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Optical coherence tomography is a new imaging technique that can perform high-resolution, micrometre-scale, cross-sectional imaging in biological systems. The technology has been developed, and reduced to, preliminary clinical practice in ophthalmology. The challenging problem that OCT may address is the development of 'optical biopsy' techniques. These techniques can provide diagnostic imaging of tissue morphology without the need for excision of specimens. Many investigations remain to identify optimal areas for clinical application, and additional engineering must be done to integrate vertically the technology and to reduce it to clinical practice. Nevertheless, preliminary studies indicate the feasibility of developing this technology for a wide range of clinical and research diagnostic imaging applications. The ability to non-excisionally evaluate tissue morphology using a catheter or an endoscope could have a significant impact on the diagnosis and management of a wide range of diseases.

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Purpose-Optical coherence tomography (OCT) is a new technology that uses near-infrared light in an interferometer to produce approximately 10-μm resolution cross-sectional images of the tissue of interest. The authors performed repeated quantitative assessment of nerve fiber layer thickness in individuals with normal and glaucomatous eyes, and they evaluated the reproducibility of these measurements. Methods-The authors studied 21 eyes of 21 subjects by OCT. Each subject underwent five repetitions of a series of scans on five separate occasions within a 1-month period. Each series consisted of three circular scans around the optic nerve head (diameters, 2.9, 3.4, and 4.5 mm). Each series was performed separately using internal (fixation with same eye being studied) and external (fixation with contralateral eye) fixation techniques. The eye studied and the sequence of testing were assigned randomly.Results-Internal fixation (IF), in general, provides a slightly higher degree of reproducibility than external fixation (EF). Reproducibility was better in a given eye on a given visit than from visit to visit. Reproducibility as measured by intraclass correlation coefficients were as follows: circle diameter (CD), 2. Conclusions-Nerve fiber layer thickness can be reproducibly measured using OCT. Internal is superior to external fixation; each circle diameter tested provides adequate reproducibility.Optical coherence tomography (OCT) is a new technology that allows cross-sectional imaging of the eye using light. This technology is noncontact and noninvasive and may have use in diagnosing and managing retinal disease and glaucoma. We previously reported on the quantification of nerve fiber layer (NFL) and retinal thickness using OCT; however, for this technology to provide meaningful data, measurements must be reproducible.The goal of this study is to determine the reproducibility of measurements of NFL and retinal thickness made by OCT. We also sought to evaluate the optimal circle diameter for OCT NFL