Optical Coherence Tomography (OCT) is a complex technology used to scan and measure the eye, particularly the layers of the retina. Now the standard of excellent care in optical practices, the OCT scan uses light waves instead of sound waves, similar to an ultrasound, to illuminate the retina and provide a 3D image. This allows the practitioner to see, sometimes for the first time, problems with the eye that could not be seen easily before.