10.1 Relevance to the driving task
10.1.1 Effects of vision and eye disorders on driving
Good vision, including visual acuity and visual fields, is essential to operating a motor vehicle. Any marked loss of visual acuity or visual fields will diminish the person’s ability to drive safely, including their ability to detect another vehicle, pedestrians or warning signs. It may also increase the time for a person to perceive and react to a potentially hazardous situation.
Peripheral or side vision assists the driver to be aware of the total driving environment and is particularly important in certain common driving tasks, such as merging into a traffic stream or changing lanes, and in detecting pedestrians and vehicles to the side of the line of vision.
Vision defects can develop slowly, and drivers may be unaware of their reduced abilities, particularly in relation to peripheral vision.
10.1.2 Evidence of crash risk
See references 1, 2, 3, 7, 8,15,16
The evidence is incomplete regarding visual fields and visual acuity and crash risk. This is likely due to the many methodological reasons outlined in Part A of this publication (refer to Part A section 1.5. Development and evidence base).
Identifying the degree to which reduced visual acuity increases motor vehicle crash risk is challenging. The evidence for visual acuity impairment is generally limited to drivers whose visual acuity already meets licensing standards, limiting the ability to determine whether alternative cut-points are more appropriate. While it is generally agreed that adequate visual fields are important for safe driving, the actual cut-off value that should be set remains unclear.
Most research suggests there is no association between crash risk and colour vision. While there is evidence that people with red-colour- deficient vision have difficulty in detecting red lights and stopping in laboratory and on- road testing, significant improvements in road engineering mean that people with red-colour deficiency may largely compensate for their deficiency while driving.