An Optical Coherence Tomography (OCT) is a non-invasive imaging machine. In a matter of seconds the machine uses light waves to take cross-section pictures of your retina and builds a 3D map of your eye. These images show if the retina is thickened or abnormal.
An OCT can be particularly helpful in diagnosing age-related macular degeneration, glaucoma, and diabetic retinopathy, among other macular and optic nerve disorders.
Having an OCT allows the doctor to view the eye in a way he couldn't before.