The lens is a soft, transparent tissue that sits behind the iris. It helps refract incoming light onto the retina. Common disorders of the lens include those that affect its transparency (such as cataracts), and those that affect the placement of the lens.
Cataracts are a condition in which the lens becomes cloudy, which affects sight and eventually causes total blindness.
In foals, cataracts are the most common congenital defect of the eye. They are inherited in Belgian and Morgan horses. Cataracts usually occur in both eyes. When these cataracts interfere with vision in healthy foals, surgery followed by topical therapy is successful in a majority of cases.
In adult horses, most cataracts occur as a result of the inflammation of the anterior uvea associated with equine recurrent uveitis. Horses older than 20 years of age may develop so-called senile cataracts that interfere with vision. Surgical removal of the lens is the only definitive treatment available.
Also see professional content regarding disorders of the lens in animals.