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 best correction for night myopia was obtained by measuring visual acuity and contrast sensitivity across a range of lens powers and luminances. Dark focus was measured with an infrared optometer, and CA/C ratio was measured with an infrared optometer and eyetracker. Only young subjects were used (mean age = 25.4 years). RESULTS. Optimal lens power was 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 diopters/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/MA. 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 performance in night myopia can be optimized by taking into account intersubject differences in dark focus and CA/C ratio. Best visual performance was found with a lens roughly equaling the full dark focus for subjects with low CA/C ratios and half the dark focus for subjects with high CA/C ratios.[1]References
- Optical compensation for night myopia based on dark focus and CA/C ratio. Kotulak, J.C., Morse, S.E., Rabin, J.C. Invest. Ophthalmol. Vis. Sci. (1995) [Pubmed]
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