In a 6-year-old child who had been blind since the age of 2 years, occipital potentials of normal amplitude and waveform could be evoked not only by diffuse light flashes but also by alternating checkerboard ans sinusoidal grating patterns of low spatial frequency. Computerized tomography demonstrated destruction of the occipital lobes except of the primary visual projection area. Thus, in man, destruction of visual association cortices may result in loss of vision with partial preservation of pattern-evoked occipital potentials.
SUMMARY Glaucoma affected the ability to detect low-contrast, flickering patterns ('DRC' measurement). DRC patterns were foveally viewed, of low spatial frequency, and flickering at 8 hertzInterocular comparisons were performed in control subjects, in ocular hypertensives, and in glaucoma patients with asymmetric damage. Interocular differences in DRC tended to be of greater magnitude in the glaucoma patients than in the ocular hypertensive patients or control subjects. In the glaucoma patients DRC was consistently lower in the eye with the greater field defect than in the other (more normal) eye. In patients with optic disc asymmetry DRC was lower in the eyewith the more abnormal disc. Treatment asymmetries did not appear to play a significant role in these relationships. When examined by interocular comparisons DRC showed no consistent relationship to Snellen visual acuity or to level of intraocular pressure at the time of DRC testing.The early stages of glaucomatous visual damage are generally detected outside of the central 5-10°of the visual field. As long as Snellen acuity remains good, it is ordinarily assumed that vision in the central field has not yet been affected by the disease process. However, we have found' abnormalities of central vision in glaucoma patients who had normal Snellen acuities. These abnormalities occurred in a variable named the 'dynamic response coefficient' or DRC, which is based on the contrast required for the detection of flickering patterns. Two types of stimuli, a homogeneous flickering field, and a counterphase flickering grating of low spatial frequency, were presented on a centrally fixated screen 40 of visual angle in diameter. The mean contrast sensitivity of these 2 stimuli (defined as the DRC) was consistently lower in glaucomatous than in normotensive eyes. Thus there appeared to be a relationship between central retinal performance, as measured by the DRC, and the more peripheral visual field defects detected by Goldmann kinetic perimetry.
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