Cataract consists of opacity of the crystalline lens or of its capsule, or of both together. The lens is more frequently found opaque than the capsule. In health both the lens and its investing membrane are perfectly transparent. The opacity may affect the whole or only a part of either of these structures.

The capsular variety of cataract is generally caused by inflammation, or by wounds or blows affecting the whole eyeball, or part of it. The opacity then comes on very quickly.

Opacity of the lens itself, although it may arise from the above causes, is usually found in old dogs as the consequence of senile degeneration of tissue from imperfect nutrition.

The opacity that supervenes on inflammation may be removed; whilst that form produced by old age always gets worse and worse.

Cataract is no respecter of dogs, attacking all alike, but especially those animals that are petted and highly fed, and that are thence predisposed to it from dyspeptic disorder.

Cataract may affect both eyes, or only one. In old dogs both eyes are usually cataractous, one wholly so, the other in part; whilst, if the opacity should have followed a blow or penetrating wound, the injured eye only is affected, and the other will remain sound until old age creeps on. As a rule, the blindness of old age depends on cataract.

Some writers on canine pathology mention "hereditary tendency" as one of the causes of cataract. But this in the present state of knowledge is mere theory.

Symptoms

Cataract is known by seeing behind the pupil an opaque body of a whitish-grey colour, which is best seen when the pupil is dilated by the previous application of Belladonna. This preliminary step should always be taken in aid of correct diagnosis, when the case is doubtful. Of course, vision is more or less imperfect in proportion to the size and situation of the cataract. From the movements and behaviour of the animal, the inferences may be drawn that vision is better in the evening or in a subdued light, than it is in the full sunshine; that it is improved so long as the pupil remains dilated under the action of Belladonna; and that some degree of vision remains even when the lens appears to be an opaque mass.

Treatment

As far as I am aware, there is no medicine that can clear away cataract when once fully formed. But attention to the general health, by proper exercise, change of air, good food without flesh meat, the cold bath, and friction to the skin, will probably check or moderate the progress of the disease.