Background. Smooth pursuit eye movement (SPEM) dysfunction
is considered to be a promising
candidate for a biological marker for genetic vulnerability to schizophrenia.
There are conflicting
findings regarding the question of what is exactly dysfunctional in SPEM
dysfunction and what
component of eye movements is really specific to schizophrenia. The purpose
of the current study was to help to clarify the nature of (SPEM) dysfunction
and its
specificity to schizophrenia.
Methods. Smooth pursuit eye movements of 43 schizophrenic patients,
34 patients with major
depression and 42 normal controls were examined using high resolution
infrared oculography.
These groups were compared on several indices of oculomotor functioning
(gain, different saccadic categories).
Results. Schizophrenics had a significantly higher catch-up
saccade rate than depressed patients and
normals. The percentage of subjects with an abnormally high catch-up saccade
rate defined as beyond the mean plus 2 s.d. of the normal control
group was
significantly higher in schizophrenics
(27·9%) than in depressed patients (8·8%) and normal
controls (0%). Low gain and higher
numbers of intrusive saccades tended to be more prevalent in both patient
groups but did not distinguish schizophrenics from depressed patients.
Conclusions. Low gain and high rates of intrusive saccades
contribute to SPEM dysfunction in
major depression. Abnormally high rates of catch-up saccades seem to be
the oculomotor
component in smooth pursuit, that is specific to schizophrenia.