Short and long term effects of antipsychotic medication on smooth pursuit eye tracking in schizophrenia

Rationale: Smooth pursuit abnormalities have been observed in antipsychotic naive first-episode patients, suggesting that they are intrinsic to the il lness. However, it is not clear whether these abnormalities are as severe a s those observed in more chronic patients. In addition, although research s uggests that there are no short-term effects of conventional antipsychotic medication, the effects of long-term antipsychotic medication on smooth pur suit eye movements are relatively unknown. Objectives: To determine the sho rt and long, term effects of antipsychotic medication on the smooth pursuit performance of first-episode and chronic patients with schizophrenia. Meth ods: We compared the smooth pursuit performance of antipsychotic-treated an d untreated first-episode and chronic schizophrenic patients with healthy c ontrols using a comprehensive range of performance measures. This included velocity gain, the number, type and size of intrusive and corrective saccad es, and the average time between the change in direction of the target and the change in direction of the eye movement, a measure of subjects' ability to predict target movement. Results: Chronic schizophrenic patients had si gnificantly reduced velocity gain, took longer to respond to the change in target direction and made more catch-up saccades than both first-episode sc hizophrenic patients and controls. First-episode patients were impaired rel ative to controls only on the measure of velocity gain. There were no diffe rences between antipsychotic-naive and treated first-episode patients. Anti psychotic-free chronic patients were significantly less impaired on velocit y gain than matched continuously treated chronic patients. These results we re not influenced by group differences in age and symptom severity. Conclus ions: These results show that: 1) the main index of smooth pursuit, velocit y gain, is impaired early in the course of schizophrenia; 2) whereas veloci ty gain is unaffected by short-term (weeks) medication, it is worsened by c hronic (years) treatment; 3) other indices of smooth pursuit, catch-up sacc ades and ability to predict target movement, are adversely influenced by il lness chronicity rather than medication.