Eye closure affects flash VEP latency in dementia

In a group of 27 demented patients (21 with DAT and 6 with MID) with normal pattern VEP (PVEP), the latencies of the main flash VEP (FVEP) components (P1, N2, P2 and N3) were assessed both with open and closed eyes. At variance from controls, demented patients showed that both P2 and N3 components are significantly delayed with closed eyes while neither P1 nor N2 timings are affected. Control studies ruled out the possibility that such an outcome might depend on a defective pupillary responsiveness and/or an impaired sensitivity to luminance changes. On these grounds it is suggested that the effect of mode of stimulation on FVEP latency in demented patients is more likely to depend on "central" than on "peripheral" mechanisms. The dependence of latency changes on closure of the eyes seems to negate the direct effect of lesions upon visual structures and suggests an impairment of the modulatory action of non-visual afferents upon the activity of the visual cortex.