1870.] 



form of Transient Hemiopsia. 



215 



the headache, and its advent greatly dreaded. The speech is often affected, 

 and sometimes the memory ; and on one occasion the mouth was noticed to 

 be drawn to one side. The cause has seemed to be mental anxiety. 



In the second case, which is adduced for the sake of contrast, the phe- 

 nomena are much less definite. There is no serrated margin, no colour, 

 no curve, nothing of which a picture can be made. The obscurity grows 

 from a small but ill-defined germ, and gathers like a cloudy film or gauze 

 over the field, oppressive to the eyes, and accompanied by headache and 

 nausea, and passes away after a doubtful period, leaving the impression 

 that it is caused by disorder of the stomach. 



In the third case, the blindness is sometimes brought on by looking at 

 a striped wall-paper or a striped dress. The appearance before the eyes 

 is described as zigzag, wavy, quivering, without colour. The first attack, 

 in adult age, was followed by partial paralysis of one side, and later 

 attacks have almost always had a sequel of defective speech, and tingling 

 at the tip of the tongue, at the tip of the nose, and in the fingers and 

 thumb. 



At any rate it is certain that there does exist a distinct form of transient 

 hemiopsia, presenting the following main characteristics : — 



1. Dependence on mental anxiety, bodily exhaustion, overwork to the 

 eyes, gastric derangement (?), want of exercise. 



2. Origin from a small germ near the centre of vision. 



3. Orderly centrifugal growth from the original germ. 



4. Blindness to boundaries, but not to general impressions of light and 

 colour. 



5. Proper luminosity in the dark. 



6. Bright-bastioned margin, with gleams of various colours. 



7. Tremor and " boiling." 



8. Gradual occupation of one lateral half of the field of view. 



9. Gradual recovery of clear vision in rear of the outward-growing 

 cloud. 



10. Disappearance of the phenomenon after about half an hour. 



11. Sequelae: headache and nausea, and sometimes affection of speech 

 and hearing, and even symptoms of hemiplegia. 



As to the actual scat of the visual derangement, the exact agreement of 

 the two eyes in the nature, extent, and degree of their affection proves 

 (assuming the semidecussation of the optic nerves at the chiasma) that 

 t lie seat of the affection must lie at some point behind the chiasma of 

 these nerves. All the causes that are found to lead to transient half- 

 blindness point to the brain as the seat of disturbance. Still clearer is the 

 evidence given by the loss of speech and of memory, the derangement of 

 hearing, and the partial paralysis that sometimes follow an attack of 

 teichopsia. Such cases as Sir John Herschel's, where the cloud passed over 

 the whole field from left to right, can only be explained by supposing the 

 disturbance to lie in some region of the brain where the opposite halves are 



VOL. XVIII. R 



