Visual Psychophysics / Physiological Optics - ARVO

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ARVO 2013 Annual Meeting Abstracts by Scientific Section/Group – Visual Psychophysics / Physiological OpticsThe optical bench system consisted of a model eye with phase-plateinduced SA, a liquid crystal spatial light modulator to control pupilapodization, and a camera for imaging a tumbling E letter chart.TFIQ was quantified by calculating the correlation coefficientbetween a reference image (without SA and apodization) andcaptured through-focus images (0 to 2.5D with 0.1D step). Pupilapodization was modeled as a Gaussian function with various sigmavalues (0.5 to 2.0mm). Through-focus visual acuity was measured in2 cyclopleged subjects at distance, intermediate and near objectdistances (0, 1 and 2D). Both optical bench testing and visualperformance were carried out with ±0.2µm SA over a 4mm artificialpupil.Results: Introducing Gaussian apodization improved distance imagequality, regardless of sign of SA, by 7-12% for sigma ranging from0.5 to 2.0mm. At intermediate (1D) image quality, the negative SAcase had a larger improvement (9-18%) than the positive SA case (7-11%) for sigma ranging 0.5 to 2.0mm. For near (2D), theimprovement with negative SA was even larger (14-33%) whilepositive SA showed no improvement. Visual benefits withapodization were also found. Pupil apodization with sigma=0.5 led toa 1.0, 2.6 and 4.5 line improvement in visual acuity at 0, 1 and 2D,respectively, in the presence of negative SA. For positive SA, visualacuity improved by 1.0, 1.8 and 0.1 lines, respectively.Conclusions: Pupil amplitude apodization led to a significantimprovement in through-focus image quality, especially withnegative SA. This finding suggests that halos and glare induced bymultifocal presbyopic corrections can be reduced with appropriatepupil amplitude apodization.Commercial Relationships: Hae Won Jung, None; LenZheleznyak, None; Geunyoung Yoon, Bausch & Lomb (F), Johnson& Johnson (F), Allergan (C), Staar Surgical (C), CIBA Vision (F),Acufocus (C)Support: NIH Grant EY014999, Unrestricted Grant from Researchto Prevent Blindness, NYSTAR/CEIS, Bausch & LombProgram Number: 4267 Poster Board Number: B0304Presentation Time: 8:30 AM - 10:15 AMContribution of shape and gradient index to the sphericalaberration of donor human lensesJudith Birkenfeld, Alberto de Castro, Susana Marcos. CSIC-Institutode Optica, Madrid, Spain.Purpose: The relative contribution of crystalline lens geometry andgradient index (GRIN) to its spherical aberration (SA) and its agerelatedchanges is unknown. We investigated these relationship usingOptical Coherence Tomography (OCT) and Laser Ray Tracing(LRT).Methods: 11 ex vivo human lenses (22-71 years) from an eye bankwere imaged in 3D with a custom OCT to obtain optical pathdifferences. The shape of the lens surfaces was extracted from theimages using surface segmentation and Zernike polynomial fitting.The lens power was measured using LRT for 2 and 4-mm pupildiameters. The 3D GRIN was estimated by means of an optimizationmethod based on genetic algorithms (de Castro et al. OE 2010),which searched for the parameters of a 4-variable GRIN model thatbest fits the distorted posterior lens surface of the lens in 18 differentmeridians. The SA of the lenses was estimated by computational raytracing, assuming both a homogeneous index and the estimatedGRIN.Results: Geometrical data of all lenses were reconstructed using 3DOCT images. Anterior radius of curvature and asphericity variedwidely across lenses (6.1 to 11.3 mm, and -9.9 to 5.6, respectively),and were rather constant for the posterior surface (mean: 5 mm and -0.3, respectively). Lens power ranged from 34D (younger lens) to24D (older lens). In 10/11 lens power decreased with pupil diameter,revealing a negative spherical aberration. Lens thickness (rangingfrom 3.8 to 5.2 mm) increased and mean group refractive index(ranging from 1.392 to 1.407) decreased slightly with age. Thereconstructed GRIN showed surface refractive index values between1.368 and 1.376, nucleus