Visual evoked responses in diabetes.

It is commonly believed that diabetic optic neuropathy is very rare and visual loss in diabetes usually is attributed to other causes. We studied the extent of optic nerve involvement in 16 diabetics with no retinopathy or ocular disease and having an almost visual acuity, using visual evoked responses produced by pattern reversal stimulation. Comparing the responses with a group of 35 healthy subjects, the latency was increased by more than one standard deviation in 13 diabetics (81%) and by more than three standard deviations in 10 diabetics (62.5%), often associated with marked reduction in amplitude. There was good correlation between conduction in the optic nerve and peripheral sensory nerve. No correlation was noted to occur with duration of diabetes or diabetic control except perhaps with juvenile onset diabetes. Normal visual acuity was noted in many cases with severely slowed conduction showing early subclinical affection of optic nerves in diabetes. The extent of central nervous system involvement in diabetes has only recently been realised because of lack of physiological techniques and study of optic nerves in diabetes has not been attempted so far. The high incidence of abnormality of visual evoked potentials in diabetes could invalidate the usefulness of this test in diagnosing multiple sclerosis.