All horses have what is known as corpra nigra as a normal part of their eyes. Horses have these structures hanging from the top and often bottom of the iris (colored portion of the eye); they are believed to shield the retina from overhead sunlight. In most horses, these structures are never an issue, but they can begin to interfere with sight if they become enlarged and cystic. Next time you are outside with your horse, take a close look at their eyes.
When these cysts become large, you may notice an increase in “spookiness” especially when going from dark to light areas or you may not notice any changes in behavior like our current case Sam. In Sam’s case, these were an incidental finding during a routine exam.
Sam is a 5 year old Percheron gelding. When in bright light, his pupil (circular area in iris) would adjust to the light by shrinking. The cysts were so large that they impaired his vision. This was particularly important as he is a working draft horse, proper vision is essential for him to carry out his job! Sam did not display any adverse signs despite large cysts being present on both eyes. To treat Sam, he was referred to an Ophthalmologist who lasered his eyes on farm. A quick, pain free procedure. Pictured below is an example of a cystic iris. To the right, is Sam’s eye directly after being lasered, although it may be hard to appreciate, these cysts shrunk significantly within seconds and will continue to do so over time.
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- This is an example of a cystic iris
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- This is Sam’s eye directly after being lasered
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- This is Sam’s eye directly after being lasered
