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Spherical Aberration (spherical + aberration)
Selected AbstractsA pilot study on the differences in wavefront aberrations between two ethnic groups of young generally myopic subjectsOPHTHALMIC AND PHYSIOLOGICAL OPTICS, Issue 6 2008Alejandro Cerviño Abstract A comparative population-based cross-sectional study design was used to examine the prevalence of wavefront patterns in two different ethnic groups, and the relationship of these patterns with ocular biometrics and gender. The Shin,Nippon SRW5000 open field autorefractor, the Wavefront Analysis Supported Customized Ablation (WASCA) wavefront analyser and the IOLMaster were used to determine wavefront aberrations, mean spherical equivalent (SE) refractive error and axial length (AL). Seventy-four eyes from 74 young healthy subjects (44 British Asians, 30 Caucasians; 36 men, 38 women; mean age 22.51 ± 3.89 years) with mean SE averaging ,1.90 ± 2.76 D (range ,10.88 to +2.19 D) were examined. Relationships between ethnicity, gender, AL and SE, against the wavefront high-order root mean square, and aberration components up to the fifth order, were assessed by using multiple regression and correlation analysis. AL on its own accounted for 4.7% of the variance in trefoil component (F1,72 = 4.602; p = 0.035), 13.7% of coma component (F1,72 = 12.536; p = 0.001), 6.1% of trefoil component (F1,72 = 5.705; p = 0.020) and 9.8% of coefficient (F1,72 = 8.908; p = 0.004). A significant model emerged (F2,71 = 6.164; p = 0.003) for ethnicity and axial length, accounting for 12.4% of variance in primary spherical aberration with ethnicity accounting for 8.4% of that variance. For Caucasian subjects, a significant correlation was found between axial length and (Pearson's correlation coefficient ,0.500; p = 0.005) and (Pearson's correlation coefficient ,0.423; p = 0.020). For British Asian subjects, AL was only correlated with coefficient (Pearson's correlation coefficient ,0.358; p = 0.017). Ethnicity is a factor to be considered in the variability of wavefront aberration, particularly spherical aberration. Relationship between AL and wavefront aberrations seems to vary between ethnicities. If higher order aberrations play a role in the emmetropization process, this may be different for different populations. [source] A statistical model of the aberration structure of normal, well-corrected eyesOPHTHALMIC AND PHYSIOLOGICAL OPTICS, Issue 5 2002Larry N. Thibos Abstract A statistical model of the wavefront aberration function of the normal, well-corrected eye was constructed based on normative data from 200 eyes which show that, apart from spherical aberration, the higher-order aberrations of the human eye tend to be randomly distributed about a mean value of zero. The vector of Zernike aberration coefficients describing the aberration function for any individual eye was modelled as a multivariate, Gaussian, random variable with known mean, variance and covariance. The model was verified by analysing the statistical properties of 1000 virtual eyes generated by the model. Potential applications of the model include computer simulation of individual variation in aberration structure, retinal image quality, visual performance, benefit of novel designs of ophthalmic lenses, or outcome of refractive surgery. [source] MAGNESIUM-RICH INTRALENSAR STRUCTURES IN SCHIZOCHROAL TRILOBITE EYESPALAEONTOLOGY, Issue 5 2007MARTIN R. LEE Abstract:, The interpretation of the lenses of schizochroal trilobite eyes as aplanatic doublets by Clarkson and Levi-Setti over 30 years ago has been widely accepted. However, the means of achieving a difference in refractive index across the interface between the two parts of each lens to overcome spherical aberration has remained a matter of speculation and lately it has been argued that the doublet structure itself is no more than a diagenetic artefact. Recent advances in technologies for imaging, chemical analysis and crystallographic characterization of minerals at high spatial resolutions have enabled a re-examination of the structure of calcite lenses at an unprecedented level of detail. The lenses in the eyes of the specimen of Dalmanites sp. used in the original formulation of the aplanatic doublet hypothesis are shown to have undergone diagenetic alteration, but its products reflect original differences in mineral chemistry between the upper lens unit and lower intralensar bowl. The