primary spherical aberration effects can be revealed by the cycloplegic dilation and refraction when compared to the de-novo refraction to best visual acuity ...
INFERRED EFFECT OF SPHERICAL ABERRATION ON VISUAL ACUITY AS MEASURED BY THE RABIN SMALL LETTER CONTRAST TEST (SLCT) Morris R. Lattimore, Ph.D. U.S. Army Aeromedical Research Laboratory, Fort Rucker, AL 36362 Control ID: 1266778 Poster Presentation 201214-1008P-282-Lattimore] Current Category: Human Performance Abstract Background. Visual perception is a cognitive representation of the threedimensional world as a function of a curved, concave photosensor array (i.e., rods and cones on the retina). Visual perception is thus a reverse projection of that curved array onto physical space. Lifetime experience helps fine-tune that projection in order to correctly match the accurate positioning of real objects. Yet, modern technology often presents information via flat panels, flat screens, and flat arrays for the conveyance of visual information and images. This artificial flat display lay-out makes us all subject to a progressive sequence of distortions and aberrations, requiring additional perceptual visual processing demands. Introduction. Twenty volunteer Army Special Operations Soldiers were examined at the Navy Medical Center – San Diego in preparation for possible treatment of their myopia by photo-refractive keratectomy (PRK). As a part of this baseline examination, manifest and cycloplegic refractions (to best visual acuity) were performed, in order to insure an accurate degree of ablation was programmed and achieved. The underlying primary spherical aberration effects can be revealed by the cycloplegic dilation and refraction when compared to the de-novo refraction to best visual acuity (BVA). Spherical aberration has the greatest influence on standard visual acuity as measured with the Snellen Chart. But the effect of spherical aberration upon other aspects of vision, such as contrast sensitivity, is largely unknown. Before attempting to analyze the detailed family of potential ocular aberrations that could be present, the modeling of spherical aberration can be established as a base upon which less noticeable aberrations can then be built. Methods. The chart uses a uniform, 20/25 letter-size , with log unit decrements in contrast, progressing from the top line downward. Applying a display of 10 letters per line, combined with the 1 log-unit sequential contrast deficits, provides a logMAR scoring system which permits continuous variable data analysis, something traditional Snellen acuity (as a discrete variable) does not afford. The 20 patients were refracted to best visual acuity under both manifest and cycloplegic conditions, with SLCT contrast acuity measurements recorded in the LOGMAR format. Results. Mean manifest contrast acuity was 1.159 +/- 0.006; the mean cycloplegic contrast acuity was 1.006 +/- 0.008. In descriptive terms, this represents a loss of 1.5 lines in contrast acuity under the cycloplegic condition compared to the manifest baseline. A paired t-test demonstrated the visual sensitivity responses for the two conditions to be significantly different (p
