Lesions. These are very varied. Inflammation of the iris, ciliary body and choroid and even of the cornea is not uncommon. The iris and ciliary body show round cell infiltration, as may also the choroid. In the ciliary body this is likely to be especially abundant along the drainage canal (canal of Schlemm) thereby reducing its calibre. Leber and Fuchs found drops of liquid in the epithelium and cornea. One of the most significant lesions in man is the cupping or depression of the lamina cribrosa of a depth in ratio with the force of the intraocular pressure, and inflammation or atrophy of the optic nerve, back of the eye. Möller, however, has never been able to find actual cupping of the optic papilla in animals, but instead thereof a general distension of the outer coats of the eye, a hydrophthalmos. In view of the fact that these coats have the same structure and nearly the same relative thickness as in man, this throws considerable doubt on the supposed identity of glaucoma in man and cases which have been considered such in the lower animals. The comparative absence of pulsations in the retinal arteries in animals adds to the uncertainty.
Treatment. Although such cases lack some of the diagnostic symptoms of glaucoma in man, yet they agree with that in the increase of the intraocular pressure, and demand similar measures for relief. Some reduction of the tension can be secured by careful massage over the eyeball so as to favor the progress of the lymph out of the bulb. A prompt but rather transient relief can be obtained from evacuation of the aqueous humor by puncture with a lancet close to and parallel with the margin of the cornea. The most effective treatment is, however, by iridectomy. On account of the great power of the muscles in the lower animals it is usually desirable to anæsthetize the patient and then fixing the eyeball with a pair of rat-tooth forceps, an incision is made close in front of the upper border of the cornea, and the lancet slowly withdrawn. A pair of iridectomy forceps are then introduced and the iris seized and drawn out through the wound, and a portion snipped off with a pair of fine scissors. The iris is then pushed back into the anterior chamber, and a drop of eserin solution placed in the eye. The parts and instruments must be rendered thoroughly aseptic before the operation, and the eye cocainized both before and after. The eye should be kept covered for some time with a cloth wet with a solution of mercuric chloride (1 ∶ 5000) or other antiseptic.
Appropriate treatment may be employed in case of coexistent inflammation, or to improve the general health.
EXOPHTHALMOS.
This consists in an increase of the media of the eye so as to cause an excessive increase in size, and an unsightly bulging outward from the orbit and between the lids. It may be said to be a more exaggerated enlargement of the eye ball, than has been already noticed under glaucoma.
It has been seen in nearly all classes of domestic animals. Everhardt and Möller reports it in horses, Hausmann, Pradal, etc., in cattle, LaNotte, in lambs, Cöster, Trasbot, etc., in dogs, and Trasbot, in birds (chickens and parrots). It has been found congenitally in lambs and at a few days old in foals, especially when weak and puny; in older animals it appears to be most frequent in the anæmic or starved animal, in the lymphatic, or, as in man, in the goitrous.
The manifest projection outward of the eye may occur as a nervous phenomenon, without intraocular pressure, and without abscess, neoplasm, or inflammation in the depth of the orbit. In a case of tuberculosis in a three year old cow, I have found this condition, with normal tension of the eyeball, but with acute tubercular meningitis of the pia, surrounding the pons and crura cerebri, a grayish exudate with lighter miliary centres, and a considerable clot of extravasated blood.
Symptoms. Mostly without any febrile reaction, there is a manifest enlargement and bulging of the globe of the eye, so that it stands out between the lids which can no longer cover it. The cornea, aqueous, lens, and vitreous are not usually opaque, but show only a pale, blue, opalescent tint. The pupil is often widely dilated so as to show clearly the interior of the eye. Vertiginous symptoms have been observed in the cow (Pradal), the supposed result of intraocular pressure.
Treatment has had little effect when it stops short of puncture of the cornea or iridectomy.