Effects of physiological changes of serum glucose on the pattern-VEP of healthy volunteers.

The correlation between amplitude and latencies of the pattern-reversal VEP (1.7-3.6 50% contrast) and the serum glucose was studied in six healthy, male volunteers (21-26 yr.; mean: 23.2 +/- 1.6 yr.). Pattern-VEP and serum glucose were obtained at 2-h intervals during a 8-h experimental session. The effect of spatial frequency on VEP (increased latencies and amplitude with increasing spatial frequency) was removed statistically by computing the residuals from the nonlinear regression function vs. the spatial frequency. The residuals were then processed as stimulus-independent variables. At glucose serum concentrations within the physiological range of variability (55-103 mg/dl), the P100 latency increased (p < 0.04) with increasing serum glucose, with a 6.9% estimated latency difference between lower and higher glucose concentrations. This correlation depends mostly on the association of shorter and longer P100 latencies with glucose concentration values in the lower and upper portions of the normal concentration range respectively, but accounts for about 4% of the overall variance and may be accidental (therefore a potential bias in otherwise controlled VEP studies) or suggest functional relationships between glucose availability and vision.