Optical coherence tomography (OCT) is a novel technique that allows cross-sectional imaging of the anterior and posterior eye. OCT has a resolution of approximately 10 microns, with extremely high sensitivity (approximately 10(-10) of incident light). OCT is analogous to computed tomography, which uses x-rays, magnetic resonance imaging, which uses spin resonance, or B-scan ultrasound, which uses sound waves, but OCT uses only light to derive its image. OCT is a noncontact, noninvasive system by which retinal substructure may be analyzed in vivo. OCT is useful in the evaluation of retinal pathologies and glaucoma. In retinal disease, entities such as macular holes, macular edema, central serous chorioretinopathy, retinal vascular occlusion and other factors have been examined. Separation between the posterior vitreous and retina, or lack thereof, are seen and quantitated. In glaucoma, retinal nerve fiber layer (NFL) thickness is measured at standardized locations around the optic nerve head. A circular scan produces a cylindrical cross-section of the retina, from which the NFL can be analyzed. In addition, radial scans through the optic nerve head are used to evaluate cupping and juxtapapillary NFL thickness. OCT, a new imaging technology by which the anterior and posterior segment are seen in cross-section, may permit the early diagnosis of glaucoma, and the early detection of glaucomatous progression.