To assess the accuracy of classification of narrow anterior chamber (AC) angles using quantitative imaging by optical coherence tomography (OCT) and ultrasound biomicroscopy (UBM).Design: Observational comparative study.Methods: A high-speed (4000 axial scans/s) anterior segment OCT prototype was developed using a 1.3-µm light source. Seventeen normal subjects (17 eyes) and 7 subjects (14 eyes) with narrow angle glaucoma were enrolled. All subjects underwent gonioscopy, OCT, and UBM. Quantitative AC angle parameters (angle opening distance, angle recess area, and the trabecular-iris space area [a new parameter we have defined]) were measured from OCT and UBM images using proprietary processing software.Main Outcome Measures: Specificity and sensitivity in identifying narrow angles with image-derived AC angle parameters.Results: Eight of 31 eyes were classified as having narrow angles (Shaffer grade Յ1 in all quadrants). The AC angle parameters measured by both OCT and UBM had similar mean values, reproducibility, and sensitivityspecificity profiles. Both OCT and UBM showed excellent performance in identifying eyes with narrow angles. Areas under the receiver operating characteristic curves for these parameters were all in the range of 0.96 to 0.98.Conclusions: Optical coherence tomography was similar to UBM in quantitative AC angle measurement and detection of narrow angles. In addition, it was easier to use and did not require contact with the eye. Optical coherence tomography is a promising method for screening individuals at risk for narrow angle glaucoma.
Background: Recent advances in high-speed scanning technology have enabled a new generation of optical coherence tomographic (OCT) systems to perform imaging at video rate. Here, a handheld OCT probe capable of imaging the anterior segment of the eye at high frame rates is demonstrated for the first time.Objective: To demonstrate real-time OCT imaging of anterior segment structures.Design: Survey of anterior segment structures in normal human subjects.Setting: Laboratory.
Main Outcome Measures:Achieving real-time imaging of the anterior segment, satisfactory image quality, and convenience of a handheld probe.Results: Optical coherence tomographic imaging of the anterior segment of the eyes of human subjects was performed using 1310-nm wavelength light with an image rate of 8 frames per second. Imaging trials demonstrated clear resolution of corneal epithelium and stroma, sclerocorneal junction, sclera, iris pigment epithelium and stroma, and anterior lens capsule. The anterior chamber angle was clearly visualized. Limited imaging of the ciliary body was performed. Real-time imaging of pupillary constriction in response to light stimulus was also performed.
Conclusion:High-speed OCT at 1310-nm wavelength is a potentially useful technique for noninvasive assessment of anterior segment structures.Clinical Relevance: Our results suggest that realtime OCT has potential applications in glaucoma evaluation and refractive surgery.
We describe a methodology for quantitative image correction in OCT which includes procedures for correction of nonlinear axial scanning and non-telecentric scan patterns, as well as a novel approach for refraction correction in layered media based on Fermat's principle. The residual spatial error obtained in layered media with a fan-beam hand-held probe was reduced from several hundred micrometers to near the diffraction and coherence-length limits.
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