refractive index values between 1.403 and1.415, and an exponential decay value ranging from 1.8 to 3.4 (axial)and from 1.9 to 5.8 (meridional). The estimated SA (from lensgeometry and index) ranged from -0.8 to 0.3 µm for the equivalentrefractive index, and from -2.1 to -0.3 µm for the estimated GRIN.SA shifted with age towards less negative values (slope=0.028 µm/yrand 0.022 µm/yr assuming equivalent index or GRIN, respectively).Conclusions: 3D OCT data and experimental power data of humandonor lenses of different ages allowed reconstruction of the lensGRIN and evaluation of external geometry and GRIN contribution tothe lens spherical aberration. GRIN shifted the SA towards negativevalues in all cases and played a role in the age-related shift of SA.Commercial Relationships: Judith Birkenfeld, None; Alberto deCastro, None; Susana Marcos, Essilor (F), PCT/ES2012/070185 (P)Support: FIS2008-02065, FIS2011-25637 (Spanish Government)and ERC 2011 Advanced Grant 294099 (European ResearchCouncil) to SM, CSIC JAE Program Fellowship to JB.Program Number: 4268 Poster Board Number: B0305Presentation Time: 8:30 AM - 10:15 AMCrystalline lens thickness determines transverse chromaticaberrationYun Chen, Frank Schaeffel. Section of neurobiology of the Eye,Institute for Ophthalmic Research, Tuebingen, Germany.Purpose: To describe the magnitude and variability of transversechromatic aberration (TCA) in the human eye, and to identify theocular parameters that might determine its magnitude.Methods: Two different psychophysical procedures were used toquantify TCA. First, a red and a blue square, presented on a blackscreen, had to be matched in size by the subjects with their right eyes,using the arrow keys on keyboard. Second, two filled red or bluesquares, flickering on top of each other at 2 Hz, had to be adjusted inbrightness and in size to minimize the perceived flicker by subjects.Biometric ocular parameters in the right eyes were measured with acommercially available low coherence interferometer, the Lenstar LS900 (Haag Streit, Switzerland). Corneal power, thickness, anteriorchamber depth, lens thickness, vitreous chamber depth and axiallength were correlated to psychophysical date. Sixteen subjects withno ocular pathologies other than refractive errors, with ages rangingfrom 22 to 58 years, participated in the study.Results: TCA varied widely among subjects, as was evident from theperceived differences between the red and the blue square whichranged from 0 to 3.2%. The two different psychophysical proceduresto measure TCA provided highly correlated results, suggesting thatno major confounders existed. The measurements of TCA wereaffected neither by changes in brightness of the blue or red nor byindividual refractive errors. Comparing to optical parameters in thesubjects’ eyes, only lens thickness was significantly correlated toTCA (p
ARVO 2013 Annual Meeting Abstracts by Scientific Section/Group – Visual Psychophysics / Physiological OpticsPresentation Time: 8:30 AM - 10:15 AMPrediction of human crystalline lens power and sphericalaberration using an anatomically-based discrete shell modelFabrice Manns 1, 2 , Arthur Ho 3, 4 , Jean-Marie A. Parel 1, 5 .1 Ophthalmic Biophysics Center, Bascom Palmer Eye Inst, Univ ofMiami, Miami, FL; 2 Department of Biomedical Engineering,University of Miami College of Engineering, Coral Gables, FL;3 Brien Holden Vision Institute, Sydney, NSW, Australia; 4 School ofOptometry and Vision Science, University of New South Wales,Sydney, NSW, Australia; 5 Vision Cooperative Research Centre,Sydney, NSW, Australia.Purpose: To develop an anatomically-correct aspheric discretemodel of the human crystalline lens that predicts power and sphericalaberration and the contribution of the refractive index gradient.Methods: A continuous and a discrete model of a 30 year old relaxedhuman lens were developed. The shape was modeled using data fromDubbelman et al (Vis Res, 2001): Ant Radius=11.10mm; AntAsphericity=-3.05; Post Radius = -5.82mm; Post Asphericity=-0.795;Thickness=3.69mm. In the continuous model, the refractive