Visuospatial function in ambulatory aged women with probable Alzheimer's disease: A multiple case study.

Abstract

The purpose of this study was to identify whether ambulatory women with mild and moderate levels of cognitive impairment (CI) related to probable Alzheimer's disease had similar or different visual attention, peripheral vision, contrast sensitivity, visuoconstruction, and image segmentation. The dual pathways model of visual processing, comprised of the occipital-temporal and the occipital-parietal pathways, was used to conceptualize, operationalize, and measure the above visuospatial functions. The occipital-temporal pathway processes size, location and orientation properties of an object while the occipital-parietal pathway processes edges, shape, and color. Using case study methodology, thirteen cases (7 with mild CI; 6 with moderate CI) meeting inclusion (ambulatory, female, >75 years old, LTC resident, probable AD, 8<super>th </super> grade education or >) and exclusion (acute illness, glaucoma, cataracts, macular degeneration, retinal detachment) criteria were chosen from multiple long-term care sites. Raw scores for each instrument (Cancellation of A's, Bernell's Hand-Held Perimetry, Vistech Contrast Sensitivity Chart, Benton Visual Retention Test-Copy version, Randot Fly and Circles, and the Grasping and Action Space Protocol) were used to rank order performance of cases on the instruments above and then to determine the overall rank of visuospatial function by adding the rank of each case for each visual function and dividing it by the number of instruments. These individual and overall rankings were used to make within and across case comparisons. In this study, the profile of overall visuospatial function by case showed definite variability in the discrete visual functions of peripheral vision, contrast sensitivity, visuoconstruction and stereopsis as previous studies would suggest. Using the Grasping and Action Space Protocol, right-left orientation of objects to each other in grasping space also showed definite variability. Mildly CI cases were more homogeneous in their level of impairment (normal, mild, moderate, or severe) than the moderate CI cases. However, the overall visuospatial impairments were more severe in moderate CI cases than in mild CI cases. Inferences about possible lesions related to probable AD pathology in the occipital-parietal pathway can be made based on the visual impairments of contrast sensitivity, stereopsis and right-left orientation of objects described in this study. Specifically, stereopsis and the ability to orient objects to each other spatially using right-left orientation in grasping space appear to be the first functions of the occipital-parietal pathway affected by probable AD regardless of level of cognitive impairment.