Purpose. 

To compare the repeatability of the alternate cover test between experienced and inexperienced examiners and the effects of dissociation time and examiner bias.

Methods. 

Two sites each had an experienced examiner train 10 subjects (inexperienced examiners) to perform short and long dissociation time alternate cover test protocols at near. Each site conducted testing sessions with an examiner triad (experienced examiner and two inexperienced examiners) who were masked to each other's results. Each triad performed the alternate cover test on 24 patients using both dissociation protocols. In an attempt to introduce bias, each of the paired inexperienced examiners was given a different graph of phoria distribution for the general population. Analysis techniques that adjust for correlations introduced when multiple measurements are obtained on the same patient were used to investigate the effect of examiner and dissociation time on each outcome.

Results. 

The range of measured deviations spanned 27.5 prism diopters (Δ) base-in to 17.5Δ base-out. The absolute mean difference between experienced and inexperienced examiners was 2.28 ± 2.4Δ and at least 60% of differences were ≤2Δ. Larger deviations were measured with the long dissociation protocol for both experienced and inexperienced examiners (mean difference range = 1.17 to 2.14Δ, p < 0.0001). The percentage of measured small deviations (2Δ base-out to 2Δ base-in) did not differ between inexperienced examiners biased with the narrow vs. wide theoretical distributions (p = 0.41). The magnitude and direction of the deviation had no effect on the size of the differences obtained with different examiners or dissociation times.

Conclusions. 

Although inexperienced examiners differed significantly from experienced examiners, most differences were <2Δ suggesting good reliability of inexperienced examiners' measurements. Examiner bias did not have a substantial effect on inexperienced examiner measurements; however, increased dissociation resulted in larger measured deviations for all examiners.