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Jesson Martin, Norberto Lopez Gill, Tao Liu, Arthur Bradley, Larry Thibos; Objective Measures Of Accommodation Error In Aberrated Eyes. Invest. Ophthalmol. Vis. Sci. 2012;53(14):1352.
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© ARVO (1962-2015); The Authors (2016-present)
Our goal is to improve methodologies for using wavefront error measurements to determine the eye’s accommodative response to visual stimuli
We define refractive state of an accommodating eye as the stimulus vergence required to maximize retinal image quality (Lopez-Gil et al, 2009, J Optom, 2: 223). Given a wavefront error map (relative to a reference sphere of infinite radius), we compute refractive state by optimizing the amount of defocus that must be added to the measured wavefront to maximize retinal image quality according to some scalar metric (Thibos et al, 2004, J. Vis. 4(4):329). The difference between this optimum stimulus vergence and the actual stimulus vergence (always negative for real stimuli) is the error of accommodation (i.e. "lead" or "lag"). Our wavefront approach avoids the usual paraxial approximations by taking into account pupil size, higher-order aberrations, and the specific measure of image quality deemed appropriate for the visual stimulus and/or task under investigation.
Accommodative response, as defined by the refractive state of the accommodating eye, is not determined uniquely by a wavefront error map. Instead, refractive state depends strongly on the metric of image quality chosen for the analysis. In all tested eyes, a paraxial measure of image quality makes the refractive state less negative than stimulus vergence when viewing distant targets, which results in a propensity for accommodative lag. Conversely, paraxial measures of refractive state are more negative than stimulus vergence when viewing near targets, which results in a propensity for accommodative lead. These propensities are typically reduced, and may even be reversed, for measures of image quality that assign weight to the whole pupil, not just the paraxial region. For example, the Zernike refractive state (specified by the Zernike coefficient for defocus) is more negative than paraxial refractive state when viewing distant targets and more positive when viewing near targets (lead at distance and lag at near).
The accommodative response of an aberrated eye depends on the metric used to compute refractive state from wavefront aberration maps. Functional implications drawn from measured accommodative lead and lag are therefore conditional upon the appropriate choice of image quality metric.
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