UC San Diego

Abnormal saccadic and smooth pursuit eye movements have been identified in a number of neuropsychiatric, neurodegenerative, and brain injured patient groups. Characteristics of these eye movements have shown value for differential diagnosis, tracking change with treatment, understanding brain-behavior relationships, and developing endophenotype models of diseases with genetic components. However, complications involved with traditional eye- tracking equipment preclude oculomotor assessment in many clinical and research applications. To facilitate evaluation of saccadic and smooth pursuit eye movements, a computerized battery of behavioral tests was developed and standardized. The tests provide quantitative measurements and can be administered independently of eye-tracking equipment. Smooth pursuit eye movements are assessed by a test of visual velocity discrimination. Saccadic eye movements are assessed by a series of tests that measure visuoperceptual ability without eye movement, latency of eye movements to visual targets, latency to disengage visual attention, and ability to inhibit saccades. Test validity was examined via the multi-trait, multi-method correlation matrix in a sample of 60 healthy persons. Participants completed the tests while eye movements were tracked at 250Hz using digital video eye-tracking equipment. The tests were found to elicit the intended eye movements. Split-half reliability ranged from 0.65 to 0.97. Construct validity of the saccade tests was supported by hypothesized differences in performances across tests. Convergent validity was evidenced by statistically significant correlations within-traits between behavioral and related eye-tracking measures. Although within-trait correlations were stronger than between-trait correlations, discriminant validity was not supported by formal statistical testing. A second study explored clinical utility of the tests. A sample of 11 patients with Huntington's disease (HD) was compared to an age-matched sample of 12 healthy persons. As expected, the HD group performed worse on all saccade tests. Results suggested that saccade disinhibition in HD is independent of reduced oculomotor efficiency. Furthermore, saccade slowing and disinhibition may follow different courses with respect to age of onset and disease progression. Findings from these studies support the validity of the tests in assessment of smooth pursuit and saccades. Future studies examining validity and diagnostic utility in other patient groups, age-based norm development, and potential improvements to test design are discussed