OPTICAL COMPENSATION FOR NIGHT MYOPIA BASED ON DARK FOCUS AND CA C RATIO/

Purpose. To determine whether individual differences in dark focus and convergence accommodation to convergence (CA/C) ratio can be used to prescribe the best optical correction for night myopia. Methods. The b est correction for night myopia was obtained by measuring visual acuit y and contrast sensitivity across a range of lens powers and luminance s. Dark focus was measured with an infrared optometer, and CA/C ratio was measured with an infrared optometer and eyetracker. Only young sub jects were used (mean age = 25.4 years). Results. Optimal lens power w as significantly correlated with dark focus, regardless of CA/C ratio. However, the slope of the regression line relating lens power to dark focus was steeper for subjects with CA/C ratios less than 0.4 diopter s/meter angle (D/MA, n = 7) than for subjects with CA/C ratios greater than 0.4 D/MA (n = 9). The mean CA/C ratio for the entire sample (n = 16) was 0.59 D/MAL. The mean optimal lens power and dark focus were - 0.79 and 0.74 D, respectively, for the low CA/C group, and -0.60 and 0 .91 D, respectively, for the high CA/C group. Conclusions. Visual perf ormance in night myopia can be optimized by taking into account inters ubject differences in dark focus and CA/C ratio. Best visual performan ce was found with a lens roughly equaling the full dark focus for subj ects with low CA/C ratios and half the dark focus for subjects with hi gh CA/C ratios.