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Imaging the Ocular Anterior Segment With Real-Time, Full-Range Fourier-Domain Optical Coherence Tomography

Marinko V. Sarunic, PhD; Sanjay Asrani, MD; Joseph A. Izatt, PhD
Arch Ophthalmol. 2008;126(4):537-542. doi:10.1001/archopht.126.4.537.
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  We have demonstrated a novel Fourier-domain optical coherence tomography system and signal-processing algorithm for full-range, real-time, artifact-free quantitative imaging of the anterior chamber. Cross-sectional full-range images comprising 1024 × 800 pixels (axial × lateral) were acquired and displayed at 6.7 images/s. Volumetric data comprising 1024 × 400 × 60 pixels (axial × lateral × elevation) were acquired in 4.5 seconds with real-time visualization of individual slices and 3-dimensional reconstruction performed in postprocessing. Details of the cornea, limbus, iris, anterior lens capsule, trabecular meshwork, and Schlemm's canal were visualized. Quantitative surface height maps of the corneal epithelium and endothelium were obtained from the volumetric data and used to generate corneal thickness maps.

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Figure 1.

Fourier-domain optical coherence tomography anterior segment images acquired in vivo on a human volunteer. A, Symmetric artifact between positive and negative distances observed in Fourier-domain optical coherence tomography systems. B, Quadrature projection processing of phase-stepped signals allows full-range imaging, uniquely resolving positive and negative distances. Each B-scan image, as shown previously, consists of 800 A-scans with 1024 pixels per A-scan, acquired and displayed in real time at 6.7 B-scans/s.

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Figure 2.

Optical setup of the real-time full-range Fourier-domain optical coherence tomography system using a 3 × 3 fused fiber coupler in a Michelson type interferometer. The sample arm optics were integrated into a slitlamp biomicroscope to facilitate patient imaging. The separate 2 × 2 fiber-coupled Michelson interferometer was used to generate the wave number calibration signal.35

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Figure 3.

Diagrammatic representation of the refraction correction procedure. The red arrow represents the Fourier-domain optical coherence tomography beam, incident on the cornea at angle θ1 and refracted by angle θ2. The orange arrow represents dopt, the physical distance traveled by the beam through the cornea. The green and yellow lines represent the polynomial fits to the corneal epithelium and endothelium, respectively. The magenta curve represents the calculated actual location of the endothelial surface. Corneal thickness was measured perpendicular to the epithelium, as represented by the blue arrows.

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Figure 4.

High-resolution image of the anterior chamber angle. Clearly visible is the trabecular meshwork and Schlemm's canal. Visualization of the ciliary body appears improved compared with time-domain systems.

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Figure 5.

Full-range volume reconstruction of the ocular anterior segment on a human volunteer.

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Figure 6.

Display of cross-sectional planes within a volume scan allows localization of structures. Three orthogonal planes (transverse, caudal, and sagittal) are shown through the volumetric reconstruction of the hemisphere of a human volunteer's ocular anterior chamber.

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Figure 7.

Corneal topography measurements generated from the volumetric data presented in Figure 5. The epithelial height map (A) was extracted directly from the data, but the endothelial surface height map (B) required additional processing to correct for refraction.

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Figure 8.

Corneal thickness map comparison of a volunteer with normal vision generated using a commercial system (Pentacam; Oculus, Dudenhofen, Germany) (A) and the 3 × 3 swept-source optical coherence tomography prototype (B).

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