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S. Demirel; Psychophysical Evidence For RGC Dysfunction In Glaucoma . Invest. Ophthalmol. Vis. Sci. 2004;45(13):3303.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose: To test, using psychophysical means, the hypothesis that retinal ganglion cells (RGCs) undergo a period of functional abnormality during the glaucomatous disease process. Methods: Data from Thibos et al show that normal peripheral achromatic resolution acuity remains practically unchanged when stimulus contrast is reduced from 100% down to about 10%. They also show that a sampling process with sampling–density almost identical to RGC density limits this task. This suggests that the contrast sensitivity of the limiting sampling units (RGCs) is relatively homogeneous. If dysfunctional RGCs are present in glaucomatous retinae, they may display reduced contrast sensitivity. In such a case, peripheral resolution acuity may decline as stimulus contrast is reduced in a glaucomatous retina. To investigate this, peripheral resolution acuity was measured for a range of contrasts in six normals and for three patients with diagnosed glaucoma and three patients with several risk factors for glaucoma. The contrast–vs–acuity gain relationship was investigated. Strict visual acuity limits for inclusion were imposed and an attempt to age match the recruited individuals of all groups was made. Results: Results suggest that the peripheral acuity–vs–contrast gain relationship for achromatic patterns is often different in mildly affected areas in glaucoma relative to normals. The acuity reduction in glaucoma commences at contrasts that are high enough to support maximum resolution acuity in normals. The possibility that ocular media is somehow involved cannot be totally ruled out, but is unlikely. Conclusions: These alterations support the notion that some RGCs in glaucomatous retinae stop responding at moderately high contrasts and no longer participate in a sampling–limited resolution task. There may be psychophysical evidence that RGCs undergo a period of dysfunction during the glaucomatous disease process.
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