This has been applied to a congenital enlargement of the eyes from internal distension in children. The cases in lambs and foals quoted in the last article were evidently of this nature. They are charged on intraocular pressure acting on the delicate tissues of the embryo or unborn animal. There is not necessarily cupping of the optic disc so that persistent tension after birth cannot be insisted on.
Cases occurring in older animals, may be forms of secondary glaucoma though classed under hydrophthalmos by Mayer and others.
Treatment when demanded is along the same lines as in glaucoma.
CATARACT. OPACITY OF THE LENS OR ITS CAPSULE.
Definition. Forms: lenticular, capsular, cortical, nuclear, polar, black, diabetic, traumatic, immature, mature, senile. Causes: impaired nutrition of lens, inflammation of iris, choroid, ciliary body, retina; recurrent ophthalmia. Proliferation of cells. Increased density, chemical changes, degenerations. Sugar, sodium chloride, naphthalin. Rachitis. Senile. Blood pigment. Symptoms: shrunken bulb, opalescent zone around cornea, angle on upper lid, shying, extra ear activity, high stepping, better sight in twilight, homatropia, examination facing the light, Purkinje’s images, ophthalmoscopic examination. Prognosis hopeless. Treatment: phosphureted oil, massage, operation in horses, discission, under antiseptic precautions, extraction under careful antisepsis, suction.
Definition. Any pathological change in the lens or its capsule diminishing its transparency.
Varieties. The opacity may be situated either in the lens (lenticular) or in its capsule (capsular). Again, it may be in the outer part (cortical) or in the central part (nuclear) of the lens. If the opacity is on the capsule in front of the lens it is anterior capsular; if on the portion behind the lens it is posterior capsular. If the opacity is caused by black iris pigment adherent to the capsule it has been called black cataract. If the lenticular cataract is small and round, it is polar, and it may be anterior or posterior polar according as it is situated near the front or back of the lens. Diabetic cataract is one associated with mellituria. A traumatic cataract is one resulting from a wound of the lens which admits the aqueous humor and causes softening, swelling and finally solution of the substance of the lens. The immature or unripe cataract is one in which the lens is not yet wholly involved and indurated; the mature or ripe, when such consolidation has extended throughout. Senile Cataract is seen in old horses, dogs, cats, birds and very exceptionally in cows. This usually attacks both eyes at once. A degeneration takes place in the fibres of the lens, which are invaded by sclerosis beginning at the centre of the organ.
Causes. In domestic animals cataracts are commonly the result of impairment of the nutrition of the lens in connection with inflammation of the iris, choroid, ciliary body, retina, or hyaloid membrane, and above all, in solipeds, in recurrent ophthalmia. It may be assumed that a transparent tissue composed of cells can only maintain its translucency so long as the most perfect equilibrium is maintained as regards the mutual relation of the cells, the pressure of its interstitial plasma, and the chemical composition of both plasma and cell structures. The slightest deviation in any direction will impair or abolish the transparency of the tissue. In inflammation this occurs in various ways, through the increased cell multiplication and the change in the nature of the cells, through the increased exudation and the alteration of the solid parts as regards compression and relative position, and through chemical changes in the exudate which contains more salts, fibrinogenous material, etc., than the normal plasma. The same is true of all the post inflammatory degenerative processes that take place in the lens.
The formation of cataract from chemical alteration in the fluids is familiar in diabetic subjects,—man or beast (Altenhof). It can be produced experimentally in frogs by injecting sugar, common salt or any other readily diffusible saline solution under the skin (Kunde). Rabbits that are fed naphthalin develop cataract which radiates in lines and streaks from the pole towards the periphery and in the cortical portion of the lens. Perhaps the lamellar cataract of rachitic patients is also to be attributed to the lack of earthy salts in the plasma of the lens.
Senile cataract may be hypothetically attributed to impaired nutrition, degeneration in the lens or its capsule, or less commonly to disease of the blood vessels of the eye, or gradual changes in the plasma. It occurs in horse, ox or dog at ten years old and upward.