On the ttestorat'ibn of Vision. Ill 



opnditv. Its advance, unless arrested by the appropriate medical 

 treatment, is usually slow, but progressive, until at length the 

 cornea, instead of being a regular segment of a sphere, wholly 

 losing its natural curvature, assumes a conical form. 



This change of structure produces some curious phenomena 

 in the appearances as well as the uses of the cornea. On ex- 

 amining it in front, it assumes an unusual degree of sparkling 

 brilliancy, nearly resembling crystal, except (as is sometimes the 

 case) where there is an opacity in the apex of the cone. Dr. 

 L^veille attributes this brilliancy to the cornea's strongly re- 

 flecting, instead of transmitting, the rays of light, by which lie 

 supposes that the pupil becoming contracted, in a strong light, 

 thereby produces an imperfect and confused sight ; but this ex- 

 planation of the cause of the patient's imperfect vision, it will 

 be hereafter shown, is erroneous. 



If the cornea be examined laterally, it will i)e observed that 

 the thickening gradually increases from its circumference to its 

 centre, where the apex of the cone is usually seated, although, in 

 some instances, I have seen it on one side of the centre. If 

 the cornea be simihirly examined, opposite to a strong light, its 

 thickness at the base may iu general be traced, while the sugar- 

 loaf form of the apex renders it impossible to be mistaken for 

 anv other disease of the eye. 



The change which this disease produces, in respect to vision, 

 is very important. Soon after the commencement of the dis- 

 eased growth, the patient complains of being unable to see ob- 

 jects distinctly, at the usual distance ; and his power of vision 

 becomes gradually shortened, in proportion as the disease ad- 

 vances, until at length he is unable to perceive minute objects 

 with any degree of distinctness, however near they may be placed 

 to the eye; and cannot make out large ones when above three 

 or four feet distant. In fact, vision is destroyed in relation to 

 the useful purposes of life, and lie becomes nearlv as dependent 

 as if totally blind. Indeed, I once saw a young lady labouring 

 under this disease in both eyes, who did not venture to go any 

 where without a guide. 



The disease generally- begins at the first iu one cvc, and a 

 similar affection commonly succeeds in tlie other. I have met 

 with it in almost evcrv stage of life, from a girl of sixteen to an 

 old lady of seventv, and am not aware that it is peculiar to any 

 sex or age, although I have certainly seen it much more fre- 

 quently in women than in men, and more in young than in old 

 persons. 



The opinions generally entertained of the cause of the dis- 

 ease in (|uestion, appear to me to have been incorrect, and have 

 necessarily led to an erroneous practice in the attempts vvliicli 



have 



