OCT is a new diagnostic tool that provides images of the back of the eye of unprecedented quality. This information is particularly helpful for diagnosing and monitoring many cases of retinal disease, as well as glaucoma, which previously had mystified even the most experienced clinicians.

OCT uses a principle akin to ultrasound. A beam of light is split in two, with one beam 'the reference' bouncing off a mirror a known distance away while the second passes through the pupil and is reflected off the various layers of the retina. OCT is 10 times more sensitive than ultrasound, with the ability to display objects as small as one hundredth of a millimetre wide. Unlike fluorescein angioography, previously the standard test for retinal disease, which required the injection of a contrast dye and a very bright light, OCT is much easier to perform.

OCT is helpful not just for diagnosis but also for monitoring responses to treatment. It is, for example, invaluable in assessing both the suitability and the response to treatment of patients with diabetic retinopathy. OCT is now almost mandatory for the management of "wet" macular degeneration with the new "anti-VEGF" drugs Lucentis and Avastin which are given by injection into the eye every 4-6 weeks. OCT is used to confirm that treatment has been effective by making sure there no is bleeding or swelling left. Once treatment is stopped after the macula has settled, OCT examinations are performed regularly to check for recurrence.