738 POPULAR SCIENCE MONTHLY. 



it is too small or too short and hence effort and muscular exertion are 

 necessary to bring the image forward, in proper definition upon the 

 retina. Without this exertion the image would be behind the retina. 

 Hence a similar blurring or badly defined picture as in myopia, but 

 from the reversed cause. In this kind of eye the picture is naturally 

 blurred even of the most distant object (making the term far-sighted- 

 ness a misnomer), and a slight increase of focussing power is required 

 on the part of the ( accommodation ' mechanism in each eye, in order 

 to shorten the focus of the image-forming rays of light. With every 

 lessening of the distance of the object, still greater converging power 

 is demanded, as one may understand by tests with different-power glass 

 lenses. When the object is brought within ten or fifteen inches of the 

 eye the greatest effort is required to make the image clear. The degree 

 of this effort will depend upon how much too short the eyeball is, or 

 upon the amount of hyperopia. It will also depend upon the kind and 

 amount of ocular labor, especially the continuance of ' near-work,' the 

 reading, writing, etc., required of the eyes. The farmer, ranchman or 

 sailor will obviously be able to overcome or be indifferent to higher 

 degrees of far-sightedness than those living in cities, while the literary 

 man, bookkeeper or seamstress will experience eyestrain with still lower 

 degrees of hyperopia. 



One must carry in the mind another modifying condition — the dif- 

 ference almost always existing between the far-sightedness of one eye 

 and that of its fellow. The two are under more stringent orders than 

 in myopia to work together and in harmony. When the hyperopia 

 differs in the two the chances of strain are obviously increased many 

 times. 



These chances already multiplied now become inevitables if astig- 

 matism is a complication of the hyperopia. Alas, also, it is very cer- 

 tain to complicate. I have measured something like ten thousand pairs 

 of eyes, and not one of these pairs was without some imperfection of 

 shape, size or curvature, either in one or both of the eyes. An abso- 

 lutely perfect pair of eyes does not probably exist. 



' And do tell me, what is astigmatism ? ' is the puzzling question 

 put to the oculist every day. It is one, fortunately, very simply and 

 easily answered. The front part of the eye, that behind which lies the 

 pupil, is called the cornea. It should be round or equally curved like 

 the central portion of the end of an egg. It is usually not uniform in 

 its curvature, but is more curved in one meridian than in the reverse 

 meridian — that is, it is, approximately, of the shape of the side of the 

 egg. When symmetrically curved it will naturally refract, or help to 

 focus, correctly, the entering cone of light which is to form the picture 

 on the retina. If it is unsymmetrically curved, like the side of the 

 egg, it will produce a misshapen and unsymmetrical picture which 

 does not accurately represent the object. The condition of safety, 



