Spectrum of Saccade System Function in Alzheimer Disease

Background: In Alzheimer disease (AD), tests of "first-order capabilities," such as reaction time or motor ability, might measure central nervous system integrity or disability more reliably than those of abstract, conceptual, or cognitive behavior. Saccade system impairments are present in AD, but their sensitivity or specificity remains unevaluated.

Objectives: To determine sensitivity and specificity of saccade measures for AD, precise impairments in AD, and the relationship between dementia severity and saccade system function.

Design: Case-control study comparing saccade system function between patients and control subjects, including correlations between saccade system function and dementia severity in patients and standardized scores examining impairment in individual patients.

Setting: Neuropsychiatric research institute.

Participants: Two hundred forty-five healthy volunteers from the general population, and 35 patients with AD referred by memory clinics. Age- and sex-matched controls were compared with patients on random saccade (n = 35), predictive saccade (n = 11), and antisaccade (n = 18) tasks.

Main Outcome Measures: Saccade latencies, velocities, and accuracies and antisaccade error rates. Sensitivity, specificity, and predictive positive and negative values were calculated using all control data.

Results: Patients had longer and more variable latencies, more hypometric and anticipatory random saccades, and higher antisaccade error rates (P<.01 for all comparisons). The antisaccade error rate correlated with dementia severity (Spearman r = -0.59, P =.02). Antisaccade measures were the most specific (0.70-0.90) and random saccade gain the most sensitive (0.87).

Conclusions: Despite AD group impairment, individual patients function within the control range, reducing the sensitivity and specificity of saccade measures for AD. Longitudinal evaluation may provide more reliable classification.