turbidity of the bowl and of the core within the upper part of the lens are the result of their greater microporosity and abundance of microdolomite inclusions, both of which were products of diagenetic replacement of original magnesian calcite in these areas. Such a difference in magnesium concentration in the original calcite has long been postulated as one of the ways by which the interface between these lens units could have produced an aberration-free image and the present study provides the first direct evidence of such a chemical contrast, thus confirming the doublet hypothesis. [source] Effect of convergent beam semiangle on image intensity in HAADF STEM imagesACTA CRYSTALLOGRAPHICA SECTION A, Issue 1 2010Koji Kuramochi In this study, we experimentally and theoretically show that the intensities of bright spots in a spherical aberration (Cs)-uncorrected high-angle annular dark-field (HAADF) scanning transmission electron microscope (STEM) image of [011]-oriented Co3O4, which has two different numbers of Co atoms in the projected atomic columns, are reversed with increasing sample thickness. However, Cs -corrected HAADF STEM images produce intensities that correctly depend on the average number of atoms in the projected atomic columns. From an analysis based on the Bloch-wave theorem, it is found that an insufficient semiangle of the incident convergent beam yields intensities that do not depend on the average atomic number in the atomic columns. [source] Ocular wavefront analysis and contrast sensitivity in eyes implanted with AcrySof IQ or AcrySof Natural intraocular lensesACTA OPHTHALMOLOGICA, Issue 7 2009Tamer Takmaz Abstract. Purpose:, This study aimed to compare ocular wavefront aberrations for pupil diameters of 4 mm and 6 mm, and contrast sensitivity, in eyes with AcrySof IQ and AcrySof Natural intraocular lenses (IOLs). Methods:, Sixty eyes of 60 patients were enrolled in this prospective randomized study. After phacoemulsification the eyes received either AcrySof IQ SN60WF or AcrySof Natural SN60AT IOLs. One month after surgery, all patients underwent complete ophthalmological examination including corneal topography, wavefront analysis for pupil diameters of 4 mm and 6 mm, and contrast sensitivity measurements with the CSV 1000E instrument under photopic and mesopic conditions with and without glare. Results:, There was no statistically significant difference between groups in age, sex or other preoperative ocular characteristics (p > 0.05). Patients with AcrySof IQ IOLs had higher contrast sensitivity at 6 c.p.d. under photopic conditions, at 6 c.p.d. and 18 c.p.d. under mesopic conditions, and at 6 c.p.d., 12 c.p.d. and 18 c.p.d. under mesopic conditions with glare (p < 0.05). Corneal spherical aberration was 0.273 ± 0.074 ,m in the AcrySof Natural group and 0.294 ± 0.086 ,m in the AcrySof IQ group (p = 0489). Ocular spherical aberration was 0.362 ± 0.141 ,m and 0.069 ± 0.043 ,m (p < 0.001) for 6-mm diameter pupils and 0.143 ± 0.091 ,m and 0.017 ± 0.016 ,m (p < 0.001) for 4-mm diameter pupils, with AcrySof Natural and AcrySof IQ IOLs, respectively. There were no significant differences in other higher-order aberrations between the groups (p > 0.05). Conclusions:, Aspherical AcrySof IQ IOLs significantly reduced spherical aberration for pupil diameters of both 4 mm and 6 mm and also improved contrast sensitivity more than spherical AcrySof Natural IOLs, especially in mesopic conditions. [source] Improving the optics of KProsACTA OPHTHALMOLOGICA, Issue 2009C HULL Purpose The purpose of this talk is to review the clinically relevant optical and visual requirements of keratoprostheses. Methods Modelling of designs using commerical and purpose-written optical design software as well as clinical measurments on a small number of patients implanted with the osteo-odonto keratprosthesis optical cylinder. Results The important visual optical proerties of any keratoprosthesis optic are the foveal image quality (affecting the acuity) and the field of view. These fundamentally depend upon the pupil size, and the length and diameter of the optic since the power must be fixed to give emmetropia. The axial image quality can be changed by controlling the spherical aberration. However, maximising axial (foveal) image quality causes poorer off-axis image quality potentially reducing the effective visual field. Shorter, larger diameter optics help improve the visual field as well as