162 On Light in some of its delations to Disease, 



Nor is this the only disadvantage to which the hyperme- 

 tropic eye is subjected : 



As the object viewed approaches, the eyes converge. 

 This may be easily seen by any one who will watch the 

 eyes of another before whom he moves some small object 

 backward and forward, while the person observed fixes 

 his eyes upon it. This act of convergence is accomplished 

 by a long muscle which lies at the nasal side of the eye- 

 ball, and which, by contracting, draws the eye toward the 

 nose. 



It will be seen that the effort of accommodation effected 

 by the ciliary muscle within the eye, and the effort at con- 

 vergence effected by the long straight muscle without the 

 eye, are simultaneous ; but they are also exactly propor- 

 tioned to each other, so that a pair of normal eyes accom- 

 modated for twelve inches is also converged for twelve 

 inches. In a pair of hypermetropic eyes, however, this 

 balance is lost, and a person having such eyes who accom- 

 modates for twelve inches requires an exertion on the part 

 of the ciliary muscle equal to accommodating the normal 

 eye for a nearer point — we will say, for six inches. In 

 such a case, a corresponding convergence of the eyes will 

 take place ; and so, while the eyes are accommodated for 

 twelve inches, they are converged for six. Confusion of 

 nervous and muscular action is the result ; there is dis- 

 appointment of all the parts involved in the action, and in 

 all affairs of muscles, of nerves, or of the heart, nothing is 

 so depressing or distressing as disappointment. 



To this confusion of nerve and muscle are due the pain, 

 nausea, and vertigo, of the youth who attempts to read 

 with his grandfather's spectacles, and this is the constant 

 state of confusion of nerve and muscle in cases of erroneous 

 refraction of the eyes. Let any one who imagines this 

 nervous confusion to be of slight importance, if he have 

 normal eyes, and has not reached the age when strong 



