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J. Marsack, K. Pesudovs, R.A. Applegate, L.N. Thibos; Prediction of visual acuity with combinations of wavefront aberration metrics . Invest. Ophthalmol. Vis. Sci. 2004;45(13):2768.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose: To investigate the ability of metrics based on wavefront aberration measures to predict letter visual acuity (VA) at high and low contrast and high and low luminance. Methods: Shack Hartmann wave aberration data and four different VA measures (high contrast, high and low luminance and low contrast high and low luminance) were recorded in 148 subjects (age ranged from 21.6 to 83.8 years). Wavefront metrics are mathematical functions deriving values from the wavefront shape (WF), the point spread function (PSF), the optical transfer function (OTF) and the RMS values of different groupings of Zernike terms. Stepwise multiple linear regression was performed on 37 of these metrics to determine what combination of metrics best predicted each of the four measured visual acuities. High luminance visual acuities were arithmetically transformed to normalize the distribution, thus facilitating analysis. Pupils were cyclopleged and size was identical for wavefront analysis and VA measurements. Results: Normalized high contrast, high luminance VA (HCHL) was best predicted by combining a point spread function metric describing area containing 50% of the PSF energy (D50) with the 5th order RMS (RMS5) where HCHL = 0.627 + 0.0115* D50 + 0.152*RMS5, R2 = 0.208. Normalized low contrast high luminance VA (LCHL) was best predicted by combining D50 with the visual strehl ratio calculated by the OTF method (VSOTF) where LCHL = 0.480 + 0.0176* D50 – 0.0356* VSOTF, R2 = 0.301. High contrast low luminance VA (HCLL) was best predicted by combining average blur strength (Bave), D50 and total RMS over the whole pupil (RMSw) where HCLL = 0.0578 + 0.0757* Bave + 0.0351* D50 – 0. RMSw, R2= 0.322. Low contrast low luminance VA (LCLL) was best predicted by combining area of visibility for MTF (areaMTF) and a pupil fraction metric in which the concentric area RMS is less than λ/4 (PFSc) where LCLL = 0.899 –0.899*areaMTF – 0.192* PFSc R2 = 0.38. Conclusions: Combinations of wave aberration metrics predict more variance in visual acuity than any single metric. The relationship between metrics of wave aberration and visual acuity is strongest for VA testing with low contrast letters at low luminance. The explanation of less variance for high contrast high luminance VA may indicate that these targets contain redundant information and are therefore unaffected by optical degradation by aberrations in some cases. Supported by: NEI R01 08520 grant to RAA and NEI R01 05109 to LNT.
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