Purpose: To evaluate the on-road driving performance of persons
with homonymous hemianopia or quadrantanopia in comparison
to age-matched controls with normal visual fields.
Methods: Participants were 22 hemianopes and eight quadrantanopes
(mean age 53 years) and 30 persons with normal visual fields
(mean age 52 years) and were either current drivers or aiming to
resume driving. All participants completed a battery of tests of
vision (ETDRS visual acuity, Pelli-Robson letter contrast sensitivity,
Humphrey visual fields), cognitive tests (trials A and B, Mini
Mental State Examination, Digit Symbol Substitution) and an
on-road driving assessment. Driving performance was assessed in
a dual-brake vehicle with safety monitored by a certified driving
rehabilitation specialist. Backseat evaluators masked to the clinical
characteristics of participants independently rated driving performance
along a 22.7 kilometre route involving urban and
interstate driving.
Results: Seventy-three per cent of the hemianopes, 88 per cent of
quadrantanopes and all of the drivers with normal fields received
safe driving ratings. Those hemianopic and quadrantanopic
drivers rated as unsafe tended to have problems with maintaining
appropriate lane position, steering steadiness and gap judgment
compared to controls. Unsafe driving was associated with slower visual processing speed and impairments in contrast sensitivity,
visual field sensitivity and executive function.
Conclusions: Our findings suggest that some drivers with hemianopia
or quadrantanopia are capable of safe driving performance,
when compared to those of the same age with normal
visual fields. This finding has important implications for the
assessment of fitness to drive in this population.