|Title||A VIDEO ANALYSIS OF RETINOSCOPIC MOTION|
|Author, Co-Author||Brian Adair, Donald O. Mutti|
|Abstract|| PURPOSE: A recent model of streak retinoscopic motion (Mutti, OVS, in press) makes several predictions about the appearance of the reflex. One is that "with" motion may have two speeds as the reflex moves across the pupil while "against" will only have one. The purpose of this study was to test this prediction using video recordings of retinoscopic motion on an optical bench.
METHODS: The optical system consisted of a 5.8 mm aperture, a bi-convex +20D Nikon condensing lens, and a paper screen for a "retina" mounted on an optical track. Refractive errors of this model eye ranging from-5.00D to +3.00D were set using retinoscopy and confirmed using a telescope made conjugate with the far point of the model eye with trial lens caps. The retinoscope was placed on a rotation stage with a vernier scale readable to 5’of arc. A CCD camera was placed behind the retinoscope peephole in order to record the image of the reflex.
RESULTS: Within a given refractive error, the velocity of "against" motion was uniform as a function of rotation across the entire pupil. This velocity increased as refractive error approached neutrality (-1.69D), from 2.6 mm/deg at-5.00D to 6.5 mm/deg at-2.00D. "With" motion had two velocities when refractive error exceeded neutrality by +1.50 D or more hyperopia. The fast phase appeared first, then was followed by a slower phase as the retinoscope beam moved across the pupil. The faster phase had an average velocity of 9.1 mm/deg that did not vary substantially with refractive error. The slower phase velocity increased closer to neutrality, from 1.7 mm/deg at +3.00D to 5.5 mm/deg at-1.00D.
CONCLUSIONS: Consistent with model predictions, these results suggest that the retinoscopic reflex has two sources: the edge of the retinoscope beam and the shadow cast by the edge of the entrance pupil. The edge of the beam as a source can explain the fast phase of "with" motion while the slow phase and all "against" motion would occur when the source is the shadow cast by the edge of the pupil.
ADDITIONAL COMMENTS: Supported by grants U10-EY08893 and T35-EY07151
|Affiliation of Co-Authors||The Ohio State University, College of Optometry|