a privation of the sense of sight, arising from a total deprivation of its organs, or an involuntary obstruction of their functions. See the article BLIND.
Total BLINDNESS, is that wherein all sight or perception, even of light, is wanting, as is the case of those who are said to be stone-blind. A blind man, by the civil law, cannot make a testament except under certain modifications; but in every case he is disabled from being a witness to a testament, on account of his blindness.
Partial BLINDNESS, is that wherein some faint glimmering is left, as is always the case in people who have ripe cataracts, who are never so blind but they can discern day from night.
Perpetual BLINDNESS, is that which remains alike under all the diversity of seasons, times, ages, &c.
Transient BLINDNESS, is that which gives way of itself in due time, as that of whelps, which continues for several days, sometimes nine, rarely twelve, after they are littered. The Nogais Tartars, according to Father Du Ban the Jesuit, who lived among them, are born blind, and open not their eyes till several days.
Periodical BLINDNESS, is that which comes and goes by turns, according to the season of the moon, time of day, and the like.
Diurnal BLINDNESS, is called hemeraceopia.
Nocturnal BLINDNESS, called also nyctalopia, that which ensues on the setting of the sun in persons who see perfectly in the day, but become quite blind as soon as night comes on. Brigg, in Phil. Trans. No 159. p. 560, where an instance of it is given. See a singular case of this kind related by Dr Samuel Pye, in the Medic. Observ. and Inquir. vol. i. p. III.
The causes of blindness are either ordinary, as a decay of the optic nerve (an instance whereof we have in the Academy of Sciences, where upon opening the eye of a person long blind, the optic nerve was found extremely shrunk and decayed, and having no medulla in it); or some external violence, vicious conformation, growth of a cataract, gutta serena, smallpox, or the like. See MEDICINE Index.
Extraordinary causes of blindness are malignant fleshes, poisonous juices dropped into the eye, baneful vermin, long confinement in the dark, or the like. The ducks which breed under ground, and break out into the Zirchinitzer sea in Carniola after all great storms, are blind at their first eruption; but in some time come to their sight. The author of the Embassy of D. Garcias de Silva Figueroa into Perú tells us, that in several parts of that kingdom are found vast numbers of blind people of all ages, sexes, and conditions; by reason of a species of little flies which prick the eyes and lips, and enter the nostrils, carrying certain blindness with them when they light on the eyes.
in Farriry, is a disease incident to horses, especially those of an iron-gray or dapple-gray colour, when ridden too hard or backed too young. It may be discovered by the walk or step, which in a blind horse is always uncertain and unequal, because he dares not set down his feet boldly when led in one's hand; though if the same horse be mounted by an expert horseman, and the horse of himself be mettled, the fear of the spur will make him go more freely; so that his blindness can hardly be perceived. Another mark whereby a horse may be known to have lost his sight is, that upon hearing anybody enter the stable, he will prick up his ears, and move them backwards and forwards, as mistrusting every thing, and being in continual alarm by the least noise. Dr Lower first showed the cause of the ordinary blindness in horses, which is a spongy excrescence, growing in one, sometimes in two or three places of the uvea, which being at length overgrown, covers the pupil when the horse is brought into the light, though in a dark stable it dilates again.
BLINKS, among ancient sportsmen, denoted boughs broken down from trees, and thrown in the way where deer are likely to pass, to hinder their running, or rather to mark which way a deer runs, in order to guide the hunter.