and Cure of Cataract, 429 



Neither Dr. Mitchell nor Dr. Richardson seem to have been 

 acquainted with my experiments on the changes in the lens after 

 death, published in 1837, and with the theory of the cause and 

 cure of cataract there referred to, nor with the distinct state- 

 ment of it published in 1836* and, twenty years later, in 1856f. 

 Dr. Richardson, however, has borne ample testimony to its prac- 

 ticability and safety, when he suggests, almost in my own words, 

 " that it would be worth while, in the earliest stage of cataract in 

 the human subject, to let out the aqueous humour, and to refill 

 the chamber with simple water." And he has borne still stronger 

 testimony to its value by congratulating " Dr. Mitchell in having 

 been the earliest experimentalist to elucidate the synthesis of 

 cataract, and to take the first steps towards a rational interpre- 

 tation of the disease." 



The tendency of the human crystalline lens to indurate or 

 soften, by a defect or excess of water in the aqueous humour, 

 may occur at any period of life, and may arise from the general 

 state of health of the patient ; but it is most likely to occur at that 

 age (between 40 and 60, and often much earlier) when the lens 

 experiences that change in its condition which requires the aid 

 of spectacles. This change commences at one part of the mar- 

 gin of the lens, where its density is either increased or dimi- 

 nished. Its action in forming a picture on the retina thus 

 becomes unsymmetrical, and vision is sensibly impaired. But 

 when the change has taken place round the margin of the lens, 

 its symmetrical action is restored, and by the use of spectacles 

 the vision becomes as perfect as it was before the change. If 

 glasses are not used when the change is completed, the eye must 

 either strain itself or use a strong light, to produce distinct 

 vision in reading the small type and the imperfect printing which 

 characterizes the daily press ; and by both these processes it will, 

 in a greater or less degree, be injured. 



It is a strange delusion, arising either from ignorance or 

 vanity, which induces most people to put off the use of spectacles 

 as long as possible. From the instant they are required, spec- 

 tacles of different focal lengths ought to be used for the different 

 purposes for which distinct vision is required; and the eyes should 

 never do any work, unless they can do it with perfect distinct- 

 ness and satisfaction. There is no branch of the healing art 

 where science comes so directly and immediately to the relief of 

 impaired functions as that which relates to vision, and none 

 where science has been so imperfectly applied. When the change 

 in question takes place, the eye requires to be carefully watched, 

 and used with the greatest caution ; and if there is any appear- 



* Reports of the British Association, 1836, p. Ill; and 1837, p. 12. 

 t North British Review, vol. xx. p. 167 (November 1856). 



