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Corneal surface characterization: how many Zernike terms should be used?

Iskander, D. Robert, Collins, Michael J., Davis, Brett A., & Franklin, Ross J. (2001) Corneal surface characterization: how many Zernike terms should be used? Investigative Ophthalmology and Visual Science, 42(4), S896.

Abstract

Purpose: Zernike polynomials have often been used to represent corneal height data and characterize corneal aberrations. Traditionally, vision researchers have chosen to use the first 15 or 32 Zernike terms, however the use of 64 terms has also been reported. In this study, we ask how many Zernike terms one should use to judiciously characterize the corneal surface. Methods: We use our recently reported bootstrap based method that determines the optimal number of Zernike terms for a given set of height data derived from a videokeratoscope (IEEE Trans. on Biomed. Eng. 48(1), Jan 2001). We have selected 70 eyes including 60 normals and 10 keratoconics. Corneal height data was obtained using the Keratron videokeratoscope. Three maps were taken for each eye and averaged in the analysis. For each corneal height map we have determined the optimal number of Zernike terms using the bootstrap procedure for several corneal diameters ranging from 2mm to 8mm. Results: Most corneas were objectively represented with the first 11 Zernike terms (as per Noll’s notation). A larger number of terms were needed only for corneas with significant deformities. For those subjects the fit varied widely with the corneal diameter. None of the corneas were fitted with a larger number of Zernike terms than 22. Conclusions: Fitting an arbitrary number of Zernike terms to corneal surfaces may result in over or under-parameterization. Our results show that in most cases the use of the first 11 terms is sufficient. Using a larger number of Zernike terms often results in modelling the instrument measurement noise rather than the cornea itself.

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ID Code: 12201
Item Type: Journal Article
Additional Information: For more information, please refer to the journal’s website (see hypertext link) or contact the author.
Additional URLs:
ISSN: 0146-0404
Subjects: Australian and New Zealand Standard Research Classification > MEDICAL AND HEALTH SCIENCES (110000) > OPTOMETRY AND OPHTHALMOLOGY (111300)
Australian and New Zealand Standard Research Classification > MEDICAL AND HEALTH SCIENCES (110000) > OPTOMETRY AND OPHTHALMOLOGY (111300) > Vision Science (111303)
Australian and New Zealand Standard Research Classification > MEDICAL AND HEALTH SCIENCES (110000) > OPTOMETRY AND OPHTHALMOLOGY (111300) > Optical Technology (111302)
Divisions: Current > Research Centres > Centre for Health Research
Current > QUT Faculties and Divisions > Faculty of Health
Current > Institutes > Institute of Health and Biomedical Innovation
Copyright Owner: Copyright 2001 Association for Research in Vision and Ophthalmology
Deposited On: 25 Jan 2008
Last Modified: 11 Aug 2011 00:09

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