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Lateral Pupil Alignment Tolerance in Peripheral Refractometry

Purpose. To investigate the tolerance to lateral pupil misalignment in peripheral refraction compared with central refraction. Methods. A Shin-Nippon NVision-K5001 open-view auto-refractor was used to measure central and peripheral refraction (30° temporal and 30° nasal visual field) of the right eyes of 10 emmetropic and 10 myopic participants. At each of the three fixation angles, five readings were recorded for each of the following alignment positions relative to pupil center: centrally aligned, 1 and 2 mm temporally aligned, and 1 and 2 mm nasally aligned. Results. For central fixation, increasing dealignment from pupil center produced a quadratic decrease (r ≥0.98, p < 0.04) in the refractive power vectors M and J180 which, when interpolated, reached clinical significance (i.e., ≥0.25 diopter for M and ≥0.125 diopter for J180 and J45) for an alignment error of 0.79 mm or greater. M and J180 as measured in the 30° temporal and 30° nasal visual field led to a significant linear correlation (r ≥0.94, p < 0.02) as pupil dealignment gradually changed from temporal to nasal. As determined from regression analysis, a pupil alignment error of 0.20 mm or greater would introduce errors in M and J180 that are clinically significant. Conclusions. Tolerance to lateral pupil alignment error decreases strongly in the periphery compared with the greater tolerance in central refraction. Thus, precise alignment of the entrance pupil with the instrument axis is critical for accurate and reliable peripheral refraction.