Wavefront-guided refractive surgery and custom optical corrections have reduced the residual root mean squared (RMS) wavefront error in the eye to relatively low levels (typically on the order of 0.25 μm or less over a 6-mm pupil, a dioptric equivalent of 0.19 D). It has been shown that experimental variation of the distribution of 0.25 μm of wavefront error across the pupil can cause variation in visual acuity of two lines on a standard logMAR acuity chart. This result demonstrates the need for single-value metrics other than RMS wavefront error to quantify the effects of low levels of aberration on acuity. In this work, we present the correlation of 31 single-value metrics of optical quality to high-contrast visual acuity for 34 conditions where the RMS wavefront error was equal to 0.25 μm over a 6-mm pupil. The best metric, called the visual Strehl ratio, accounts for 81% of the variance in high-contrast logMAR acuity.

^{nd}through 4

^{th}radial orders) impact letter acuity of an individual (Applegate et al., 2002). In these experiments, each subject served as his or her own control. That is, we measured how a change in aberration altered visual performance as measured by high-contrast logMAR acuity. These experiments revealed that 0.25 µm of aberration over a 6-mm pupil reduced visual acuity by an amount that depended on which Zernike mode contained the wavefront error. Modes near the center of each radial order have a greater impact on visual performance (more letters lost) than modes near the edge of the pyramid. This result is seen in Figure 1.

*R*

^{2}= 0.69), whereas RMSw (wavefront error) was least predictive. Because RMS values were fixed at 0.25 µm in the Applegate, Marsack et al. (2003) experiment, RMSw has zero predictive power for variation in visual acuity as is evident in Figure 5.

_{w}, HWHH, and VOTF).

- RMSw — root-mean-squared wavefront error computed over the whole pupil (µm).
- PV — peak-to-valley difference (µm).
- RMSs — root-mean-squared wavefront slope computed over the whole pupil (arcmin).
- Bave — average blur strength (diopters)
- PFWc — pupil fraction when critical pupil is defined as the concentric area for which RMSw < criterion (λ/4).
- PFSc — pupil fraction when critical pupil is defined as the concentric area for which RMSs < criterion (1 arcmin).
- PFCc — pupil fraction when critical pupil is defined as the concentric area for which Bave < criterion (0.25 D).
- PFWt — pupil fraction when a “good” sub-aperture satisfies the criterion PV < criterion (λ/4).
- PFSt — pupil fraction when a “good” sub-aperture satisfies the criterion horizontal slope and vertical slope are both < criterion (1 arcmin).
- PFCt — pupil fraction when a “good” sub aperture satisfies the criterion Bave < criterion (0.25 D).
- D50 — diameter of a circular area centered on PSF peak, which captures 50% of the light energy (arcmin).
- EW — equivalent width of centered PSF (arcmin).
- SM — square root of second moment of light distribution (arcmin).
- HWHH — half width at half height (arcmin).
- CW — correlation width of light distribution (arcmin).
- SRX — Strehl ratio computed in spatial domain.
- LIB — light in the bucket.
- STD — standard deviation of intensity values in the PSF, normalized to diffraction-limited value.
- ENT — entropy of the PSF inspired by an information —theory approach to optics (Guirao & Williams, 2003).
- NS — neural sharpness (Williams, 2003).
- VSX — visual strehl ratio computed in the spatial domain.
- SFcMTF — spatial frequency cutoff of radially averaged modulation-transfer function.
- SFcOTF — cutoff spatial frequency of radially averaged optical transfer function.
- AreaMTF — area of visibility for rMTF, normalized to diffraction-limited case.
- AreaOTF — area of visibility for rOTF, normalized to diffraction-limited case.
- SRMTF — Strehl ratio computed in frequency domain, MTF method.
- SROTF — Strehl ratio computed in frequency domain, OTF method.
- VSMTF — visual Strehl ratio computed in frequency domain, MTF method.
- VSOTF — visual Strehl ratio computed in frequency domain, OTF method.
- VOTF — volume under OTF normalized by the volume under MTF.
- VNOTF — volume under neurally weighted OTF, normalized by the volume under neurally weighted MTF.

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*Subjective image quality metrics from the wave aberration*. Paper presented at the 4

^{th}International Congress of Wavefront Sensing and Aberration – Free Refractive Correction, San Francisco, CA.