consideration of off-axis image quality. Conclusion The theoretical properties of keratoprosthesis optics must be balanced against other clinical requirements such as longterm complications and stability. The clinical requirements provide the constraints on the optical design. However, discussions can usefully happen between surgeons and those involved in the design of the optics to give the best possible visual rehabilitation. [source] Purkinje based IOL centrationACTA OPHTHALMOLOGICA, Issue 2008MJ TASSIGNON Purpose Surgeon-controlled centration of IOLs might be an issue when introducing IOL optics yielding additional properties aiming at correcting spherical aberrations, astigmatism and accommodation or pseudoaccommodation. Methods First and third Purkinje reflexes can be used during cataract surgery for the purpose of IOL alignment provided the IOL allows that freedom of action. The bag-in-the-lens (BIL) concept has been designed to add this dimension of freedom to the surgeon. Results When using the Purkinje alignment method, a physiological nasally positioning of the IOL can be observed. Aberrometry shows an increased spherical aberration but no increase of other HO aberrations. Conclusion Surgeon-controlled centration of IOL is possible with the BIL implantation technique. This opens new perspectives for further development and alignment of the optic. Commercial interest [source] Effects of higher-order wavefront aberrations on the eye's depth of focusACTA OPHTHALMOLOGICA, Issue 2008N CHATEAU Purpose To evaluate the impact of higher order aberrations (HOA), defined by individual Zernike polynomial coefficients, on the eye's depth of focus using an adaptive optics (AO) system. Methods A crx1 AO visual simulator (Imagine Eyes, France) was used to introduce different amounts of individual 3rd and 4th order HOA in 10 healthy eyes. These HOA included coma (Z(3,-1)) and trefoil (Z(3,-3)) at magnitudes of +/-0.3 µm, and spherical aberration (SA) (Z(4,0)) at magnitudes of +/-0.3,+/-0.6 and +/-0.9 µm through a fixed 6-mm pupil diameter. A through-focus response (TFR) curve was assessed by recording the percentage of optotype letters of fixed 20/50 size that the subject could identify while these letters were presented at various target distances. Testing was performed under cycloplegia. For each applied HOA, the subject's depth of focus (DoF) and center of focus (CoF) were computed as, respectively, the half-maximum width and the midpoint of the TFR curve. Results The introduction of SA resulted in linearly shifting the CoF by 1.3 D for each 0.5 µm of wavefront. The shift was hyperopic with positive SA, myopic with negative SA. The simulation of either positive or negative SA also had the effect of enhancing the DoF, up to a maximum increase of 2 D with 0.6 µm of SA. The enhancement became smaller when the SA was further increased. Trefoil and coma appeared to neither shift the CoF nor significantly modify the DoF. Conclusion AO technology allowed us to selectively test the visual impact of several HOA on the DoF. The introduction of SA significantly shifted and expanded the subjects' overall DoF. This technique could help in designing optimal corrections for presbyopia and allowing patients to preview refractive surgery outcomes. Commercial interest [source] Aberration and contrast sensitivity comparison of aspherical and monofocal and multifocal intraocular lens eyesCLINICAL & EXPERIMENTAL OPHTHALMOLOGY, Issue 4 2007Mingbing Zeng PhD MD Abstract Background:, Higher-order aberrations and contrast sensitivity were evaluated in patients who underwent phacoemulsification cataract extraction followed by implantation of aspherical, monofocal or multifocal intraocular lens (IOL) replacements. Methods:, In this comparative trial, 124 patients with an average age of 66.8 ± 5.2 years and their 124 eyes were randomly divided into three surgical implantation groups to receive one of three types of IOLs in replacement of cataract lenses. The patients of group 1 were given an aspherical IOL Z9001 (AMO, Santa Ana, CA, USA) replacement, and group 2 was implanted a monofocal IOL SA60AT (Alcon, Fort Worth, TX, USA) and group 3 the multifocal IOL SA40N (AMO). Post-surgical best-corrected visual acuity, corneal aberrations, total ocular aberrations, pupil diameters, capsulorhexsis sizes and contrast sensitivity were measured and compared. Results:, There was no statistical difference for mean best-corrected visual