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M. Kobayashi, Y. Hirohara, T. Fujikado, H. C. Howland, T. Mihashi; Infrared Cover Test: Measurement of Binocular Eye Positions and Accommodation Using an Open-View Binocular Wavefront Sensor With Monocular Stimulation. Invest. Ophthalmol. Vis. Sci. 2008;49(13):2571. doi: https://doi.org/.
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© ARVO (1962-2015); The Authors (2016-present)
To develop a method for measuring binocular accommodation and eye position with monocular stimulation.
We have developed a binocular open-view wavefront sensor (BOVWS) (Hirohara, ARVO, 2007). We added spectacle lens test frames to the BOVWS to correct the refraction of a subject. We inserted an infrared filter into the test frame in front of one eye, allowing the other eye to view a visual target. The instrument could measure the accommodation and position of the covered eye using infrared light (840 nm to measure accommodation and 940 nm to measure the position), the latter using the position of the first Purkinje image relative to the pupil center. We examined the patterns of eye positions of eight subjects under three conditions: both eyes, or the left or right eye only viewing a Maltese cross target at two distances, 1 m and 2 m from the eye. The duration of the single measurement sequence was five seconds, and measurements were made at 24 Hz.
Phoria: Of our eight subjects, five yielded useful data showing interpretable patterns with little scatter. Of these, two were esophoric (+2.71 PD ± 0.77 SE), and three were exophoric, one only at far and another only at near. (-2.39PD ± 0.46 SE). The average absolute phoria for all five subjects was 2.39 PD ± 1,65 SD. The average phoria, sign retained, for all subjects did not differ significantly from zero. Accommodation: We observed small (up to 0.2D) differences in accommodation in the three viewing conditions.
The small phorias measured in this sample of subjects were clinically not significant; however they showed the power of the measurement method. Thus, the infrared cover test may become an easy and accurate clinical method. We also found that the Shack-Hartman Sensor can measure accommodation through an infrared filter.
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