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Gerard Cairns

Publications and source records attributed to Gerard Cairns.

4 recordsLinked to original sources
PubMed2005

Orbscan computerized topography: attributes, applications, and limitations.

An extensive electronic search was undertaken in January 2004 to identify all relevant peer-reviewed publications on Orbscan slit-scanning/Placido computerized topography. Ninety-one publications were identified. These address elevation topography and best-fit sphere, accuracy and repeatability of anterior and posterior corneal elevation and keratometric maps, comparison of Orbscan-acquired data and Placido-based computerized videokeratography instruments, pachymetry measurement and correlation with ultrasound, screening eye-bank corneas, detection of keratoconus, identifying corneal ectasia after refractive surgery, and miscellaneous applications. Studies were analyzed and critically compared in relation to attributes, applications, and limitations of Orbscan corneal topography. The review highlights advantages of this technique in assessing the cornea in health and disease and after surgery and identifies specific aspects that require further investigation and clarification.

Cornea↗
PubMed2005

Assessing the accuracy of Orbscan II post-LASIK: apparent keratectasia is paradoxically associated with anterior chamber depth reduction in successful procedures.

PURPOSE: To establish a relationship between the forward protrusion of the cornea (keratectasia), following successful LASIK, and anterior chamber depth. METHODS: One hundred and fifteen eyes of 59 patients who had undergone Zyoptix LASIK and 39 eyes of 21 patients who had undergone PlanoScan LASIK at the Eye Institute, Centre for Refractive Surgery, Remuera, Auckland, New Zealand, were included in the study. The results of Orbscan II acquisitions, taken before and 8.3 weeks +/- 4.0 (mean +/- standard deviation) following the procedure, were analysed to determine the amount of forward protrusion of the central 2 mm diameter of the posterior surface. The apparent keratectasia was then related to the Orbscan II anterior chamber depth (ACD) measurement in a linear mixed model analysis that included 'right or left eye', 'sex', 'type of LASIK procedure', 'change in pachymetry', 'postoperative pachymetry', 'change in anterior corneal curvature', 'postoperative anterior corneal curvature', 'planned ablation depth' and 'time until follow-up' as factors and covariates. RESULTS: The mean +/- SD amount of keratectasia determined by Orbscan II was 22.8 +/- 26.8 microm for the Zyoptix group and 16.9 +/- 24.6 microm for the PlanoScan group. The reduction in depth of the anterior chamber was 14.7 +/- 79.3 microm for the Zyoptix group and 18.2 +/- 68.8 microm for the PlanoScan group. The mixed model analysis demonstrated strong relationships with postoperative pachymetry and change in anterior corneal curvature (P < 0.001 and P < 0.001, respectively). Furthermore, the statistical model showed a marked significant difference in the Orbscan II assessment of keratectasia and change in ACD (P < 0.001). CONCLUSION: Using the Orbscan II device, the forward protrusion of the posterior corneal surface appears to coincide with a paradoxical reduction in depth of the anterior chamber. Although the keratectasia found in this study is accompanied by thin postoperative corneas and larger central pachymetry change, the contradictory decrease in anterior chamber depth creates uncertainty of measurement, and of ectasia as a mechanism of regression.

Adult↗
PubMed2002

Accuracy of Orbscan II slit-scanning elevation topography.

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 microm centrally and 0.70 microm 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.

Contact Lenses↗