[The prism loupe spectacles used as low vision aid and in microsurgery (author's transl)].
In 1970 Biessels developed and constructed the new binocular prism loupe spectacles, mainly as improved low vision aids. They were derived from the Zeiss 8 x 20 prism binoculars, however, with different lenses and mechanical parts. They are quite different from the Galilean telescopic spectacles, hitherto available, with their lower mangifications, short working distances, chromatic aberration, and peripheral unsharpness. The Biessels prism loupes with variable magnification up to 12 times, and working distances of 18 to 30 cm, are mounted into spectacles. They provide for a comfortable stereoscopic vision with normal convergence. The visual field is virtually 20 cm at 25 cm distance, and sharp to the edges. The weight of a complete binocular prism loupe, including the frame, is from 100 to 110 grammes. In the past 7 years more than 500 of such visual aids have been delivered to low vision patients, half of them binocular, also 40 operating spectacles for microsurgery, all of them with great success. Here we report on the technical details and good results.