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Ying-Ling Chen, Lei Shi, J W L Lewis; Pilot testing of a miniature autorefractor. Invest. Ophthalmol. Vis. Sci. 2017;58(8):1135.
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To develop and test a cost-effective, palm-size autorefractor.
The presented infrared autorefractor employs the eccentric photorefraction (EPR) technique and a Badal optometer system similar to what was proposed by Roorda in 1998 . The refractive state of the eye is measured by moving the EPR camera behind the Badal lens until the crescent shape of pupil light distribution reverse to opposite side like the retinoscopy. The reversing of light corresponds to the situation when the EPR camera is conjugate to the eye’s retina. Several modifications were made to the system. To reduce the system size, a miniature camera with an entrance pupil less than 1.5 mm was used together with fiber optics that provided accurate positioning of illumination. The Badal optometer used a 25 diopter lens to extend the measurement capability. A 0.5-second full-range pre-scan estimated the region of spherical equivalent and determined the subsequent fine scanning region for astigmatic assessment. The resolution of scanning step-motor was 0.08 diopter. We tested the functional prototype on our own eyes with contact lenses and with an artificial eye with adjustable pupil size from 3.3 to 8.8 mm and refractive error from -7 diopters to +6 diopter. A. Roorda, W. R. Bobier, M. C. W. Cambell, Vis. Res. 38, 1934 (1998)
Using the artificial eye with pupil size between 3.3 to 8.8 mm and refractive error between +6 and -7 diopter, the testing result showed an overall accuracy of 0.135 diopter (standard deviation). Our testing on non-cyclopleged human eyes showed repeatability with variation less than 0.25 diopter. The human images also revealed some considerations including mono-chromatic and chromatic aberrations and correlation with pupil size that require further investigation.
The EPR optometer presents a technique that is easy to perform without need of careful alignment or calibration for individual or environment differences. This pilot study showed that it is capable to rapidly determine refraction in extended range with decent accuracy.
This is an abstract that was submitted for the 2017 ARVO Annual Meeting, held in Baltimore, MD, May 7-11, 2017.
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