Night myopia: implications for the young driver

A total of 380 randomly selected patients aged 16 to 80 years who did not have eye disease underwent testing for night myopia between August and October 1989 with a laser speckle generator under both photopic and scotopic conditions. For the first 308 subjects the speckles were continuously run, and for the next 72 subjects a timer was used to minimize the accommodative stimulus. An increase in myopia of 0.75 dioptres or more from the photopic to the scotopic state, equivalent to a visual acuity of 20/45 or less, was considered indicative of night myopia. Overall, 17% of the subjects were found to have night myopia. Of the 26 subjects aged 16 to 25 years in the timer group 38% had night myopia of 0.75 D or more, 23% had night myopia of 1.00 D or more, and 4% had night myopia of 2.50 D, which is equivalent to an acuity of 20/265. The results indicate that driving in the dark could create visual difficulties for certain younger patients that a night myopic correction would eliminate.