Risley prism system

Risley prism system

[′riz·lē ′priz·əm ‚sis·təm]
(optics)
A type of dispersing prism used to test ocular convergence in ophthalmology; consists of two thin prisms mounted so that they can be rotated simultaneously in opposite directions.
McGraw-Hill Dictionary of Scientific & Technical Terms, 6E, Copyright © 2003 by The McGraw-Hill Companies, Inc.