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Bing Qin, Yan Li, Maolong Tang, Xinbo Zhang, David Huang; Anterior Chamber Angle Measurement Using Fourier Domain Optical Coherence Tomography. Invest. Ophthalmol. Vis. Sci. 2011;52(14):6278.
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To introduce angle opening distance at Schwalbe's line (AOD-SL) as a new measurement to help evaluate angle closure risks using optical coherence tomography (OCT).
An 830-nm wavelength Fourier-domain OCT (RTVue, Optovue, Inc.) was used to perform horizontal scans of the nasal and temporal anterior chamber angles in glaucoma subjects. Images were graded by two ophthalmologists who assessed the visibility of landmarks and measured AOD-SL (Figure 1) with computer calipers. Gonioscopy was performed by a glaucoma specialist and classified using the Shaffer system. Shaffer grade of 1 or less was considered occludable. Spearman's rho was used to evaluate correlation between AOD-SL and Shaffer grade. A cut-off value of AOD-SL for occludability was determined with receiver operating characteristic (ROC) analysis. Areas under the ROC curve (AROC) was used to assess the accuracy of angle classification.
Thirty five subjects (65 eyes) were enrolled. Averaging the 2 graders and angle positions, the Schwalbe's line, anterior limbus, angle recess and scleral spur were visible in 85.8%, 85.8%, 40.8% and 15.0% of eyes, respectively. Correlation coefficient between AOD-SL and Shaffer grade were 0.80 (nasal) and 0.81 (temporal). The optimized diagnostic cut-off point for AOD-SL was 290µm. The AROC/sensitivity/specificity were 0.90/0.80/0.87 (nasal) and 0.90/0.85/0.77 (temporal).
Anterior segment OCT at the 830 nm wavelength has shallower limbal penetration, therefore scleral spur is poorly visible. But the Schwalbe's line and anterior limbus can be visualized clearly in most of the OCT images. Measuring AOD-SL by OCT is highly correlated with gonioscopy and may be useful as a noncontact method of assessing angle closure risk.
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