acuity, pupil diameter, curvilinear capsulorhexis size and corneal aberration among the three groups. For the spherical aberration, fourth-order higher-order aberration and total ocular higher-order aberration, the SA40N group was higher than the SA60AT group and the SA60AT group was higher than the Z9001 group, and the differences between the three groups were statistically significant for these measurements. Contrast sensitivity was higher for the Z9001 group than the SA60AT group and the SA60AT group was higher than the SA40N group, and the difference was statistically significant in all the spatial frequencies of 3, 6, 12 and 18. Conclusions:, Although the multifocal IOL can provide near vision, it can increase higher-order aberration and negatively influence contrast sensitivity. However, the aspherical IOL can reduce aberration and improve contrast sensitivity as compared with the monofocal IOL. [source] Repeatability of corneal and ocular aberration measurements and changes in aberrations over one weekCLINICAL AND EXPERIMENTAL OPTOMETRY, Issue 3 2009Marco A Miranda MSc Background:, Both Shack-Hartmann aberrometry (IRX3, Imagine Eyes, Orsay, France) and Scheimpflug photography (Oculus Pentacam, Oculus Inc Wetzlar, Germany) are known to provide repeatable measurements. The variability in measurements of corneal and ocular aberrations obtained with these instruments over one week had not been assessed. The aim was to study the variability in corneal and ocular aberrations in the human eye over one week and to determine the impact of age on corneal and crystalline lens aberrations and on the variability of these measurements. Methods:, Monochromatic ocular aberrations were measured with the IRX3 and monochromatic corneal aberrations were measured using Scheimpflug photography on one eye of 23 normal subjects at periods of a few seconds, one hour and one week after the initial measurement. Results:, No significant differences were found between the initial aberrations and aberrations measured at 59 ± 24 seconds, 1.10 ± 0.24 hours and 7.11± 0.31 days later. Analysis with Bland and Altman plots showed that measurements with both instruments were highly repeatable over the times studied. There was no relationship between age and the variance of corneal and ocular aberrations (higher order, spherical and coma aberrations). Corneal spherical aberration did not show a significant correlation with age, whereas the lens aberrations changed from being negative in the younger age groups to positive in the older age group, however, these differences failed to reach statistical significance (p > 0.05). Conclusion:, The variability found in all the measurements was small and not clinically significant and could be attributable to instrument noise, changes in the tear film and to small fixational eye movements. [source] Clinical outcomes of corneal wavefront customized ablation strategies with SCHWIND CAM in LASIK treatmentsOPHTHALMIC AND PHYSIOLOGICAL OPTICS, Issue 5 2009Maria Clara Arbelaez Abstract Purpose:, To evaluate the clinical outcomes of aspheric corneal wavefront (CW) ablation profiles in LASIK treatments. Methods:, Thirty eyes treated with CW ablation profiles were included after a follow-up of 6 months. In all cases, standard examinations including preoperative and postoperative wavefront analysis with a CW topographer (Optikon Keratron Scout) were performed. Custom Ablation Manager (CAM) software was used to plan corneal wavefront customized aspheric treatments, and the ESIRIS flying spot excimer laser system was used to perform the ablations (both SCHWIND eye-tech-solutions, Kleinhostheim, Germany). Clinical outcomes were evaluated in terms of predictability, refractive outcome, safety, and wavefront aberration. Results:, In general, the postoperative uncorrected visual acuity and the best corrected visual acuity improved (p < 0.001). In particular, the trefoil, coma, and spherical aberrations, as well as the total root-mean-square values of higher order aberrations, were significantly reduced (p < 0.05) when the pre-existing aberrations were greater than the repeatability and the biological noise. Conclusions:, The study results indicate that the aspheric corneal wavefront customized CAM approach for planning ablation volumes yields visual, optical, and refractive results comparable to those of other wavefront-guided customized techniques for correction of myopia and myopic astigmatism. The