Smooth-pursuit eye movements: alterations in Alzheimer's disease.

Smooth-pursuit eye movement induced by targets moving at constant velocities (from 5 to 100 deg/sec) were recorded from 13 patients with Alzheimer's disease (AD) and from 11 healthysubjects. Four variable were evaluated to quantify the patients' response to the eye movement tests: (1) average peak velocity of smooth-pursuit; (2) percent target matching index after saccade removal (percent ratio between the area of the velocity curve of smooth-pursuit eye movement after saccade removal and the area of target velocity) which is related to the eye performance for each value of target velocity; (3) total amplitude of anticipatory saccades; (4) total number of anticipatory saccades. Compared to the controls, AD patients were found to have significantly lower values of average peak velocity of smooth pursuit and of percent target matching index and a significantly increased number and amplitude of anticipatory saccades. A discriminant stepwise analysis indicated that 5 oculographic variables were significantly associated with the patient's clinical condition (healthy volunteer or AD patient). These statistics yielded an equation for predicting the patient's status according to which the percentage of cases classified correctly was 82.6% in the overall group (n = 23). The predictive performance was between the healthy volunteers subgroup (81.8%, n = 11) and the AD subgroup (83.3%, n = 12). The discriminant score was significantly correlated with the score resulting from the MiniMental test (r = 0.67). A significant correlation was also found between the MiniMental score and the number of anticipatory saccades (r = −0.61). No significant correlation was present between the gain of smooth pursuit and the patients' cognitive decline. Our study shows that smooth-pursuit movements are altered in AD patients and suggests that a quantitative analysis of these eye movements can provide useful nonverbal indexes of the disease.