Keratoconus Diagnosis with Optical Coherence Tomography Pachymetry Mapping
Presented in part at: Association for Research in Vision and Ophthalmology (ARVO) annual meeting, May 9, 2007, Fort Lauderdale, Florida.
Received 14 March 2008; received in revised form 18 June 2008; accepted 1 August 2008. published online 03 November 2008.
Objective
To detect abnormal corneal thinning in keratoconus using pachymetry maps measured by high-speed anterior segment optical coherence tomography (OCT).
Design
Cross-sectional observational study.
Participants
Thirty-seven keratoconic eyes from 21 subjects and 36 eyes from 18 normal subjects.
Methods
The OCT system operated at a 1.3 μm wavelength with a scan rate of 2000 axial scans per second. A pachymetry scan pattern (8 radials, 128 axial scans each; 10 mm diameter) centered at the corneal vertex was used to map the corneal thickness. The pachymetry map was divided into zones by octants and annular rings. Five pachymetric parameters were calculated from the region inside the 5 mm diameter: minimum, minimum–median, inferior–superior (I-S), inferotemporal–superonasal (IT-SN), and the vertical location of the thinnest cornea. The 1-percentile value of the normal group was used to define the diagnostic cutoff. Placido-ring–based corneal topography was obtained for comparison.
Main Outcome Measures
The OCT pachymetric parameters and a quantitative topographic keratoconus index (keratometry, I-S, astigmatism, and skew percentage [KISA%]) were used for keratoconus diagnosis. Diagnostic performance was assessed by the area under the receiver operating characteristic (AROC) curve.
Results
Keratoconic corneas were thinner. The pachymetric minimum averaged 452.6±60.9 μm in keratoconic eyes versus 546±23.7 μm in normal eyes. The 1-percentile cutoff was 491.6 μm. The thinnest location was inferiorly displaced in keratoconus (−805±749 μm vs −118±260 μm; cutoff, −716 μm). The thinning was focal (minimum–median: −95.2±41.1 μm vs −45±7.7 μm; cutoff, −62.6 μm). Keratoconic maps were more asymmetric (I-S, −44.8±28.7 μm vs −9.9±9.3 μm; cutoff, −31.3 μm; and IT-SN, −63±35.7 μm vs −22±11.4 μm; cutoff, −48.2 μm). Keratoconic eyes had a higher KISA% index (2641±5024 vs 21±19). All differences were statistically significant (t test, P<0.0001). Applying the diagnostic criteria of any 1 OCT pachymetric parameter below the keratoconus cutoff yielded an AROC of 0.99, which was marginally better (P = .09) than the KISA% topographic index (AROC, 0.91).
Conclusions
Optical coherence tomography pachymetry maps accurately detected the characteristic abnormal corneal thinning in keratoconic eyes. This method was at least as sensitive and specific as the topographic KISA.
Financial Disclosure(s)
Proprietary or commercial disclosure may be found after the references.
Available online: October 24, 2008.
1Center for Ophthalmic Optics and Lasers, Doheny Eye Institute and Department of Ophthalmology, Keck School of Medicine of the University of Southern California, Los Angeles, California
2Department of Biomedical Engineering, Case Western Reserve University, Cleveland, Ohio
3Cole Eye Institute, Cleveland Clinic Foundation, Cleveland, Ohio
Correspondence: David Huang, MD, PhD, Doheny Eye Institute, 1450 San Pablo Street, DEI 5702, Los Angeles, CA 99033
Manuscript no. 2008-343.
Financial Disclosure(s): David Huang receives royalties from the Massachusetts Institute of Technology derived from an optical coherence tomography patent licensed to Carl Zeiss Meditec, Inc. (Dublin, CA). David Huang and Yan Li receive research grant support from Carl Zeiss Meditec Inc. The other authors do not have proprietary interest in the topic of this manuscript.
Supported by NIH R01 EY018184, Carl Zeiss Meditec, Inc., NIH Core Grant EY03040.
ABSTRACT