Visual Retinocortical Function in Dementia of the Alzheimer Type

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Abstract
Some histological investigations have reported anomalies in the primary visual pathways of individuals with dementia of the Alzheimer type (DAT), while others have suggested that these visual structures are spared by the disease process. This study was conducted to address this issue of substantial controversy. We determined in vivo whether DAT alters the functioning of the primary visual pathways by evaluating pattern-reversal electroretinograms (ERGs) and cortical visual evoked potentials (VEPs). Twenty-seven individuals with mild to moderate DAT and 27 age- and sex-matched control subjects were included in the investigation. ERG and VEP recordings were obtained from all participants with the use of a clinical electrodiagnostic system. Stimulus conditions were biased towards a preferential response from the magnocellular and parvocellular subdivisions of the visual system. Amplitude and latency of the ERG were not affected by DAT. The VEP amplitude was not attenuated in DAT individuals, but there was a delay in the latency of the VEPs arising from both magnocellular and parvocellular streams of visual processing. Our results indicate that while the inner retina appears to be spared by the disease process, the visual function is altered upstream in the retinocortical visual pathways of individuals with DAT.