Purpose: The purpose of this study was to determine the reliability of the prism neutralized alternate cover test (ACT) used to measure near phoria in non-strabismic participants as measured by experienced and novice examiners and to compare the values to results obtained by eye tracking.
Methods: Two experienced optometrists and two optometry students performed the ACT at 40 cm on 50 non-strabismic participants. The ACT was then repeated with the subjects wearing an eye tracker. The saccade amplitude of the eye movement recordings was used to determine the phoria. The reliability was determined using Bland–Altman analysis to determine the mean of the differences in the groups and the 95% limits of agreement.
Results: The phoria range determined by the eye tracker was between 6 pd eso and 19 pd exo. The mean of the difference in values and 95% limits of agreement between the experienced examiners was 0.7 ± 3.0 pd; between the novice examiners was −0.1 ± 4.4 pd; between the experienced and novice examiners was 0.8 ± 3.5 pd; between the eye tracker and the experienced examiners was 0.6 ± 3.5 pd; between the eye tracker and novice examiners was 1.4 ± 3.6 pd.
Conclusions: The mean differences of the ACT result between experienced examiners, novice examiners, and the eye tracker, were not clinically meaningful. However, the 95% limits of agreement were quite high (±3.0–4.4 pd). This information is useful for clinical decision making, student education and student evaluation.