Biomedical subjects
Publications and source records attributed to G Fonda.
Physicians and ophthalmologists must know the vision standards for driving motor vehicles, as they are requested by patients to complete the necessary forms to obtain a restricted license. Physicians also should know why some standards are not in the best interests of their patients.
The objective of the study is to present evidence that some people with 20/200 visual acuity and a field of vision greater than 120 degrees can drive safely in the daytime at a speed of not more than 40 mph. Eight individuals with 20/200 visual acuity (legally blind) were tested for the distance at which they could recognize six traffic symbols. The study was done to see whether a person with 20/200 visual acuity could recognize symbols at a distance great enough to stop safely. Subjects recognized the symbols at a distance, determined by the U.S. Bureau of Public Roads, within which a vehicle traveling 40 mph could stop safely.
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The purpose of our chart is to show all scientific and practical demands for near-vision testing. Comparable notations of measurement of visual acuity are explained, and the method of conversion from different notations is presented. One side of the chart has continuous, informative text in eight sizes progressing from 4 point to 24 point. The reverse side of the chart shows eight methods for testing visual acuity, namely: samples of the telephone directory, music, words, numbers, symbols, and a reduced distant chart. This side of the chart is designed especially for testing the vision of the partially sighted patient. The type size is designated using five methods of measurements.
Two wall test charts with Snellen letters on both sides have been designed for the purpose of testing vision accurately, especially for the patient with low vision. Visual designations of 20/160 (6/48) and 20/125 (6/37.5) are included on the chart. This makes each line 26% larger. Sloan letters are used and arranged so that each line is of equal difficulty.
This article creates two categories for individuals with vision ranging from 20/175 (6/52) to 20/50 (6/15). Statistically, there are approximately 532,000 drivers with vision ranging from 20/175 (6/52) to 20/100 (6/30) and 56,000 drivers with vision ranging from 20/80 (6/24) to 20/50 (6/15). The author contends that the plan to test the vision of a number of drivers over the next four years will turn up a large number of failures. This will result in the loss of licenses and conceivably cause many people to lose their jobs. One way to avoid this is to issue limited licenses. It is important for the Department of Motor Vehicles to consider this step.
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One hundred and sixteen patients with Stargardt's disease demonstrated the most useful optical aids that enabled them to obtain an education and employment. The most useful optical aid for distance was the 8X monocular focusable telescope. For near, high-add bifocals, tri-focals, half-eye binocular spectacle magnifiers, paperweight-type magnifiers and hand magnifiers were most useful. Optical aids were prescribed for 102 patients with a success rate of 96%. The progression of visual loss is generally gradual and symmetrical terminating within ten years after onset and not becoming worse than 20/800 (6/240). Academic success seems to be related more to intellectual ability than degree of visual impairment. Highly trained and educated individuals with Stargardt's disease were able to find employment and perform duties usually associated with normal vision.
The primary cause of impaired vision was retinal pathology for 414 (83%) patients, optic nerve pathology (including glaucoma) for 33 patients (7%), other pathology for 53 (11%) patients. The following optical aids were prescribed: 35 distant spectacle corrections, 159 high-add bifocals, five high-add trifocals, 52 full-size magnifying spectacles, 102 half-eye magnifying spectacles, four stand magnifiers, and 44 paperweight type magnifiers. Of 193 patients evaluated, 122 (63%) were considered to have success with the aid prescribed.
The primary purpose of the bioptic telescopic spectacle is to permit the driver to pass the visual requirement to operate a motor vehicle. It is paradoxical that a driver can pass the vision test only by the use of a telescope but that he cannot drive while looking through the telescope. Rather, he must drive with his limited vision (sometimes legal blindness) while looking through the carrier lens. He can use the telescope only for reading a sign or for distinguishing an object, and even then he must lower his head to look through it. This is hazardous: he becomes thus "blind" to the traffic while reading the sign through the telescope. Such a driver could never pass a peripheral vision test due to the blind areas created in the peripheral field. It is more humane and reasonable to grant a waiver for the impaired vision than to compel a handicapped person to purchase a bioptic telescopic spectacle to pass the visual requirement.
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Retinitis pigmentosa was considered unfavorable for low vision corrections before it was recognized that the term retinitis pigmentosa as frequently used referred to a group of disease entities including Leber's congenital amaurosis, centro-peripheral dystrophy, typical retinitis pigmentosa and Usher's syndrome. The success rate for use of optical aids was Leber's congenital amaurosis 66%, centro-peripheral dystrophy 75%, typical retinitis pigmentosa 95%. This data shows that the poor success rate is not due to the constricted visual field but to the combined central and peripheral visual impairment. The type of aids most commonly prescribed were spectacle corrections, bifocals, hand magnifiers and the Visolett (paperweight type magnifier). The Visolett (paperweight type magnifier) has proven to be the most suitable non-spectacle magnifier used by itself, or in addition to a spectacle magnifier. Telescopic spectacles were rarely found to be of any value. The data showed that the correction of these diseases consisted of a refraction and strong reading addition in 65% of the patients.
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The Visolett is a glass, nonspectacle magnifier that rests on the paper, producing 1.8X to 2.5X magnification. It is one of the most useful nonspectacle magnifiers, because it is simple to use and diffusely concentrates illumination on its own field, enhancing the magnification. The optics differ from usual hand magnifiers in that the magnification does not increase with the dioptric power.
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