indexgradient is represented as a set of aspheric iso-indicial surfaces withradius of curvature R(z) and asphericity Q(z) that vary linearly fromthe lens equator to the value at the surface. The axial refractive indexfollows a power-dependence in each half of the lens (Kasthuriranganet al, IOVS 2008): n(z)=1.41-0.032×(z/t) 4 , where t is the anterior orposterior half-thickness and z is the distance, both measured from theequator. The discrete shell model was created by sampling isoindicialsurfaces of the continuous model at regularly spacedintervals. The ith shell of a model with K shells has thicknesst K =t lens /K, is located at position z i = i*t K , radius R i =R(z i ), asphericityQ i =Q(z i ), and is surrounded by refractive indices n i-1 =n(z i-1 ) andn i =n(z i ). The number of shells ranged from K=6 to K=3000. Thecontribution of each surface to lens power and Seidel primaryspherical aberration was calculated from a paraxial ray trace. Thecontributions were plotted as a function of axial position and summedto provide the Seidel wavefront aberration coefficient W 040 , and totalpower contribution P sum . The power P sum was compared to theeffective power P eff .Results: The spherical aberration coefficient and lens powerconverge as the number of shell increases. The asymptotic valueswere W 040 =0.053mm -3 , P sum =22.2D, and P eff =22.3D. For lens power,the number of shells required to reach 90%, 95% and 99% of theasymptote are 20, 40, and 200. For spherical aberration the values are160, 320, and approx. 1000. The contributions of the anterior andposterior halves of the lens were -0.015mm -3 and 0.068mm -3 .Conclusions: The power and spherical aberration of the crystallinelens can be predicted using a discrete model with tightly packedshells.The discrete model allows calculation of contributions ofspecific regions of the lens to total spherical aberration from aparaxial ray trace.Commercial Relationships: Fabrice Manns, None; Arthur Ho,None; Jean-Marie A. Parel, CROMA (F), InnFocus (F), Abeamed(F), University of Miami (P)Support: NIH Grants R01EY14225, R01EY021834, and CenterGrant P30EY14801; Australian Government CRC Scheme (VisionCRC); Florida Lions Eye Bank; an unrestricted grant from Researchto Prevent Blindness; Henri and Flore Lesieur Foundation (JMP).Program Number: 4270 Poster Board Number: B0307Presentation Time: 8:30 AM - 10:15 AMAge-related Stiffening of Human Lens Measured by In VivoBrillouin MicroscopySebastien Besner 1, 2 , Giuliano Scarcelli 1, 2 , Roberto Pineda 3 , Seok H.Yun 1, 2 . 1 Department of Dermatology, Harvard Medical School,Boston, MA; 2 Wellman Center for Photomedicine, MassachusettsGeneral Hospital, Boston, MA; 3 Department of Ophthalmology,Massachusetts Eye and Ear Infirmary, Boston, MA.Purpose: The loss of accommodation power with age is thought tobe related to the increase of the stiffness of the crystalline lens. Morerecently, evidences have shown that the change in the stiffnessgradient may also play a dominant role in accommodation amplitude.In order to investigate the contribution of lens sclerosis to loss ofaccommodation with age, we present a novel optical, non-contact andnon-destructive method based on Brillouin scattering, whichmeasures the local elastic modulus of the crystalline lens in vivo withmicron size resolution.Methods: Brillouin confocal microscopy was performed on 5 dilatedeyes (2.5% phenylephrine and 0.5% tropicamide) of 5 patients withan age range of 23 to 47 years. The Brillouin spectral shift, which isproportional to the longitudinal modulus of elasticity, was acquiredalong the optical axis of the crystalline lens with an axial resolutionof about 60 microns and a lateral resolution of less than 10 microns.Ongoing study will include 10 eyes from 10 patients with age rangingbetween 20 and 60 years.Results: At all ages, the elastic modulus was found to increase fromthe lens cortex to the nucleus with a general steeper increase in theposterior part of the lens. The overall lens stiffness was found toincrease with age (p
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