Effect of Examiner Experience and Technique on the Alternate Cover Test

Abstract

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.

Inter-examiner variability and agreement of the alternate prism cover test (APCT) measurements of strabismus performed by 4 examiners

“…1,2,8,10,11 Holmes et al 1 reported inter-examiner variability of the APCT in adults with sixth nerve palsy and suggested a change in measurements of 10 PD or more was suggestive 96 Â standard deviation of the difference) to be ±4.9 PD for near fixation and ±4.6 PD for distance fixation. The solid line shows the mean of the differences to be À0.16 vs À0.14 PD for near and distance fixation, respectively.…”

“…Deviations, based on the fixation of preference, were recorded as the value of the prism that reached the first neutral endpoint. To ensure full dissociation, the cover paddle was held as closely as possible to the patient's eye in combination with the ''long dissociation protocol'' of Anderson et al 2 The cover paddle was initially held in front of the non-dominant eye for 5 seconds. ''The eye was alternately occluded for a count of 2 seconds for nine additional excursions of the cover paddle.…”

“…The right and the left eye were covered five times each, leading to a total dissociation time of 23 seconds,'' (p. 170). 2 Cooperation of participants aged 512 years was rated during each of the 4 measurements by every examiner. A 5-point coping scale was used, modified from the Distress and Approach-Avoidance score scale of Blount et al 12 The scale ranged from extreme distress/agitation/screaming (score 1) to no distress/ calm/no crying (score 5).…”

“…Several factors have been reported to play a role in the measurement of strabismus, such as examiner experience, examiner bias, positioning of the examiner and target, dissociative techniques, test being used (eg, APCT and simultaneous prism and cover test), neutralization endpoint employed, calibration and position of the prism in front of the eye, magnitude of deviation (eg, 20 PD vs420 PD), test distance, age, and type of strabismus. [1][2][3][4][5][6][7][8][9][10] A number of studies have reported inter-examiner variability and agreement in children and adults comparing 2 examiners. 1,2,8,10,11 In large eye clinics more than 2 examiners often measure the angle of deviation on a patient on separate visits.…”

“…[1][2][3][4][5][6][7][8][9][10] A number of studies have reported inter-examiner variability and agreement in children and adults comparing 2 examiners. 1,2,8,10,11 In large eye clinics more than 2 examiners often measure the angle of deviation on a patient on separate visits. The inter-examiner variability and agreement between more than 2 examiners assessing children and adult patients is however unknown.…”