Optical Coherence Tomography (OCT) is a non invasive diagnostic instrument used for imaging the retina. With an OCT, doctors are able to see a cross section or 3D image of the retina and detect the early onset of a variety of eye conditions and eye diseases such as macular degeneration, glaucoma and diabetic retinopathy (the top three diseases known to cause blindness). It is similar to a CT scan which is used to image internal organs inside the body.