Eye tracking in schizophrenia: does the antisaccade task measure anything that the smooth pursuit task does not?

Smooth pursuit and antisaccade eye-tracking abnormalities have been proposed as endophenotypes for schizophrenia. However, it is not clear whether these tasks measure the same underlying abnormality. We hypothesised that these measures would be correlated. The association between smooth pursuit and antisaccade task performance was assessed in 50 schizophrenic patients, 80 unaffected first-degree relatives and 40 unaffected controls. Smooth pursuit measures included gain, number of saccades and a qualitative measure of smooth pursuit. The antisaccade distractibility error (ADE) score was the only measure of the antisaccade task. A significant correlation was found between reduced gain and an increased ADE score for all the subjects in the three groups combined. The total number of saccades was negatively correlated with the ADE score in the schizophrenic group, but positively in the relative group. Qualitative ratings of smooth pursuit correlated with the ADE score. Our results suggest that the antisaccade distractibility error score is related to gain and qualitative measures of smooth pursuit, although the relationship with number of saccades did not conform to this pattern. The finding may reflect a shared genetic liability, that affects both eye-tracking phenotypes. It is likely that both measures reflect frontal cortical dysfunction.