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R. Legras, Y. Benard; Comparison Between Simulated and Measured Subjective Depth of Focus in Presence of Various Monochromatic Aberrations. Invest. Ophthalmol. Vis. Sci. 2010;51(13):3963.
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The two objectives were to measure the impact of spherical aberration (SA) and vertical coma on subjective depth-of-focus (DoF) and to examine the accuracy of simulated images, calculated from a numerical eye model, in predicting those impacts.
Subjective DoF was defined as the range of defocus for which the target was still perceived acceptable (objectionable blur), and was measured on two letter sizes (i.e. three high contrast letters of 20/50 or 20/25). We used an adaptive optics system to dynamically control the observer’s wavefront aberration and accommodation. The subject’s head was stabilized with a bite bar. The subjective DoF was measured with a 0.18-D step using two procedures. In the first one, the subject changed the defocus by reshaping the mirror, when viewing the original letters (i.e. unaberrated target). In the second procedure, the subject changed displayed images, which were calculated for various defocus, using a numerical eye model. We measured the DoF of 4 non-presbyopic subjects corrected for their entire eye aberrations (i) with a 6-mm and (ii) a 3-mm pupil size, (iii) and (iv) with the addition of 0.3-µm and 0.6-µm of positive SA, (v) and (vi) with the addition of 0.3-µm and 0.6-µm of vertical coma. Conditions (iii) to (vi) were measured with a 6-mm pupil size.
Using the 20/50 letter size, we obtained a mean DoF of 1.35-D for the naked eye with a 6-mm pupil size. Subjective DoF increased by 25, 45, 53, and 60% with the addition of respectively 0.3-µm of coma and SA, and 0.6-µm of SA and coma. Using the 20/25 letter size, compared to the naked eye condition (1.10-D), DoF increased by 6, 15, 14 and 19%. DoF measured on simulated images calculated from a numerical eye model were comparable to DoF measured using the mirror, whatever the condition and letter size (r² = 0.79 and 0.71 for the 20/50 and 20/25 letter sizes respectively). rMTF- or rOTF-based image quality metrics were not able to predict subjective DoF (r²=0.24) or DoF measured with calculated images (r² = 0.24).
Vertical coma and SA increased subjective DoF. Subjective DoF could be predicted using simulated images.
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