Mary Allen
There is hardly anything that horse owners are more afraid of than periodic inflammation of the eyes, also known as moon blindness. To prevent this, horses should never drink from puddles or standing water and avoid contact with rodent urine.
Studies have shown that moon blindness is more common than most riders realize. Almost every 20th horse is affected by this insidious disease, which without a special operation sooner or later leads to blindness. The eyes become inflamed in recurring cycles, sometimes it is just one, but both can become ill at the same time.
The outbreak of the disease can initially go almost unnoticed by the owner. But the flare-ups usually become more violent and painful, and the intervals between them become shorter and shorter. Usually, the eyelid is very swollen and the eye becomes sensitive to light, causing the horse to squint. In addition, it dries a lot. Several such inflammatory phases in succession, so-called recurrences, ultimately lead to blindness.
But where does this dramatic illness come from? And can any animal be infected? Moon blindness is caused by bacteria called leptospira. In principle, they occur everywhere and grow and multiply where it is moist. They feel particularly comfortable in puddles or wet bedding. They are spread by rodents such as mice and rats. To be more precise, it is their urine that allows the leptospira to be deposited in all imaginable places in the barn – sometimes even in the sacks with oats or pellets.
Ointments Only Heal the Current Flare-Up
Ointments only heal the current flare-up If a horse is infected, the bacteria migrate to the vitreous body of the eye. This is the part behind the lens that forms the eyeball from a liquid, transparent substance. Although it is called vitreous, the only thing it has in common with glass is transparency. This is where the leptospires like it. They can live and multiply in it unnoticed for years. The immune system in the eye is constantly busy suppressing inflammation. Until day X comes when it no longer works. Even a small stressful situation like being transported or starting at a tournament can lead to an inflammatory flare-up. Then the external defense comes into play with a heavy flow of tears. There is also reddened conjunctiva, and the cornea is often clouded.
Depending on the stage of the periodic eye inflammation, intensive drug treatment follows. Eye ointments are needed that dilate the pupil. One that lowers the immune system and one that is supposed to fight inflammation. Everything always depends on the specific course. After a flare-up, the eyes should be checked by a vet every three to four months.
Therapy with ointments can only heal the current flare-up, but cannot prevent a relapse. Towards the end of the 1980s, experts developed a new surgical method with the complicated name “vitrectomy”. The vitreous body and the liquid contaminated with leptospires are removed from the eye and replaced with artificial material. This process, which was primarily promoted at the University of Munich, is already showing success. Dr. Hartmut Gerhards says: “For eyes that are not severely damaged at the time of the operation, vision can be preserved with a good prognosis.”
As a precautionary measure, Gerhards recommends never allowing horses to drink from standing water. Because leptospires like to slumber in it. And: If you keep the number of rodents in the barn small (the classic barn cat makes a valuable contribution here) and pay attention to good hygiene, you reduce the risk. Antibody studies show that almost every horse will come into contact with leptospira at some point in their lives. Why some go blind while others don’t is a mystery.