Optical compensation for night myopia based on dark focus and CA/C ratio.
OBJECTIVE
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.
Kotulak
J C
JC
Evans US Army Community Hospital, Fort Carson, Colorado, USA.
Morse
S E
SE
Rabin
J C
JC
D000065:Accommodation, Ocular / Q000502:physiology*; D000328:Adult; D015350:Contrast Sensitivity / Q000502:physiology*; D003290:Convergence, Ocular / Q000502:physiology*; D003624:Darkness; D005139:Eyeglasses; D006801:Humans; D008027:Light; D008297:Male; D009216:Myopia / Q000503:physiopathology / Q000628:therapy*; D009801:Oculomotor Muscles / Q000502:physiology; D055095:Optics and Photonics; D014792:Visual Acuity / Q000502:physiology