Bioptic Telescopic Spectacles and DrivingBy: Stanley Woo - OD, MS, FAAO
Bioptic telescopic spectacle (BTS) systems provide magnification for distance viewing. In clinical settings, a clinician should consider a BTS when a patient needs to improve his/her distance vision while maintaining their hands free and for spotting tasks (See M. Politzer on BTS). For example, BTS are prescribed along with training for spotting in the classroom, watching television, and ambulating.
One of the primary objectives identified by patients with low vision is to maintain their independence. This often leads to the specific goal of driving. Driving requirements for the visually impaired varies from state to state and are regulated by either the Department of Motor Vehicles or the Department of Public Safety. In 2003, the American Medical Association and the National Highway Traffic Safety Administration published an excellent resource entitled the “Physicians guide to Assessing and Counseling Older Drivers” that identifies variations by state, and also elaborates on some of the areas of concern for normally-sighted older adults including cognition, reflex time, and motor skills. Not every patient with low vision is a candidate for driving; however, in some states the use of bioptic telescopic spectacles (BTS) has proven to be an effective and safe adaptive aid to maintain a driver’s license.
Driving is integral to quality of life, independent travel, maintenance of employment, and financial independence for both the normally sighted and the visually impaired. Cessation of driving is linked to social isolation and subsequent depression (Owsley et. al., 1999; Baron, 1991). Regrettably, adults who lose driving privileges as a result of acquired vision loss may experience a lowering of self-esteem and a declining level of social status (Appel et al, 1990).
In some countries and states, a bioptic telescopic spectacle (BTS) may be utilized by the visually impaired to qualify for a driver’s license. A BTS is composed of 2 optical elements – a carrier lens with the traditional distance prescription and a telescope usually mounted in the glasses (Figure 1).
The visually impaired driver spends the majority of their time processing visual information acquired through the relatively unobstructed view of the carrier lens and regular prescription portion of the lens. When distance detail information is required, the user simply tilts their chin down slightly to align the telescope in the straight-ahead position (Figure 2). The magnified image is viewed briefly and the eye is returned to the resting position through the carrier lens. The strategy is analogous to the brief look through the side or rear view mirror in a car, which is an important component of good defensive driving.
the telescope is aligned in the straight-ahead position for the
magnified view. Spotting through the BTS is brief.
Bioptic telescopic spectacles (BTS) have been used to aid the visually impaired to maximize distance detail vision for tasks including driving as early as 1969 in the United States (Korb, 1970). Initial experience in the United States in the 1970’s raised some controversy regarding the balance between the need for detail vision and the concomitant decrease in field of view through the BTS (Fonda, 1974; Feinbloom, 1978; Kelleher, 1979; Lippman et. al., 1988). Critics of BTS driving cite the decreased field of view when looking through the telescope as well as the visual field loss secondary to the ring scotoma created by the housing of the telescope itself. In addition, concern about disturbances in spatial judgment as a result of the magnified view through the BTS may lead to difficulty in accuracy of alignment. Supporters for BTS use in driving cite the improved visual acuity resulting from the magnified image through the telescope, and consider proper training an essential component for successful use of the device for driving. They emphasize the very brief time spent in the telescope to access visual information as a key element to safe driving. Moreover, they argue that there are no laws prohibiting normally sighted people from driving under adverse conditions resulting in poor visibility such as heavy rain, fog, and snow. It has been suggested that poor visibility from inclement weather may have an even greater impact than that experienced by the visually impaired (Appel et al, 1990).
Driving is a complex task requiring the driver to integrate and process visual information “from both central and peripheral vision in a visually cluttered environment with little or no advance warning” (Owsley et. al., 1999). In spite of its complexity, crash risk comparisons have been done for handicapped versus visually handicapped drivers who score approximately the same. The accident rate per 100 drivers was 8.50 for those with neurological problems, 5.63 for those with cardiovascular impairments, and only 4.86 for those with a vision handicap (Baron,1991). In Texas, Lippman found that after normalizing the control group for sex and age distribution to match that of the bioptic drivers, it was found that the BTS drivers had a 1.34 times higher accident rate than the control group. They concluded that BTS users did not have a significantly higher chance of having a first accident (Lippman O, et al., 1988). Similarly, Korb found that during a 6 year period, 128 patients in Massachusetts wearing a BTS had a lower accident rate than the general driving population (1970). Given the positive safety profile of BTS drivers, it is not surprising than that the Texas Department of Public Safety (DPS) permits the use of these devices to assist the visually impaired to drive safely (AMA, 2003; Texas Administrative Code).
More recently, investigators have asked whether patients simply use the BTS to meet the visual acuity criteria or whether they actually use the device when diving (Bowers et. al., 2005). The conducted a survey of BTS drivers with moderately reduced visual acuity using a modified Driving Habits Questionnaire previously used to study patients with age-related macular degeneration (DeCarlo et. al., 2003). Interestingly, they found that 74% indicated that the BTS was helpful and 90% would continue to use it for driving even if it were not required. The bad news was that only 62% reported always wearing the BTS. Ultimately, as with all patient counseling and education, it takes time to ensure that the BTS driver understands that the guidelines are in place to maximize their personal safety as well as those around them.
We have had great success at the University of Houston College of Optometry Center for Sight Enhancement in utilizing a multi-disciplinary approach to assist patients with visual impairments to successfully obtain a driver’s license in Texas. The emphasis on training to assure safe and effective use of the BTS during the driving task is an integral component of the program and helps to reinforce compliance. We also collaborate with a driving rehabilitation instructor who is also an occupational therapist to reinforce that the skills of BTS use may be successfully transferred to the dynamic task of driving. Other groups have also described various approaches to integrating the skills necessary for BTS use and driving (Huss, 1988; Park et. al., 1995; Politzer, 1995). As demand grows for these services, occupational therapists and driving schools are evolving to help meet these needs and may offer excellent opportunities for collaboration.
The purpose of this article is to dispel some of the prejudice and anxiety associated with the goal of driving in low vision rehabilitation. Persons with low vision may drive safely and confidently given the right adaptive aids, training, and evaluation. In partnership with the state DPS or DMV, along with other providers such as occupational therapists and driving instructors, optometrists are well positioned to be able to offer advanced care and services to maximize their patient’s goal for independent travel. A subsequent article will address the topics of prescribing a BTS, training, and driving rehabilitation.
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