DR, HUBERT AIRY OH A DISTINCT EORM OE TRANSIENT HEMIOPSIA. 249 
A great part of Dr. Wollaston’s paper is quoted and corroborated by Dr. Pravaz, 
in the ‘Archives Generates de Medecine’ (tom. viii. p. 76, P re serie). 
From Sir David Brewster’s interesting paper “ On Hemiopsy, or Half-vision” (pub- 
lished in the Edinburgh Transactions, vol. xxiv. part i., and also in the Philosophical 
Magazine for 1865, vol. xxix. p. 503), I must quote one or two passages for the sake of 
illustration. 
“ The blindness,” he says, “ or insensibility to distinct impressions, exists chief y in a 
small portion of the retina to the right or left hand of the foramen centrale *, and 
extends itself irregularly to other parts of the retina on the same side, in the neighbour- 
hood of which the vision is uninjured.” 
“ In the case of ordinary hemiopsy, as observed by myself, there is neither darkness 
nor obscurity, the portion of the paper from which the letters disappear being as bright 
as those upon which they are seen. Now this is a remarkable condition of the retina. 
While it is sensible to luminous impressions, it is insensible to the lines and shades of 
the pictures which it receives of external objects ; or, in other words, the retina is in 
certain parts of it in such a state that the light which falls upon it is irradiated, or 
passes into the dark lines or shades of the pictures upon it, and obliterates them.” 
“ The parts which are in these cases affected extend irregularly from the foramen 
centrale to the margin of the retina, as if they were related to the distribution of its 
blood-vessels, and hence it was probable that the paralysis of the corresponding parts of 
the retina was produced by their pressure. This opinion might have long remained 
merely a reasonable explanation of hemiopsy, had not a phenomenon presented itself to 
me which places it beyond a doubt. When I had a rather severe attack, which never 
took place unless I had been reading for a long time the small print of the ‘ Times ’ 
newspaper, and which was never accompanied either with headache or gastric irritation, 
I went accidentally into a dark room, when I was surprised to observe that all the parts 
of the retina which were affected were slightly luminous, an effect invariably produced 
by pressure upon that membrane. If these views be correct, hemiopsy cannot be regarded 
as a case of amaurosis, or in any way connected, as has been supposed, with cerebral 
disturbance.” 
“ The two great facts of hemiopsy in both eyes, and of what is called single vision with 
two eyes, do not require the hypothesis of semidecussation to explain them. If hemiopsy 
is produced by the distended blood-vessels of the retina, these vessels must be similarly 
distributed in each eye, and similarly affected by any change in the system ; and conse- 
quently must produce the same effect upon each retina, and upon the same part of it.” 
* Under this term Brewster appears to have confounded what are now called the “ optic disk ” and the 
“ yellow spot.” F or when he localizes the first beginning of the affection “ to the right or left hand of the 
foramen centrale ,” he certainly means the centre of vision, as also below when he speaks of vision being perfect 
at the foramen centrale : yet when he afterwards speaks of the parts affected extending from the foramen 
centrale to the margin of the retina, “ as if they were related to the distribution of its blood-vessels,” he is 
certainly thinking of the optic disk, the punctum caecum, whence the vessels radiate over the retina. 
