| Risley's rotary prism | A prism with a circular base that is rotated in a metal frame marked with a scale; used in examination of ocular muscle imbalance. (05 Mar 2000) |
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| Risley, Samuel | <person> U.S. Ophthalmologist, 1845-1920. See: Risley's rotary prism. (05 Mar 2000) |