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R. A. Applegate, L. He, A. S. Vilupuru, A. Glasser, A. Roorda; Estimating Crystalline Lens Decentration as a Function of Accommodation From Measured Changes in WFE. Invest. Ophthalmol. Vis. Sci. 2010;51(13):5791.
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© ARVO (1962-2015); The Authors (2016-present)
Background: According to the Helmholtz’s theory of accommodation, ciliary muscle contraction results in a release of zonular tension during accommodation. Release of zonular tension provides the opportunity for the crystalline lens to fall downward due to gravity. Such lens decentration will induce a change in whole eye wavefront error (WFE).
To estimate crystalline lens decentration as a function of accommodative response from the measured aberration structure of two iridectomized monkey eyes reported by Vilupuru et al (2004).
In the Vilupuru et al (2004) study, accommodation was centrally stimulated to a range of different response amplitudes (0 -11 D), and ocular aberrations were measured with a Shack-Hartmann wavefront sensor in both iridectomized eyes of a 10-year old rhesus monkey. To estimate crystalline lens WFE, ocular first surface WFE was subtracted from whole eye WFE for each level of accommodative response over 8 mm pupil diameter. The analysis aperture was resized to 7 mm and the lens decentration in millimeters (mm) was estimated by displacing downward the WFE of the lens with respect to the aperture and first surface WFE for each accommodative response until measured values of vertical coma matched experimental data using a formula by Comastri et al (2007). Lens decentration was also calculated using an approximation formula that only included spherical aberration and vertical coma.
Change in calculated vertical coma was consistent with a downward lens decentration. The lens decentration increased with accommodation up to an accommodative response of about 5D. Calculated downward lens decentration was found to peak around 0.48 mm of vertical decentration for the right eye and around 0.31 mm of decentration for the left eye using all Zernike modes through the 7th radial order. Calculated lens decentration by the approximation formulae was found to peak around 0.45 mm for the right eye and around 0.23 mm for the left eye.
Lens decentration as a function of accommodative response can be quantified from measured changes in WFE and the changes in vertical coma are primarily driven by the accommodation induced changes in spherical aberration. Inaccuracy of calculated decentration amount can occur if other uncertain sources of vertical coma are introduced.
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