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October 1974

Field Loss vs Central Magnification: Telescopes and the Driving Risk

Arch Ophthalmol. 1974;92(4):273. doi:10.1001/archopht.1974.01010010283001

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Telescopic spectacles and similar low vision aids are currently being advocated to assist patients with poor vision in passing the static visual acuity tests for driver licensing. Such devices are invoked primarily to enable an applicant to pass the artificial hurdle of visual screening. They have not evolved from field use nor from trial by drivers under adverse conditions to augment subnormal visual acuity. Indeed, they flout a fundamental optical law that magnification is obtained only at the expense of visual field encompassed. More than a dozen states and their medical advisory boards have apparently yielded to requests to permit telescopic spectacle systems in driver license examinations. With one of the all-plastic ×2 telescopic units, currently marketed to be worn in a carrier spectacle lens, the magnified field is about seven degrees in diameter. Surrounding this is a ring scotoma about 12° wide to either side and even broader than

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