BOWMAN LECTURE. CXXI 



HEREDITARY NYSTAGMUS (Sections a and 6). 



Without attempting a thorough search, I have found 

 about twenty-five pedigrees in literature under the title of 

 " Hereditary or Family Congenital Nystagmus," and 

 have added a few of my own. Generally speaking, more 

 attention has been paid to the oscillation than to its 

 causes, so that we are often unable to classify the cases 

 in any natural order. One is almost reminded of the 

 time when every case of obscure blindness was called 

 " amaurosis." 



It may safely be asserted that infantile nystagmus, as 

 a family affection, is in the vast majority of cases a 

 symptom of defective sight, and not due to a primary 

 central cause. Our business is to find out the nature of 

 the amblyopia, and to arrange the cases accordingly. 

 The defect of sight is always dated either from birth or 

 early infancy ; it is often due to some affection that causes 

 little or no ophthalmoscopic change ; and as the oscil- 

 lation, especially in a baby or young child, often renders 

 a refined ophthalmoscopic examination impossible, we 

 may be unable to make an exact diagnosis until the 

 patient is old enough to answer questions and have his 

 visual functions tested. In some cases, however, we can 

 come to a conclusion before that period. 



Perhaps the first thing to note is that nystagmus in 

 general is more easily produced in some persons than 

 others ; this is evident enough in cases where it follows 

 blindness; and I am told that coal-miners and others do 

 not all acquire it with equal facility under like conditions 

 of work.* The same surely must be true for nystagmus 

 produced in early infancy by defective sight ; some 

 infants will learn steady fixation sooner, more readily and 

 with less perfect vision than others ; those who have most 



* The last letter I received from Mr. Simeon Snell, written a few 

 weeks before his death, was in reply to a question I had asked him on 

 this subject ; it was to the effect that some coal-miners are more sus- 

 ceptible than others. 



