from light to dark, and reduced vision.
So my research has set my mind at rest, but it does seem that Otis has large ones so it’s probably worth keeping an eye on them to make sure they don’t get bigger because that might suggest cysts.
Take a look at your horse’s eyes though, and see if you can identify the corpora nigra. A bright torch makes it a bit easier!
Below is an excellent article on the subject – http://thalequine.com/the-equine-eye-what-horse-owners-should-know/
And another – http://www.doctorramey.com/eyes/
The Rubber Curry Comb 
Great post. I’ve often wondered about these too, since my boy has them. Questions answered!