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Elizabeth Shumard Bell, Gareth D Hastings, Jos J Rozema, Raymond A Applegate, Jason D Marsack; The Influence of Pupil Size on Visual Image Quality and Optimal Refraction during Simulated Spectacle Wear in Keratoconus. Invest. Ophthalmol. Vis. Sci. 2018;59(9):5800. doi: https://doi.org/.
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© ARVO (1962-2015); The Authors (2016-present)
Recent work has attempted to objectively determine the best possible sphero-cylindrical spectacle prescription by optimizing visual image quality from a wavefront error measurement over a fixed pupil size for an individual suffering from keratoconus (KC). The purpose of this study was to assess the impact of varying pupil size on visual image quality and optimal dioptric correction of KC eyes.
Zernike aberration data of 100 keratoconic wavefronts over a 5mm pupil diameter were scaled to 4mm and 3mm, resulting in 300 total aberration structures. The spectacle correction that optimized the visual image quality metric visual Strehl ratio (VSX) was identified for each pupil size using a simulated through focus experiment. For each eye, the dioptric distances between the refractions determined at the three pupil sizes were calculated using power vectors.
With a 2mm change in pupil diameter, outcomes varied substantially from optimum: The median dioptric distance from the optimized 3mm to the optimized 5mm refraction was 1.90D (range(R)=0-25.50D, 1st quartile (1Q)= 0.65D, 3rd quartile (3Q)=3.56D). The relative contributions of the power vector components (M:J0:J45) to the change in refraction was (1.00:0.68:0.46). Mean optimized VSX decreased 51.5% from 0.204±0.095 at 3mm to 0.099±0.039 at 5mm. However, across 1mm changes in pupil diameter, the difference from optimum was reduced: The median dioptric distance from the 3mm to 4mm refraction was 0.44D (R= 0-26.42D, 1Q=0.21D, 3Q=0.21D) and 0.82D (R=0-13.68D, 1Q=0.35D, 3Q=2.17D) from the 4mm to 5mm refraction. When using the optimized 4mm refraction on a 3mm pupil, the VSX was reduced 13.3% from the maximum at 3mm. When using the 4mm refraction over a 5mm pupil, the VSX was reduced 23% from the maximum at 5mm.
Wavefront error is often measured over the largest pupil diameter. However, in cases where significant residual aberration exists (here, an individual with keratoconus wearing a spectacle) building a correction based on a mid-point (here, a 4mm pupil) rather than an extreme in pupil size works to mitigate the variation in refraction that is experienced over the full pupil range. Even when this precaution is taken, a reduction in visual image quality is nonetheless still experienced as pupil size changes.
This is an abstract that was submitted for the 2018 ARVO Annual Meeting, held in Honolulu, Hawaii, April 29 - May 3, 2018.
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