Reliability and application variability of a commercially available infrared videonystagmography unit

Abstract

Purpose: Nystagmus is a condition of involuntary eye movement. The causes for nystagmus may be congenital, idiopathic, or acquired. Considerable debate exists on the therapeutic potential of various surgical techniques. Currently, there are neither standardized protocols nor devices to record quantitative data on patients with clinical nystagmus undergoing various procedures at multiple centers to facilitate randomized prospective clinical trials.

Methods: The authors evaluated the reliability and variability of a commercially available infrared videonystagmography unit by recording eye movement waveforms elicited from normal volunteers (n = 117, 13 patients, 9 trials) by different examiners (A, B, and C). Five movement characteristics were examined, including saccadic latency, velocity and precision, and pursuit gain and velocity.

Results: The overall test/retest variability was low, where the median coefficient of variation of the three testers for all five eye movement categories was less than 15%, and less than 10% of the coefficients of variation calculated were more than 20%. However, there was a significant difference in interobserver variability for all outcomes, except saccade latency.

Conclusions: The between-tester analysis was found to have greater variability than the test/retest reliability analysis. Future studies at multiple sites using videonystagmography measurements should aim to have each patient repeatedly tested by the same tester. In anticipation of multicenter, randomized, prospective clinical trials of surgical procedures for nystagmus, standardized protocols for nystagmographic data collection and analysis must be validated both within and among participating centers.

Figure 1

Box-and-whisker plot for coefficient of variation (CV) from three trials performed by the same tester for the same subject (n=13). Circles represent individual CV (%); boxes represent the 1^st quartile (Q1), median, and the 3^rd quartile (Q3); the lower whisker extends to the minimum observation; the upper whisker extends to the maximum observation below upper fence, (where upper fence = Q3+1.5*(Q3-Q1)); and observations above the upper fence are outliers. The dashed line shows a reference line of 20% CV.

Figure 2

Box-and-whisker plot, for each tester (n=39), of the difference between the observed value and the mean value of each study subject. Circles represent individual difference; boxes represent the 1^st quartile (Q1), median, and the 3^rd quartile (Q3); the lower whisker extends to the minimum observation above the lower fence, (where lower fence = Q1-1.5*(Q3-Q1)); the upper whisker extends to the maximum observation below upper fence, (where upper fence = Q3+1.5*(Q3-Q1)); and observations beyond the lower or upper fences are outliers. The dashed line shows the reference line of 0.