1911.] The Causes and Prevention of Miners' Nystagmus. 



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stooping position. A pencil of light may be focussed at the junction of the 

 cornea and sclerotic in ,a dark room. 



The rotation test advised by Eeid (19) should not be used, as normal 

 people give the test. I have found the ophthalmoscope of no assistance. 

 Several examinations may be necessary. 



A test which is valuable, although not absolutely conclusive, is the 

 following " head test." If the patient is asked to look up while the head is 

 kept strongly flexed by the observer's hand a head tremor may often be felt 

 in cases where the movement of the eyes is absent. This test is frequently 

 given by long-standing cases in which movement has disappeared. 



When movement occurs the character must be noted, as true miners' 

 nystagmus gives a rotatory movement. If the movement is purely lateral 

 and is not equal on both sides grave suspicions should be aroused. The case 

 may be one belonging to the group of nervous diseases, such as disseminated 

 sclerosis, syringomyelia, or cerebellar tumour, which give the symptom of 

 nystagmus. 



It is also necessary to exclude cases of high myopia, of which I have seen 

 two examples, and the congenital conditions, such as hereditary nystagmus 

 or albinism, of which I have seen several examples. Lastly, some people 

 can produce nystagmus voluntarily (27, 28). I have seen one case. 



Prognosis. 



Slight cases recover quickly and completely; severe cases slowly and often 

 incompletely. Table VI, containing so many bad cases, is not so just as the 

 following, taken from the three large colliery companies for a period of four 

 years : — 



Back at old work 57 



Left employ = recovery 5 



Surface work (including six who failed underground) 68 



Still idle 30 



The prognosis in individual cases depends on the age, length of symptoms 

 before failure, degree of elevation necessary to produce movement, visual 

 acuity, presence of error of refraction and the presence or absence of tremor 

 of the head. 



Causes of Nystagmus, 

 I regard the disease as one of extreme complexity and one in which many 

 factors are at work. The chief factor is strain caused by deficient light. 

 Error of refraction, deficiency of retinal pigment, position assumed at work > 

 accident and ill-health are all factors of less importance. 



