Faculty Bibliography

The basic rule, when using the flow charts for detecting and localizing visual abnormalities is to be mindful of the level of recorded activity. Lesions affecting cellular behavior at or close to the source (i.e. at the photoreceptors) necessarily impair the flow of visual information downstream from that level. A disturbance in the macular region may produce activity loss indistinguishable from a disease affecting the optic nerve. However, separate recordings of the focal ERG, pattern ERG, and VEP provide information from three major levels of current flow which greatly assists identification of the lesion site as well as providing a certain amount of quantitative data about the extent of damage and a clue to the nature of the disease itself

Visual evoked potentials (VEPs) and contrast sensitivity measurements were determined in normally sighted patients with Parkinson's disease (PD). Prolonged latencies of the first major positive (P100) wave of the VEP elicited by an alternating vertical grating were noted. The delay in latency was positively correlated with the severity of the movement disability. Subjective testing of contrast thresholds demonstrated significant elevation of thresholds in PD. Electroretinographic oscillatory potentials were elicited to determine if the delay in P100 latency was of retinal origin. No specific lesion could be identified to account for the abnormality in VEP or in contrast testing results

Contrast thresholds were determined for patients with compressive lesions of the chiasm or optic nerve but whose visual acuity was 20/20 on the Snellen scale. A generalized loss of contrast sensitivity for spatial frequencies ranging from 0.2 to 6.4 cycles per degree was found even in patients with normal color vision and full visual fields. After surgery was performed, improvements in the fields and color vision were seen in those patients who also showed a significant increase in their postoperative contrast sensitivity scores. Contrast sensitivity is shown to be a useful procedure for evaluating very mild visual complaints as well as for establishing early diagnosis and evaluation of surgical therapy in patients with compressive lesions of the anterior visual pathway

In a survey of 546 rhesus monkeys of various ages, 6.1% of the animals showed ophthalmoscopically visible hypopigmented spots in their maculas. There was a statistically significant correlation between the age of the animal and the degree of hypopigmentation. Electroretinographic responses and visually evoked potentials were evaluated in a selected group of monkeys with and without hypopigmented macular spots. No significant change in retinal function as a result of the macular abnormalities could be detected.

Visual evoked potentials (VEPs) were recorded from four patients with surgically verified chiasmal gliomas. Despite good visual acuity, 6/12(20/40) or better in each eye, these patients showed substantially reduced VEP amplitudes to a diffuse flash stimulus and hardly detectable responses to a highly textured checkerboard-pattern stimulus. The dissociation between evoked electrical activity and visual acuity is noteworthy; this differs from previously reported findings in patients with extrinsic compressing lesions of the chiasm or with lesions of demyelinating disease, which usually reduce VEP amplitude and increase conduction time in rough proportion to a loss of visual acuity

A clinical procedure for determining contrast sensitivity was performed on patients with suspected sella area masses. The test consisted of a series of six plates, each containing a bar pattern of fixed sinusoidal spatial frequency in which contrast varies along the length of the bar. Patients with compressive lesions of the chiasm of optic nerve showed loss of contrast sensitivity over the whole range of spatial frequencies. The general loss in contrast was evident even in patients with 20/20 Snellen acuity. After surgery, contrast sensitivity improved, as did other measures of vision, but significant contrast deficits remained. Contrast sensitivity is a sensitive indicator for the diagnosis and evaluation of compressive lesions of the chiasm