CW customized approach shows its strength in cases where abnormal optical systems are expected. Apart from the risk of additional ablation of corneal tissue, systematic wavefront-customized corneal ablation can be considered as a safe and beneficial method. [source] Purkinje based IOL centrationACTA OPHTHALMOLOGICA, Issue 2008MJ TASSIGNON Purpose Surgeon-controlled centration of IOLs might be an issue when introducing IOL optics yielding additional properties aiming at correcting spherical aberrations, astigmatism and accommodation or pseudoaccommodation. Methods First and third Purkinje reflexes can be used during cataract surgery for the purpose of IOL alignment provided the IOL allows that freedom of action. The bag-in-the-lens (BIL) concept has been designed to add this dimension of freedom to the surgeon. Results When using the Purkinje alignment method, a physiological nasally positioning of the IOL can be observed. Aberrometry shows an increased spherical aberration but no increase of other HO aberrations. Conclusion Surgeon-controlled centration of IOL is possible with the BIL implantation technique. This opens new perspectives for further development and alignment of the optic. Commercial interest [source] Aberration controll with contact lensesACTA OPHTHALMOLOGICA, Issue 2007A LINDSKOOG PETTERSSON Purpose: To investigate and compare the reduction in ocular aberrations with standard hydrogel contact lenses (i.e., lenses not designed to control aberrations) and with aberration controlled hydrogel and silicon-hydrogel contact lenses. Methods: The aberrations with and without contact lenses were measured in 42 subjects between 20 and 37 years of age using a Zywave wave front sensor (B&L). 22 subjects were fitted a standard contact lens and an aberration controlled hydrogel lens. The remaining 20 subjects were fitted aberration controlled silicon-hydrogel lenses Results: With the standard lens the aberrations were controlled (i.e., close to zero) with a 4.0 mm pupil. Whereas, with both the aberration control lenses the residual spherical aberrations became negative. The reduction in aberrations differed significantly (p<0.05) between all lenses. Conclusions: Since aberration controlled contact lenses in many subjects overcorrect the spherical aberrations when the pupil size is normal (~4.0 mm) we suggest measuring wave front aberrations in each patient both with and without contact lenses in order to achieve the desired effect. [source] Treatment of post-keratoplasty astigmatism by topography supported customized laser ablationACTA OPHTHALMOLOGICA, Issue 4 2001Jesper Ø. Hjortdal ABSTRACT. Purpose: To evaluate the clinical and optical efficiency of topography modulated customized corneal ablations for irregular corneal astigmatism. Material & methods: Sixteen eyes of 16 patients with iatrogenic corneal astigmatism (post keratoplasty) were consecutively included. Based on preoperative corneal topographic measurements height deviations from a spherical corneal shape were calculated and transferred to a flying-spot excimer laser. Photo-refractive keratectomy of the topographic irregularities was then performed. Clinical and optical efficiency was evaluated by best corrected visual acuity and by computation of corneal wavefront aberrations before and up to one year after treatment. Wavefront aberrations were decomposed by Zernike polynomial analysis. Results: Before treatment the average best-corrected visual acuity was 0.23. Three and 12 months after PRK the average best-corrected visual acuity had increased to 0.37 (p<0.05) and 0.45 (p<0.05), respectively. Corneal wavefront aberrations (root-mean-square) were 3.35 before surgery and 1.88 (p<0.05) and 1.51 (p<0.05) at three and 12 months after treatment. Zernike polynomial decomposition of the wavefront aberrations revealed that regular corneal astigmatism was the most important aberration component before and after surgery. Regular astigmatism was significantly decreased by the procedure, whereas coma, spherical aberrations, and higher-order aberrations were not reduced significantly. Conclusion: Topography modulated photorefractive keratectomy of highly astigmatic corneal grafts can improve best corrected visual acuity and reduce corneal wavefront aberrations. Even in apparently irregular topographic astigmatism, regular astigmatic wavefront aberration may be the most important contributor to wavefront errors. [source] | ||||||||||