What is an OCT scan?
An optical coherence tomography scan (commonly referred to as an OCT scan) helps us to view the health of your eyes in greater detail, by allowing us to see what’s going on beneath the surface of the eye.
Imagine your retina like a cake – we can see the top of the cake and the icing using the 2D digital retinal photography (fundus camera), but the 3D image produced from an OCT scan slices the cake in half and turns it on its side so we can see all the layers inside.
Our opticians can then examine these deeper layers to get an even clearer idea of your eye health.
OCT scans can help detect sight-threatening eye conditions earlier. In fact, glaucoma can be detected up to four years earlier than traditional imaging methods.
What is the difference between an OCT scan and an eye test?
OCT is separate to an eye test. An eye test checks your eye health as well as how well you can see. Part of that often involves taking an image of the back of the eye (digital retinal photography), but an OCT scan takes this a step further, allowing your optician to look even deeper into your eyes and the structures within them.
Essentially, an OCT scan gives your optician a clearer idea of your eye health when testing your eyes.
Traditional fundus test image
OCT scan image
What is anterior segment optical coherence tomography (ASOCT)?
Though not used very often, anterior segment optical coherence tomography (ASOCT) is a highly-effective, non-invasive test that takes images of the anterior segment of your eye. The anterior segment is the front third of the eye. The structures in this segment control the amount of light that enters the eye, allow the light to pass through to the lens, and help to focus light rays on the retina in order to form images. The main parts of the eye within the anterior segment include the iris, cornea, sclera, ciliary body, lens and anterior chamber.
ASOCT can be used to help detect and monitor a number of anterior segment diseases and conditions, including:1
OCT scan risks
An OCT scan is a safe procedure that involves using reflected visible light from a low-power laser to obtain images of your retina — the principle is similar to ultrasound, but uses light instead of sound. The scan is non-invasive (does not touch your eye), quick, painless and doesn’t hurt, and there are no known side effects or complications.
Can OCT scans misdiagnose?
Optometrists carry out specialist training on how to use and interpret the results from OCT scans correctly and effectively. An OCT machine takes a 3D scan of the eye, allowing optometrists to see a clear representation of your eye’s health — it is incredibly accurate in its detail. If anything, misdiagnosis risk decreases with its usage as it distinguishes features that are not visible with traditional retinal photography.2
How does optical coherence tomography work?
Taking just a few seconds, an OCT scan uses light to take over 1,000 images of the back of your eye and beyond, looking right back to the optic nerve.
A layered image is created that gives us an incredibly accurate picture of your eye and its structures, allowing us to check your eye health. The images will then be stored so we can note changes over time.
I have a diabetic check annually; do I still need an OCT scan?
Yes – while both the diabetic screening check and OCT involve taking images of the back of the eye, there are significant differences.
Diabetic checks involve a fundus picture – this is an image of the surface of the back of the eye (the retina) also known as digital retinal photography. OCT images allow us to look at the many layers beneath the surface of the retina, which helps us to spot changes to eye health earlier than just looking at the surface.
OCT scans also help in the detection of a range of other eye problems, not just those that are linked to diabetes.
OCT scans to check retinal health
A healthy retina is important for eyesight. When the retina is damaged, it can lead to impairment or loss of vision. Many eye conditions involve the retina, most commonly macular degeneration, diabetic retinopathy and central serous retinopathy. Often, the most successful treatment or management of these conditions relies on early detection, which is why it's so important to have your retinal health checked every year or two years.
Being able to identify and distinguish the different layers of the retina using an OCT scan allows opticians to pinpoint any abnormalities to a specific layer, which provides clues about the possible cause.2 This can help differentiate between two conditions that have very similar clinical signs and symptoms but require different treatment, such as for dry and wet macular degeneration.
For example, when using an ophthalmoscope or fundus photo, drusen and exudates (which are different types of deposits under the retina) often look similar.2 An OCT eye scan can easily distinguish between the two based on their location in the retinal layers. Knowing where these deposits are help to determine what's causing them, and can give your optometrist a more accurate picture of what is happening in your eye.
1. Han SB, Liu YC, Noriega KM, Mehta JS. Applications of Anterior Segment Optical Coherence Tomography in Cornea and Ocular Surface Diseases. J Ophthalmol. 2016;2016:4971572. [Online]. Available at: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5046038/ [Accessed 13 November 2019].
2. Morgan JI. The fundus photo has met its match: optical coherence tomography and adaptive optics ophthalmoscopy are here to stay. Ophthalmic Physiol Opt. 2016;36(3):218–239. [Online]. Available at: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4963017/ [Accessed 13 November 2019].
3. Heidelberg Engineering. (no date). Know Your Retinal Layers. [Online]. Available at: https://www.heidelbergengineering.com/int/news/know-your-retinal-layers-33401465/ [Accessed 21 November 2019].