Tuesday, June 11, 2013

Corpora Nigra Cyst?

Last Saturday, when I went on a (mostly) very nice trail ride with Pie, there was one odd incident - Pie caught sight of a group of people walking, about 75 yards away, and was very worried about them - I actually thought he might spin and bolt (even though we were with another, calm, horse) - he clearly was having trouble seeing them well enough to know what they were.  Once they got closer, he was fine.  It was a very bright, sunny day, and they were to his left - this is relevant information.  Then later this week, when I was riding him in the indoor arena, he was very nervous and spooky about an area where there was high contrast between dark and light.  Pie'd had some spooky moments in the past - we think mostly attributable to Lyme disease - but they'd stopped being a problem a while ago - and all of a sudden the problems - which seem to be visual - are back.  Pie is not normally a spooky, nervous or reactive horse - his idea of a good time is to stand still and chill out.

I took a good look at his left eye - his spookiness is usually on the left side - and saw something that concerned me enough that I made an appointment for our vet to come out next week.  We'll have them look at his right eye too, but that appears to be less of an issue.

All horses have what is called corpora nigra in their eyes - they're sort of ruffled curtains that extend from the iris and are supposed to provide extra eye protection in bright light.  Some horses, however, develop cysts - round growths - either attached to the corpora nigra or free floating.  Sometimes these don't cause vision problems, but sometimes they do - if they're large enough, they block all or part of the horse's vision, particularly in bright sunlight.

This site has a lot of gruesome eye photos, but if you scroll down, you'll see several corpora nigra cysts - the one in Pie's left eye is larger than any of the ones pictured.

This site also has some good information about various eye ailments, including cystic corpora nigra.

And here are a pair of photos (found on a forum site) showing a cyst in lower light and then in bright light.  The larger cyst is on the front end of the eye (to the right in the pictures) - Pie's is on the back end of the eye:

Pie's pupil does not appear as obstructed as that in the photos in bright light, although his single cyst is even larger than the one pictured - I think it has gotten much larger over the last year.

Dawn has what appear to be several small cysts, but they've never caused her a problem, and Red's vet check noted that he had very large corpora nigra - but no cysts.

We'll see what the vet has to say - the good news is that, if this is the problem, treatment with laser surgery is often very effective in resolving the issue - the surgery deflates the cyst, resulting in much improved vision.


  1. Interesting reading.Poor Pie, he has had some troubles

  2. Wow, good for you for noticing. I've never seen anything like that, and now I'm thinking I should pay more attention to my horse's eyes! Hope Pie is ok & his issue gets resolved quickly.

  3. Have been busy and haven't been around much on my horse blog, but have been busy at the barn. I just checked in here and now I'm going to go gaze into my horse's eyes. I will be following this - glad laser is highly successful if needed.

  4. A side note - once you start looking closely at your horse's eyes, you'll see a lot of weird stuff - even normal corpora nigra look strange, and there's a lot of variation from horse to horse. Red's vet check commented that he had unusually large corpora nigra, but that they might never give him a problem, and so far they haven't.

    1. Just saw this post. Have same issue with my horse and vet is recommending laser surgery for both eyes. It would be great to see an update and know what to look for and expect from the horse owners point of view.

    2. Janet - we haven't done anything yet - just watchful waiting - so I don't have any further info to offer.

  5. Looking at eye structure in horses isn't something that many of us think to do. Myself included! Hope the treatment works, and Pie can stop worrying.

  6. Good for your for checking his eye. I am going to mention this to a fellow boarder because I believe her horse has vision problems. Thanks, once again, for a very informative post. I have my fingers and toes crossed that the laser surgery is a go and that Pie is his old self again soon.

  7. Oh, I'm so sorry to hear this! Eye issues are certainly nothing to overlook, and can be devastating. That's how our issues with Harley began, becoming spooky, then graduating to several other key areas, like not liking to be too far away from other horses, tripping, not wanting to go down hills, but mostly the spooking kept getting worse and worse to the point I became a very nervous rider anticipating the spooks, which he, in turn, became worried. We fed off each other and it became a vicious cycle. Until that fateful morning when he galloped straight into our hay cart, his vision never occurred to me as a potential cause. I hope you can get him some help before it's too late. Contrary to what some people may say, riding a blind horse anywhere except in an enclosed arena; is not fun. Poor Pie, he seems to have more than his fair share of problems.

  8. I'm So Glad You Caught It...I Know That You've Mentioned Eye Sight In The Past...Good Follow Through And Research!
    Good To Know He'll Can Be Had In The Laser Surgery.

    And Yes, Tomorrow This Oregon Girl It's Going To Do Some Eye Gazing Too!


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