Nyctalopia etymologically means night blindness, but the general usage, making the term mean night-vision, is so strongly intrenched that it is useless and confusing to attempt any reinstatement of the old significance. The condition in which one sees better by night, relatively speaking, than by day is due to some lesion of the macular region, rendering it blind. At night the pupil dilates more than in the day-time, and hence vision with the extramacular or peripheral portions of the retina is correspondingly better. It is, therefore, a symptom of serious retinal disease. All night-prowling animals have widely dilatable pupils, and in addition to this they have in the retina a special organ called the tapetum lucidum, the function of which is to reflect to a focus in front of them the relatively few rays of light that enter the widely-dilated pupil and thus enable them the better to see their way. Hence the luminous appearance of the eyes of such animals in the dark.
Hemeralopia (etymologically day-blindness, but by common usage meaning day-vision or night-blindness) is a symptom of a peculiar degenerative disease of the retina, called retinitis pigmentosa.
It also occurs in some cases of extreme denutrition, numerous cases having been reported among those who make the prolonged fasts customary in the Russian church. In retinitis pigmentosa the peripheral or extramacular portions of the retina are subject to a pigmentary degeneration that renders them insensitive to light, and patients so afflicted are consequently incapable of seeing at night as well as others. They stumble and run against objects easily seen by the normal eye.
Snow-blindness occurs from prolonged exposure of the eyes to snow upon which the sun is shining. Some years ago, some seventy laborers, who were clearing away snow-drifts in the Caucasus, were seized, and thirty of them could not find their way home, so great was the photophobia, conjunctivitis, and lacrimation.
Graddy reports six cases, and many others are constantly occurring.
Other forms of retinal injury from too great or too prolonged exposure to light are "moon-blindness," due to sleeping with the eyes exposed to bright moonlight, and that due to lightning--a case, e.g., being reported by Knies. Silex also reports such a case and reviews the reported cases, 25 in number, in ten of which cataract ensued. In the Annual of the Universal Medical Sciences, 1888, there is a report of seven cases of retinal injury with central scotoma, amblyopia, etc., in Japanese medical students, caused by observation of the sun in eclipse.
In discussing the question of electric-light injuries of the eyes Gould reviews the literature of the subject and epitomizes the cases reported up to that time. They numbered 23. No patient was seriously or permanently injured, and none was in a person who used the electric light in a proper manner as an illuminant. All were in scientific investigators or workmen about the light, who approached it too closely or gazed at it too long and without the colored protecting spectacles now found necessary by such workers.
Injuries to the Ear.--The folly of the practice of boxing children's ears, and the possible disastrous results subsequent to this punishment, are well exemplified throughout medical literature. Stewart quotes four cases of rupture of the tympanum from boxing the ears, and there is an instance of a boy of eight, who was boxed on the ear at school, in whom subsequent brain-disease developed early, and death followed. Roosa of New York mentions the loss of hearing following a kiss on the ear.
Dalby, in a paper citing many different causes of rupture of the tympanic membrane, mentions the following: A blow in sparring;violent sneezing; blowing the nose; forcible dilatation of the Eustachian canal; a thorn or twig of a tree accidentally thrust into the head; picking the ear with a toothpick. In time of battle soldiers sometimes have their tympanums ruptured by the concussion caused by the firing of cannon. Dalby mentions an instance of an officer who was discharged for deafness acquired in this manner during the Crimean War. He was standing beside a mortar which, unexpectedly to him, was fired, causing rupture of the tympanic membrane, followed by hemorrhage from the ear.
Similar cases were reported in the recent naval engagements between the Chinese and Japanese. Wilson reports two cases of rupture of the membrane tympani caused by diving. Roosa divides the causes into traumatic, hemorrhagic, and inflammatory, and primary lesions of the labyrinth, exemplifying each by numerous instances. Under traumatic causes he mentions severe falls, blows about the head or face, constant listening to a telegraphic instrument, cannonading, and finally eight cases of boiler-makers' deafness. Roosa cites a curious case of sudden and profound deafness in a young man in perfect health, while calling upon the parents of his lady-love to ask her hand in marriage.
Strange to say that after he had had a favorable reply he gradually recovered his hearing! In the same paper there is an instance of a case of deafness due to the sudden cessation of perspiration, and an instance of tinnitus due to the excessive use of tobacco; Roosa also mentions a case of deafness due to excessive mental employment.
