Article ID | Journal | Published Year | Pages | File Type |
---|---|---|---|---|
6203742 | Vision Research | 2011 | 9 Pages |
We seek unbiased methods for estimating the target vergence required to maximize visual acuity based on wavefront aberration measurements. Experiments were designed to minimize the impact of confounding factors that have hampered previous research. Objective wavefront refractions and subjective acuity refractions were obtained for the same monochromatic wavelength. Accommodation and pupil fluctuations were eliminated by cycloplegia. Unbiased subjective refractions that maximize visual acuity for high contrast letters were performed with a computer controlled forced choice staircase procedure, using 0.125 diopter steps of defocus. All experiments were performed for two pupil diameters (3Â mm and 6Â mm). As reported in the literature, subjective refractive error does not change appreciably when the pupil dilates. For 3Â mm pupils most metrics yielded objective refractions that were about 0.1Â D more hyperopic than subjective acuity refractions. When pupil diameter increased to 6Â mm, this bias changed in the myopic direction and the variability between metrics also increased. These inaccuracies were small compared to the precision of the measurements, which implies that most metrics provided unbiased estimates of refractive state for medium and large pupils. Thus a variety of image quality metrics may be used to determine ocular refractive state for monochromatic (635Â nm) light, thereby achieving accurate results without the need for empirical correction factors.
⺠Most image quality metrics may be used to determine ocular refractive state for monochromatic light accurately without the need for empirical correction factors. ⺠There is a bias in some metric-based objective refractions which grows in magnitude when the pupil expands from 3 mm to 6 mm. ⺠Subjective refractive error of the eye does not change appreciably with the change in pupil size.