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Accuracy of Orbscan II slit-scanning elevation topography

Cairns, Gerard; McGhee, Charles N.J; Collins, Michael J; Owens, Helen; Gamble, Greg D


Gerard Cairns

Charles N.J McGhee

Michael J Collins

Helen Owens
Senior Lecturer in Optometry

Greg D Gamble


Purpose: To establish the accuracy of Orbscan II (Orbtek Inc.) slit-scanning elevation topography in analyzing the anterior surface of complex test objects. Setting: Discipline of Ophthalmology, University of Auckland, Faculty of Medical and Health Sciences, Auckland, New Zealand. Methods: Six test objects were created from 2 materials: standard calibration poly(methyl methacrylate) (PMMA) (Orbtek Inc.) and a research PMMA material. The test objects were produced with spherical (radii of curvature 6.00 mm, 7.67 mm, and 8.88 mm), aspherical (apical radius 7.67, eccentricity 0.5, Q -0.25), and toroidal (7.67/7.92 mm radii of curvature) surfaces. The accuracy of the test surfaces was established by Form Talysurf Analysis. A single calibrated Orbscan II device was used to obtain 20 separate anterior elevation maps of each test object. The data obtained from Orbscan II, at 0.2 mm intervals along the chosen meridian, were directly compared with the Talysurf values for each test surface. Results: Orbscan II measurements of all test objects were statistically significantly different from the Talysurf values (P < .001). The test objects produced from standard calibration material were more accurately measured by Orbscan II than the objects produced from the research material. Data obtained by Orbscan II from the central 3.5 mm of all test objects were more accurate than peripheral data when compared with the Talysurf values (P = .001). Conclusions: Orbscan II anterior surface elevation measurements differed significantly from Form Talysurf Analysis of complex test surfaces. However, the magnitude of the errors in the measurement of standard test objects was small, less than 0.20 μm centrally and 0.70 μm peripherally. Clinically, if similar accuracy of measurement is confirmed in the human eye, anterior surface elevation maps can be considered accurate representations of corneal shape. © 2002 ASCRS and ESCRS.


Cairns, G., McGhee, C. N., Collins, M. J., Owens, H., & Gamble, G. D. (2002). Accuracy of Orbscan II slit-scanning elevation topography. Journal of Cataract and Refractive Surgery, 28(12), 2181-2187.

Journal Article Type Article
Acceptance Date Jan 1, 2002
Online Publication Date Dec 17, 2002
Publication Date Dec 1, 2002
Journal Journal of Cataract and Refractive Surgery
Print ISSN 0886-3350
Publisher Elsevier
Peer Reviewed Peer Reviewed
Volume 28
Issue 12
Pages 2181-2187
Keywords accuracy, orbscan, slit-scanning, elevation, topography
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