The Effect on Visual Electrophysiological and Psychophysical Investigations of Substances Primarily inducing a Deleterious effect on the Retinal Ganglion Cells and/or Higher up the Visual Pathway

Abstract

This project has been designed to study the visual effects of three conditions which produce a deterioration in vision with, in most instances, little or no fundus changes. These conditions are namely, 1) tobacco-alcohol amblyopia, 2) visual disturbances due to drugs used in tuberculotic therapy and 3) West Indian amblyopia. For the first two conditions, two patient groups were studied. One group was composed of visually symptomatic patients who were suffering from the condition whilst the other group was composed of visually asymptomatic patients who were receiving the causative substance (for example, Ethambutol) on a chronic basis. The latter group acted as 1) a control for the affected group and 2) a group of patients who might demonstrate early visual changes. The tests which have been used to examine these patients consisted of a cross-section of objective electrophysiological and subjective psychophysical tests. They are as follows: dark-adapted low-intensity and photopic electroretinograms, transient visual evoked responses to flash and pattern stimulation, visual field assessment using the Friedmann visual field analyser, determination of flicker fusion thresholds at three representative frequencies, and assessment of visual acuity for distance and near. In the two groups of visually symptomless patients, it has been found that the most sensitive test in detecting subclinical changes is the visual evoked response. However, for the chronic alcoholic group, it is the foveal pattern stimulation which has produced the most significant results whilst for the tuberculotic group, it has been flash stimulation which has been most effective in monitoring visual changes during therapy. For both the symptomatic and asymptomatic patients in all three conditions, visual disturbances have been observed at the retinal level although the results have indicated more marked changes occurring higher up the visual pathway. In the visually affected patients, all of the tests used demonstrated abnormal changes in the visual system.