Smooth pursuit eye movements in schizophrenia in New Zealand

The objective of this study was to answer the following questions: what is the frequency of smooth pursuit dysfunction in schizophrenia in New Zealand; is it comparable to that observed in other populations; is it specific to schizophrenia; and is it represented in major ethnic groups present in New Zealand?

Patients with schizophrenia (n = 26) were recruited at five clinical facilities in the Auckland region. Diagnoses were taken from clinical records. Patients' smooth pursuit eye movements while following sinusoidal and triangular wave targets were recorded and their performance compared to a control population (n = 34). Eye movements were scored using the In(s/n), pursuit gain, and saccadic frequency measures.

Patients with schizophrenia scored significantly worse than controls using the in(s/n) measure and had significantly higher saccadic frequencies for both targets. Percentile equivalents allow the estimation that about 50% of patients with schizophrenia have smooth pursuit dysfunction (SPD). There was no difference between groups for pursuit gain score, although low gain pursuit was significantly correlated with higher medication in the schizophrenia patient group. There were no differences associated with age, sex or ethnicity. The SPD marker was found in European- and Polynesian-derived New Zealanders.

The results of the present study are consistent with results of previous studies performed elsewhere. Differences are at least partly ascribable to variations in methods. Smooth pursuit dysfunction is a robust marker for schizophrenia. Its application would be particularly useful in the New Zealand context as part of a first admission study looking at the effects of ethnicity on schizophrenia prognosis and on the stability of psychiatric diagnoses.