Anterior Capsular Cataract sometimes results from the deposition of blood pigment on the capsule in cases of extravasation into the anterior chamber. This is closely allied to the black or spurious cataract which consists in the adhesion of the uveal pigment to the capsule, and its detachment from the iris.
Kunde who caused cataract in frogs by injection, subcutem or ingestion of concentrated solutions of sugar or salt, attributes the result to the sudden abstraction of water from the crystalline lens. Even the cell multiplication in inflammatory cases, he holds to favor this, since the new cells having little vitality are especially subject to granular and other deposits and degenerations, with loss of water or of transparency.
Symptoms and diagnosis. The examiner should apprehend cataract after internal ophthalmia. Much more so, if there is apparent diminution of the bulb, an opalescent zone around the outer border of the cornea, or a marked angle in the curvature of the upper eyelid, as usually occurs in recurrent ophthalmia. When a horse suddenly acquires a habit of shying, of starting back or to one side when approached, when confronted with strange or unexpected objects, or with deep shadows like those from electric lights, he is to be suspected. When he carries his ears in an unusually alert manner, turning one forward and the other back, when he steps higher than before to avoid unseen objects, suspicion should attach to him. If he sees better in twilight than in the full sunlight, central cataract may be feared, while the periphery which is exposed by the dilatation of the pupil in semi-darkness is still clear. In all examinations for soundness, the greatest care should be taken to exclude the possibility of overlooking an existing cataract.
In the very early stages, while internal inflammation and photophobia are still present, the pupil may be contracted so that lesion can easily escape notice. Any contraction of the pupil therefore disproportionately to the light, should demand a careful examination with the pupil dilated in darkness or by the action of atropia or homatropin. In the more advanced cases with no persistent inflammation and an advanced opacity of the lens, sensitiveness to light is greatly lessened, the pupil is dilated and the cataract is easily detected.
In cases approximating to the condition last named it is usually only necessary to place the animal in a sombre or dark building, with his head facing the light at an open door, or window and best with full sunlight. Let this fall full upon the eye, and let the observer view the pupil diagonally from each side when any opacity may be detected.
When the pupil is too narrow, several drops of a one per cent. solution of atropia sulphate may be dropped within the lower lid and left for ten minutes until the pupil is widely dilated. Then the examination may be made as above, or still better the animal may be taken into a dark chamber and examined by one of the following methods:
A light, preferably a candle, is placed in front of the eye and moved from side to side, upward and downward, so as to bring its images over all parts of the cornea and lens. In the normal eye there are reflected three images of the light, one large, clear, and upright from the anterior surface of the cornea, one, much smaller but still upright, from the anterior capsule of the lens, and one, small and inverted, from the posterior surface of the lens and capsule. Any opacity in the lens or on its posterior capsule, will cause the posterior (inverted) image to become indistinct, and as it were a diffuse white blur, as it passes over that spot. The other small (erect) image may be even clearer than normal in passing over the opaque area because of the mirror-like reflecting action of the white cloud behind it. The movement of the light so as to pass its image over all parts of its surface in succession will certainly reveal the existence and seat of the cataract, by the blurring of the inverted image of the flame.
Another method is by oblique illumination, the patient’s head being turned away from the light and the interior of the eye being lighted up by reflection from a mirror. If the pupil has been sufficiently dilated all parts of the lens can be scrutinized in this way and the slightest opacity detected by the grayish or whitish haze.
If there is still doubt as to the nature of such appearances, it may be set at rest by illuminating the depth of the eye with the ophthalmoscope when the opacities will appear as dark areas in the general red ground. (See Systematic Examination of the Eye.)
The prognosis of cataract is almost invariably hopeless. I have seen newly formed opacities of the capsule clear up in a day or two, and such recovery in very slight traumatic injury and superficial exudation is recognized as possible, but a slowly forming cataract is usually there to stay. Those that clear are presumably only exudates on the capsule and not true cataracts.