Tips on prescribing and fitting a bioptic telescope system for driving: part II
| Written by Raman Deol, O.D., a member of the AOA's Vision Rehabilitation Committee
In part I of this article, I presented thoughts to consider prior to fitting a patient with a bioptic telescope system (BTS) for driving. Once I determine the patient to be a good candidate to drive with a BTS, I design and order the system as follows:
Telescope power. I estimate the starting power of a BTS using the formula, "Power = Best Corrected Distance VA/Goal VA". If the patient's BCVA is 20/100 and the goal VA is 20/50, then Power = 100/50 = 2X. Remember, as power increases, field of view decreases, so often stronger is not better. When determining power, I also consider the nature of the patient's eye disease. If the disease is progressive, I consider prescribing a slightly stronger TS so that the device will continue to be adequate if the patient's acuity declines. Also, I prefer ordering a focusable TS rather than fixed focus for greater flexibility with working distance. This is an expensive device to acquire, so the longer it will last and the greater the flexibility, the better it may be for the patient.
Monocular or binocular. If a patient has asymmetric VA, for example 20/400 right eye and 20/100 left eye, then I consider a monocular system. Many states require only one eye to meet the visual acuity requirement for driving privileges; also a monocular system is generally more affordable and will be lighter weight. Upon fitting a monocular system, the better-seeing eye is chosen for the telescope. If considering a monocular system for an individual with symmetric acuities, I generally fit the dominant eye. I have prescribed binocular systems for patients who request them, for patients whose nystagmus slows with binocular lock, and if acuities are similar.
TS design. Designs for Vision, Conforma (BITA), and Ocutech are manufacturers of bioptic telescopes. Each manufacturer has an easy-to-follow order form. Commonly required measurements include monocular/binocular PD, spectacle Rx, telescope power and Rx, and frame size if the manufacturer is to provide the frame. The manufacturer will mount the TS a standard distance from the top of the spectacle frame, unless specified. The exception here is the BITA system; this manufacturer will mount the TS on spectacles provided by the patient, at a set distance above the patient's pupils as marked on the spectacle lenses. BITA has specific spectacle lens material and thickness requirements, which they provide with their fitting manual. Because I do not practice in a setting with an optical lab, I attach a copy of BITA's lens requirements to the patient's spectacle Rx so that they may obtain the necessary lenses from the optical of their choosing. I carry BTS demos of each manufacturer, mounted in a demo frame, and in commonly prescribed powers (2 X to 4 X); this helps patients get a feel for what it would be like to use the device, allows me to determine if the height of the TS is appropriate, and allows me to determine if they can efficiently spot through the device despite any central field loss. In addition, I carry several frame styles offered by Desings for Vision and Ocutech as this helps to determine which style will offer the patient the best access to the TS and sufficient lens area to view beneath the TS. In-office trial and error will help determine which system will be best for the patient. I find it helpful to have numbers or characters on a wall and/or mock road signs and traffic lights in a long room or hall, which I can ask the patient to try to view and identify through the various TS powers/models.
Carrier lens design. If the carrier lens is deep enough, I consider bifocal or progressive lens designs for patients who have adapted well to such lens types in the past; this may help with viewing their dashboard or GPS. Usually a lower add is beneficial, to allow a 17-24 inch working distance.
Tint preference. In addition to reduced visual acuity, many of my patients have significant glare sensitivity and/or reduced contrast sensitivity and/or color vision deficiency. These patients may benefit from a TS cap filter, carrier lens tint, or TS tint. Monochromats often benefit from red-tinted lenses to enhance visibility of brake lights and red traffic lights. In-office trial and error, and sometimes trial outdoors on sunny days, can help to determine the best tint for the patient, if any. If the patient plans to use the BTS for night driving or for indoor use, consider a slip-behind tinted filter, which can be used outdoors during daytime and removed as needed. Both Ocutech and Designs for vision offer slip-behind tinted filters.
Optometry is an art. The art we practice extends from prescribing lenses, to counseling patients with vision loss, to managing ocular pathology, and on. Prescribing a BTS is not an exception; our skills improve with practice. It is my sincere hope that the information above is helpful in your journey to improve the lives of your patients.
Learn more about vision rehabilitation and how to manage individuals with low vision and/or brain injury.
Disclaimer: The information contained in this article represents the opinion of the author and not the AOA. These are not clinical practice guidelines, nor has the evidence been peer reviewed. Reference to a particular product does not constitute an endorsement.
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