188 COLOUR VISION 



lowered illumination. Uhthofi found the maximum at 12 metre- 

 candles ; the normal maximum is 30 metre-candles or over. The 

 scotopic visual acuity resembles the normal, and the light sense of the 

 totally colour-blind, whenever it has been tested, has been found good. 

 No objective cause can be found for the photophobia. The unpleasant 

 sensation experienced in a bright light is due rather to the interference 

 with vision than to any painful sensation. Thus Nagel and May's 

 patient 1 could look at an Auer burner without discomfort ; she was, 

 however, practically blind for several minutes after doing so. Simi- 

 larly, examination with Thorner's ophthalmoscope and dilated pupil 

 caused no discomfort, but great diminution of vision followed for a 

 quarter of an hour. 



The nystagmus is not found quite so often as the amblyopia and 

 photophobia. Amongst Grunert's last 23 cases it is not mentioned by 

 Fukala 2 , nor in two cases recorded by Hess. In Nagel's case it was 

 absent in one eye. In v. Hippel's first case it was present, but had 

 disappeared four years later when examined by Hess and Hering 3 . 

 Grunert noticed diminution in one case in the course of eleven years. 

 These were all elderly people, whereas most of the recorded cases were 

 children. The nystagmus, sometimes rather slow in the condition of 

 rest, becomes very rapid, with short excursions, on fixation. There is 

 a striking resemblance between the nystagmus and that met with in 

 miners 4 . Many cases showed divergent strabismus, and when absent 

 it could be elicited by eliminating the tendency to binocular vision, as 

 on shutting the eyes or going to sleep. The defect of foveal vision 

 renders binocular fixation difficult and the eyes readily take up a 

 position of rest, which is usually one of divergence. 



The field of vision is generally normal, though Grunert found ring 

 scotomata in one of his cases. Of greater theoretical interest is the 

 frequency of an absolute central scotoma. Owing largely to the 

 accompanying nystagmus its presence is very difficult to demonstrate, 

 and certainly undue importance has been attached to it since Mrs Ladd- 

 Franklin (1892) and Konig (1894) hypothecated it on theoretical 

 grounds. Nearly 30 cases have been carefully examined as to 

 this point. Central scotoma was absent in 14 cases, published by 

 v. Hippel (1), Pfluger (1), v. Kries (1), Hess (5), Grunert (2), Juler (3), 



1 Ztsch. /. Sinnesphysiol. XLII. 69, 1907. 



2 Klin. Monatsbl. f. Augenhlk. xxxvi. 175, 1898. 



3 Arch. /. d. ges. Physiol. LXXI. 105, 1898. 



4 Llewellyn, Miners' Nystagmus, London, 1912. 



