Age-related deterioration in stereoacuity is reflected not only by a linear correlation between age and threshold but also by a catastrophic factor that produces more marked deterioration after age 60. Both factors are probably cerebral and not specifically related to stereopsis. The prevalence of fixation disparity in the normal population is probably more common than previously reported.

In the parafoveal retina of human observers, cone-mediated sensitivity to flicker decreases as rods become progressively more dark-adapted. This effect is greatest when a rod response to flicker is precluded. These results indicate that rods tonically inhibit cone pathways in the dark.

The PERG evoked by black-and-white patterns is partly pattern specific and partly evoked by local changes in luminance. When a chequerboard reverses, the increase in brightness of part of the screen is exactly matched by decreases in other parts. It follows that the average response of many different

The effects of iontophoretically applied GABA (gamma‐aminobutyric acid) and bicuculline on retinal ganglion cells were studied in the optically intact eye of the anaesthetized cat. GABA suppressed both the spontaneous activity and light‐evoked discharge of all retinal ganglion cells, regardless of their type and regardless of the visual stimulus used. Bicuculline antagonized the action of iontophoretically applied GABA. Bicuculline enhanced the spontaneous activity of on‐centre cells, but suppressed the spontaneous activity of most off‐centre cells. The light‐evoked response of on‐centre cells was increased by bicuculline. A more complicated picture emerged for off‐centre cells. Weak light responses were suppressed by bicuculline, but during strong light responses the initial transient phase of the response was dramatically enhanced. Amacrine cells of the inner nuclear layer and displaced amacrine cells of the ganglion cell layer were labelled, using glutamic acid decarboxylase (GAD) immunohistochemistry and [3H]muscimol uptake. GAD‐positive dendrites were found throughout the inner plexiform layer and no sign of dendritic stratification was detected.

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