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It is frequently stated that 90% of the sensory information required for driving is "visual." The fact that virtually all countries, including most states in the United States, require some form of vision test as a prerequisite for driver licensure is certainly consistent with this viewpoint. Currently, the most prevalent vision standard for an unrestricted driver's license is 20/40 visual acuity. Unfortunately, it remains the case that there is little empirical evidence that could be used to justify this standard. The traditional research paradigm, which consists of correlating traffic accident records and vision characteristics of licensed drivers, has failed to provide the empirical evidence that would justify any of the existing vision standards for driver licensure.

Former Lighthouse Research Investigator Dr. Kent Higgins attributes the failure of the traditional research paradigm to its almost exclusive reliance on real-world traffic accidents as a measure of driver performance. Nearly all of the previous studies that have correlated visual acuity and accidents in samples of licensed drivers have found that less than 1% of the variance in the accident database can be explained by acuity variations. Traffic accidents are statistically rare events and, consequently, do not provide for a fine-grained discrimination of differences in driving performance. The rarity of traffic accidents was recently underscored by estimates that "a U. S. driver can expect to travel for 102 years before experiencing a disabling-injury accident, and one is not likely to fall victim to a fatal accident for 3,738 years" (Owens, Helmers, & Sivak, 1993, p. 363). Reviews of the earlier research on vision and driving appeared in two chapters (Higgins, 1996a; Higgins & Bailey, 2000).

Dr. Higgins proposed new methodologies for determining the minimal visual requirements (e.g., visual acuity, visual fields) for the different components of the overall driving task such as steering, reading signs, and recognizing road hazards. In one approach, normally sighted subjects with artificially degraded vision performed driving tasks on a special closed-road test track which allowed the measurement of different aspects of their driving performance. During the summer of 1995, Dr. Higgins was awarded a Visiting Research Fellowship by the School of Optometry of the Queensland University of Technology (QUT) in Brisbane, Australia. This fellowship allowed him to conduct a 2-month collaborative study with Dr. Joanne Wood of QUT in which this approach was used to determine the effect of degraded visual acuity on the driving performance of otherwise normally-sighted subjects.

Using this approach, each subject drove a full-size vehicle on a closed-road test track that was specially designed to measure different components of overall driving performance. Twenty-four subjects were tested on the series of driving tasks (e.g., sign recognition, steering accuracy, maneuvering, road hazard recognition and avoidance, etc.) while their visual acuity was degraded to each of five levels. One level was produced by normal viewing (20/20); three by optical blur (20/40, 20/100, 20/200); and the fifth was produced by special filters which simulated mild cataracts (this method produced only a minor loss in acuity). This latter condition was termed 20/40g to indicate that the level of acuity was the same as that of the 20/40 optical blur condition. In addition, subjects were administered a battery of vision tests (including measurements of glare and contrast sensitivity) under the same visually degraded conditions.

One objective of this project was to determine whether the different components of closed-track driving performance were selectively or uniformly degraded by reductions in visual acuity. A second objective of this research was to determine, for those tasks affected by acuity reduction, the precise form of the relationship between visual acuity degradation and driving performance. A preliminary report on this project was published in Vision Science and Its Applications (Higgins, Wood, & Tait, 1996a). Additional findings describing the quantitative relationship between acuity loss and driving performance were presented at the Association for Research in Vision and Ophthalmology and summarized in Investigative Ophthalmology & Visual Science (Higgins, Wood, & Tait, 1996b).

Overall, the results indicated that acuity degradation produced selective losses in some aspects of driving performance (e.g., decreased ability to recognize high contrast signs and to avoid large, low contrast road hazards; slower driving times). However, other aspects of driving performance (perception of lateral clearance, maneuvering or "slaloming" through a series of traffic cones) were largely unaffected.

Further, when acuity degradation was produced solely by optical blur, the driving tasks that were affected evidenced a linear relationship between acuity degradation and performance. For example, in the case of the sign recognition and road hazard avoidance measures, 50% of the variance in performance was explained by variations in visual acuity. This stands in marked contrast to previous research indicating that variations in acuity account for less that 1% of the variance in accident statistics and serves to underscore the important role of vision in driving. These results were described in the journal Human Factors (Higgins, Wood, & Tait, 1998). When, however, the results of the 20/40g condition (cataract simulation) were included in the analysis, the limitations of high contrast visual acuity as a predictor of driving performance became evident. Although acuity in the 20/40g condition was the same as that in the 20/40 condition produced by optical blur, driving performance was markedly degraded in the 20/40g condition. Overall driving performance in the 20/40g condition was as poor as that for individuals driving with an amount of optical blur sufficient to reduce acuity to 20/200. These results appeared in the proceedings of the International Vision in Vehicles VII conference (Wood & Higgins, 1999).

