504 Sir David Brewster on Hemiopsy, or Half- Vision. 



than twenty years/' he says, " since I was first affected with this 

 peculiar state of vision, in consequence of violent exercise I had 

 taken for two or three hours before. I suddenly found that I 

 could see but half the face of a man whom I met, and it was the 

 same with every object I looked at. In attempting to read the 

 name Johnson over a door, I saw only son, the commencement 

 of the name being wholly obliterated from my view. In this 

 instance, the loss of sight was towards my left, and was the 

 same, whether I looked with my right eye or my left. This 

 blindness was not so complete as to amount to absolute black- 

 ness, but was a shaded darkness, without definite outline. The 

 complaint lasted only about a quarter of an hour/' In 1822, 

 Dr.Wollaston had another attack of hemiopsy, with this differ- 

 ence, that the blindness was to the right of the centre of vision; 

 and he has referred to three other cases among his friends ; but 

 in these the affection was accompanied with headache and indi- 

 gestion. 



In republishing Dr. Wollaston's paper in the Annates de 

 Chimie et de Physique*, M. Arago says that he knows four cases 

 of hemiopsy, and that he himself had experienced three attacks 

 of it, followed by headache above the right eye. 



In the ' Cyclopaedia of Practical Surgery/ published in 1841, 

 Mr. Tyrrell describes Hemiopsy as " Functional amaurosis from 

 genera] disturbance." He informs us that " he has experienced 

 this form of amaurosis several times," and that he has been con- 

 sulted by several fellow- sufferers of both sexes. In all these 

 cases the affection was attended with severe headache, giddiness, 

 and gastric irritation, sometimes preceding, and sometimes fol- 

 lowing the attack. 



In the accounts which have been given of these different 

 cases of hemiopsy, no attempt has been made to ascertain the 

 optical condition of the eye when it is said to be half-blind, or 

 to determine the locality and immediate cause of the complaint. 

 Dr. Wollaston describes the blindness as a shaded darkness with- 

 out definite outline. M. Arago says nothing about darkness ; 

 and the insensibility of the retina, of which he speaks, must 

 mean its insensibility to visual, and not to luminous impressions. 

 Mr. Tyrrell, on the other hand, simply states that the obscurity 

 takes place in different portions of the retina, and varies in its 

 extent at different times. 



Having myself experienced several attacks of hemiopsy, I have 

 been enabled to ascertain the optical condition of the retina when 

 under its influence, and to determine the extent of the affection, 

 and its immediate cause. 



In reading the different cases of hemiopsy, w 7 e are led to infer 

 * 1824, vol. xxvii. p. 109. 





