Stereopsis in Alzheimer’s Disease: Measuring Binocular Eye Movement
Alzheimer’s disease (AD) is a disease characterized by memory impairment and visual special cognitive dysfunction. AD was however, difficult to diagnose in its early stage, because we did not have the methods to estimate this memory impairment and visual spatial cognitive dysfunction. Recently, the technique of measuring higher brain function has been developed. We focused on one of the clinical symptoms which was visual spatial cognitive dysfunction such as reconstructive apraxia and observed it in the early stage of AD. Earlier reports have indicated that patients with AD had an atrophy of cerebral cortex with parietal and occipito-temporal lobe and pathological changes found in association areas. Also decreased glucose metabolism was observed in visual association and inferior parietal cortex. The neural function of the parieto-occipital association area was reported to be related to visuospatial cognition and skills (Mishkin et al., 1991). Saccadic and smooth pursuit eye movement in AD were studied and the response time was found to be prolonged, while the gain of smooth pursuit eye movement following a sinusoidal moving target was reduced, but the motor control of eye movement was almost intact (Fletcher and Sharpe, 1986; 1988). Therefore, we thought that patients with AD might have a dysfunction of processing to create visual spatial cognition from visual information and other information about space, head position, and body position, resulting in a shift of their eyes toward the target of interest in order to get enough visual and spatial information around it. We planned to approach the visual spatial dysfunction in AD by measuring the eye movement in the patient’s visual field, to establish a diagnosis of AD in its early stage.
KeywordsConvergence Angle High Brain Function Decrease Glucose Metabolism Target Paradigm Visuospatial Cognition
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