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. 121.
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 stench, 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 Zircnitzer 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 Sylva Figueroa into Persia 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.