Objective To compare the angle of deviation measured from Photo-Hirschberg testing and Krimsky testing, with that from an alternate prism cover test (APCT) in strabismus patients. Methods A cross-sectional study was conducted in Songklanagarind Hospital, Thailand. Thirty-three strabismus patients were photographed for analysis by Photo-Hirschberg testing using computer software. The corneal light reflex displacement, converted into prism diopter (PD), was compared to the angle of deviation measured with APCT. Twenty-eight strabismus patients were tested with the Krimsky test. Data were analyzed using Pearson correlation and paired t-tests. The study excluded 4 intermittent exotropia cases, 1 intermittent esotropia case and 2 which cases missing data for krimsky test. Results The mean±SD of the deviation angle, measured by APCT with a fixation target at 30 cm and 6 m; were 48.09±16.34PD and 47.82±15.73 PD, respectively. At 1 m, the difference in the angle of deviation measured from APCT and the Photo-Hirschberg test within 10 PD were 58.8% and 63.6%, for ET and XT, respectively. The difference in the angle of deviation measured from APCT and Krimsky tests within 10 PD in ET and XT were 86.7% and 80.0%, respectively. At 4 m, the difference in angle of deviation measured from APCT and Photo-Hirschberg tests within 10 PD in ET and XT were 58.8% and 54.5%, respectively; whereas, the difference in the angle of deviation measured from APCT and Krimsky tests within 10 PD in ET and XT were 80.0% and 70.0%, respectively. Conclusion The reliability of Krimsky test was better than Photo-Hirschberg test for measuring an angle of deviation.