Diurnal variation of visual functions for driving with and without orthokeratology: A multicenter study

Purpose: To investigate orthokeratology-related diurnal variations in visual acuity, contrast sensitivity, mesopic (twilight) vision, and glare sensitivity, and to verify compliance with requirements for driver licensing.

Methods: In this prospective, multicenter, controlled study, fifty myopic (range, -1.00 to -4.50 D) and non-presbyopic glasses or soft contact lens wearers (age range, 16-39 years) were fitted with orthokeratology (OK) contact lenses. Before and after completion of OK lens fitting, measurements of visual acuity, contrast sensitivity, mesopic vision and glare sensitivity were performed at three times of the day, morning, afternoon and evening using a standardized binocular vision testing device (Oculus Binoptometer 4P). Monocular and binocular visual acuity were tested according to ISO 8596 and compared to requirements of cars and motorcycles drivers in different countries.

Results: Compared to the prior correction, binocular visual acuity (logMAR) with orthokeratology was statistically significant better in the morning (0.04 ± 0.12; p < 0.05) and afternoon (0.04 ± 0.10; p < 0.05), while the difference was not statistically significant in the evening (p = 0.512). Furthermore, there was no statistically significant difference in contrast sensitivity in the morning (p = 0.813), afternoon (p = 0.742) or evening (p = 0.945). For both mesopic vision and glare sensitivity, there was no statistically significant difference between the contrast levels achieved with orthokeratology compared to the prior correction in the morning (p = 0.083; p = 1.000), afternoon (p = 0.054; p = 0.125) or evening (p = 0.195; p = 0.635). With orthokeratology, no statistically significant diurnal variation was found for binocular visual acuity, contrast sensitivity, mesopic vision or glare sensitivity (p > 0.05).

Conclusions: These results provide evidence, that visual functions of OK lens wearers are stable throughout the day and comparable to the prior correction. Although the visual standards for driving are not uniform within countries, the requirements for visual acuity are met in all of the countries. Mesopic vision and glare sensitivity, which are suggested as other aspects to influence driving performance, also appear to be constant over the course of the day.