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F. Harms, K. Maia Rocha, L. Vabre, N. Chateau, R. R. Krueger; The Effects of Spherical Aberration on Depth of Focus as a Function of Pupil Size Measured Using an Adaptive Optics Visual Simulator. Invest. Ophthalmol. Vis. Sci. 2009;50(13):1121.
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© ARVO (1962-2015); The Authors (2016-present)
Our objective was to evaluate the effect on depth of focus (DoF) of applying spherical aberration (SA) as a function of pupil size, using an adaptive optics (AO) visual simulator.
We used a crx1 AO visual simulator (Imagine Eyes, France) based on a Shack-Hartmann wavefront sensor and an electromagnetic deformable mirror to manipulate the wavefront aberrations in ten eyes under cycloplegia (1% Tropicamide). The crx1 was used to generate pure SA (Z 4,0) in magnitudes of +/- 0.6 µm through fixed pupil diameters of 3.0, 4.5 and 6.0mm. Through-focus responses (TFR) were assessed for each optically simulated aberration, and for each pupil size. A randomized set of 10 Sloan letters optotypes of fixed 20/50 size were displayed to the subjects at a miniature monitor situated inside the instrument. This target defocus was varied by adjusting a Badal system based on a trombone optical configuration, also included in the instrument. Each subject’s TFR was assessed by plotting the number of identified letters as a function of the induced defocus. The DoF and the center of focus (CoF) were computed, for each amount of SA and each pupil size, as the width at half maximum and the midpoint of the TFR curve respectively.
The introduction of SA increased the DoF for all pupil sizes with a maximum enhancement of 1.75 D on average for a 3mm pupil. SA also caused the CoF to shift in the direction of its sign. The average shift was up to 1.5 D. DoF also increased with decreasing pupil size. This pupil effect was smaller than the SA effect. Changes in CoF with pupil size were limited to less than 0.5 D on average.
Using AO visual simulation, we were able to draw quantitative results on the effects of SA as a function of the pupil diameter on the DoF of normal subjects. Both positive and negative SA significantly improved the subjects’ overall DoF. Our results suggest that the more positive central refractive power associated with negative SA, in combination with accommodative miosis, should provide the greatest compensation for the loss of accommodative amplitude.
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