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Cathleen Fedtke, Klaus Ehrmann, Darrin Falk, Elsbeth Harms-Biβ, Arthur Ho, Brien A. Holden; Means to Rectify Pupil Alignment Errors in Peripheral Refractometry. Invest. Ophthalmol. Vis. Sci. 2011;52(14):2850.
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© ARVO (1962-2015); The Authors (2016-present)
To establish and validate a method to rectify errors arising from pupil misalignment during peripheral refractometry.
Phase 1: A Shin-Nippon NVision K5001 autorefractor was used to measure refraction in 40 adults along horizontal (central 0° and, 20°, 30° and 40° temporal and nasal) and inferior (20° and 30°) visual fields (VF). For each VF, readings were taken with the instrument aligned at pupil center (reference reading) and at 4 horizontally and 4 vertically de-aligned positions relative to pupil center. 3 candidate correction algorithms based on least-squares were established and validated against the reference. Phase 2: Refraction was measured in 4 adults at the same horizontal VF positions with the instrument axis aligned approximate to the pupil center. The image on the pupil alignment monitor was captured together with the measured refraction. Pupil misalignment was determined and refraction readings corrected.
Phase 1: De-alignment along the same meridian as the measured VF, increasingly affected power vectors M and J180 as VF increased. Conversely, only J45 was affected when pupil de-alignment was orthogonal to VF meridian. Linear slope coefficients (D/mm) ranged from 1.65 to -1.47 for M, 1.11 to -0.78 for J180 and 0.82 to -0.50 for J45, for 40° nasal and temporal VFs. Correction algorithms reduced measurement error (ME) by ≥59% for M, J180 and J45. Phase 2: For larger VF angles, the applied algorithms corrected mean M values by up to 1.14D (40° nasal VF). After correction, overall ME of M, J180 and J45 using the best algorithm were reduced by 37%, 29% and 25% respectively. In some adults, individual variations within repeats remained, even after correction.
After correction of refraction measurement with pupil misalignment using candidate correction algorithms, ME of the corrected mean peripheral refraction profile improved by ≥25%. However, sample size was small and individual variations remained even after correction possibly due to the quality of captured images.
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