The reliability, stability, and concurrent validity of a test of gaze stabilization

The gaze stabilization test (GST) is a computerized test of the vestibulo-ocular reflex that reports maximum head velocity while maintaining fixed visual acuity. The GST thus assesses the vestibulo-ocular reflex differently from the dynamic visual acuity test (DVAT). The purpose of this study was to assess the reliability, stability, and validity of the GST in a healthy young and older population. Forty subjects (20 older adults with mean (SD) age of 76.3 (5.3) and 20 young controls with mean (SD) age of 25.2 (3.2)) performed the GST and DVAT assessments. The version of the GST used in this study has a tunneled mirror system to ensure a consistent participant distance of 4 m from the computer screen. All subjects repeated trials within 30 minutes of initial testing. Twenty subjects (10 from each age group) returned 7-10 days later to repeat the GST and DVAT assessments. Vestibular symptoms were assessed before and after GST and DVAT assessments. The mean (SD) GST scores for the older group were 123 (33) deg/s in the yaw plane and 108 (27) deg/s in the pitch plane. For the young group, mean (SD) GST scores were 157 (34) deg/s in the yaw plane and 141(25) deg/s in the pitch plane. There was a significant between-group difference for GST scores in both yaw and pitch planes (p< 0.01). The intraclass correlation coefficient (ICC) for GST scores performed on the same day was 0.75 in the yaw plane and 0.69 in the pitch plane. The ICC including the 20 subjects who repeated the GST within 7-10 days was 0.59 in the yaw plane and 0.54 in the pitch plane. In general, GST was more stable than DVAT. GST was more stable in younger vs. older subjects whereas DVAT was more stable in older vs. younger subjects. Concurrent validity, determined by Spearman correlation coefficients between GST and DVAT loss results were -0.62 in the yaw plane and -0.38 in the pitch plane (p< 0.02). These results suggest that the gaze stabilization test (GST) has good same-day test-retest reliability and stability in healthy young and older adults. The moderate correlation between same-day GST and DVAT loss scores suggest the two tests may be measuring similar, but different constructs.