Author
Robert M. Webb
Other affiliations: Queensland University of Technology
Bio: Robert M. Webb is an academic researcher from Indiana University. The author has contributed to research in topics: Cadastre & Curriculum mapping. The author has an hindex of 5, co-authored 24 publications receiving 1037 citations. Previous affiliations of Robert M. Webb include Queensland University of Technology.
Papers
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TL;DR: 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 as discussed by the authors.
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.
749 citations
11 Feb 2000
TL;DR: 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 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. The following summary of the committee’s recommendations is available also in portable document format (PDF) on OSA Optics Net at http://www.osa.org/.
116 citations
95 citations
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.
85 citations
01 Jan 2001
TL;DR: Recreational geocaching is a 21st century recreation and adventure game that came about as a result of the improving accuracy of electronic Global Positioning System (GPS) devices as discussed by the authors.
Abstract: Recreational Geocaching is a new 21st century recreation and adventure game that came about as a result of the improving accuracy of electronic Global Positioning System (GPS) devices. With improved positional accuracy, of the order of five to ten metres, hand-held GPS's now allow unskilled users the ability to find geographic locations with precision and repeatability. With this new ability, people can now place geocaches in interesting places so that others can enjoy the challenge of finding them. In the rapidly developing sport of Recreational Geocaching, the Internet is used as a medium for the distribution of geocache locations. Web-sites have now been set up to support this new activity. The Internet allows communication between the geocacher and those searching for the geocache. Posted on the Internet along with the geographic coordinates, are clues, pictures, and other information about the geocache. This paper describes the recent history of recreational geocaching, some basic rules of the adventure game, some inclusions and exclusions of a cache, and adventure variations. An additional description of the survey methods used to confirm positional location and repeatability is included along with some surveying experiences around the SouthEast Queensland region.
7 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: In this paper, a modified Hartmann-Shack wavefront sensor was used to measure the monochromatic wave aberration of both eyes for 109 normal human subjects across a 5.7mm pupil.
Abstract: From both a fundamental and a clinical point of view, it is necessary to know the distribution of the eye's aberrations in the normal population and to be able to describe them as efficiently as possible. We used a modified Hartmann-Shack wave-front sensor to measure the monochromatic wave aberration of both eyes for 109 normal human subjects across a 5.7-mm pupil. We analyzed the distribution of the eye's aberrations in the population and found that most Zernike modes are relatively uncorrelated with each other across the population. A principal components analysis was applied to our wave-aberration measurements with the resulting principal components providing only a slightly more compact description of the population data than Zernike modes. This indicates that Zernike modes are efficient basis functions for describing the eye's wave aberration. Even though there appears to be a random variation in the eye's aberrations from subject to subject, many aberrations in the left eye were found to be significantly correlated with their counterparts in the right eye.
614 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