Corneal Pachymetry Mapping with High-speed Optical Coherence Tomography
Received 5 July 2005; accepted 31 January 2006.
Objective
To map corneal thickness before and after LASIK with optical coherence tomography (OCT).
Design
Cross-sectional observational study.
Participants
Forty-two eyes of 21 normal subjects undergoing LASIK.
Methods
A high-speed (2000 axial scans/second) 1.3-μm-wavelength corneal and anterior segment OCT prototype was used for corneal scanning. The scan pattern consisted of 10-mm radial lines on 8 meridians centered on the vertex reflection. The entire scan pattern of 1024 a-scans was acquired in 0.5 seconds. We developed automated computer processing for 3-dimensional corneal reconstruction and measurement. Corneal thickness was measured normal to the anterior surface and presented as color pachymetry maps and zonal statistics. The maps were divided into a central zone (<2 mm) and 3 annular areas (pericentral, 2–5 mm; transitional, 5–7 mm; peripheral, 7–10 mm), which were further divided into quadrantal zones. The average, minimum, and maximum corneal thicknesses were computed for zones within the 7-mm diameter. Optical coherence tomography and ultrasound pachymetry were measured 3 times at the preoperative and 3-month postoperative visits. Reproducibility was assessed by the pooled standard deviations (SDs) of the repeated measurements.
Main Outcome Measures
Optical coherence tomography pachymetric map and zonal statistic, and ultrasound pachymetry.
Results
Before LASIK, central corneal thicknesses (CCTs) were 546.9±29.4 μm (mean ± SD) for OCT and 553.3±33.0 μm for ultrasound. After LASIK, CCTs were 513.7±44.5 μm for OCT and 498±46.6 μm for ultrasound. Optical coherence tomography and ultrasound CCT were highly correlated (Pearson correlation r = 0.97 before LASIK and 0.98 afterwards). Optical coherence tomography CCT was slightly less than ultrasound CCT before surgery (mean difference, −6.4 μm; 95% limits of agreement, −23.2 to 10.4 μm) but slightly greater after LASIK (15.7 μm; −1.6 to 33 μm). These differences were statistically significant, but no more than the CCT measurement differences between ultrasound pachymeters. The reproducibility of the OCT zonal pachymetry averages was roughly 2 μm.
Conclusions
High-speed OCT provided noncontact, rapid, reproducible pachymetric mapping over a wide area of the cornea. It is equivalent to ultrasound for CCT measurement before and after LASIK. This technology could be valuable for planning keratorefractive procedures and diagnosis of corneal diseases.
1Department of Biomedical Engineering, Case Western Reserve University, Cleveland, Ohio
2Department of Biomedical Engineering, Cleveland Clinic Foundation, Cleveland, Ohio
3Cole Eye Institute, Cleveland Clinic Foundation, Cleveland, Ohio
Correspondence and reprint requests to David Huang, MD, PhD, Doheny Eye Institute, 1450 San Pablo Street, DEI 5702, Los Angeles, CA 99033
Manuscript no. 2005-599.
Financial support: National Institutes of Health, Bethesda, Maryland (grant no.: R24 EY13015), and Carl Zeiss Meditec Inc., Dublin, California.
Dr Huang has a patent royalty interest in optical coherence tomography technology. Drs Huang and Li receive research grant support from Carl Zeiss Meditec Inc. Dr Shekhar does not have a proprietary interest in the topic of the article.
ABSTRACT