Purpose: To examine the reliability and usefulness of a video-based Hirschberg test under clinical conditions.
Methods: The authors estimated ocular deviation in 87 patients with strabismus through automated analysis of corneal reflex displacement using a video refractor. The reproducibility of measurement, the comparison with the prism and alternate cover test (PACT), and the distribution of the Hirschberg ratio were investigated.
Results: The 95% limits of agreement of the video-based Hirschberg test evaluated by repeated measurements were +/- 0.18 mm (equivalent to +/- 2.2 degrees or +/- 3.8 prism diopters [PD] of calculated strabismic deviation) for the horizontal deviation and +/- 0.28 mm (equivalent to +/- 3.4 degrees or +/- 5.9 PD) for the vertical deviation. The 95% limits of agreement between the Hirschberg measures and the PACT were within +/- 7.8 degrees or +/- 13.7 PD. The average (+/- SD) Hirschberg ratio was 12.3 +/- 1.2 degrees/mm or 21.8 +/- 2.1 PD/mm.
Conclusions: The video-enhanced Hirschberg measurement shows good reproducibility and ease of application, even in the testing of infants. In quantitative analysis, however, systematic measurement error resulting from intersubject variance of the Hirschberg ratio should be taken into consideration.