OCT eye scan: what it is and what it shows

Optical Coherence Tomography (OCT) is an advanced imaging technology that uses light waves to create high resolution cross sectional images of the eye's internal structures. Similar to how ultrasound uses sound waves, OCT uses light to measure the echoes reflected from eye tissues. This allows the ophthalmologist to visualize the different layers of the retina, optic nerve, cornea, and other parts of the eye in microscopic detail.

An OCT scan is crucial for diagnosing and monitoring a wide range of eye conditions. It is used to evaluate retinal diseases such as age related macular degeneration (AMD), diabetic retinopathy, macular hole, epiretinal membrane, and macular edema. Additionally, it helps identify changes in the optic nerve, particularly in glaucoma follow up, and detect retinal damage caused by certain medications. The information obtained from the scan aids in making treatment decisions.

OCT Angiography (OCT A) is a variation of the OCT scan that provides non invasive imaging of blood flow in the tiny vessels of the retina and choroid. Unlike traditional fluorescein angiography, OCT A does not require the injection of a contrast dye. It helps identify vascular pathologies, such as blockages or abnormal blood vessel growth, associated with conditions like diabetic retinopathy and macular degeneration. However, a key limitation compared to traditional angiography is that OCT A cannot show fluid leakage from blood vessels. Despite this, it allows for precise monitoring of structural changes and treatment effects.

Before the scan, dilating eye drops may be administered. These drops widen the pupil, allowing the light beams to scan a broader area of the retina and optic nerve, thereby improving the quality of the images obtained. Pupil dilation can cause temporary blurred vision, especially for near tasks, and light sensitivity for several hours. It is advisable to arrange for someone to drive you home after the scan. If you wear contact lenses, you may be asked to remove them before the procedure.

The scan is performed while you are seated in front of the OCT machine, with your chin and forehead resting on supports and your eyes focused on a small light target. Pupil dilation may be used when needed but is not always required. The machine scans the eye with light without direct contact. The procedure is painless and non invasive. Image acquisition usually takes only a few minutes, although positioning, additional scans and waiting for any dilating drops can make the appointment longer. Follow the technician's instructions about keeping still and blinking between scans.

OCT scans are considered very safe. They do not involve ionizing radiation (unlike CT scans) and do not include direct contact with the eye. The main side effects are related to the dilating eye drops, which can cause temporary blurred vision, difficulty focusing on near objects, and light sensitivity. These effects usually subside within a few hours. Wearing sunglasses after the scan is recommended to alleviate light sensitivity.

After the scan, you can usually resume normal activities. If dilating drops were used, do not drive until your vision is clear, comfortable and safe for driving. The images are available immediately, but the timing of their clinical interpretation and discussion varies between clinics. Your ophthalmologist interprets them together with your examination and other tests to assess the eye, help establish a diagnosis, monitor changes and plan treatment. Ask the clinic when and how you will receive your results.