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Alessandra Marie Carmichael Martins, Maria Vinas, Ana Gonzalez-Ramos, Clara Benedi-Garcia, Carlos Dorronsoro, Susana Marcos, Brian Vohnsen; Influence of the Stiles-Crawford effect of the first kind on visual acuity for decentered pupils. Invest. Ophthalmol. Vis. Sci. 2019;60(9):5943.
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© ARVO (1962-2015); The Authors (2016-present)
The purpose of this study is to measure the Stiles-Crawford effect of the first kind (SCE-I) under normal visual conditions (Newtonian view) using a horizontally-decentered small pupil rather than the commonly used Maxwellian view and analyze the potential impact of the SCE-I on the corresponding off-centered visual quality.
A spatial light modulator (PLUTO, Holoeye) is used to sequentially create horizontally displaced aperture masks of 1.5mm in a monocular viewing system across a 6.5mm pupil size. Measurements were performed in 4 subjects (OD, dilated pupil, ages:25-48; SE: 0 to -5.75D). The SCE-I was measured psychophysically, by the subjects adjusting the brightness of a 1.8-deg natural stimulus on the retina (using a liquid crystal variable attenuator for intensity control, Meadowlark) alternating at 1Hz, with a centered reference stimulus of the same size. Visual acuity (VA) was measured using a tumbling E test (8AFC QUEST algorithm), in natural viewing for 1.5 mm pupils. A control VA was obtained under natural SCE for a 6-mm pupil. A total of 4 sets of 7 displaced apertures were performed for all subjects. Finally, the VA test was performed a second time, accounting for these variations with the variable attenuator, such that subjects perceived the same brightness for each aperture location.
A slight variation in the SCE-I directionality parameter was found in Newtonian view compared to Maxwellian view within subject intervariability. Monocular decimal VA for 6-mm pupil was 0.62±0.02 on average and increased by 39% for a centered 1.5mm pupil. A decay in VA between 50-70% was observed for a horizontal displacement of 2.5mm nasal and 20-40% when displaced temporally. Correction of the SCE-I produced an average difference of VA up to 30%. In a 1.6mm nasal and 2.5mm temporal decentration range, the difference in VA with and without SCE correction was negligible (<8%) in subjects with large ocular aberrations (RMS wavefront error=0.87µm). In subjects with lower aberrations (RMS<0.4µm) statistical differences in VA were found between data obtained with and without SCE-I compensation.
The VA is noticeably reduced with decentered small pupils, mostly due to an increased impact of ocular aberrations. The reduced differences between the SCE-I corrected and uncorrected VA results indicate a small effect of the SCE-I in visual degradation with decentered pupils.
This abstract was presented at the 2019 ARVO Annual Meeting, held in Vancouver, Canada, April 28 - May 2, 2019.
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