BLINDNESS
—in a horse (whether in one or both eyes) may originate in a variety of well-known causes, many of which are occasioned by means of violence, and may at all times be prevented by proper care and humane attention. If a horse, having naturally good eyes, is observed to undergo a sudden change in the external appearance, from enlargement of the lids, or a discharge of hot watery serum, with a visible heat and pain of the part, (the horse constantly shaking his head and ears,) it may reasonably be attributed to some cause originating in external injury: if not by such means, it must be from some morbid affection in the system, acting more immediately and powerfully upon the most irritable parts.
The eyes of some horses are periodically affected, even for months and years, before they terminate in total blindness: to this species of ocular defect, the illiterate and less enlightened of former times gave the appellation of "moon-blind," under the weak and ridiculous idea, that such changes were produced by the gradational stages of the moon; an opinion too trifling to render animadversion necessary, it being one of the very few remaining traits of superstition which will speedily be totally done away. Many horses lose their eyes from extreme exertion, as by over racing; in proof of which, a very long list of instances might be adduced: the same effect has been produced upon STALLIONS in being permitted to cover mares not only in an unlimited degree in respect to number, but stimulated so to do by the use of powerful and prejudicial provocatives: in both these cases the loss of sight is occasioned by a total subversion of the nervous system, reducing it to a fixed or partial debility of those particular parts, from which they never recover.
Horses are frequently found to inherit constitutional defects from SIRE or DAM; and none are, perhaps, to be considered more justly hereditary than defects of the eyes; and to render such fact the more extraordinary, it generally happens to have lain dormant for the first three or four years, and never to display itself to any visible inconvenience till a colt is broke, and brought into work. The eyes of a horse inheriting this taint by hereditary transmission, are much less prominent than a natural, well-formed and good eye; they have a kind of indented furrow in the lid above the orb, and a wrinkled contraction in the part immediately over that, constituting a kind of "vinegar aspect," better conceived than described: this kind of eye should be carefully avoided in purchase; for however they may vary by changes in work, and a diversity of seasons, they, nine times out of ten, terminate in blindness; a circumstance fairly to be presumed, no professional man living can prevent.