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Higher-order Aberrations (higher-order + aberration)

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Medical Sciences	100%

Selected Abstracts

Aberration and contrast sensitivity comparison of aspherical and monofocal and multifocal intraocular lens eyes

CLINICAL & EXPERIMENTAL OPHTHALMOLOGY, Issue 4 2007
Mingbing 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]

Assessing computerized tomography and higher-order aberration in the diagnosis of manifest and subclinical keratoconus

CLINICAL & EXPERIMENTAL OPHTHALMOLOGY, Issue 9 2008
Charles NJ McGhee PhD FRCOphth FRANZCO
No abstract is available for this article. [source]

Aberration and contrast sensitivity comparison of aspherical and monofocal and multifocal intraocular lens eyes

Limits of spherical blur determined with an adaptive optics mirror

OPHTHALMIC AND PHYSIOLOGICAL OPTICS, Issue 3 2009
David A. Atchison
Abstract We extended an earlier study (Vision Research, 45, 1967,1974, 2005) in which we investigated limits at which induced blur of letter targets becomes noticeable, troublesome and objectionable. Here we used a deformable adaptive optics mirror to vary spherical defocus for conditions of a white background with correction of astigmatism; a white background with reduction of all aberrations other than defocus; and a monochromatic background with reduction of all aberrations other than defocus. We used seven cyclopleged subjects, lines of three high-contrast letters as targets, 3,6 mm artificial pupils, and 0.1,0.6 logMAR letter sizes. Subjects used a method of adjustment to control the defocus component of the mirror to set the ,just noticeable', ,just troublesome' and ,just objectionable' defocus levels. For the white-no adaptive optics condition combined with 0.1 logMAR letter size, mean ,noticeable' blur limits were ±0.30, ±0.24 and ±0.23 D at 3, 4 and 6 mm pupils, respectively. White-adaptive optics and monochromatic-adaptive optics conditions reduced blur limits by 8% and 20%, respectively. Increasing pupil size from 3,6 mm decreased blur limits by 29%, and increasing letter size increased blur limits by 79%. Ratios of troublesome to noticeable, and of objectionable to noticeable, blur limits were 1.9 and 2.7 times, respectively. The study shows that the deformable mirror can be used to vary defocus in vision experiments. Overall, the results of noticeable, troublesome and objectionable blur agreed well with those of the previous study. Attempting to reduce higher-order aberrations or chromatic aberrations, reduced blur limits to only a small extent. [source]

A statistical model of the aberration structure of normal, well-corrected eyes

OPHTHALMIC AND PHYSIOLOGICAL OPTICS, Issue 5 2002
Larry 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]

3234: Stability of corneal shape and morphology in patients with Fuchs' dystrophy after phacoemulsification with soft shell technique.

ACTA OPHTHALMOLOGICA, Issue 2010
M MILKA
Purpose To evaluate effectiveness of soft shell cataract surgery technique on the corneal structure in group of Fuchs' dystrophy patients. Methods 24 patients (mean age 52,7±13,8), 31 eyes after phacoemulsification were examined before and 10 months after surgery. BCVA, mean central corneal thickness (CCT) and corneal endothelial cell density (CD) were evaluated. Corneal aberrations root-mean-square (RMS) was calculated 1 and 10 months after surgery for 4.0mm pupil. Results Corneal higher-order aberrations (RMS) 1 month after surgery was 0,372±0,058 and 10 months after surgery was 0,345±0,076, BCVA 10 months after surgery was 0,75±0,27 (before surgery 0,32±0,28), the mean CCT was 563,37±21,42µm (before surgery 559,62±45,29µm), CD 1786,341±493,127 (before surgery 1912,783±381,963). Conclusion All patients revealed good stability and protection of the cornea confirming safety of the soft shell technique. [source]

Ocular wavefront analysis and contrast sensitivity in eyes implanted with AcrySof IQ or AcrySof Natural intraocular lenses

ACTA OPHTHALMOLOGICA, Issue 7 2009
Tamer 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]

Measuring the refractive properties of the diabetic eye during blurred vision and hyperglycaemia using aberrometry and Scheimpflug imaging

