1870.] 



form of Transient Hemiopsia. 



213 



between the transient and permanent forms, which have all been included 

 under the same name Hemiopia or Hemiopsia. 



It seems that Wollaston, Arago, Brewster, and Tyrrell are describing 

 one form of the transient affection, while Sir John Herschel, Sir Charles 

 Wheatstone, the Astronomer Royal, Professor Dufour, and the author agree 

 in describing another. 



In the experience of the former group, the limits of the blind region, as 

 projected on the field of view, are ill-defined ; there is no variety of colour, 

 and the progress of the disease presents no remarkable features. 



In the latter group, the blind region is at first very small, and gradu- 

 ally spreads outwards, to left or right, with a zigzag margin of bright and 

 dark lines, tinged in most cases with various colours, — clear vision gradually 

 returning in the centre and following the outward advance of the curved 

 cloud ; usually the blindness occupies only one lateral half of the field of 

 view ; but in one very remarkable instance recorded by Sir John Herschel, 

 the course of the cloud was from the extreme left to the extreme right, 

 sweeping over the whole of the visual area. 



Possibly the gap between these two forms may be filled by connecting 

 links, as further evidence arises, and it may be found that they differ only 

 in degree of prominence of different features. The remarkable account 

 given by Sir Charles Wheatstone (who has kindly given permission for its 

 publication), where the zigzag luminous lines are strongly marked, but 

 without colour, perhaps offers the first link in the connecting chain. 



The author's experience dates from 1854. Since then he has repeatedly 

 suffered from these attacks. The circumstances and features of the com- 

 plaint have varied somewhat in different attacks, but the type has remained 

 unaltered from that time to this. 



- The blindness comes on usually while the eyes are engaged in toilsome 

 reading : some word or letter on the page near the sight-point (generally 

 below to the left) is found to be obliterated ; this germ of blindness slowly 

 spreads, with zigzag margin, defined by alternate bright and dark lines, 

 with gleams of colour, the margin rapidly trembling and slowly rolling at 

 the same time. 



These three orders of motion, (1) gradual outward growth of the whole, 

 (2) slow rolling of parts, (3) rapid tremor of the margin, are especially 

 characteristic of this affection. 



The region of blindness takes a horseshoe shape ; the upper arm points 

 to the centre of sight, while the lower spreads downwards and outwards 

 away from the centre. The zigzag pattern is minute near the centre, and 

 grows larger the further it recedes. The gleams of colour, most con- 

 spicuous at the margin, are red and blue, yellow, green, orange, in order of 

 frequency. As the blindness spreads outwards, clear vision returns gradu- 

 ally in the concavity of the horseshoe. The sight of both eyes is affected at 

 once, exactly in the same manner and in the same degree ; though naturally 

 that eye seems most affected which corresponds to the obliterated side of 



