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Published Online First: 6 July 2006. doi:10.1136/bjo.2006.096057 British Journal of Ophthalmology 2006;90:1277-1280 Copyright © 2006 by the BMJ Publishing Group Ltd.
Bilateral cataract surgery and driving performanceJ M Wood, T P Carberry
School of Optometry and Institute of Health and Biomedical Innovation, Queensland University of Technology, Brisbane, Australia
Correspondence to:
Accepted 6 June 2006
Background: Cataract surgery is one of the most common medical procedures undertaken worldwide. Aims: To investigate whether cataract surgery can improve driving performance and whether this can be predicted by changes in visual function. Methods: 29 older patients with bilateral cataracts and 18 controls with normal vision were tested. All were licensed drivers. Driving and vision performance were measured before cataract surgery and after second eye surgery for the patients with cataract and on two separate occasions for the controls. Driving performance was assessed on a closed-road circuit. Visual acuity, contrast sensitivity, glare sensitivity and kinetic visual fields were measured at each test session. Results: Patients with cataract had significantly poorer (p<0.05) driving performance at the first visit than the controls for a range of measures of driving performance, which significantly improved to the level of the controls after extraction of both cataracts. The change in contrast sensitivity after surgery was the best predictor of the improvements in driving performance in patients with cataract. Conclusions: Cataract surgery results in marked improvements in driving performance, which are related to concurrent improvements in contrast sensitivity.
Abbreviations: BAT, Brightness Acuity Tester; BGT, Berkeley Glare Test Older people comprise the fastest growing sector of the driving population; this has important implications for road safety as they are also reported to have high crash rates per distance travelled.1 However, not all older drivers are unsafe, and many continue to drive safely well into older age. Recent research has sought to identify tests that can accurately differentiate between safe and unsafe drivers, recognising that it is functional rather than chronological age that best predicts driving ability, as well as seeking interventions, which can extend the time that older drivers can drive safely. Cataract surgery has been suggested as an intervention that can potentially improve the performance of older drivers. A growing body of evidence suggests that older drivers with cataracts are less safe to drive than their counterparts without cataracts. People with cataracts experience more problems when driving, drive shorter distances and avoid challenging driving situations.2 Nevertheless, despite limiting their driving exposure, drivers with cataracts have 2.5 times more crashes than controls2; and crash involvement is predicted by deficits in contrast sensitivity.3 Further evidence comes from closed-road and open-road studies, which have shown that drivers with either simulated4,5 or true cataracts6–8 have considerably impaired driving performance compared with controls. The presence of cataracts has also been associated with driving cessation.9 The positive benefits of cataract surgery on vision and quality of life have been widely reported; however, fewer studies have investigated the impact of cataract surgery on real-world activities such as driving. Crash rates have been shown to halve after cataract surgery compared with controls, suggesting that cataract surgery can result in tangible benefits to road safety.10 Self-reported improvements in driving have been described within 1 year11,12 and 5 years after surgery,13 and the driving subscales of the Activities of Daily Vision Scale improve after cataract surgery, particularly for night driving.14,15 This study investigated the effect cataract surgery on real-world measures of driving performance for patients undergoing bilateral cataract surgery within a 3-month period, and determined how well these measures related to changes in visual performance.
Participants Thirty eight patients with cataract scheduled for bilateral cataract surgery were recruited, of whom two withdrew, one had age-related maculopathy and six patients decided to have only one cataract removed; the final sample consisted of 29 patients with cataract, ranging in age from 50 to 89 years (mean (standard deviation (SD)) 73 (8)). The patients with cataract had no ocular disease except cataracts; most patients (75%) had nuclear cataracts or a combination of nuclear and cortical cataracts. Eighteen controls were also tested, who ranged in age from 53 to 78 years (mean (SD) 68 (7)), had normal visual acuity (better than 20/25 or 6/7.5) and were free of ocular pathology. All participants were in good general health and were licensed drivers who drove regularly. In Queensland, Australia, the visual acuity standard is 6/12 binocularly or better, which at the time of the study was tested at 5-yearly intervals on licence renewal. The study was conducted in accordance with the requirements of the Queensland University of Technology Human Research Ethics Committee. All participants were given a full explanation of experimental procedures and written informed consent was obtained, with the option to withdraw from the study at any time. Participants attended a series of vision and driving test sessions. Patients with cataract were tested within a month before their first operation and at least 1 month after the second (mean length of time since the last cataract surgery was 80 days). The controls followed a similar testing pattern. The driving and visual performance measures were undertaken with participants wearing the spectacle correction usually worn for driving, and the patients with cataract wearing any new spectacles prescribed after cataract surgery.
Driving performance
Vision performance Disability glare sensitivity was assessed using both the Berkeley Glare Test (BGT) and the Brightness Acuity Tester (BAT). Both these tests have been used to measure disability glare in previous studies investigating the functional effect of cataract surgery.3,14 The BGT can assess glare sensitivity monocularly and binocularly, and measures the ability to recognise low-contrast letters (10% contrast) in the presence and absence of a glare source at the medium setting of 750 cd/m2.17 The glare score is the difference in visual acuity for glare and no-glare conditions. Disability glare was also estimated with the BAT using the Pelli–Robson chart. Disability glare was defined as the Pelli–Robson score without the BAT minus that with the BAT. Kinetic fields were measured binocularly using a large low-contrast target (size IV4B) moving at a speed of 4°/s along 12 meridians of the visual field. The area of the kinetic field was calculated using a custom-designed programme.
Statistical methods To determine whether any of the changes in visual performance after cataract surgery could predict the improvements in driving performance, a bivariate Pearson’s correlation matrix was constructed with overall driving score as the outcome measure. A regression model (using a forward stepwise model) was then constructed, including only the significant vision predictors from the bivariate correlations.
