CXX1I BOWMAN LECTURE. 



difficulty are likely, other things being equal, to develop 

 nystagmus. Therefore, from time to time we meet with 

 nystagmus dated from birth, or soon after, with only 

 slight defect of visual acuity, such as may perhaps be due 

 to nothing more than a moderate degree of astigmatism"* ; 

 but as a rule the defect of acuity required to produce 

 the oscillation is considerable. 



Nystagmus dating from early life often becomes less 

 marked in later years ; it may even cease entirely, 

 although such complete cure seems to be rare. Nys- 

 tagmus is often less marked in some one position of the 

 eyes, a position constant for the same person, but not the 

 same for different persons ; it also varies much in the 

 rapidity and range, and also the direction, of the move- 

 ments. 



We can seldom be sure of the precise date at which 

 the nystagmus begins in albinos and others with con- 

 genitally defective vision. In some albinos, however, the 

 oscillation has certainly not been noticed until the child was 

 many weeks or even some months old, and the movements 

 are slower and perhaps less rhythmical at first than they 

 become afterwards. Albinotic infants not infrequently 

 keep their eyelids closed for weeks after birth, and this 

 has sometimes led to the report that albinos were born 

 blind ; but when such infants have been seen it has 

 been found that, with the eyelids held open, they evidently 

 perceived the difference between light and shade, and 

 that the pupils responded to light. 



There must be several different intra-uterine, or very 

 early infantile, diseases or defects of retina, choroid, or 

 optic nerve that, running in families, cause hereditary 

 nystagmus ; but for the present the two that stand out 

 as best known are albinism of various degrees and the 

 affection called, for want of a better name, " total colour- 

 * I am not yet convinced that astigmatism alone can produce nys- 

 tagmus, because the frequency of astigmatism in albinos suggests a cor- 

 relation between deficient pigmentation and the corneal deformity, and 

 in cases of nystagmus apparently due to astigmatism only we are not 

 yet in a position to exclude a defect in the retinal epithelial pigment. 



