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Moshe Eizenman, Dmitri Model, Howard Bunting, Jennifer Sacco, Stephen P. Kraft; Evaluation of an Automated Method to Measure Eye Misalignment. Invest. Ophthalmol. Vis. Sci. 2011;52(14):6350.
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© ARVO (1962-2015); The Authors (2016-present)
To evaluate a novel automated method to measure the maximum (manifest + latent) angle of deviation. The method uses an eye-tracking system to measure the direction of the visual axes of the two eyes and it does not require either prisms or alternate occlusion.
The novel automated method is based on an advanced infrared remote eye-gaze tracking system that estimates the position of the centre of the cornea and the direction of the optical axis of each eye without any subject calibration procedures. The maximum angle of deviation was measured in the primary position while patients fixated on a distant target at 6 meters. The measurements were done first by an orthoptist with the Alternating Prism Cover Test (APCT) and then by the Eye Tracker Based Test (ETBT). During the ETBT, the eyes were dissociated by covering one eye with an infrared transparent occluder. The measurements by the ETBT were repeated twice to assess repeatability.
Twenty two patients were tested: 4 with esotropia, 9 with exotropia, 4 with IV nerve palsy, 2 with VI nerve palsy, 2 with thyroid eye disease, and one with dissociated vertical deviation. The maximum angle of deviation was between 27.5 Δ eso to 35 Δ exo, and up to 18 Δ vertically. The mean difference (± standard deviation, SD) between the measurements with ETBT and APCT was 1.2 ± 2.9 Δ and 0.1 ± 3.3 Δ for horizontal and vertical angles, respectively. The mean difference between repeated measurements by ETBT was 0.7 ± 2.3 Δ and -0.1 ± 2.3 Δ for horizontal and vertical angles, respectively (only 17 out of the 22 patients were tested twice).
The pilot data suggest that there is a small bias (1.2 Δ) in the measurements of the horizontal angle between ETBT and APCT. The SD of the difference between measurements of the maximum angle of deviation by ETBT and APCT is similar to the SD of the difference between APCT measurements by different orthoptists (±3.0 Δ for horizontal angles and ±2.5 Δ for vertical angles, Schutte et al, 2009). The pilot data suggest that the automated ETBT has similar accuracy and repeatability to that of the APCT.
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