ACTA OPHTHALMOLOGICA, Issue 2 2009
Nanouk G. M. Wiemer
Abstract. Purpose:, This study aimed to measure the refraction and geometry in the diabetic eye during the presence and absence of hyperglycaemia and blurred vision, using aberrometry and Scheimpflug imaging. Methods:, Aberrometry and Scheimpflug imaging were used to examine ocular refraction and higher-order aberrations, as well as the shape of the cornea and the lens, in 25 patients with diabetes mellitus. From these parameters, the equivalent refractive index of the lens was calculated. Using paired t -tests, comparisons were made between a first series of measurements (Visit 1) taken in the presence of blurred vision and hyperglycaemia (> 10.0 ,mol/l), and a second series of measurements (Visit 2) taken under normal conditions. Results:, The mean difference in blood glucose between Visits 1 and 2 was 5.9 mmol/l (standard deviation [SD] 3.1) (p < 0.0001). Both small hyperopic and myopic shifts of equivalent refractive error (ERE) were found in nine patients (mean absolute difference ERE: 0.38 D [SD 0.12]; p = 0.02). Furthermore, higher-order aberrations (root mean square [RMS] error) were slightly increased in four patients (mean difference RMS error: 0.07 ,m [SD 0.02]; p = 0.04) at Visit 1, compared to Visit 2. No significant changes were observed in the shape of the cornea or lens in any of the patients. No significant correlations were found between changes in blood glucose levels and the measured parameters in diabetic eyes. Conclusions:, The present study suggests that subjective symptoms of blurred vision during hyperglycaemia are not necessarily caused by changes in the refractive properties of the diabetic eye. [source]

Optical aberration measurements in dog and cat eyes: interest & limit

ACTA OPHTHALMOLOGICA, Issue 2008
SG ROSOLEN
Purpose To measure the ocular optical aberrations in dog and cat using a wavefront aberrometer based on Hartmann-Shack technology. Methods Two dogs and one cat were sedated (Medetomidine, 0.1 mg/kg) and their right eye (RE) pupils were artificially dilated (tropicamide). Wavefront aberrations were measured using an irx3 aberrometer (Imagine Eyes, Orsay, France). Prior to each measurement, the eye was aligned with the instrument optical axis by centering both the eye pupil and Purkinje images. The Hartmann-Shack spot images were produced by an array of 1024 microlenses that defined a 7.2x7.2 mm square area in the pupil plane. In preliminary tests, spot image histograms were optimized by adjusting the sensor acquisition time. Wavefront aberrations were then repeatedly measured 10 times in each animal's RE. Spherical defocus, astigmatism and Zernike coefficients up to the 8th order were finally analyzed. Results The optimal acquisition time was 10 ms for all animals, instead of 33 ms when measuring human eyes. Refractive errors could be analyzed in a 6 mm pupil diameter in all cases. The dilated pupil often exceed the sensor area. The average refractive errors in dog #1, dog #2 and the cat were +2.9D(-2.0D)111°;-0.8D(-0.8D)126° and +3.3D(-2.1D)98°, respectively while their Root Mean Square (RMS) higher-order aberrations amounted to 1.9, 1.1, and 2.1 µm RMS respectively. Standard deviation in sphere and cylinder was 1.0D in the cat and less than 0.5D in both dogs. Standard deviation in the higher-order RMS was 0.8 µm in the cat and less than 0.5 µm in both dogs. The observation of individual data revealed that a significant part of this variability was due to blink-related changes in aberrations. Conclusion Ocular optical aberrations can be easily measured in dog and cat using a Hartmann-Shack aberrometer with reduced image acquisition time. The tested animals had relatively large higher-order wavefront aberrations when compared to date measured in healthy human eyes. Measurement reproducibility was notably affected by tear layer effects. This variability could probably be reduced using a larger sensor area, specific head contention device and artificial tears. This new diagnostic technique is easily feasible without any use of anaesthesia and provides less variability and more detailed information than skiascopy. Wavefront aberrometry could be useful in both research and clinical applications. [source]

Treatment of post-keratoplasty astigmatism by topography supported customized laser ablation

ACTA OPHTHALMOLOGICA, Issue 4 2001
Jesper 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]