EFFECTS OF STUDY ON THE EYESIGHT. 81 



of instead of xipon, the retina. This is near-sight, as it may he rec- 

 ognized hy ohject-tests or trial-glasses. But near-sight is sometimes 

 simulated. This is caused hy a spasmodic action of the muscle of ac- 

 commodation. To determine absolutely, therefore, whether or not the 

 eyeball has taken this abnormal shape, or whether the apparent near- 

 sight is due to this spasmodic action of the focalizing muscle, the 

 oculist must paralyze that muscle. He does this by a simple and, 

 in his hands, a harmless application of a weak solution of sulphate of 

 atropia. 1 Then the object-tests and trial-glasses will determine the 

 question with certainty. But, if it be impracticable to apply the 

 atropia, then the ophthalmoscope 2 must be resorted to, as offering 

 the nearest approach to certainty of results when the accommodating- 

 muscle cannot be paralyzed, because its contraction is not very likely 

 to occur under the operation of that instrument. Thus provided, the 

 oculist proceeds to examine the interior of the eye, and, his own eye 

 being normal, and his own accommodation relaxed, if he sees the 

 retina of the examined eye perfectly, he pronounces the refraction to 

 be correct ; or, technically, the eye is emmetropic. But, if he finds the 

 retina is not clearly visible, there being no opacity of the refracting 

 media, he knows it can only be because the rays reflected from the 

 ophthalmoscope have not converged upon it. Assuming it to be a 

 case of anterior convergence, he interposes a concave glass, which 

 lengthens the focus and removes the point of convergence back upon 

 the retina. Thereupon he pronounces the ej e near-sighted ; or, techni- 

 cally, myopic, of a degree indicated by the strength of the glass. 



JVear-sight, then, is that condition ofihe eye in which the rays from 

 distant objects reach the retina after convergence. 



On the other hand, if, instead of the eyeball becoming elongated, 

 it is flattened, then the visual axis is too short ; that is, the retina is 

 brought too near the lens, which consequently requires the contrac- 

 tion of the accommodating muscle to focalize the parallel rays upon 

 the retina ; whereas, had the eye been normal, the lens would have 

 performed this function while in a state of rest, and would have re- 

 quired the contraction only for divergent rays. 



1 Though this is frequently done with individual patients, yet schools have generally 

 objected to it. Dr. Cohn enjoyed an exceptional opportunity to examine the eyes of 240 

 scholars after the application of sulphate of atropia. Dr. Callan's colored subjects, he 

 relates, refused to permit this application. Therefore, wishing " to place the results of 

 his examination beyond dispute " in point of accuracy, he adopted the alternative course, 

 and " kept both of his own eyes under the influence of a four-grain solution of sulphate 

 of atropia, applied three times daily during a period of five weeks, so that the accommo- 

 dation was completely paralyzed for that length of time." Sometimes the examining 

 oculist has acquired the power to perfectly relax his accommodation at will. But the 

 relaxation of the accommodation of the subject, as well as that of the examiner, is essen- 

 tial to entire accuracy. 



2 A small mirror with a hole in the centre. The mirror is held close to the patient's 

 eye, so as to reflect into it the light of a gas-jet back of him. The oculist then places 

 his eve close to the hole, and looks into f he illuminated interior of the eyeball. 



vot,. xii. G 



