The presented eye tracking-based system for measuring strabismus angle, aims to replace the standard manual “prism cover test (PCT)” procedure. PCT is performed by occluding one eye and observing the compensatory contralateral eye movement. Our innovative wavelength selective goggles enable accurate monitoring of both eyes constantly even during the occlusion of the eye, by blocking visible light while transmitting the IR light for the eye tracker.
The test procedure detects and measures both manifest [heterotropia] and latent [heterophoria] strabismus, it also detects the deviating eye - right, left or alternating,
This patent pending system is using a short video game and doesn’t require calibration and thus is suitable for all ages including infants and toddlers. The system alternately displays two moving monocular targets on a 45 cm. display until the line-of-sight of each eye coincides with its corresponding target as determined by the eye tracker. The efficacy of system was proven in a clinical study comparing the manual PCT results of two experienced examiners with repeated automatic test results.
31 adult subjects (26.8±4.6 y/o, mean±SD) were tested. The eye-tracking results were 13.7±1.54, compared to PCT results of 14.3±1.35 prism diopters (mean±SE) - correlation of over 89%. The automatic test demonstrating was twice as repeatable as the conventional measurement (P<0.005 paired t-test). The duration of the test was under 30 sec. These results indicate the feasibility of accurate and repeatable measurements of strabismus angles by the automatic objective system which can be used for screening, diagnosis and monitoring of strabismus and heterophoria.