The effect of hypoglycaemia on visual function: a clinical and electrophysiological study

Abstract

Disturbance of vision commonly accompanies hypoglycaemia. This study was designed to investigate the nature of the visual disturbance, the blood glucose threshold at which the disturbance occurred and the physiological basis. Measurements were made of the corrected visual acuity, colour vision (100 Hue test), visual evoked potentials (VEP), electroencephalography (EEG) frequency analysis and psychometry (digit recall) during stepwise induction of controlled hypoglycaemia produced by an intravenous insulin infusion. Six male volunteers and five insulin-dependent diabetic subjects were studied. During hypoglycaemia corrected visual acuity was unchanged. Colour vision was significantly impaired. Baseline VEP were normal in both groups but significantly prolonged during hypoglycaemia (mean increment 10.8 ms) and increased by greater than 5 ms in nine out of 11 subjects. Quantitative EEG analysis demonstrated slowing with a power density spectral shift from fast alpha to slow alpha, theta and delta which correlated with VEP latency and amplitude changes. The findings have clinical implications. A deterioration in colour vision is likely to impair the ability to read reagent strips by eye. VEP measurements in diabetic patients are likely to be misleading if hypoglycaemia is present; EEG changes are a sensitive index of cortical dysfunction during hypoglycaemia and provide a theoretical basis for developing a portable device to detect early hypoglycaemia.

Seeing Beyond Retinopathy in Diabetes: Electrophysiological and Psychophysical Abnormalities and Alterations in Vision

“…This conflicts with the results of another study, which failed to show any effect of moderate hypoglycemia (venous blood glucose 2.4 mmol/liter) on VEP latency in nondiabetic subjects (61). Concurrent EEG changes were observed in both studies (57,61) with an increase in slow waves (␦-and -bands) at the expense of fast ␣-waves, particularly in the frontal regions of the brain. (64)].…”

“…Several studies have shown no change in corrected visual acuity during acute hypoglycemia (57, 58) despite a fall in intraocular pressure (59) and a reduction in volume and depth of the anterior chamber of the eye (60). Measurement of VEPs during acute hypoglycemia (venous blood glucose levels below 2.5 mmol/liter) has demonstrated prolongation of the P100 latency, which did not differ significantly between diabetic and nondiabetic subjects (57). This conflicts with the results of another study, which failed to show any effect of moderate hypoglycemia (venous blood glucose 2.4 mmol/liter) on VEP latency in nondiabetic subjects (61).…”

Short-Term, Delayed, and Working Memory Are Impaired During Hypoglycemia in Individuals With Type 1 Diabetes

“…In some studies (6,7,9,16,17), memory functions were impaired during acute hypoglycemia, whereas in other studies (8,18,19), memory was apparently unaffected. Variability of results may relate to methodological differences.…”

Differential changes in brain glucose metabolism during hypoglycaemia accompany loss of hypoglycaemia awareness in men with type 1 diabetes mellitus. An [11C]-3-O-methyl-d-glucose PET study

“…The reduction in relative CMG uptake identified in regions of occipital cortex and cerebellum probably reflects deactivation of these regions during hypoglycaemia. The occipital cortical region is centred on the striate visual cortex, con-cerned with primary visual processing, and colour vision and visual discrimination are known to be impaired during hypoglycaemia [51]. Similarly, impairment in function of the cerebellar vermis may lead to decrement, not only in motor function and coordination, but in cognitive, predominantly executive, processes [52].…”