Determining more appropriate visual function predictors of driving performance: can we do better than current visual standards?

Abstract

Background: Driving occurs in complex real-world environments with varying contrast and luminance. However, in the UK, current vision standards rely primarily on the number-plate test under photopic conditions. Given that safe driving requires not only good photopic vision but also the ability to detect and respond to hazards, there is a need to consider additional visual function measures. This thesis evaluated visual function parameters and luminance levels that are more sensitive to vision loss and examined the impact of visual degradation conditions on hazard perception performance and eye movements.

Method: Media opacity was simulated using cataract-simulating filters (LEE Fog 1–5) in 47 healthy drivers to assess effects on visual function under varying luminance (Study 1). Optical blur was then induced with +1.00, +2.00, and +3.00-dioptre spherical lenses in five drivers performing the UK Hazard Perception Test (HPT) (Study 2) to determine suitable blur for the final study. The final study evaluated how visual degradation conditions, singly and combined, affected eye movements, HPT scores, and reaction time (RT) to hazards in 31 younger and 28 older drivers (Study 3).

Results: Mesopic vision was more sensitive than photopic vision for detecting vision loss under simulated media opacity. Mesopic high-contrast visual acuity (VA) and contrast sensitivity, photopic low-contrast VA, and intraocular straylight were most affected. Optical blur significantly slowed RT and reduced HPT scores in older drivers, while the combined effect of contrast reduction and other visual degradation had a greater impact on younger drivers. Night-time driving and adverse weather conditions further worsened performance. Eye-movement behaviour, particularly visual field eccentricity, was significantly affected by visual degradation (singly and combined); however, HPT scores did not correlate with eye-movement measures.

Conclusion: Assessment of mesopic visual function, hazard RT, and eye-movement behaviour is critical for identifying vision loss relevant to driving, particularly under low-light and visually demanding conditions. These findings highlight the importance of incorporating sensitive visual function measures beyond standard photopic testing when advising drivers of all ages on visual fitness to drive.

Date of Award	Apr 2026
Original language	English
Supervisor	Julie-Anne Little (Supervisor), Roger Anderson (Supervisor) & Padraig Mulholland (Supervisor)