The mean age of the cataract group was slightly higher than that of the controls by about 5 years (t(45) = 2.49; p = 0.02); this difference was of magnitude similar to the age difference of a cataract and control group in previous studies.2 Because of this age differential, we considered the association between the change in overall driving score and age and found it to be non-significant (r = 0.1; p = 0.48); therefore, no further adjustment for age was made in the data analysis.
Driving performance
Driving performance was shown to improve significantly after cataract surgery for overall driving score (F1,28 = 14.88; p = 0.001), road sign recognition (F1,28 = 20.51; p<0.001), road hazards recognised (F1,28 = 14.72; p = 0.001) and avoided (F1,28 = 17.28; p<0.001). Both the patients with cataract and controls showed a significant improvement in the number of reaction lights seen over the two visits (divided attention task), but there was no significant groupxtest session interaction, indicating that the improvements may have resulted from the effects of repeated testing rather than improvements in driving function after cataract surgery.
Vision performance
Cataract surgery resulted in four lines of improvement in visual acuity for the first operated eye and 1.5 lines for the second operated eye for the cataract group, with just over two lines binocularly. Mean contrast sensitivity improved by 0.30 log units (two steps) for the first operated eye, 0.20 log units for the second operated eye and 0.25 log units binocularly. Vision performance improved significantly for the patients with cataract after surgery for binocular visual acuity (F1,28 = 56.62; p<0.001), visual acuity in the first operated eye (F1,28 = 20.971; p<0.001) and second operated eye (F1,28 = 20.29; p<0.001), binocular contrast sensitivity (F1,28 = 85.40; p<0.001), contrast sensitivity in the first operated eye (F1,28 = 25.35; p<0.001) and second operated eye (F1,28 = 37.16; p<0.001), and BAT in the first operated eye (F1,27 = 12.89; p = 0.001).
Relationship between the change in vision and driving performance after cataract surgery
The difference in contrast sensitivity scores in the second operated eye was the only visual measure that appeared in the final multiple regression model, showing that it alone was the single best predictor of the change in driving performance after bilateral cataract surgery; the other predictors were highly correlated with this measure and do not appear in the final model.
Our findings showed that objective measures of driving performance improved markedly after bilateral cataract surgery compared with a control group, and the improvement in overall driving performance score after cataract surgery was best predicted by the change in contrast sensitivity in the second operated or better eye. Bilateral cataract surgery resulted in marked improvements in sign recognition, ability to detect and avoid hazards, and overall driving score. In most cases, these improvements brought the performance of the patients with cataract to levels similar to those of the controls. This provides objective evidence of specific improvements in driving performance skills after cataract surgery and has important implications for road safety of older drivers. It is also in accord with the crash data of Owsley et al10 which showed that cataract surgery halved crash rates compared with controls. Similarly, self-reported data suggest that cataract surgery improves many aspects of driving performance and 25% of patients with cataract who had ceased to drive before surgery resumed driving afterwards.12 Bilateral cataract surgery also resulted in improvements in both binocular and monocular visual acuity, contrast sensitivity and BAT glare sensitivity, which is in agreement with previous studies.14,18,19 The changes in visual performance were of a similar order to that reported by Elliott et al14 for visual acuity and contrast sensitivity, but slightly more than that reported by Owsley et al.10 The improvement in driving performance after cataract surgery was best predicted by the concomitant change in contrast sensitivity scores. This is in accord with the findings of Owsley et al,3 who reported that crash-involved participants were eight times more likely to have reduced contrast sensitivity than controls and that this relationship was strongest for the worst eye, whereas in our study it was strongest for the better eye. Our study does, however, agree with other studies that have shown that vision in the better eye is predictive of real-world visual tasks including face recognition and reading,20 mobility,14 as well as Activities of Daily Vision Scale scores.14,20 Importantly, the study of Elliott et al14 specifically looked at this relationship in patients following cataract surgery. Together, these findings provide a better understanding of the functional benefits of cataract surgery. The finding that contrast sensitivity is an important predictor of changes in driving performance after cataract surgery both in our study and in that of Owsley et al3 is also supported by previous research. Decina and Staplin21 reported that contrast sensitivity is a significant factor contributing to the prediction of crash rates in older drivers, and our previous studies found a strong relationship between contrast sensitivity and driving performance for simulated22 and true cataracts,7 and also found contrast sensitivity to be a predictor of drivers’ recognition performance (signs, hazards and pedestrians) under daytime and night-time conditions.23 Neither our study nor that of Owsley et al3 found a predictive relationship between glare sensitivity and driving. Although this study is limited by relatively small subject numbers, resulting from the stringent inclusion criteria and experimental demands at a time when patients are preparing for surgery, it has some important advantages. In particular, our experimental approach meant that any changes in driving were recorded over a relatively short period, so that their additional effects of ageing were minimised; those participants who experienced other events that might affect their driving ability were excluded from the experimental design. Our findings show that cataracts can markedly impair many aspects of driving performance and that cataract extraction has the potential to improve driving performance to normal age-matched controls. Importantly, these benefits in driving performance can be best predicted by changes in contrast sensitivity in the better eye. Cataract surgery can thus be considered to be an important intervention for road safety for older people with cataracts, and potentially has the effect of usefully prolonging the period over which older people can drive, resulting in improved mobility and independence.
We thank the Mt Cotton Driver Training Centre for permission to use the closed-road circuit; the vision and driving team for their assistance with data collection; and the referring ophthalmologists for their contribution to this study.
Published Online First 6 July 2006 Funding: This study was funded by MAIC—RAPRS and the Australian Research Council. Competing interests: None declared.
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