Hyperopic shift during subjective refraction under dim illumination

Purpose The aim of this study was to compare subjective refraction under two lighting conditions to understand whether illumination affects the correction of myopia. Patients and methods This is a prospective, comparative study that was carried out on 33 myopic patients with corrected visual acuity of both eyes of 1.0 or better (in decimal unit). The included patients had a refractive error greater than −1.50 D. Examinations were carried out under two levels of lighting conditions. The patients underwent objective refraction followed by subjective refraction, pupil diameter measurement, visual acuity assessment, and intraocular pressure measurement. Results The mean subjective refraction under room illumination at 2, 4, and 6 m was −0.65, −0.48, and +0.29 D, respectively, compared with −0.42, +0.39, and +0.60 D without room illumination, respectively. There was a statistically significant difference between mean value of subjective refractions under the two lighting conditions at 4 m ( P =0.00) and 6 m ( P =0.00). However, the mean subjective refraction at the distance of 2 m was not statistically significantly different between the two lighting conditions ( P =0.25). At 2 m, the pupil size and subjective refraction did not show significant differences under both lighting conditions (with and without room illumination). Conclusion There was a hyperopic refractive shift during subjective refraction in dim illumination, which may cause undercorrection of myopia that may trigger myopia progression.