Ophthalmia
is a disease to which the dog is often liable. It is the result of exposure either to heat or to cold, or violent exertion; it is remedied by bleeding, purging, and the application of sedative medicine, as the acetate of lead or the tincture of opium. When the eye is considerably inflamed, in addition to the application of tepid or cold water, either the inside of the lids or the white of the eye may be lightly touched with the lancet. From exposure to cold, or accident or violence, inflammation often spreads on the eye to a considerable degree, the pupil is clouded, and small streaks of blood spread over the opaque cornea. The mode of treatment just described must be pursued.
The crystalline lens occasionally becomes opaque. There is cataract. It may be the result of external injury or of internal predisposition. Old dogs are particularly subject to cataract. That which arises from accident, or occasionally disease, may, although seldom, be reinstated, especially in the young dog, and both eyes may become sound; but, in the old, the slow-growing opacity will, almost to a certainty, terminate in cataract.
There is occasionally an enlargement of the eye, or rather an accumulation of fluid within the eye, to a very considerable extent. No external application seems to have the slightest effect in reducing the bulk of the eye. If it is punctured, much inflammation ensues, and the eye gradually wastes away.
In
amaurosis
, the eye is beautifully clear, and, for a little while, this clearness imposes upon the casual observer; but there is a peculiar pellucid appearance about the eye — a preternatural and unchanging brightness. In the horse, the sight occasionally returns, but I have never seen this in the dog.
The occasional glittering of the eyes of the dog has been often observed. The cat, the wolf, some carnivora, and also sheep, cows, and horses, occasionally exhibit the same glittering. Pallas imagined that the light of these animals emanated from the nervous membrane of the eye, and considered it to be an electrical phenomenon. It is found, however, in every animal that possesses a
tapetum lucidum
. The shining, however, never takes place in complete darkness. It is neither produced voluntarily, nor in consequence of any moral emotion, but solely from the reflection that falls on the eye.