FATIGUE FACTOES INCIDENTAL IN THE USE OF 

 CERTAIN OPTICAL INSTRUMENTS. 



By Surgeon-Commander R. J. E. Hanson, O.B.E., 

 M.A. (Cantab.), R.N.V.R. 



Fatigue — when it exceeds physiological limits — is one of the most 

 potent drawbacks to industrial efficiency. 



Moreover, it is usually of no sudden onset after commencing the 

 use of optical instrument or projection apparatus, but is rather the 

 result of summation of effect. 



The causation of undue fatigue may be summarized under three 

 headings : — 



Section 1. — Faulty environment. 



(A) Mai Hygiene of the home. 



(B) Mai Hygiene of the workshop. 



(In connection with "A," the influence of day and continuation 

 school conditions to be reckoned with. 



Section 2. — Defects in the Eye. 



(A) Extrinsic, e.g., Heterophoria. 



(B) Intrinsic, e.g., Ametropia, etc. 



Section 3. — Central and Psychological. 

 (Or a combination of any, or all, the above.) 



The illuminating engineer is at work to secure good lighting 

 conditions, with beneficial results in many directions. Of great 

 importance also are satisfactory conditions of ventilation, tem- 

 perature and hygrometry. 



In this short communique, I desire particularly to consider 

 defects in, or misuse of, the muscular mechanism of eye movement, 

 resulting in mal-orientation of the eyes, i.e.. Section 2 (A). 



In the use of the bioscope one has opportunity to study the fatigue 

 resulting from flicker; excessive contrast (defective retinal adapta- 

 tion) ;* inadequate stimulation of the retinal periphery, and dis- 

 proportion between dimensions and illumination of screen picture 

 and the distance therefrom of the seat occupied by the observer. 



The distance between audience and picture screen should not be 

 less than 3 x D (D = diagonal measurement of the picture). 



* The retinal periphery is best stimulated by means of clusters of 

 frosted ruby (Fig-, i) coloured lamps suspended on brackets at intervals 

 along-side the auditorium. 



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