A third objective was to determine which measure(s) of visual function, alone or in combination, was most predictive of changes in driving performance. As already noted, visual acuity was an excellent predictor when the sole source of the acuity reduction was optical blur, accounting for as much as 50% of the variance in some driving tasks. When the effect of cataract-like changes was included in such analyses, the percentage of variance explained by visual acuity alone dropped to a maximum of about 15-18%. When, however, the results of a visual acuity test (a test that is more sensitive to blur than glare) were supplemented by results of vision tests that were more sensitive to glare than blur, the percentage of variance explained by the combined vision tests was increased to about 45-50%. Drs. Higgins and Wood found that there are a number of tests that are particularly sensitive to glare while being relatively independent of optical blur and could, therefore, be used to supplement acuity testing. These results were described in Investigative Ophthalmology & Visual Science (1997). More recently, Drs. Higgins and Wood have been working on a multiple regression model to describe the efficacy of different combinations of vision tests for predicting changes in driving performance produced by glare as well as optical blur. A preliminary version of this model appeared in Vision Science and Its Applications (Higgins & Wood, 1998). The complete model was recently published in a feature issue of the journal Optometry and Vision Science (Higgins & Wood, 2005) dedicated to the subject of vision and driving. Also, Drs. Higgins and Wood have shown, using an approach based on signal detection theory, that traditional vision tests are indeed important for predicting certain aspects of closed road driving performance (Higgins & Wood, in press).

The second method that Dr. Higgins proposed for determining the minimal visual requirements for driving involved the development of a driving simulator with high-resolution visual graphics sufficient to simulate the resolution of the human visual system. The intent was to use the simulator to study the visual requirements for driving using paradigms similar to those already used by Dr. Gordon Legge (1991), who studied the visual requirements for reading. Using the simulator, each individual's vision could be progressively degraded to determine the level at which different components of driver performance began to deteriorate, just as in the case of the closed track approach described previously. In addition, the simulator would permit the testing and training of driving performance in an increasing number of individuals with visual loss due to age and/or ocular disorder who may have lost their license for failure to meet existing vision standards (Horowitz & Higgins, 2000; Higgins, 2003).

Dr. Higgins also collaborated on a multiyear research project that employed both on-road and simulator tests of driving performance in normally sighted and visually-impaired individuals. The Department of Veterans Affairs provided funds for the purchase of a driving simulator and, to conduct the research, the National Eye Institute awarded a five-year Bioengineering Research Partnerships Grant. The Principal Investigator on this multidisciplinary grant is Dr. Eli Peli of the Schepens Eye Research Institute, Harvard Medical School. The objectives of this proposal are to a) develop optical and electronic devices aimed at restoring the interplay of central (high-resolution) and peripheral (wide-field) vision for persons with different types and amounts of vision loss and b) test the efficacy of the proposed devices through laboratory (virtual-world) and field (real-world) tests of pedestrian and driving mobility. Dr. Higgins' role in this research was to assist in the design of the on-road testing protocols and oversee the design and conduct of the driving simulator evaluation of normally sighted subjects and of persons with different types and amounts of vision loss. Two manuscripts have been accepted for publication; they describe important methodological considerations underlying the design of the on-road (Sodhi et al., in press) and simulator (Peli et al., in press) driving evaluations. This research will provide important evidence concerning the relationship between vision loss and driving performance and, in addition, the efficacy of the proposed low vision devices for improving driving related mobility.

On-road testing of patients with vision loss commenced in late 2002 and is being conducted in The Netherlands and in Alabama. The simulator was delivered and installed in March of 2003. A initial series of driving scenarios was created and preliminary testing with the simulator began in June of 2003. Additional scenarios have been developed and refined over that past year, and the first major study is scheduled to begin in the Fall of 2004 and conclude by the end of 2005.

