Standards for reporting the optical aberrations of eyes
01 Sep 2002-
TL;DR: An OSA taskforce was formed at the 1999 topical meeting on vision science and its applications and charged with developing consensus recommendations on definitions, conventions, and standards for reporting of optical aberrations of human eyes.
Abstract: In response to a perceived need in the vision community, an OSA taskforce was formed at the 1999 topical meeting on vision science and its applications (VSIA-99) and charged with developing consensus recommendations on definitions, conventions, and standards for reporting of optical aberrations of human eyes. Progress reports were presented at the 1999 OSA annual meeting and at VSIA-2000 by the chairs of three taskforce subcommittees on (1) reference axes, (2) describing functions, and (3) model eyes.
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157 citations
Journal Article•
TL;DR: In this paper, a large-stroke deformable mirror (Mirao 52D; Imagine Eyes) and a Shack-Hartmann wavefront sensor were used in an adaptive optics system.
Abstract: PURPOSE
To investigate the optical performance of a large-stroke deformable mirror in correcting large aberrations in highly aberrated eyes.
METHODS
A large-stroke deformable mirror (Mirao 52D; Imagine Eyes) and a Shack-Hartmann wavefront sensor were used in an adaptive optics system. Closed-loop correction of the static aberrations of a phase plate designed for an advanced keratoconic eye was performed for a 6-mm pupil. The same adaptive optics system was also used to correct the aberrations in one eye each of two moderate keratoconic and three normal human eyes for a 6-mm pupil.
RESULTS
With closed-loop correction of the phase plate, the total root-mean-square (RMS) over a 6-mm pupil was reduced from 3.54 to 0.04 microm in 30 to 40 iterations, corresponding to 3 to 4 seconds. Adaptive optics closed-loop correction reduced an average total RMS of 1.73+/-0.998 to 0.10+/-0.017 microm (higher order RMS of 0.39+/-0.124 to 0.06+/-0.004 microm) in the three normal eyes and 2.73+/-1.754 to 0.10+/-0.001 microm (higher order RMS of 1.82+/-1.058 to 0.05+/-0.017 microm) in the two keratoconic eyes.
CONCLUSIONS
Aberrations in both normal and highly aberrated eyes were successfully corrected using the large-stroke deformable mirror to provide almost perfect optical quality. This mirror can be a powerful tool to assess the limit of visual performance achievable after correcting the aberrations, especially in eyes with abnormal corneal profiles.
37 citations
Journal Article•
TL;DR: In this article, the authors compare and evaluate four methods for eccentric refraction: photorefraction with a PowerRefractor, wavefront measurements with a Hartmann-Shack sensor, and retinoscopy.
Abstract: Purpose. When performing perimetry, refracting subjects with central visual field loss, and in emmetropization studies, it is important to accurately measure peripheral refractive errors. Traditional methods for foveal refraction often give uncertain results in eccentric angles as a result of the large aberrations and the reduced retinal function. The aim of this study is therefore to compare and evaluate four methods for eccentric refraction. Methods. Four eccentric methods were tested on 50 healthy subjects: one novel subjective procedure, optimizing the detection contrast sensitivity with different trial lenses, and three objective ones: photorefraction with a PowerRefractor, wavefront measurements with a Hartmann-Shack sensor, and retinoscopy. The peripheral refractive error in the horizontal nasal visual field of the right eye was measured in 20° and 30°. Results. In general, the eccentric refraction methods compared reasonably well. However, the following differences were noted. Retinoscopy showed a significant difference from the other methods in the axis of astigmatism. In 30° eccentric angle, it was not possible to measure 15 of the subjects with the PowerRefractor and the instrument also tended to underestimate high myopia (<-6 D). The Hartmann-Shack sensor showed a myopic shift of approximately 0.5 D in both eccentricities. The subjective method had a relatively larger spread. Conclusions. This study indicates that it is possible to assess the eccentric refraction with all methods. However, the Hartmann-Shack technique was found to be the most useful method. The agreement between the objective methods and the subjective eccentric refraction shows that detection contrast sensitivity in the periphery is affected by relatively small amounts of defocus.
34 citations
01 Jun 2002
TL;DR: As measured by the CSF and an apodisation model, this study is in agreement with previous theoretical work and one experimental study in indicating that the SCE plays a minor role in improving spatial visual performance.
Abstract: We investigated the influence of the Stiles–Crawford effect (SCE) of the first kind on the contrast sensitivity function using the
apodisation model of the SCE. The SCE was measured for the right eyes of two subjects using an increment threshold technique
involving a two-channel Maxwellian-viewing system. Filters made of photographic film neutralised or doubled the SCE. Contrast
sensitivities were measured with a 6 mm pupil diameter, defocus to 2D, and three SCE conditions (normal, neutralised and
doubled). Modulation transfer functions were derived after measuring transverse aberrations with a vernier alignment technique,
and were used to predict contrast sensitivity functions (CSFs). The measured CSFs were, in general, reasonable matches with the
predicted CSFs. In particular, both demonstrated definite undulations (‘‘notches’’) as defocus level increased. The influences of the
SCE-modifying filters were generally of similar magnitude and direction to predictions, thus supporting the apodisation model of
the SCE. The magnitudes of SCE influence between SCE-neutralised and SCE-doubled conditions were usually small at about 0.2–
0.3 log unit, with a maximum influence of 0.5 log unit. Influences of the SCE were greater for myopic than for hypermetropic
defocus. As measured by the CSF and an apodisation model, this study is in agreement with previous theoretical work and one
experimental study in indicating that the SCE plays a minor role in improving spatial visual performance.
