Reliability of and comparisons among three variations of the alternating cover test.

One of the most commonly used methods for measuring heterophoria is the alternating cover test. Differences in specific procedures and observational criteria used by examiners may result in different measurements of heterophoria on the same patient. This study evaluated the inter-examiner reliability of three different cover test techniques: the estimated cover test, the prism neutralized objective cover test, and the prism neutralized subjective cover test. Two examiners performed each technique on each of 72 subjects. Reliability was assessed using correlational methods and mean difference calculations. Although there were some inter-examiner differences for the different techniques, all of these differences were within previously determined minimum detectable eye movement ranges. Therefore, when used by experienced clinicians, each of these techniques appears to be a reliable method of heterophoria determination, and their results are comparable.