In cataract the crystalline lens becomes opaque and loses its transparency, the power of refraction is lost—the animal can not see.
Causes.—Cataract generally arises from a diminution (atrophy) or other change in the nutrition of the lens; it may occur as a result of inflammation of the deep structures of the eye. Cataract may be simple, or complicated with amaurosis, adhesions, etc.
Symptoms.—It is known by the whiteness or loss of transparency of the lens, although the pupil dilates and contracts. Sight may be totally lost; however, evidence is usually manifested that the animal distinguishes light when brought out of a darkened stable. For the most part the formation of cataract takes place slowly, the cases in which it originates very quickly being but few.
Treatment.—There is only one method for the treatment of cataract—a surgical operation for the removal of the lens; but this is not advisable, for the sight can not be perfectly restored, and objects would be seen imperfectly without the aid of glasses.
AMAUROSIS.
This is a paralysis of the nerve of sight or the expansion of the retina.
Causes.—This is the result of concussion from a blow upon the forehead, fracture of bone over the eye (causing downward pressure), rheumatic inflammation of the optic nerve, or from extension of deep inflammation of the eye involving the retina. It sometimes occurs as the result of excessive loss of blood or of great debility.
Symptoms.—In this disease observation is seldom made until the animal in its gait and by its action indicates blindness. Generally both eyes are affected. The eyeball remains clear, and the pupil is permanently dilated. No response to light is manifested.
Treatment.—If caused by debility, loss of blood, or associated with rheumatism, general blood tonics may be given in the feed, namely, powdered sulphate of iron, 1 dram; gentian, 2 drams; nux vomica, one-half dram; to be given twice a day. In cases of rheumatism, one-half ounce of saltpeter may be added.