31 citations
TL;DR: This work presents the experimental performance of a 91-actuator deformable mirror made of a magnetic liquid (ferrofluid) using a new technique that linearizes the response of the mirror by superposing a uniform magnetic field to the one produced by the actuators.
Abstract: We present the experimental performance of a 91-actuator deformable mirror made of a magnetic liquid (ferrofluid) using a new technique that linearizes the response of the mirror by superposing a uniform magnetic field to the one produced by the actuators. We demonstrate linear driving of the mirror using influence functions, measured with a Fizeau interferometer, by producing the first 36 Zernikes polynomials. Based on our measurements, we predict achievable mean PV wavefront amplitudes of up to 30 {\mu}m having RMS residuals of {\lambda}/10 at 632.8 nm. Linear combination of Zernikes and over-time repeatability are also demonstrated.
28 citations
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01 Jan 2010
TL;DR: The proofs of your article above are available for your review and can be downloaded using the file located at this URL address: http://rapidproof.cadmus.com/RapidProof/retrieval/index.jsp.
Abstract: IOVS MS 11-7777 (Article 2207) Proofs Available _______________________ Dear Author: The proofs of your article above are available for your review. Please download the file located at this URLaddress: http://rapidproof.cadmus.com/RapidProof/retrieval/index.jsp Login: [your e-mail address]Password: 99S4UntgTcU9 You will need to have Adobe Acrobat Reader software to read this file. This is free software and is availablefor user downloading at http://www.adobe.com/products/acrobat/readstep.html. If you experience technical problems, please contact Tracey Ritchey(e-mail: ritcheyt@cadmus.com; phone: 717-721-2646) This file contains: -- Instructions to Author-- Adobe Acrobat Comments and Notes Instructions-- Publication Fees and Reprint Order Form-- Page Proofs for your article, table of contents precis blurb, and author queries - containing 5 pages Please insert your comments electronically (instructions enclosed), or print the PDF proofs and add yourcomments manually. Follow the enclosed instructions for emailing, faxing, or mailing your corrections.Return all materials within 48 hours (two business days) to assure quick publication of your article. NOTE: Effective with the January 2010 issue IOVS will be available online only. No printed issues will beproduced. Printed reprints may still be ordered using the file provided. If you have any questions regarding your article, please contact me. ALWAYS INCLUDE YOURARTICLE NO. (IOVS MS 11-7777) WITH ALL CORRESPONDENCE. Cathy FreyTel: 717-721-2616Fax: 717-738-9479 or 717-738-9478freyc@cadmus.com
1,575 citations
TL;DR: It is inferred that subjective best focus occurs when the area of the central, aberration-free region of the pupil is maximized, and that correction of the 12 largest principal components, or 14 largest Zernike modes, would be required to achieve diffraction-limited performance on average for a 6-mm pupil.
Abstract: A Shack-Hartmann aberrometer was used to measure the monochromatic aberration structure along the primary line of sight of 200 cyclopleged, normal, healthy eyes from 100 individuals. Sphero-cylindrical refractive errors were corrected with ophthalmic spectacle lenses based on the results of a subjective refraction performed immediately prior to experimentation. Zernike expansions of the experimental wave-front aberration functions were used to determine aberration coefficients for a series of pupil diameters. The residual Zernike coefficients for defocus were not zero but varied systematically with pupil diameter and with the Zernike coefficient for spherical aberration in a way that maximizes visual acuity. We infer from these results that subjective best focus occurs when the area of the central, aberration-free region of the pupil is maximized. We found that the population averages of Zernike coefficients were nearly zero for all of the higher-order modes except spherical aberration. This result indicates that a hypothetical average eye representing the central tendency of the population is nearly free of aberrations, suggesting the possible influence of an emmetropization process or evolutionary pressure. However, for any individual eye the aberration coefficients were rarely zero for any Zernike mode. To first approximation, wave-front error fell exponentially with Zernike order and increased linearly with pupil area. On average, the total wave-front variance produced by higher-order aberrations was less than the wave-front variance of residual defocus and astigmatism. For example, the average amount of higher-order aberrations present for a 7.5-mm pupil was equivalent to the wave-front error produced by less than 1/4 diopter (D) of defocus. The largest pupil for which an eye may be considered diffraction-limited was 1.22 mm on average. Correlation of aberrations from the left and right eyes indicated the presence of significant bilateral symmetry. No evidence was found of a universal anatomical feature responsible for third-order optical aberrations. Using the Marechal criterion, we conclude that correction of the 12 largest principal components, or 14 largest Zernike modes, would be required to achieve diffraction-limited performance on average for a 6-mm pupil. Different methods of computing population averages provided upper and lower limits to the mean optical transfer function and mean point-spread function for our population of eyes.
