We present a new technique for coherent optical imaging of ocular structure based on optical coherence tomography (OCT). OCT is a noncontact, noninvasive, tomographic imaging technique with superior spatial resolution to ultrasound (< 20 micrometers ) and high sensitivity (100 dB dynamic range). We have used OCT to perform direct imaging of ocular structure in the anterior and posterior segments of human eyes in vitro and in vivo. In the anterior segment, we have measured corneal thickness and profile, anterior chamber depth and angle, and iris thickness and profile. These and other possible measurements have potential applications in diagnosis of pathologies of the cornea, angle, and iris, as well as in noncontact biometry for applications in cataract and corneal refractive surgeries. In the posterior segment, we have obtained high-resolution images of retinal structure in human subjects in vivo. These images demonstrate higher resolution than available with any other existing technique, and include characterization of optic disk morphology and topology. These measurements have potential applications in early diagnosis and assessment of glaucoma and other retinal diseases.