Optical coherence tomography (OCT) is recognized all over the world as an essential device for diagnosis, assessment, and follow-up of retinal diseases and glaucoma in clinical work and in research. This handbook first two editions are now sold out. This handbook's third edition is a completely new volume. OCT developed so much in these last 10 years that we had to modify deeply most chapters and some are entirely original ones. We offer, in it, a step-by-step guide for interpreting data acquired by OCT. The first step subdivides each image into its smallest elementary parts. The second step combines these elementary components allowing an accurate diagnosis and treatment decision. We then describe and update the structural OCT aspects of retinal disorders and report the great advances that OCT has obtained in the clinical field: All the new syndromes, disorders, and diseases that OCT has revealed and precised, and new classification that OCT has suggested. Optical coherence tomography allowed to understand new syndromes, recognize new pathologies, expand or limit diagnoses, organize disorders in new classifications, and detect imaging elements by the OCT. Known diseases have been better understood and different diseases and morphologies have been described and identified after the introduction of structural OCT. This handbook will help ophthalmologists, residents, ophthalmic technicians, orthoptists, and optometrists in their everyday clinical work to understand and use in clinical practice the possibilities offered by OCT devices.