The results of visual assessments demonstrated that older drivers with cataract had significantly worse visual acuity, contrast sensitivity, and they also showed a significantly higher level of intraocular straylight, which agrees with previous studies9,22,31. This impairment is manifested in all visual parameters for both the worse and better eyes in our sample, given that most drivers with cataract had lens opacity in both eyes.
Drivers typically self-regulate their behavior to compensate for such limitations. Thus, the cataract group adopted lower speeds than the control group in all scenarios except scenario 3, a straight segment where they drove at similar speeds (mean difference of approximately 1.0 kph). This agrees with previous research in real10,32,33 and simulated driving situations9. Moreover, the difference in speed selection between the two groups was more accentuated in roads with a higher speed limit, such as scenarios 1 and 2, with a limit of 120 kph, and scenarios 4, 7, and 8, with a limit of 90 kph. Although this tendency was not observed in scenario 3, these results indicate that drivers with cataract may feel less safe on high speed roads. This is congruent with previous studies based on self-reported data collected from questionnaires and naturalistic driving data, which have shown that drivers affected by cataract often avoid driving on highways/freeways2,34 and report driving more slowly than the general traffic flow11.
Road features selected for the different scenarios proved to be significant predictors of speed management. To the best of the authors’ knowledge, this is the first study into how road traffic complexity influences the speed behavior of drivers with cataract. In general, drivers modified their speed behavior under the presence of certain road features that add complexity35. The main cause of speed reductions was a curved layout, such as those in scenarios 1 to 6. This finding agrees with previous research in older drivers with no visual impairment36. On the other hand, when driving in an urban environment, participants adopted speeds well under the limit (50 kph). Contrastingly, we did not observe the same result on the mountain road at a comparable speed limit (40 kph). This may reflect that urban environments are perceived as more complex due to the presence of greater visual clutter35,37,38. For the inner-city section drivers need to interact with a more visual information (road signs, traffic lights, roundabouts, roadside advertising, and buildings) and more road users (pedestrians, moving or parked cars). Visual impairment when driving along city rods could therefore generate a greater feeling of insecurity in drivers37.
Apart from environment complexity, some driver characteristics were also significant predictors of driving speed. Our sample consisted exclusively of older drivers, so we could not assess whether age had a significant effect. However, other works have found that older drivers adopt lower speeds than younger ones, in an attempt to compensate for declines in their motor, cognitive, and sensory capacities32,33,35−37. Gender was a significant predictor of speed management, with men adopting higher speeds. Gwyther and Holland (2012) demonstrated that a high proportion of women of all ages avoid high-speed roads, while this behavior is much less frequent among men39. Research has also revealed that men are greater risk takers, as they are more likely to adopt behaviors such as speeding40–42. Among visually impaired older drivers, women are known to self-regulate their driving to a greater extent34. Nevertheless, it should be taken into consideration that our sample contained fewer women than men, so further research is necessary to confirm this finding.
Of the visual tests used, intraocular straylight in the better eye was a significant predictor of speed behavior. This is the first time that this parameter has been associated with self-regulation patterns in older drivers. Other authors have reported the importance of scattering-related visual parameters (i.e., straylight or disability glare) in drivers, proposing a straylight cut-off value of 1.4 for safe driving22,29,30. Our recent studies have shown that higher levels of intraocular scattering are associated with a poorer simulated driving performance in drivers of different ages and older drivers with and without cataract – in fact, it is a better predictor of driving ability than the visual acuity test9,27,43. The intraocular straylight parameter could provide an accurate quantification of the detrimental effects of intraocular scattering on visual perception, being particularly important for people with cataract44. Nevertheless, at the time of writing we lack a standardized method to assess the effects of intraocular scattering. Although several glare assessment devices have been used in previous studies, these devices base their evaluations on the effect that glare has on visual perception (i.e., they measure the effect of glare on visual acuity or contrast sensitivity), while they do not appear to correctly assess the conditions that can affect driving performance44. In fact, for older drivers, different authors have not found any relationship between the results obtained with this type of glare tests and a poorer driving performance10,33,45,46, a higher risk of accidents8,47,48, or a greater level of self-reported driving difficulty and self-regulation patterns49,50.
On the other hand, contrast sensitivity has proved to be a non-significant predictor of speed management. However, the driving environment comprises stimuli of different contrast levels, some of them are low contrast, so drivers need good contrast sensitivity in order to drive safely30. Owsley et al. (2001) found that impaired contrast sensitivity was the only predictor of crash involvement in drivers with cataract, with a stronger correlation with the worse eye8. Furthermore, contrary to our result, Agramunt et al., (2017) and Fraser et al., (2013) demonstrated that reduced contrast sensitivity is associated with driver self-regulation in drivers with bilateral cataract19,34. Similarly, on-road studies including drivers with cataract have also highlighted the importance of CS as a predictor of driving performance10,33. However, some of these differences could be due to the reduced number of subjects with cataract who were included in our study. After cataract surgery, the increase in contrast sensitivity is associated with improved driving performance10 and a reduced likelihood of self-regulation19,51.
Other studies have also found results along the same lines as the findings of the present work, highlighting the importance of non-standardized visual tests such as the straylight parameter. For example, Bal et al., (2010) reported that straylight and, to a lesser extent, contrast sensitivity are complementary tests to visual acuity, as their consideration is important in terms of programing surgery and driving legality22. On the other hand, West et al., (2003) studied 629 drivers aged over 55 years and found an association between vision-related self-restricted driving and some visual tests such as acuity at different contrast levels or in the presence of glare4. Their results show that the subjective perception of visual disability could also be better predicted by tests other than the commonly used visual acuity test.
In a similar vein, our results of the DHQ show that drivers with cataract perceive greater visual difficulties when driving. It is important to note that all the participants who reported that they no longer drove in certain situations had cataract. As such, 27% of the total sample indicated they self-regulated. Other authors have obtained greater percentages of drivers with cataract who self-regulate (~40%)2,34, possible because a visual acuity below the legal limit for driving was not an exclusion criteria in their studies. In our study, driving at night was the most commonly avoided situation, in agreement with previous works2,31,34. Other commonly avoided situations are driving in heavy traffic or at rush hour2,31,34. Some studies also indicate that these drivers with cataract tend to avoid high-speed roads such as freeways2,34. None of the participants in our study indicated that they avoided driving on freeways, although results from the driving simulator showed that they drove much slower than the control group in sections with a high speed limit.
This study shows some promising results with regard to the visual assessment of drivers with cataract; however, the results should be interpreted cautiously given several methodological limitations. Firstly, the sample size was limited due to the difficulty enrolling older drivers who are both active drivers and free from any eye diseases other than cataract. Moreover, simulator sickness is a very common symptom in older participants, which also hinders the recruitment of larger sample sizes52. Lastly, the use of a driving simulator cannot replicate the true nature of actual driving, although it can be used to assess the impact of cataract in a safe manner. However, driving simulators offer a reproducible method and the opportunity to choose specific features in the environment, which was a very important factor in our study12.