3. On Hemiopsy, or Half Vision

Extract

After describing the phenomena of hemiopsy, as observed by Dr Wollaston, M. Arago, and Mr Tyrrell, the author remarked that no attempt was made by these writers 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. Having experienced several attacks of hemiopsy, unaccompanied with any affections of the head or stomach, the author found that there was no insensibility to light, but merely an insensibility to the lines and shades of the object which disappeared. This insensibility commenced in both eyes, a little to the left of the foramen centrale, and extended itself irregularly to the margin of the retina on the left side. The parts of an object, or the letters of a word which disappear, are as bright as the ground around them, and are white if the ground is white, and always of the colour of the ground, so that the light of the ground has irradiated into the dark lines or shades of the picture on the retina, a phenomenon which can be produced in a sound eye by oblique vision.