Abstract

Photorefractive methods provide rapid photographic measures of the refractive and accommodative states of infants and young children whose brief attention spans and limited cooperation reduce the effectiveness of more traditional methods such as retinoscopy and autorefraction. Three photographic methods have been designed: orthogonal¹,², isotropic²,³ and eccentric⁴,⁵,⁶. In all three methods, light from a small flash source set near the aperture of a camera lens is reflected from the eye and photographed as a pattern of light whose extent varies with the refractive error and pupil size of the eye. In the past, complicated ray traces, using detailed optical specifications of the camera system, were required to determine the theoretical relationship between the blur size and the refractive error. The authors have developed a novel geometrical optical analysis for all three methods in which the pattern is defined at the plane of focus of the camera. Because this plane is conjugate with the detector plane of the camera, the predicted size of the pattern can be determined simply by measuring the magnification of an object located at the camera’s plane of focus. This does not require knowledge of the optical design of the camera lens.

© 1992 Optical Society of America