Visual information processing and dementia

Pattern electroretinogram and luminance electroretinogram in Alzheimer's disease

Visual symptoms are often among the first complaints of patients suffering from Alzheimer's disease and several studies showed a delay in flash visual evoked potentials. Hinton et al. (1986) described optic nerve degenerations in patients with Alzheimer's disease and Sadun published a dropout of retinal ganglion cells that range from 30% to 60%. The reduction of neurotransmitters, especially of acetylcholine, found in the brain might also occur in the retina. Therefore we examined the retinal functions of patients suffering from Alzheimer's disease. In eight patients the pattern-electroretinograms and the scotopic and photopic luminance-electroretinograms were recorded and compared to an age-matched control group. We could not find any abnormalities in the pattern- and the luminance electroretinograms of patients with Alzheimer's disease. Although cholinergic cells have been found in the retina, our results did not reveal an involvement of retinal functions in Morbus Alzheimer.

Balint's syndrome in Alzheimer's disease: visuospatial functions

A subgroup of patients with Alzheimer's disease (AD) developed Balint's syndrome, an uncommon and incompletely understood disorder of visuospatial processing. We characterized the visuospatial features of three AD patients with Balint's syndrome and compared them to three comparably demented AD patients without this syndrome. On visuospatial tasks, the Balint patients were unable to integrate visual stimuli over space. On contrast sensitivity testing, the Balint patients had significantly decreased contrast sensitivities for low spatial frequency gratings (0.5, 1.0 and 2.0 cpd) alternated at 7.5 Hz. Furthermore, the Balint patients had left visual field attentional deficits and normal hemifield P100 visual evoked potentials. In AD, Balint's syndrome involved decreased sensitivity to low spatial frequencies necessary for global visuospatial analysis, a disturbance suggesting damage to the magnocellular visual system in the occipitoparietal association cortex and, possibly, in the optic nerves.