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A. L. Hickenbotham, A. Roorda; The Effect of Higher and Lower Order Aberrations on Best Mean Visual Acuity Across a 2.5 Diopters Vergence Range. Invest. Ophthalmol. Vis. Sci. 2010;51(13):4297.
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© ARVO (1962-2015); The Authors (2016-present)
We present an efficient and principled way to find the best aberration profiles that relieve focus problems with presbyopia. First, we define a specific task. Then, we find the aberration profile that will provide the best performance on that task. The specific task for presbyopia relief is to optimize vision from infinity to a 40 cm viewing distance (0 to 2.5 diopters vergence range) The metric we chose to optimize is the Best Mean Visual Acuity (BMVA) over that range, assessed experimentally and by computation.
A random choice visual performance experiment was performed using 20 Snellen letters presented on an 11-bit display monitor. Letters were convolved with the PSF of 0.25µm step Zernike aberrations (c5, c6, c7, c12, c24, and c40) and 0.25 diopter defocus steps for a 5 mm pupil. Visual performance for each PSF was measured for each Snellen Acuity letter size, which ranged from 20/40 and smaller but was magnified, after blurring, to 20/200 to decouple the size aspect (minimizing effects of viewer’s aberrations and negating limits of photoreceptor spacing). A power fitting was used to correlate subjective performance with calculated Strehl Ratio of aberration profile (r=0.879). BMVA was computed as the highest average acuity value across a 2.5 diopters vergence range for each aberration profile.
Decoupling size from blur resulted in higher acuities than standard testing due to an absence of limiting factors such as photoreceptor spacing. All aberrations tested increased BMVA scores across a 2.5 diopters vergence range. Correlation between experimental results and predicted values for BMVA across 2.5 diopters was r=0.932. Primary spherical aberration (c12) showed the highest BMVA values followed by secondary and tertiary spherical aberration (c24 and c40). Astigmatism (c5) and then Trefoil (c6) showed the lowest values for BMVA for the Zernike aberrations tested.
Using BMVA as a measurement of visual performance for a specific vergence range allows direct comparison of various aberration profiles. Using this metric for depth of focus provides an efficient way to compute the best aberration profile for a 2.5 diopters vergence range.
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