Elsevier

Ophthalmology

Volume 109, Issue 9, September 2002, Pages 1642-1646
Ophthalmology

Role of Orbscan II in screening keratoconus suspects before refractive corneal surgery1

Presented in part at the annual meeting of the American Society of Cataract and Refractive Surgery, April 2000, San Diego, California.
https://doi.org/10.1016/S0161-6420(02)01121-1Get rights and content

Abstract

Objective

To evaluate the relationship between videokeratographic keratoconus screening programs and Orbscan II topography.

Design

Prospective, observational case series and instrument validation study.

Participants

Sixty consecutive eyes with suspicious videokeratography (TMS-1, Tomey Technology, Waltham, MA) were evaluated before undergoing laser in situ keratomileusis (LASIK) surgery. A control group of 50 consecutive eyes without suspicious features by videokeratography was also evaluated.

Methods

Keratoconus screening programs, using the Rabinowitz and Klyce/Maeda methods and Orbscan II (Bausch & Lomb, Claremont, CA) topographies were performed on these patients.

Main outcome measures

Specific parameters evaluated on the Orbscan II topographies were anterior elevation, posterior elevation, and thinnest pachymetry.

Results

Compared with a control group of patients without suspicious videokeratography, there was a statistically significant difference in the mean posterior elevation and mean anterior elevation in the groups with positive keratoconus testing with the Rabinowitz or Klyce/Maeda methods. For patients who met both the Rabinowitz and Klyce/Maeda criteria for keratoconus, the mean posterior elevation was 44 ± 2.5 μm compared with a posterior elevation of 21 ± 0.6 μm for the control group. There was no statistically significant difference in the mean thinnest pachymetry between the control group and all keratoconus suspect groups.

Conclusions

Patients with positive keratoconus screening tests have higher anterior and posterior elevation on Orbscan II topography. When used in combination with videokeratography, the Orbscan II topography system may be helpful in identifying patients who are potentially at high risk for developing ectasia after LASIK.

Section snippets

Material and methods

Sixty consecutive eyes with suspicious videokeratography (TMS 1, version 1.61, Tomey, Waltham, MA) were evaluated as part of a routine preoperative LASIK examination. Suspicious videokeratography was determined for the purpose of this study as an area of central, inferior, or superior steepening; oblique cylinder > 1.5 diopters (D); and a steep keratometric curvature greater than 47 D. The preoperative workup of candidates for LASIK included a detailed medical history, manifest and cycloplegic

Results

Table 1 compares the Orbscan II data between the keratoconus suspects group and the control group. The mean anterior elevation of the keratoconus suspects group was 0.009 ± 0.007 mm. The mean posterior elevation of the keratoconus suspects group was 0.035 ± 0.015 mm. The mean thinnest pachymetry of the keratoconus suspects group was 515 ± 44 μm. The mean anterior elevation of the control group was 0.005 ± 0.002 mm. The mean posterior elevation of the control group was 0.021 ± 0.006 mm. The

Discussion

The role of Orbscan II in screening patients for refractive surgery has not been well defined. Previous authors have shown that Orbscan II topography can provide useful and accurate information in defining the morphology of keratoconus and in detecting subtle topographic changes present in early keratoconus.16 In addition, Wang et al17 have shown that the posterior elevation increases after LASIK, and the increase is correlated with residual corneal bed thickness.

We have shown that patients

References (17)

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1

None of the authors has a financial or proprietary interest in any material or method mentioned.

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