COL O UR-BLINDNESS. 



1089 



v. Kries 1 has found that the curve of luminosity of total colour- 

 blindness is not affected by change of intensity, and that colour equations 

 are also not affected by change of intensity. Uhthoff 2 has found that the 

 equation of Ebbinghaus and Franklin (p. 1083), which is correct for the 

 normal eye, is not so for the achromatic eye, the mixture of red and 

 blue-green being much the brighter; in fact, the appearance of this 

 match to the achromatic eye is the same as that found for the normal 

 eye in the condition of dark adaptation. 



Nearly all the recorded cases have presented certain features which 

 are not found in other forms of colour-blindness, namely, diminished visual 

 acuity, photophobia, and nystagmus. Their presence has led to total 



FIG. 392. Konig. 



colour-blindness being regarded as a pathological condition, originating 

 probably in early life, and differing altogether in nature from the 

 common form of colour-blindness. As will be seen later (p. 1102), how- 

 ever, there is a possible explanation of these features, which makes them 

 consistent with a developmental rather than a strictly pathological 

 anomaly. The diminution of visual acuity seems to exist only for 

 ordinary illumination ; with feeble light, vision may be as acute or even 

 more acute than normal, especially at first, and the visual acuity in differ- 

 ent parts of the retina shows a very close agreement with that of the 

 normal eye when adapted to the dark. The photophobia seems to be 

 nearly always present in some degree ; nystagmus has been recorded in 

 most cases. Nettleship 3 found a central scotoma of considerable 

 extent in several cases of this kind, and a small absolute central 

 scotoma has been found by many recent observers. One feature in which 

 this differs from the common form of colour-blindness is its frequent 

 occurrence in females. It may occur in several members of one family. 

 Red-green blindness. In considering the common form of colour- 

 blindness, it is especially difficult to avoid terms which imply theory, but 



1 Ztsdir.f. PsychoL u. Physiol. d. Sinnesorg., Hamburg u. Leipzig, 1897, Bd.xiii. S. 295. 



2 Ibid., 1899, Bd. xx. S. 326. 



* St. Thomas's Hosp. Rep., London, 1880, vol. x. p. 37. 



VOL. II. 69 



