The influence of pupil size, accommodation and higher order aberrations on the retinal image of a Rarebit Fovea Test‐stimulus

Abstract

Abstract Purpose: To study the influence of pupil size, accommodation and higher order aberrations on the retinal image of the small test stimulus (<0.5´) used in the Rarebit Fovea Test (RFT). Methods: Eleven subjects aged between 22‐36 years participated. All subjects had a corrected visual acuity of 6/6 or better and a refractive error within ± 6 diopters. A PowerRefractorTM measured pupil size and accommodation continuously in all subjects during performance of the RFT. Aberrations were measured with a Zywave aberrometer and Matlab software was used for analysis. Results: Mean variation in accommodation was 0.4D (range 0.22‐0.61D) and mean pupil size was 6.1 mm (range 5.0‐7.8 mm). The aberrations induced a smearing of the retinal image to ~3.5x the stimulus size. When the variation in accommodation was added the total smearing of the retinal image increased to ~4x the stimulus size. Conclusions: The minimum retinal image size of a RFT stimulus is given by aberration and defocus rather than the actual size of the object (stimulus).