Further Reading

Higgins, K. E. (1996a). Low vision driving among normally-sighted drivers. In R. Cole & B. Rosenthal (Eds.), Remediation and management of low vision (pp. 225-236). St. Louis, MO: Mosby.

Higgins, K. E. (1996b). Vision standards for driving in an aging society. Aging & Vision News, 8 (No. 2).

Higgins, K. (2003). Driving and vision in an aging society. Generations, 27, 57-63.

Higgins, K. E., & Bailey, I. (2000). Vision disorders and the performance of specific tasks requiring vision. In B. Silverstone, M. A. Lange, B. Rosenthal, & E. Faye (Eds.), The Lighthouse handbook on vision impairment and vision rehabilitation: Vol. I. Vision impairment (pp. 287-315). New York: Oxford University Press.

Higgins, K., & Reich, L. (1991). Driving and visual impairment. Proceedings, World Congress on Technology, 2, (pp. 557-580).

Higgins, K. E., & Wood, J. M. (1997). Effect of glare vs. blur on Pelli-Robson, skill, and Berkeley glare tests. Investigative Ophthalmology & Visual Science, 38 (Suppl.), S69.

Higgins K. E., & Wood, J. M. (1998). Predicting closed road sign recognition performance from vision tests. In Vision science and its applications, OSA technical digest series (pp. 42-45). Washington, DC: Optical Society of America.

Higgins, K. E., & Wood, J. M. (in press). Sensitivity and specificity of vision tests for predicting driving performance. In A. G. Gale (Ed.), Vision in Vehicles VIII. Amsterdam, The Netherlands: Elsevier.

Higgins, K. E., Wood, J. M., & Tait, A. (1996a). Closed road driving performance: Effect of degradation of visual acuity. In Vision science and its applications, OSA technical digest series (pp. 78-81). Washington, DC: Optical Society of America.

Higgins, K. E., Wood, J. M., & Tait, A. (1996b). Vision and driving: Selective effect of visual acuity reduction on closed road driving performance. Investigative Ophthalmology & Visual Science, 37 (Suppl.) S525.

Higgins, K. E., Wood, J. M., & Tait, A. (1998). Vision and driving: Selective effect of optical blur on different driving tasks. Human Factors, 41, 224-232.

Higgins, K. E., Woods, J. M. (2005). Predicting components of closed road driving performance from vision test results. Optometry and Vision Science, 82, 647-656.

Horowitz, A., & Higgins, K. E. (2000). "Older" driver and failing vision: Time to surrender the keys? Consultant, 40 (7), 1310-1316.

Legge, G. E. (1991). Glenn A. Fry Award Lecture 1990: Three perspectives on low vision reading. Optometry and Vision Science, 68, 763-769.

Owens, D. A., Helmers, G., & Sivak, M. (1993). Intelligent vehicle highway systems: A call for usercentered design, Ergonomics, 36, 363-369.

Sodhi, M., Reimer, B., Tant, M., Peli, E., Bowers, A., Woods, R., Higgins, K., & Turco, P. (in press). Driver performance evaluation: Considerations underlying selection and design of routes, Vision in Vehicles X, Elsivier Sciences Publishers B.V. Amsterdam.

Peli, E., Bowers, A., Mandel, A., Higgins, K., Goldstein, R., & Bobrow, L. (in press). The design of driving simulator performance evaluations for driving with vision impairments and visual aids, Transportation Research Record.

Rinalducci, E. J., Cinq-Mars, S., Mapes, D., & Higgins, K. (1996). Determining the field of view in HMDs: A psychophysical method. Presence, 5, 353-356.

Sodhi, M., Reimer, B., Tant, M., Peli, E., Bowers, A., Woods, R., Higgins, K., & Turco, P. (in press). Driver performance evaluation: Considerations underlying selection and design of routes, Vision in Vehicles X, Elsivier Sciences Publishers B.V. Amsterdam.

Wood, J. M., & Higgins, K. E. (1999). How well does high contrast acuity predict driving performance? In A. G. Gale, I. D. Brown, C. M. Haslegrave, & S. P. Taylor (Eds.), Vision in Vehicles VII (pp. 33-42). London: Elsevier.

Wood, J. M., Higgins, K. E., & Tait, A. (1996). Driving with reduced (but legal) acuity: Are all 20/40 drivers equal? Investigative Ophthalmology & Visual Science, 37 (Suppl. S525).

 

 

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