Anterior chamber angle evaluation with fourier-domain optical coherence tomography

Abstract

New advances in anterior segment optical coherence tomography (OCT) technology development allow visualizing the anterior chamber angle of the eye with high speed and high resolution. Fourier-domain (FD) OCT instruments working at 840 nm can reliably identify fine angle structures such as the Schwalbe's line. This paper demonstrates quantitative angle assessment with 840 nm FD-OCT and provides diagnostic cutoff values for occludable angle detection. This is useful for angle closure glaucoma diagnosis and management. Moreover, 840 nm FD-OCT is a useful tool for postsurgical evaluation in glaucoma patients.

Figure 1

Two scans of the same nasal angle in a normal subject. (a) Fourier-domain RTVue OCT image using a 6 mm CL-Angle scan pattern. Schwalbe's line (SL), trabecular meshwork (TM), Schlemm's canal (SC), and scleral spur (SS) are visible. However, the iris root (IR) and angle recess (AR) are not visible in this image. (b) Time-domain Visante OCT image using a 10 mm high-resolution corneal scan pattern. In this image, both the scleral spur and angle recess are visible, but the trabecular meshwork, Schlemm's canal, and Schwalbe's line are not resolvable.

Figure 2

Frame-averaged cross-sectional OCT image of the nasal angle in a normal subject. The high resolution helps to visualize the termination of the endothelium and Descemet's membrane (Schwalbe's line, SL), which is a useful landmark on these images. Also visible are the external limbus (EL), Schlemm's canal (SC), and the trabecular meshwork (TM). The scleral spur (SS) is faintly visible in this case. The angle recess, iris root, and ciliary body are not visible due to blocking by the sclera. The angle opening distance between SL and the anterior surface of the iris (AOD-SL, dotted line) was 361 μm, indicating that the angle is open.

Figure 3

Frame-averaged cross-sectional OCT image of a closed angle with modified Shaffer grade of 0 by gonioscopy. The high definition of the image allows the visualization of the Schwalbe's line (SL) and the contact between the iris and the trabecular meshwork (TM). The AOD-SL is obviously zero in this case.

Figure 4

Frame-averaged cross-sectional OCT image of the nasal angle in an eye with primary narrow angle glaucoma. The AOD-SL (dotted line) was measured at 177 µm, below the diagnostic cutoff value of 230–290 μm, indicating a potentially occluded angle. This agreed with a gonioscopic grade of 1 on the modified Shaffer scale. The trabecular meshwork (TM) and Schwalbe's line (SL) can be distinguished.

Figure 5

Pre- and postlaser peripheral iridotomy OCT images of an eye with narrow angles. (a) Preoperative image of the nasal angle with frame averaging. The short distance between the trabecular meshwork (TM) and the iris indicates a narrow, potentially occluded angle. The AOD-SL (dotted line) measured 120 μm. An aqueous collector vein and the Schlemm's canal (SC) are also visible. (b) Frame-averaged cross-sectional OCT image of the same angle following laser peripheral iridotomy. The procedure nearly doubled the AOD-SL (dotted line) to 220 μm, reprinted with permission from SLACK Incorporated: Huang D, Duker JS, Fujimoto JG, Lumbroso B, Schuman JS, Weinreb RN. Imaging the Eye from Front to Back with RTVue Fourier-Domain Optical Coherence Tomography. Thorofare, NJ: SLACK Incorporated; 2010.

Figure 6

A cross-sectional OCT image of the nasal angle following trabectome surgery. This frame-averaged image shows that the posterior trabecular meshwork has been removed, leaving a 374 μm wide trabecular cleft (TC) and an anterior trabecular meshwork remnant (TMR). Although scleral shadowing has caused the iris root (IR) to appear indistinct, it was possible to trace its position by contiguity with the iris. The limbal girdle of Vogt is the cause of the shadowing in the peripheral cornea. (Courtesy of Brian A. Francis, MD, USA), reprinted with permission from SLACK Incorporated: Huang D, Duker JS, Fujimoto JG, Lumbroso B, Schuman JS, Weinreb RN. Imaging the Eye from Front to Back with RTVue Fourier-Domain Optical Coherence Tomography. Thorofare, NJ: SLACK Incorporated; 2010.