EFFECTS OF RADIANT ENERGY ON THE EYE. 745 



that to which glass blowers are exposed, few glasses except such 

 special ones as have recently been devised by Crookes, are very 

 effective, the deep green copper oxide glasses being perhaps as good 

 as any. Such glasses combined with amber or yellow green tints so 

 as to reduce the transmitted light to a moderate amount in the middle 

 of the spectrum are probably the most efficient protection against 

 extreme radiation of all kinds, except that of direct sunlight. In the 

 case of glass blowers, it is difficult and perhaps futile for them to make 

 use of any sort of glasses, owing to excessive perspiration. 



So far then as concerns actual injury by light, the eye under ordi- 

 nary conditions of modern life is in no danger. The question of wear- 

 ing protective glasses so far as concerns the ordinary individual there- 

 fore narrows itself down to the determination of those best adapted to 

 obviate the sensations resulting from too intense illumination. These 

 are unpleasant in the same way as are extremely loud noises, and for 

 protection against them one wears glasses that reduce the light as one 

 plugs the ears with cotton in a boiler factory. Any glass that reduces 

 the light is effective for this purpose, but preferably, perhaps, a glass 

 that transmits light chiefly in the middle of the spectrum, for which the 

 eye is customarily focussed. The question of the color of the glass is, 

 however, of little importance and the personal idiosyncrasies of the 

 individual may be safely allowed free play here. It is probable that 

 if such glasses are too long worn they will increase the sensitiveness of 

 the individual to light. 



The question of the use of protective glasses in pathological condi- 

 tions of the eye does not specially concern us here, but it may be stated 

 that it is one simply of reducing the intensity of light reaching the 

 retina. In cases of iritis this is possibly of some importance since it 

 favors dilatation of pupil. In cases of glaucoma, on the other hand, 

 excess of light is desirable, since it contracts the pupil. As Hess ^^* 

 has pointed out, the sensations incident to the so called photophobia, 

 associated with keratitis and other irritable conditions of the eye, are 

 present in the dark as well as in the light, so that it is evident that 

 undue importance has been attached to the exclusion of light in these 

 conditions. As regards fundus conditions, the use of protective 

 glasses has no rational basis, except possibly in the case of retinitis 

 pigmentosa and allied conditions, as suggested by Axenfeld^. 



The exaggerated attention that has been paid in recent years to the 

 harmful effects of ultra violet radiations has had one good effect in 

 modifying the character of the protective glasses prescribed by 

 ophthalmologists. Earlier practice was based on a general desire to 



