Oculomotor fingerprint: eye movements of patients with schizophrenia and healthy controls
Eye movements of patients with schizophrenia have been examined for already more than 100 years under laboratory conditions; investigations in natural environment, however, have only been started recently. This study, designed as follow-up to the first project that measured eye movements of schizoph...
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|Eye movements of patients with schizophrenia have been examined for already more than 100 years under laboratory conditions; investigations in natural environment, however, have only been started recently. This study, designed as follow-up to the first project that measured eye movements of schizophrenic patients in natural environment, is the first one that has combined both: All participants, consisting of 25 patients with the diagnosis schizophrenia according to ICD-10 and 25 healthy controls, matched in age, gender, educational level, intelligence (IQ) and urban influence, performed a smooth pursuit specific task under laboratory conditions and additionally a similar task in real-life. Besides, everybody fulfilled a free-viewing task which contained simple everyday-activities like walking down a corridor or tracking a target during self-motion. Thereby, oculomotor parameters were recorded continuously and binocularly by the EyeSeeCam, a mobile video-based eye-tracker and afterwards gain and RMSE of smooth pursuit eye movements as well as saccades, fixations, blinks and eye velocities have been calculated. Referring to indices of the vestibular system as influencing factor on eye movements in schizophrenia, all participants completed a second run with restricted head (neck brace/chin rest). The tracking task, constructed referring to the former study, could reflect its results: significantly greater RMSE but normal velocity gain which differs from literature values obtained in laboratory studies. More astonishing was the outcome of smooth pursuit in laboratory compared to natural environment: Both tasks revealed similar findings as described in tracking and head restrictions did not seem to have huge impact either. During free-viewing, mostly saccadic parameters, such as amplitude, peak and average velocity as well as the horizontal eye velocity were significantly decreased in patients. The further selection of the most affected patients, classified in a positive-symptom group and a negative-symptom one, depending on their results in psychological rating scales (SANS and SAPS), confirmed these findings. Indeed, the decrease of the saccadic amplitude seems to be rather connected to negative symptoms while saccade and eye velocities and additionally saccade duration and Q-value are reduced in consequence of malfunctions associated with positive symptoms. Due to conspicuous eye movements in laboratory and real-life, a far-reaching neural malfunction can be concluded as a result of the disease. Surprisingly, all these results could have only been proven during free movability of eye, body and head, whereas head restriction led to congruent results between the two groups. However, the direct comparison of reduced and normal head movability within the same group could mainly indicate reduced fixations during head restriction but no differences in saccadic and velocity parameters. Nonetheless, the stabilizing effect of the neck brace might influence the oculomotor system positively. Therefore, the impact of associated systems, such as vestibular and visual motion systems, on eye movements as well as search of additional compensation mechanisms needs further investigation in the future. It is imaginable that one day the reliability of the diagnosis schizophrenia could be supported by a short examination of eye movements.