OPHTHALMIC PRISMS
- 1 May 1945
- journal article
- research article
- Published by American Medical Association (AMA) in Archives of Ophthalmology (1950)
- Vol. 33 (5) , 381-384
- https://doi.org/10.1001/archopht.1945.00890170057005
Abstract
CORRECTIVE PRISMS Seventy-five years ago, in 1870, lenses were still being prescribed in terms of their radiuses of curvature (a description) rather than in terms of their power (an operational specification). Twenty years later the metric operational system of numbering lenses according to the work they did (in refracting light rays) was almost universal, and this proved to be so much more satisfactory that progressive ophthalmologists began to turn their attention to similar problems with prisms, which were labeled in terms of the apex angle, a unit of shape rather than a unit of strength. In 1887 Jackson1 examined the prisms in seven trial cases, representing four well known manufactures ; he found that "in only one set did they all come within 16 per cent of the proper standard," and recommended that prisms should be marked according to their angle of minimal deviation. Landolt approved this recommendation, and aThis publication has 0 references indexed in Scilit: