A study by the Royal School of Veterinary Studies in Scotland looked at the eyes of 83 geriatric horses and ponies, age 15 or older, and found degenerative conditions in 67 (81%). The most common problem was vitreous degeneration, followed by retinal changes. Not surprisingly, the older the horse, the more likely the problems.
The vitreous is a clear, jelly-like mass located between the back of the iris/pupil and the retina. It’s composed primary of water, with high levels of hyaluronic acid and some free-floating collagen fibers. It helps shape the eye, support the lens, cushion and stabilize the retina, and nourish and remove wastes.
Vitreous degeneration can mean the development of cloudiness or “floaters” or a change in consistency from a slippery gel to more watery as a result of decreased levels of hyaluronic acid. Previous inflammation can cause these changes or they may be age-related, as in other species.
Retinopathy refers to degenerative changes/scarring of the retina, where the actual vision occurs. Previous inflammation, conditions like insulin resistance that cause circulatory problems, and aging are among the causes. The changes are irreversible, although laser surgery may halt the progression of retinal detachment.
Horses typically adapt well to poor vision, but it’s important to realize your senior may have trouble seeing. With poor vision, the horse tends to stay within familiar areas or stick close to a buddy. He’ll move slowly but likely find his food and water OK. However, he’s at a higher risk of injury, especially related to holes or poor/rough ground conditions.
A fascinating Russian study looking at people with vitreous degeneration identified several nutritional risk factors, including insufficient calcium intake and abnormal calcium-to-phosphorus ratios, both insufficient and excessive vitamin C, low chromium intake, and deficiencies/imbalances in zinc and copper. Other studies looking at dietary influences on age-related retinal changes in people identified antioxidant vitamins (C, A and plant antioxidants) and trace minerals (zinc, copper) as being important in slowing these changes and poor intakes as a risk factor for developing them.Interestingly, these deficiencies are also common in equine diets. Of course, this isn’t a call to overdo it either, as oversupplementation may be as bad as a low intake.
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