EFFECTS OF RADIANT ENERGY ON THE EYE. QQ3 



fore not included in the following description, but will be given sepa- 

 rate consideration. A description of combined thermic and abiotic- 

 effects on the cornea in certain experiments, resulting from prolonged 

 intense exposures is given on page 694. 



After exposure of a rabbit's eye to light containing abiotic rays,, 

 no immediate changes take place, however great the intensity, pro- 

 vided a heat effect is not produced, and symptoms of irritation do 

 not usually appear for several hours. In other words, there is a latent 

 period before any visible effects are produced. This exists not only 

 as regards clinical symptoms but also as regards histological changes. 

 In a general way it varies inversely as the severity of the exposure, 

 but in no case is the first appearance of symptoms delayed longer 

 than twenty-four hours. That is to say, a latency longer than this 

 corresponds to an exposure too slight to produce any demonstrable 

 effects. The shortest latent period observed by us was thirty min- 

 utes. This occurred after intense exposure to the short waves of the 

 magnetite arc, as described later. The least effect that occurs after 

 exposure to abiotic radiation consists in slight hyperemia of the 

 conjunctiva. After more intense exposures the congestion is corre- 

 spondingly greater and is associated with edema and purulent exuda- 

 tion. There also may be conjunctival ecchymoses. The cornea, 

 after exposures sufficient to produce slight conjunctivitis, remains 

 clear and shows only slight stippling of the. surf ace. After longer 

 exposures the cornea becomes hazy in a rather sharply defined central 

 area. This delimitation is no doubt due chiefly to the fact that the 

 rays strike the periphery of the cornea obliquely so that there is less 

 light here per imit area, and to a less extent to the greater loss by 

 reflection at the periphery (see diagram, page 634). Over the central 

 area the epithelium shows marked stippling and is then cast off, 

 usually, however, not until about 24 hours. The loss of epithelium 

 sometimes cannot be determined without the use of fluorescine stain- 

 ing, owing to the margins of the defect not then being sharply defined. 

 This is due to the fact as shown by microscopic examination, that the 

 epithelium usually becomes thinned by desquamation before solution 

 of continuity occurs.* The haziness of the cornea usually reaches its 



* The cornea of a rabbit's normal eye often shows punctate spots and irregu- 

 lar lines after staining with fluorescine that closely resemble the lesions of 

 dendritic keratitis. These are due to defects in the epithelium so small that 

 they do not easily become visible until the stain has diffused through them into 

 the corneal stroma, which requires one or two minutes. They are possibly 

 due to the infrequent winking for which rabbits are noted. They cannot be 

 mistaken by anyone familiar with their appearance for erosions due to ex- 

 posure to abiotic radiations, because the latter stain almost instantaneously 

 and are much larger and sharply defined. 



