EYESTRAIN. 737 



the variations, only one two-hundredth or one four-hundredth of an 

 inch from the normal in the dimensions of the eyeball or in its corneal 

 curves which may prevent the accurate photographic ' definition ' of the 

 retinal image. To this must be added a knowledge of the means or 

 lack of means possessed by the eye to overcome or neutralize these results 

 of deviations from the standard of size and contour. What are the 

 kinds of deviations that may be cancelled, how far the neutralizing is 

 possible, what kinds may not be overcome, and the mechanism of the 

 overcoming, these are all pretty well understood. 



In the briefest way we may say that if an eyeball is too long (from 

 the cornea to the retina) it is near-sighted or myopic. One can not see 

 well at a distance, for everything appears blurred and hazy. The focus 

 of the image is in front of the retina, and there is no device of the 

 unaided eye which can transpose it to its proper position upon the 

 retina. Any effort to do so is by the nature of the conditions a nega- 

 tive one, an endeavor, if one may so speak, and of course, unconsciously, 

 to lessen muscular effort. There is as result no eyestrain, no morbid, 

 or wearying, or hurtful attempt at muscular exertion. 



The supposition, in this case, is that a pure or uncomplicated 

 myopia exists, and that it is of the same degree or amount in both eyes. 

 In truth, however, that supposed condition never exists. No oculist 

 probably ever tested a pair of eyes having no astigmatism, and having 

 exactly the same over-length, or myopia. And this astigmatism, or 

 the difference in lengths of the two eyeballs, or both factors combined, 

 brings always the possibility of ' eyestrain.' For eyestrain is the name 

 given to any unphysiologic, i. e., pathologic ocular action or function 

 which is wearying, excessive or unnatural. It thus becomes clear how 

 it is that the two eyes by reason of the presence of a difference in their 

 relative lengths, or because of astigmatism in one or both, may result 

 in morbid effort or strain, although if both were alike in over-length, 

 and without other optical defect, there could be no such strain. This 

 general fact makes evident the truth that in general those with (mod- 

 erately) myopic eyes have far less ocular diseases and pains in the eyes, 

 less headaches and other general disorders, than those whose eyes are 

 hyperopic, or ' far-sighted.' For in all ' far-sighted ' eyes there is a 

 never-to-be-renounced effort to overcome the trouble. But this freedom 

 from pain and other symptoms in myopia may lull the patient with a 

 false security and costly neglect. The great danger is that without 

 the attention of a skilled specialist the myopia may increase, become 

 1 malignant,' as it is termed, and the eyeball continue to elongate, with 

 imperilled or fatal loss of vision. The myopic eye is one abnormally 

 elongated, enlarged or stretched, and once having lost its tonicity or 

 normal measurement, it tends to extremes of enlarging. 



The far-sighted or hyperopic eye is the reverse of the myopic eye: 

 vol. lxvii. — 47. 



