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R.B. Barlow, M. Khan, B. Farell; Metabolic Modulation of Human Visual Sensitivity . Invest. Ophthalmol. Vis. Sci. 2003;44(13):2708.
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Purpose: Investigate how blood glucose levels influence human visual sensitivity. Methods: Measure contrast sensitivity of central and peripheral human vision using a 2AFC psychophysical paradigm (photopic luminance levels). Assess retinal sensitivity of the same subjects by recording their multifocal ERG (mERG). Test subjects at various times of the day and in various metabolic states attained either by the Glucose Clamp Technique (GCT) for hypoglycemia or the Glucose Tolerance test (GTT) for hyperglycemia. Results: Nighttime increases in contrast thresholds (up to 4 fold) correlate with mild nocturnal hypoglycemia (~60-80mg/dl) controlled by endogenous circadian oscillators. Moderate hypoglycemia (~50-60mg/dl) induced artificially with GCT decreases contrast sensitivity (up to 6 fold), and, surprisingly, hyperglycemia (more than 200mg/dl) induced artificially with GTT can increase sensitivity (up to 3 fold). Severe hypoglycemia (~40mg/dl) can transiently block central vision. Corresponding mERG recordings show that moderate hypoglycemia can decrease by up to ~50% the amplitude of the "b-wave" (first order analysis) generated by the macula (0-5deg) but not that generated by peripheral retina (beyond 5deg). On the other hand, hyperglycemia can increase "b-wave" amplitude (up to ~40%) uniformly throughout the central visual field (40deg). Contrast sensitivity and mERG results can vary within and between subjects for unknown reasons. Conclusions: Both circadian and metabolic state can modulate human visual sensitivity. Vision mediated by the macula appears to be more sensitive to metabolic stress (hypoglycemia) than that mediated by peripheral retina. Metabolic effects on visual sensitivity may begin at the retina.
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