On the Uestorallon of Vision. 119 



to the habitual use of convex glasses, of 2\ or 2| for near, and 

 4 or A\ for distant objects, he has irot since reacquired. 



From a consideration of these three ca'^es, am I not then jus- 

 tified in hazarding the conclusion, that wliatever power the cry- 

 stalline lens possesses of adjusting the eve to different distances, 

 yet, after its removal, there is another power of adjustment, 

 which (as in the former cases) can be subsequently brought into 

 action by exercising the organ without glasses, but which power 

 (as in the latter) is not called into action when glasses are con- 

 tinually employed ? — I have myself full confidence in this opinion, 

 having, after the removal of the crystalline lens, almost uniformly 

 witnessed similar results from similar exercise of the eye. 



The partial insensibility of the retina before spoken of, as a 

 cause for the necessity of using a deeper convex glass soon after 

 the operation, for the purposes of vision, than is afterwards re- 

 quired, cannot apply to the best eye of this gentleman, for to the 

 period of the operation he exercised it in the prosecution of his 

 studies ; while its necessity for the other, the retina of which 

 had become torpid for want of being exercised, was strikingly 

 exemplified, it being a considerable time after the operation, even 

 with the assistance of the deep convex glass, before this eye had 

 acquired any degree of useful vision. At the present time its 

 powers are very inferior to the other, from being less employed 

 in consequence of the patient's chiefly relying on his best eye- 

 In returning to the consideration of the case detailed of the 

 young woman with the conical cornea; it may perhaps be sup- 

 posed, that, by admitting the susceptibility of the retina to have 

 been increased by its being twelve months exercised after the 

 operation, and the adjusting powers of the eye to have been ac- 

 quired from the same cause, I abandon my opinion that the 

 morbid degree of refraction of the light in its passage through 

 the thickened cornea, together with the natural refraction pro- 

 duced by the (-rystalline lens, were the cause of tlie confused and 

 imperfect vision previously experienced by the patient : this how- 

 ever is not the case, as the fact of the girl I^eing capable of seeing 

 after the removal of the lens, which was not in the disliiest de- 

 gree opake, after having been blind previously, convinces me that 

 the refractive powers (the conical cornea and crystalline) were 

 too powerful, and that the cure was effected by the removal of 

 one of them. But what 1 conceive proves the accuracy of these 

 inductions is, that in the earlier stages of tlie disease, when 

 the thickening has not attained the height it had reached in the 

 case alluded to, the greatest assistance is afforded to the patient's 

 vision by the employment of concave glasses. 



It is not, however, my intention to urge that the refractive 



power is ccjually great in the thickened cornea as in the cry.slal- 



II i line 



