NYCTALO'PIA AND HEMERALOPIA. Terms employed for affections of the eye. and which have been indiscriminately employed. Mr. Lawrence, an English surgeon, and one of the pioneers in scientific ophthalmology, says "A great confusion has arisen in the application of these learned terms, each word being nearly as often used to express one affection as the other. Hippocrates used the term hemeralopia to denote night-blindness, and we may as well follow his eiimple." And this is good etymology, for nyctalopia signi fies " T see by night," while hemeralopia signifies " I see by day." 'Still it is not unconunon for nyctalopia to be defined as ''night-blindness." " Hemeralopia," says Mr. Law rence, " is that state of vision in which the patient sees well during the day, but imper fectly as twilight comes on; and when the affection is fully formed IM loses his sight entirely at the approach of night, not being able to see a lighted candle brought arse to the eye. In the commencement of the affection the person can see by moonlight, or when the room is lighted by a candle, hut as it proceeds he can discern nothing after sun set; in the morning vision returns. There is no unnatural appearance in the eye; indeed if a person can see perfectly during the day, the organ can have undergone no import ant change (structural). There is little increased irritability in the commencement,. but as the affection proceeds the pupil becomes rather dilated. The duration of the disease varies from one night to six or twelve months, or even longer. More generally it lasts from two weeks to three or six months. when left to itself. Relapses are frequent so long as persons remain exposed to the exciting cause, which seems to he the exhaustion of the power of the retina by exposure to strong light during the day." The disease is most prevalent in hot climates, and where there is much glare of sunlight, as in the East and West Indies. It is not also infrequent in high latitudes where the snow reflects the sun's rays for a great many hours during the day. Dr. Matthew Guthrie states that peasants in the interior of 'Russia are subject to it, where it is called kieritsba aepotm, or hen blindness, and occurs during the harvest in June and July. He also says that several hundred ibleOlp,soiliers inthe war in Finlamtwere attacked by the, affection. It has been recordelliaSacirring eliidelnically, and an insteneels'relatodi in the 8th vol. ot the Dublin Journal of medical and chemical science of such an epidemic among some Prussian soldiers stationed on the Rhine; hut Mr. Lawrence observes that all the cases which he had seen commenced in the East or West Indies and were brought to England. 2vItiekenzie, another high British authority, says that the disease does not appear to be necessarily connected by any constitutional symptoms, and Mr. Bampficld, in the British .11edica-chirurgleal Trancactions, states that of more than three hundred cases in his prac tice in different parts of the globe, but chiefly in the East Indies, all perfectly recovered.
The prognosis is, therefore, very favorable. In some instances night-blindness, or hem eralopia, is congenital. Richter relates three cases in a family of nine children. The only abnormal appearance of the eyes was the excessive dilation of the pupils after sun down. When the account was given these children had reached the age of from 20 to 30 years, without any alteration in their sight. One of them had never seen any stars. Dr. Cunier, of Ghent, relates some remarkable cases of hereditary hemeralopia (Annalea de la eueiete de inedecine de Gand 1840). In the official capacity of an army surgeon, in the case of a conscript claiming exemption from night-blindness, Dr. Cunier made an examination in the commune of Vendemain, near Montpellier, and reported upon informa tion and observation that one Jean Nougaret was the first of the family known to be hameralopic• his children, one daughter, and two sons, were all affected with night blindness. The second generation included 16 individuals of whom ten were thus affect ed; in the third generation there were 14 out of 81; in the fourth 28 in 208; in the fifth, not then completed. 24 in 218; in the sixth, including 103 persons, there were 11. But one of the remarkable facts in the case, and worthy of much consideration by those studying of heredity, because varying in this respect from most hereditary laws, is that among all these descendants, numbering more than 600. and of whom nearly one-seventh were affected with night-blindness, there was not a :Angle case in those fami lies where both parents were free from the affection; that is, there was no intermediate transmisssion. Anctalopirt, or "night-seeing" (day-blindness) is a state opposite to hem eralopia, and is a disease of a very different nature. Mr. Lawrence states that in opacity of the cornia, in certain forms of cataract, in incipient opacity of the lens, in central opacity of the capsule, in contractions of the pupil from prolapse of the iris, the patient will often see best in a weak light, and find vision very imperfect in a strong light. In scrofulous affections of the eyes (strumous ophthalmia) the intolerance to light amounts to badness during the day. while in the evening, with a faint light the patient saes quite \veil. Albinos are frequently nyctalopic, the absence of pigmentum nigrum, rendering the aye extremely sensitive. iron' its want of absorptive power'. Barron Larrey records a remarkable ease of day blindness, occurring in an old man, one of the galley slaves at Brest, who had been shut up in a subterranean dungeon 33 years. He had become so affected that he could only see in a shady light. As this condition is generally accom panied with some observable affection of the ocular apparatus its treatment will vary with circumstances.