Vision and Optical Glasses. I8C 



ticularly if we assist the sight by glasses. It very 

 often happens that the crystalline humour loses 

 its transparency, and thus prevents the admis- 

 sion of the visual rays to the back parts of the 

 eye. This disorder is called by the surgeons a 

 cataract. As we know that the crystalline hu- 

 mour stands edgeways behind the pupil, all 

 then that we have to do, is to make it lie flat in 

 the bottom of the eye, and it will no longer bar 

 out the rays that come in at the pupil. A sur- 

 geon, therefore, takes a fine straight awl, and 

 thrusting it through the coats of the eye, he de- 

 presses the crystalline humour into the bottom of 

 the eye, and there leayes it. Or sometimes he cuts 

 the coats of the eye, the crystalline and the 

 aqueous humour burst out together; in some 

 hours the wound closes, a new aqueous humour 

 returns, and the eye continues to see, by means 

 of a glass, without its crystalline humour. This 

 operation is called couching for the cataract. 

 Cheselden once couched a boy who had been 

 blind from his birth with a cataract. Being thus 

 introduced, in a manner, to a new world, every 

 object presented something to please, astonish, 

 or terrify him. The most regular figures gave 

 him the greatest pleasure, the darkest colours 

 displeased, and even affrighted him. The first 

 time he was restored, he thought he actually 

 touched whatever he saw; but by degrees his 

 experience corrected his numberless mistakes. 

 More recently an interesting case of this kind 



