Forty-three bioptic drivers were eligible to participate in the study based on their having licensure through Alabama's bioptic telescope program at the time of the study. The final sample consisted of 23 bioptic licensed drivers; reasons for declining participation in the study have been reported previously.
19 None of the bioptic drivers were licensed for night driving. The bioptic drivers had on average 3.7 years of driving experience with a bioptic telescope (SD 5.8 years), ranging from starting bioptic driving less than a year before they enrolled in the study to 28 years of bioptic driving experience. Seven of the bioptic drivers had nonbioptic driving experience before they became bioptic drivers; they averaged 21.7 years of nonbioptic driving (SD 14.8 years).
Twenty-three age-matched normally sighted licensed drivers were also enrolled.
Table 1 provides information on demographics and visual function for drivers in both groups. By design, the ages of the two groups were the same. Men were more common among the bioptic drivers than among the normally sighted. Whites and African Americans were similarly distributed in the two groups. As would be expected, the bioptic drivers had worse visual acuity through the carrier lens as compared to the normally sighted drivers. Through the bioptic telescope, the visual acuity of all the bioptic drivers was much improved, with all drivers being 20/60 or better.
Table 2 provides information on the bioptic driver sample with respect to etiology of vision impairment, nystagmus, and telescope characteristics. Nearly all bioptic drivers had received formal on-road training with the bioptic telescope (22 of 23, 96%); and on average, bioptic drivers had 6 years (SD 8 years) of experience driving with the bioptic telescope after they were licensed.
Figure 1 displays whether or not bioptic drivers reported that they used the telescope in various on-road situations and that it was helpful. Over 50% of drivers reported that they used the telescope because it was helpful in judging when to make turns and when safe to pass; identifying pedestrians, other roadway hazards, brake/signal lights on the vehicle in front, and traffic lights; and reading street-name signs and road signs. Very few drivers reported that the telescope was useful in checking the speedometer or judging distance. All but one driver reported using the telescope in at least one or more driving tasks. This driver, who had 20/80 binocular acuity through the carrier lens, did not report using the telescope in any tasks. Over half the sample (56%) reported using the telescope in three or more tasks. The number of tasks for which drivers reported using the telescope was unrelated to binocular acuity (
P = 0.413) and contrast sensitivity (
P = 0.580).
Driving space refers to the spatial extent one drives in one's environment. Bioptic drivers were very similar to normally sighted drivers with respect to reported driving space (
P = 0.29;
Fig. 2). All drivers, regardless of whether they were bioptic telescope users or normally sighted, drove to neighboring towns, and all but one in each group drove to more distant towns. There was a small tendency for normally sighted drivers to be more likely to venture outside Alabama; however, both groups had four drivers who drove outside the southeast region of the United States.
Bioptic drivers reported driving fewer miles per week as compared to normally sighted drivers (
P = 0.0224;
Table 3). In addition, they traveled to slightly fewer places per week (
P = 0.0022) and made fewer trips per week than did normally sighted drivers (
P = 0.0002). All but one driver in each group preferred to be the driver when traveling with another driver, rather than have the other person drive (
P = 1.0). Bioptic drivers were more likely to report that they drove more slowly than the general traffic flow (
P = 0.0006). Only one bioptic driver reported that someone had suggested she stop driving, with none of the normally sighted drivers reporting this (
P = 0.5). When asked to rate the quality of their driving as excellent, good, average, fair, or poor, the distribution of ratings was shifted to lower ratings among the bioptic drivers as compared to normally sighted drivers (
P = 0.0035).
Bioptic drivers reported difficulty levels statistically similar to those of normally sighted drivers in a number of driving situations, including left-hand turns across oncoming traffic (
P = 0.935), interstate/expressway (
P = 0.488), high-traffic roads (
P = 0.071), rush hour (
P = 0.069), changing lanes (
P = 0.233), merging (
P = 1.0), driving in areas with traffic lights (
P = 0.215), driving long distance (
P = 0.460), backing up (
P = 1.0), seeing objects on side of road (
P = 0.243), and finding the places they wanted to go (
P = 0.266). However,
Figure 3 shows five driving situations in which the bioptic drivers reported significantly more difficulty than normally sighted drivers, specifically, driving into bright light, driving in unfamiliar areas, identifying traffic lights, driving in rain, and driving when alone. Although not shown in
Figure 3, the following situations also elicited more self-reported difficulty from bioptic drivers: driving at dusk (
P = 0.046) and driving into the sun when it is near or at the horizon (
P = 0.005).
We examined whether self-reported overall quality of driving by the bioptic drivers corresponded to the backseat evaluator ratings. We had only one bioptic driver who was rated unsafe (defined as overall ratings of 1 or 2 on the 5-point scale) by the backseat evaluator, yet this driver rated her driving as good. The remaining bioptic drivers were rated as safe, and all described their driving as good or average. None of the normally sighted drivers were rated as unsafe, and all normally sighted drivers self-rated their driving as average, good, or excellent. There was a great deal of agreement between the backseat evaluator ratings of driving skills and bioptic drivers' self-ratings of driving difficulty in various situations. Backseat evaluators rated all bioptic drivers as having excellent or good scanning skills, and all reported either no or a little difficulty in seeing objects off to the side, changing lanes, merging, and passing vehicles on a two-lane road—maneuvers that involve scanning. Backseat evaluators also rated all bioptic drivers as 2 or 3 (i.e., good or some problem but not complete failure) in lane positioning, and all bioptic drivers reported no or little difficulty in changing lanes, merging, and passing. With the exception of one driver in each of the following comparisons, bioptic drivers expressed no or a little difficulty in changing lanes, merging, and passing another vehicle, and correspondingly the backseat evaluators also rated steering steadiness as 2 or 3. There was good agreement between bioptic drivers' self-rating of their ability to identify traffic signals and the ratings by backseat evaluators, with ratings for 20 out of 23 drivers being commensurate between bioptic drivers and the evaluators.