88 THE MICROSCOPE. 



[Read before the Northern Medical Association, of Philadelphia.] 



AN EYE PROTECTOR FOR USE WITH THE MONOCULAR 



MICROSCOPE. 



BY L. BREWER HALL, M. D., OF PHILADELPHIA. 



SO many physicians use the microscope, or are interested in the 

 care of the eyes of those who do so, that I present this evening 

 a Httle appliance, designed to be used with the monocular instru- 

 ment, for the purpose of protecting the unemployed eye. 



We are all of us more or less familiar with the loss of vision ac- 

 companying squint, and the prevention of it by the use of proper 

 spectacles; but do we recognize the fact that the failure to use is 

 the cause of the loss of sight; and do we appreciate that our em- 

 ployment of one and the same eye at the tube of an optical instru- 

 ment is the same practice that cost the squinting eye of childhood 

 its power of vision ? 



So many of us are contented when we have trained one eye so 

 as to be able to do acceptable work, that we think we cannot spare 

 the time to discipline the other. If this process ended upon the 

 withdrawal of the head from the instrument, the practice would be 

 less dangerous, but the trained eye finding an unequal companion, 

 performs reading and all other near work with greater ease than its 

 fellow; sees so much more distinctly that the other is left without 

 exercise, except for large objects, and becomes of less and less 

 value as the process goes on. 



I could point to those who have practically lost one eye by this 

 process, and I think I am much below the warrant of fact when I 

 estimate that one-half of all those who have used the monocular 

 microscope any considerable amount during five years are monocu- 

 lar men for all fine work. I mean by this that every such person 

 who can "resolve" one of the more difficult "tests" with one eye 

 will find himself unable to do so with the other. 



How often have we heard persons exclaim, upon looking into 

 a binocular microscope for the first time, "Oh, how much easier it 

 is to see with this instrument, and how much plainer everything ap- 

 pears," this with one field quite dark (which provokes a smile from 

 an amateur). I am now fully convinced that we cannot ascribe 

 such expressions wholly to dissimulation or flattery, and for the fol- 

 lowing reasons, viz.: — 



