120 BIOPHYSICAL CHARACTERISTICS OF THE EYE 



near infra-red. Even colored glasses have fairly high transmission 

 factors in this region. The clear glasses, including quartz, are almost 



o 



perfectly transparent to 28,000 A and quite effectively transmit energy 

 as far as 40,000 A. Special glasses of the cobalt blue type, however, 

 have marked absorption bands between 5000 and 7000 A. 



A 2.5 per cent solution of crystallized cupric chloride is most effective 

 in absorbing the long infra-red wavelength region. A layer of this fluid 



o 



2 cm thick absorbs nearly all the radiation beyond 8000 A and still 

 transmits rather freely in the visible region. 



Very high-temperature furnaces, and the products from such furnaces, 

 immediately after withdrawal as in rolling mills or in glass-blowing 

 establishments, subject the workmen to intense radiations. Goggles 

 must be worn by the operators to protect the eyes against these radia- 

 tions. 



For some operations such as welding, especially arc welding on iron, 

 where the emission is not only rich in infra-red but exceptionally high in 

 ultra-violet radiation, protective goggles must have a high absorption 

 in the visible in addition to a well-nigh complete absorption in both 

 the infra-red and ultraviolet region. For such purposes, special weld- 

 ing glasses are available to meet the specifications drafted by the Federal 

 Government in 1930 and published as " Federal Master Specifications. " 



The windows in aviator goggles, which are light green in color, are 

 now being made which possess transmission properties very similar to 

 the daylight visibility curve of the normal eye (Fig. Ill— 9) . If the 

 windows in these goggles are 2 mm thick they have a total transmission 

 of approximately 50 per cent in the visible. 



Cataracts or Lenticular Opacities 



The prevalence of lenticular opacities in the eye of tinplate mill men 

 has been studied by Healy. In all, about 350 men were examined. 

 The men entered the mill at about 18 years of age and developed an 

 opacity about 15 years later. In this group 40 per cent of the men over 

 35 years of age had lenticular opacities (see Fig. Ill— 11) apparently 

 caused by the manipulation of the red-hot tinplate at distances which 

 vary from 2 to 5 ft from the eyes. A similar affliction, called " bottle- 

 maker's cataract," is attributed by most ophthalmologists to infra-red 

 absorption. In connection with these studies may be mentioned the 

 experiments of Burge [1924], who investigated the cataracts produced in 

 the eyes of fish living in water containing small quantities of calcium 

 chloride or sodium silicate. His conclusions, briefly stated, were that, 

 when excessive salts exist in the humor and the nutritive sources of the 



