Moon Blindness, technically known as Equine Recurrent Uveitis or ERU, is one of the most common eye diseases of horses and the leading cause of equine blindness. It gets its name from the waxing and waning course of the disease, where active bouts of inflammation are followed by weeks, months or even years of apparent inactivity. However, ERU is an immune-mediated disease where the body’s own immune cells may continue to attack eye tissue in between obvious episodes. These attacks produce signs such as squinting, tearing, “red eye,” a cloudy eye, swelling and sensitivity to the sun.
If an underlying cause for the condition can be found during the physical or ophthalmolgical examinations, this should be specifically treated. Aggressive anti-inflammatory medications – steroid and non-steroidal–are generally prescribed both topically (in the eye) and systemically (injected or fed) to limit eye tissue damage. Dilating agents may also be used to relieve pain and prevent complications. Naturally occurring compounds such as MSM that help fight inflammation may be helpful as well. Consistent treatment and follow-up are important because each attack causes more permanent damage, which can eventually lead to blindness. Some horses remain on anti-inflammatories for life, in an attempt to prevent flare-ups of the disease. Fly masks can be a helpful management tool during and between attacks to protect the eyes.
There is a genetic component to this disease, as appaloosas are more likely than other breeds to develop ERU and more likely to become blind as a result. While there is a surgical procedure to save severely affected eyes, an eye that is blind and painful should probably be removed (enucleated).
By: Dr. Lydia Gray