Night myopia: cause and a possible basis for amelioration.

The relationship between night myopia under simulated night driving conditions and the dark focus accomodation was examined. Over a range of luminance and contrast conditions typical of the night driving situation, college-age subjects accommodated to about one-half the difference between a distant simulated road sign and their individual dark focus. Subsequent laboratory and field experiments demonstrated that: (1) a negative correction equal to one-half the value of the dark focus significantly improved night visual performance as compared with their normal or full dark-focus correction, and (2) greater improvements in performance were obtained for subjects who exhibited a relatively near dark focus.