Forward light scatter analysis of the eye in a spatially-resolved double-pass optical system.
Bottom Line: An optical analysis is developed to separate forward light scatter of the human eye from the conventional wavefront aberrations in a double pass optical system.We prove an additivity property for radial variance that allows us to distinguish between spot blurs from macro-aberrations and micro-aberrations.When the method is applied to tear break-up in the human eye, we find that micro-aberrations in the second pass accounts for about 87% of the double pass image blur in the Shack-Hartmann wavefront aberrometer under our experimental conditions.
Affiliation: School of Optometry, Indiana University, 800 Atwater Avenue, Bloomington, Indiana 47405, USA. firstname.lastname@example.orgShow MeSH
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Mentions: In order to describe ocular aberrations with a wavefront error map spanning the full extent of the eye's pupil, we sample the emerging wavefront at numerous locations using an array of non-overlapping sub-apertures. For an aberrometer employing a Shack-Hartmann wavefront sensor (SHWFS), the subapertures are defined by the faces of individual lenslets in the array. If the wavefront over individual subapertures is not flat, local small scale aberrations are present which will cause blur in the spot image produced by the lenslet. The classical design of the SHWFS assumes the lenslets have sufficiently small diameter that the wavefront is approximately planar over each subaperture. In this case, all of the spot images are diffraction-limited Airy-disks free of aberration-induced blur and spot displacement is a measurement of wavefront tilt over each lenslet. In effect, the wavefront for the whole pupil is being approximated by a surface tessellated by flat tiles. The SHWFS determines the slope of each tile by measuring the displacement of each spot from the optical axis of the corresponding lenslet. The wavefront is then reconstructed from slope measurements mathematically by algorithms that either retain all features of the slope data (i.e. zonal reconstruction) or that smooth the wavefront to deemphasize local irregularities (i.e. modal reconstruction) (Fig. 1Fig. 1
Affiliation: School of Optometry, Indiana University, 800 Atwater Avenue, Bloomington, Indiana 47405, USA. email@example.com