One of the most common eye problems in horses is chronic uveitis, or intraocular inflammation (itīs the same = Moon Blindness, Equine Periodic Ophthalmia, ERU).
The technical term for this disease is Equine Recurrent Uveitis (ERU).
The causes of ERU are not nailed down, unfortunately. ERU is a non-specific, immune-mediated disease that results in repeat episodes of attacks of inflammation of the eye or eyes.
There is a current theory, it says that the body develops antibodies to certain infectious organisms, such as the organisms causing leptospirosis, a bacterial infection, and onchocerciasis, a parasitic infection (many other infectious diseases including viral diseases can also trigger ERU). These antibodies are produced by a special white blood cell called a T-lymphocyte. and the antibodies may mistakenly attack tissues in the eye, creating inflammation. The antibodies can continue to attack the eyes months and years after the organism has left the body, either constantly, or intermittently. With each new ERU attack, the eyes are more and more painful and undergo more damage.
However, not all horses with antibodies to some of these organisms will develop ERU.
Genetics play a role too, and unfortunately, Appaloosas with antibodies to Leptospira are 8 times more likely than other breeds to develop ERU and 4 times more likely to become blind as a result of the ERU.
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