Where partial cataract is feared but cannot be detected, then artificially dilate the pupil. Rub down two drachms of the extract of belladonna in one ounce of water. Have this applied, with friction, to the exterior of the lids and about the eye; mind none gets into the eye. The belladonna, acted upon by the secretions, turns to grit; inflammation is the consequence, and the clearness of the cornea is impaired. When the belladonna is properly used, it dilates the iris and exposes the margin of the lens, thus enabling the practitioner to inspect the eye in a full light.
DIAGRAM ILLUSTRATING THE
ACTION OF BELLADONNA.
The inner space represents the natural pupil, on which no cataract is to be observed. The second space represents the pupillary opening as it may be enlarged by the application of belladonna, whereon two partial cataracts are to be remarked. The other space merely represents the dilated pupil.
To tell a spurious cataract, which defect is never permanent, first observe the spot. Note if it present any metallic appearance, and try whether, as the horse's head is moved, it alters in shape, catching irregular lights. Then inspect the exterior of the eye; see if it retain any signs of recent injury. Subsequently endeavor, so far as may be possible, to ascertain the exact position occupied by the defect: upon all this evidence put together, make up your opinion.
To distinguish between the different kinds of cataract, apply the belladonna. Next place the horse near a window or under a door. Should the sun shine, have the animal led into the full glare of day. Look steadily into the eye from different points of view. Then have the horse's head moved about, all the time keeping your sight fixed upon the part you are desirous of inspecting.
Should one spot continue in every position, of one bulk, and of one aspect, never becoming very narrow and always occupying one place throughout the examination,—it is a lenticular cataract that is beheld.
DIAGRAM ILLUSTRATING THE DIFFERENT KINDS OF CATARACT.
1. A capsular cataract or an opacity, situated on the envelope of the lens.