Study of luminance effects on pinhole test results for visually impaired patients

Purpose. The visual acuity of visually impaired patients has been reported to improve after a refraction, despite pinhole test results that show a dec line or no change in acuity. Our aim was to investigate whether the pinhole -induced reduction in retinal illuminance accounted for these unreliable pr edictions of best-corrected acuity. Methods. Participants were 64 adult pat ients referred for low-vision rehabilitation. Neutral density filters repro duced the pinhole-induced luminance loss, allowing pinhole test and postref raction acuities to be measured at essentially equivalent levels of retinal illuminance. The following data were collected in random order from each s ubject's better eye: (1) habitual visual acuity, (2) habitual visual acuity with filter, (3) habitual visual acuity with pinhole, (4) best-corrected/p ostrefraction visual acuity, (5) postrefraction visual acuity with filter. Results. On average, the pinhole test under-estimated postrefraction visual acuity by six letters (95% confidence limits = +/- 20). The pinhole test u nderestimated postrefraction visual acuity with the filter by two letters ( 95% confidence limits = +/- 16). Among subjects whose acuity improved with the pinhole test (N = 24), 83% experienced better postrefraction visual acu ity. Among subjects whose acuity declined or remained unchanged with the pi nhole test (N = 40), 50% achieved better postrefraction visual acuity. Conc lusions. The pinhole-induced luminance loss contributed to inadequate predi ctions of postrefraction visual acuity. Pinhole test results were enormousl y variable, underestimating and overestimating postrefraction visual acuity . The pinhole test was less reliable when improvements in postrefraction vi sual acuity were small. Visually impaired patients deserve periodic refract ions, and the pinhole test result should not be used as a dichotomizer for clinical decisions regarding the need for a refraction.