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Impact of Stiles-Crawford peak decentration with small apertures


Purpose : The small aperture approach (implemented in corneal inlays or IOLs) is used to extend depth of focus in presbyopic patients. The Stiles-Crawford (SC) effect produces a change in the apparent brightness of rays entering the eye through different pupil positions. Since the SC can be significantly decentered in some eyes, the purpose of this study was to evaluate the potential impact of the SC peak location on visual performance with a small aperture.

Methods : We used a research version of an adaptive optics vision simulator to measure high and low contrast visual acuity (VA) with a small aperture (1.6 mm). The instrument allows for modifying the magnitude and phase of the eye’s complex pupil function. It incorporates two liquid-crystal spatial light elements: a phase-only modulator for wavefront shaping, and an intensity modulator to create the small aperture artificial pupil. A micro-display presents tumbling E letters through the controlled eye’s optics. Measurements were performed in 3 normal subjects at best focus, with corrected astigmatism, white light and for a variety of conditions of stimuli luminance and/or relative decentration of the small aperture. The values of luminance were set according to the expected reduction produced by a decentred Stiles-Crawford peak (89% and 63% for decentrations of 1 and 2 mm respectively).

Results : The impact on high and low contrast VA of the reduction in effective luminance due to realistic SC peak decentrations is modest at all considered luminances. A maximum of a 1-line reduction with respect to the centered small aperture case was found for an equivalent luminance to a relative decentration of the SC peak as large as 2 mm.

Conclusions : The impact of luminance reduction equivalent to a SC decentration was measured. The experimental results were in good agreement with theoretical predictions. At mesopic ambient luminance levels, a severely decentered SC peak (2-mm) could decrease visual acuity in approximately one line. In practical terms, these results suggest that the location of the SC peak does not require to be routinely evaluated in small aperture prospective patients.

This is an abstract that was submitted for the 2016 ARVO Annual Meeting, held in Seattle, Wash., May 1-5, 2016.

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