615 citations
TL;DR: It is concluded that objective methods of refraction based on wavefront aberration maps can accurately predict the results of subjective refraction and may be more precise and wavefront methods may become the new gold standard for specifying conventional and/or optimal corrections of refractive errors.
Abstract: We determined the accuracy and precision of 33 objective methods for predicting the results of conventional, sphero-cylindrical refraction from wavefront aberrations in a large population of 200 eyes. Accuracy for predicting defocus (as specified by the population mean error of prediction) varied from -0.50 D to +0.25 D across methods. Precision of these estimates (as specified by 95% limits of agreement) ranged from 0.5 to 1.0 D. All methods except one accurately predicted astigmatism to within +/-1/8D. Precision of astigmatism predictions was typically better than precision for predicting defocus and many methods were better than 0.5D. Paraxial curvature matching of the wavefront aberration map was the most accurate method for determining the spherical equivalent error whereas least-squares fitting of the wavefront was one of the least accurate methods. We argue that this result was obtained because curvature matching is a biased method that successfully predicts the biased endpoint stipulated by conventional refractions. Five methods emerged as reasonably accurate and among the most precise. Three of these were based on pupil plane metrics and two were based on image plane metrics. We argue that the accuracy of all methods might be improved by correcting for the systematic bias reported in this study. However, caution is advised because some tasks, including conventional refraction of defocus, require a biased metric whereas other tasks, such as refraction of astigmatism, are unbiased. We conclude that objective methods of refraction based on wavefront aberration maps can accurately predict the results of subjective refraction and may be more precise. If objective refractions are more precise than subjective refractions, then wavefront methods may become the new gold standard for specifying conventional and/or optimal corrections of refractive errors.
560 citations
TL;DR: A new IOL with a prolate anterior surface, designed to partially compensate for the average spherical aberration of the cornea, is intended to improve the ocular optical quality of pseudophakic patients.
Abstract: PURPOSE: The aim of this study was to design and evaluate in the laboratory a new intraocular lens (IOL) intended to provide superior ocular optical quality by reducing spherical aberration. METHODS: Corneal topography measurements were performed on 71 cataract patients using an Orbscan I. The measured corneal surface shapes were used to determine the wavefront aberration of each cornea. A model cornea was then designed to reproduce the measured average spherical aberration. This model cornea was used to design IOLs having a fixed amount of negative spherical aberration that partially compensates for the average positive spherical aberration of the cornea. Theoretical and physical eye models were used to assess the expected improvement in optical quality of an eye implanted with this lens. RESULTS: Measurements of optical quality provided evidence that if this modified prolate IOL was centered within 0.4 mm and tilted less than 7 degrees, it would exceed the optical performance of a conventional spherical IOL. This improvement occurred without an apparent loss in depth of focus. CONCLUSION: A new IOL with a prolate anterior surface, designed to partially compensate for the average spherical aberration of the cornea, is intended to improve the ocular optical quality of pseudophakic patients. [J Refract Surg 2002;18: 683-691] T
498 citations
Journal Article•
TL;DR: In this paper, the root-mean-square (RMS) wavefront error of 22 normal myopic eyes (preoperative refraction ranged from -13 to -2 D) were measured before and after LASIK refractive surgery using a laser ray tracing technique.
Abstract: PURPOSE
To determine objectively the changes in the ocular aberrations (3rd order and above) induced by myopic LASIK refractive surgery and its impact on image quality.
METHODS
The ocular aberrations of 22 normal myopic eyes (preoperative refraction ranged from -13 to -2 D) were measured before (2.9 +/- 4.3 weeks) and after (7.7 +/- 3.2 weeks) LASIK refractive surgery using a laser ray tracing technique. A set of laser pencils is sequentially delivered onto the eye through different pupil locations. For each ray, the corresponding retinal image is collected on a CCD camera. The displacement of the image centroid with respect to a reference provides direct information of the ocular aberrations. Root-mean-square (RMS) wavefront error was taken as image quality metric.
RESULTS
RMS wavefront error increased significantly in all eyes but two after surgery. On average, LASIK induced a significant (P = 0.0003) 1.9-fold increase in the RMS error for a 6.5-mm pupil. The main contribution was due to the increase (fourfold, P < 0.0001) of spherical aberration. The increase in the RMS for a 3-mm pupil (1.7-fold) was also significant (P = 0.02). The modulation transfer (computed for 6.5-mm pupil) decreased on average by a factor of 2 for middle-high spatial frequencies.
CONCLUSIONS
(1) Laser ray tracing is a well-suited, robust, and reliable technique for the evaluation of the change of ocular aberrations with refractive surgery. (2) Refractive surgery induces important amounts of 3rd and higher order aberrations. The largest increase occurs for spherical aberration. Decentration of the ablation pattern seems to generate 3rd order aberrations. (3) This result is important for the design of customized ablation algorithms, which should cancel existing preoperative aberrations while avoiding the generation of new aberrations.
436 citations