Also found in: Medical.
astigmatic interval[¦a·stig‚mad·ik ′in·tər·vəl]
The portion of a pencil of rays in an astigmatic optical system that lies between the primary and secondary foci. Also known as conoid of Sturm; interval of Sturm.
McGraw-Hill Dictionary of Scientific & Technical Terms, 6E, Copyright © 2003 by The McGraw-Hill Companies, Inc.