Deficits in antisaccade and smooth pursuit eye movements are promising endophenotypes in genetic studies of schizophrenia. Patients with schizophrenia and their relatives have worse performance on these tasks compared to healthy subjects. These oculomotor impairments may be caused by the same brain dysfunctions underlying many of the symptoms of schizophrenia. This study aimed to validate antisaccade and smooth pursuit eye movements as endophenotypes in a genetically homogenous Icelandic sample to use them for studying potential risk genotypes in schizophrenia.

Patients with schizophrenia (N=116) and healthy controls (N=108) matched for age and gender underwent infrared oculographic assessment (sampled at 500Hz) of antisaccades and smooth pursuit (at target velocities of 0.25, 0.50 and 0.75Hz).

On the antisaccade task, patients displayed significantly more reflexive errors, longer antisaccade latency, and reduced antisaccade amplitude gain compared to controls. However, spatial error and the variability of amplitude gain and spatial error did not differ between groups. On the smooth pursuit task, patients had significantly lower velocity gain and more frequent saccades during pursuit. Group differences in velocity gain increased with increasing target velocity. Internal consistency of performance was high for all variables in both groups except for antisaccade spatial error in patients (Cronbach's alpha >0.77 for antisaccades and >0.85 for smooth pursuit).

Our findings confirm the existence of robust oculomotor deficits in schizophrenia in a large sample. These measures can therefore be used as valid endophenotypes in future studies of potential schizophrenia risk genotypes in the genetically homogenous Icelandic population.