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Y. Benard, R. Legras; Optimization of Subjective Depth of Focus With Combinations of Spherical Aberration and Secondary Spherical Aberration. Invest. Ophthalmol. Vis. Sci. 2010;51(13):3964. doi: https://doi.org/.
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© ARVO (1962-2015); The Authors (2016-present)
To optimize the subjective depth of focus (DoF) by introducing combinations of spherical aberration (SA) and secondary SA.
We measured subjective DoF for various aberration conditions at 3 pupil sizes (i.e. 3, 4.5, and 6-mm) using through-focus simulated images calculated from a numerical eye model. We dynamically controlled the observer’s wavefront aberration and accommodation with an adaptive optics system. Subjective DoF was defined as the range of defocus for which the target was still perceived acceptable (objectionable blur). The subject viewed the target through an artificial pupil conjugated to the pupil plane and changed the defocus term in a 0.18-D step by changing the displayed images which were calculated for various defocus. We measured the subjective DoF on 3 non-presbyopic subjects, while fully correcting their aberrations. We displayed images calculated with various levels of SA (i.e. -0.6-µm, -0.3-µm, 0-µm, +0.3-µm, +0.6-µm), secondary SA (i.e. -0.3-µm, -0.15-µm, 0-µm, +0.15-µm, +0.3-µm) and combinations of SA and secondary SA (i.e. 25 combinations of aberrations).
We found a mean subjective DoF of 1.97-D with a 3-mm pupil size, which decreased by 34% with a 6-mm pupil diameter and by 28% with a 4.5-mm pupil. Two distinct DoF separated by 0.14-D to 1.26-D were sometimes observed with combinations of SA and secondary SA of opposite signs. However, considering the DoF as the range between the two extreme limits, we observed with the 6-mm pupil size, an increase of subjective DoF of 45% and 64% with the addition of 0.3 and 0.6-µm of SA (i.e. positive and negative averaged), and of 52% and 117% with the addition of 0.15 and 0.3-µm of secondary SA. The combinations of SA and secondary SA that most increased the DoF are the one with opposite signs: a DoF up to three and a half times larger (i.e. 4.78-D) than the naked eye. Reducing the pupil size minimized the effect of aberrations on subjective DoF.
The sign of SA or secondary SA is not important as long as they are introduced in opposite signs. Subjective DoF was multiplied by 3.6 with 0.6-µm of SA and 0.3-µm of secondary SA of opposite signs, but with a range of unacceptable vision in it.
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