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Forward light scatter analysis of the eye in a spatially-resolved double-pass optical system.

Nam J, Thibos LN, Bradley A, Himebaugh N, Liu H - Opt Express (2011)

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.

View Article: PubMed Central - PubMed

Affiliation: School of Optometry, Indiana University, 800 Atwater Avenue, Bloomington, Indiana 47405, USA. jnam@indiana.edu

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Graphical representation of scatter analysis in the double pass setup for Gaussian xerop. (a) PSF on the retina from the first pass is the object to be imaged on the second pass. Pixel size = 2.72 arcmin. (b) Beam location (1) and several Gaussian xerops (2-4). The Gaussian perturbation at location 3 is a drop of wetness that increases optical path length. The Gaussian xerops at locations 2 and 4 represent thinning of the tear film that shortens the optical path length. (c) PSFs for the second pass. Pixel size = 0.97 arcmin. (d) Double pass SH image. Pixel size = 0.97 arcmin. Note that the PSFs in (c) are computed for a point source on the retina. Since the retinal image formed from the first pass will contain blur to become an extended object for the second pass, the SH images in (d) are not strictly PSFs. For display, a square-root transformation was applied to the computed image.
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g005: Graphical representation of scatter analysis in the double pass setup for Gaussian xerop. (a) PSF on the retina from the first pass is the object to be imaged on the second pass. Pixel size = 2.72 arcmin. (b) Beam location (1) and several Gaussian xerops (2-4). The Gaussian perturbation at location 3 is a drop of wetness that increases optical path length. The Gaussian xerops at locations 2 and 4 represent thinning of the tear film that shortens the optical path length. (c) PSFs for the second pass. Pixel size = 0.97 arcmin. (d) Double pass SH image. Pixel size = 0.97 arcmin. Note that the PSFs in (c) are computed for a point source on the retina. Since the retinal image formed from the first pass will contain blur to become an extended object for the second pass, the SH images in (d) are not strictly PSFs. For display, a square-root transformation was applied to the computed image.

Mentions: In this section, we test the assertion that radial variances of object and PSF can be added together to produce the radial variance of the image by using the concept of a localized Gaussian disturbance of the wavefront. This validation is placed in the context of tear film breakup by modeling the localized thinning of the tear film as an application of a small drop of dryness called a “xerop” (from the Greek word xeros (ξερός) for “dry”) to the tear layer. The result is a localized shortening of the optical path length from retina to SH wavefront sensor that perturbs the wavefront aberration function. For demonstration purposes, we assume this perturbation is small enough to fit inside a lenslet face. For simplicity, we choose a Gaussian xerop,W(x,y)=Cexp[−x2+y22σ2].(14)In the first pass, a narrow beam of light goes through the pupil center when tear film is smooth. This first pass optical system is assumed to be diffraction limited in our validation test case. This diffraction-limited retinal image from the first pass becomes an object for the second pass. Light passing through a xerop on this second pass forms a blurred image in the SH image (Fig. 5Fig. 5


Forward light scatter analysis of the eye in a spatially-resolved double-pass optical system.

Nam J, Thibos LN, Bradley A, Himebaugh N, Liu H - Opt Express (2011)

Graphical representation of scatter analysis in the double pass setup for Gaussian xerop. (a) PSF on the retina from the first pass is the object to be imaged on the second pass. Pixel size = 2.72 arcmin. (b) Beam location (1) and several Gaussian xerops (2-4). The Gaussian perturbation at location 3 is a drop of wetness that increases optical path length. The Gaussian xerops at locations 2 and 4 represent thinning of the tear film that shortens the optical path length. (c) PSFs for the second pass. Pixel size = 0.97 arcmin. (d) Double pass SH image. Pixel size = 0.97 arcmin. Note that the PSFs in (c) are computed for a point source on the retina. Since the retinal image formed from the first pass will contain blur to become an extended object for the second pass, the SH images in (d) are not strictly PSFs. For display, a square-root transformation was applied to the computed image.
© Copyright Policy - open-access
Related In: Results  -  Collection

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getmorefigures.php?uid=PMC3368325&req=5

g005: Graphical representation of scatter analysis in the double pass setup for Gaussian xerop. (a) PSF on the retina from the first pass is the object to be imaged on the second pass. Pixel size = 2.72 arcmin. (b) Beam location (1) and several Gaussian xerops (2-4). The Gaussian perturbation at location 3 is a drop of wetness that increases optical path length. The Gaussian xerops at locations 2 and 4 represent thinning of the tear film that shortens the optical path length. (c) PSFs for the second pass. Pixel size = 0.97 arcmin. (d) Double pass SH image. Pixel size = 0.97 arcmin. Note that the PSFs in (c) are computed for a point source on the retina. Since the retinal image formed from the first pass will contain blur to become an extended object for the second pass, the SH images in (d) are not strictly PSFs. For display, a square-root transformation was applied to the computed image.
Mentions: In this section, we test the assertion that radial variances of object and PSF can be added together to produce the radial variance of the image by using the concept of a localized Gaussian disturbance of the wavefront. This validation is placed in the context of tear film breakup by modeling the localized thinning of the tear film as an application of a small drop of dryness called a “xerop” (from the Greek word xeros (ξερός) for “dry”) to the tear layer. The result is a localized shortening of the optical path length from retina to SH wavefront sensor that perturbs the wavefront aberration function. For demonstration purposes, we assume this perturbation is small enough to fit inside a lenslet face. For simplicity, we choose a Gaussian xerop,W(x,y)=Cexp[−x2+y22σ2].(14)In the first pass, a narrow beam of light goes through the pupil center when tear film is smooth. This first pass optical system is assumed to be diffraction limited in our validation test case. This diffraction-limited retinal image from the first pass becomes an object for the second pass. Light passing through a xerop on this second pass forms a blurred image in the SH image (Fig. 5Fig. 5

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.

View Article: PubMed Central - PubMed

Affiliation: School of Optometry, Indiana University, 800 Atwater Avenue, Bloomington, Indiana 47405, USA. jnam@indiana.edu

Show MeSH
Related in: MedlinePlus