What is an Optical Coherence Tomography (OCT)?

Reviewed by: HU Medical Review Board | January 2019

When diagnosing macular degeneration, including Stargardt disease and myopic macular degeneration, or MMD, your doctor may perform optical coherence tomography (OCT), a type of retinal scan, in addition to a standard dilated eye exam to better assess the health of your retina.

Importance of early diagnosis

Macular degeneration is not always symptomatic; in fact, early macular degeneration is asymptomatic, and while intermediate macular degeneration may cause some vision loss, for most people, there are no symptoms.1 It’s not until the condition progresses that the vision loss tends to be markedly noticeable, prompting one to seek medical attention. A regularly scheduled comprehensive eye exam with retinal imaging can reveal early signs of macular degeneration, which can then prompt appropriate treatment and lifestyle changes that may help slow the progression of the disease and help to preserve one’s current vision.

What is OCT used for?

While OCT is used in patients with macular degeneration, it is also used in patients with other eye conditions such as intraocular tumors, inherited retinal diseases, glaucoma, diabetic retinopathy, and other kinds of retinopathy.2 This has been tremendously beneficial from both a diagnostic and treatment standpoint. For instance, OCT may allow eye doctors to monitor changes in the retina that reveal whether treatments are effective or not, allowing them to decide whether you should continue your current treatment or switch to a different regimen.

What is OCT?

OCT is similar to ultrasound, but whereas ultrasound uses sound waves to obtain images of tissues, OCT uses light waves.1 OCT can provide high-resolution, cross-sectional images of the retina, retinal nerve fiber layer, and the optic nerve head – any tissue that is able to be penetrated by light can be imaged using OCT.1,2 The images help to provide measurements for each layer of the retina, as well as a visual map of the tissues. It is noninvasive and is used for clinical decision-making and disease management.

What happens during OCT?

Your pupils are usually (but not always) dilated for OCT, so your eye doctor will likely put dilating drops in your eyes. This allows more light to enter the eye, and will also make it easier for him/her to examine your retina as part of a comprehensive dilated eye exam. The OCT machine has a chin rest, allowing you to rest your head in front of the device while staying completely still. The machine will scan your eye; during this process, you may see a series of lines or lights of various colors, but the machine will not touch your eye. The entire process takes approximately 3-5 minutes and is completely noninvasive. There may be some mild light sensitivity from pupil dilation, but otherwise, you should experience minimal discomfort.


In AMD, OCT is often used for both disease management and for monitoring treatment response, especially in those with wet AMD or MMD who have received corticosteroids or anti-VEGF drugs.2 It is unclear whether choroidal thickness may also be a marker of macular degeneration progression; OCT can help monitor any changes in choroidal thickness if such monitoring is necessary.2

What can you do?

Talk with your doctor about whether they use OCT as part of their regular comprehensive dilated eye exam, and whether they use OCT in macular degeneration management. If not, some doctors choose to use other retinal imaging tools in order to monitor both your macular degeneration and response to treatment. It’s worth discussing with your doctor how your response to the prescribed treatment course is monitored and evaluated so that you know whether your treatment is appropriate and beneficial.

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