What’s this test? Optical coherence tomography (OCT)

An OCT is a non-invasive imaging device that uses light waves to examine each layer of the eye. It provides high-resolution images of the retina and optic nerve and measures each layer’s thickness so optometrists can detect and track the progression of diseases such as glaucoma, macular degeneration and diabetic retinopathy.

Though mainly used to look at the layers of the retina and the optic nerve at the back of the eye, some OCTs can also examine the front of the eye. 

An optometrist may request OCT imaging if a patient has, or is suspected of having, a retinal disease or condition, like diabetic retinopathy or macular degeneration, or an optic nerve disease like glaucoma.  

Patients may also be recommended for an OCT scan if they are experiencing vision problems and the cause cannot be determined through a routine eye exam. 

Using an OCT scan, optometrists can assess the health of the optic nerve and track early thinning in that area. These changes are hard to detect in a traditional eye exam, so the OCT enables early identification and treatment of vision- threatening diseases.  

Early damage to the retina and optic nerve may cause no symptoms, or only subtle symptoms that are hard to self-detect, which is why it’s important to get comprehensive eye exams and recommended tests before vision loss occurs.  

OCT imaging is non-invasive. Patients are asked to sit in front of an instrument with a small camera. With your face comfortably positioned against a chin and forehead rest, you will be asked to look into the camera with your right or left eye.  

You will be asked to sit still and look directly into the camera. You can usually blink throughout the test, although you may be asked to look into the camera without blinking for a couple seconds. There is no flash of light, but there may be a moving target. In this case, you will be asked to focus on the target. The target will not touch the eyes and there is no pain associated with the test. The camera will move around your eye to take detailed pictures of the retina and optic nerve. 

There will likely be a screen in front of the optometrist or technician that shows images of the back of your eye while the test is happening.  

The scan usually takes about five minutes per eye, but additional time will be needed to set up, switch eyes, etc.

There is little to no preparation required for OCT imaging. If you wear glasses and/or contacts, please bring them in. If you wear contacts, please note that you may need to remove them for the scan. It is best to wear glasses and simply take them off before OCT imaging.  

Typically, an OCT scan does not require patients’ eyes to be dilated. However, the optometrist or imaging technician may put dilating drops in your eyes if a special filter needs to be applied to the camera to image a deep layer of the retina. If dilation is required, you will receive advance notice. If you are doing OCT imaging shortly after a dilated eye exam, don’t worry – the scan can still be completed. The dilation won’t interfere with the procedure, and the results will still be accurate.  

Unless you are asked to follow a target, the most important part of the test is that you stay very still so the clinician can take clear pictures. Any unwanted movement from the patient could blur the images.  

Your optometrist will review the imaging results and then go over them with you, usually at a later appointment date. The optometrist will discuss a treatment or management plan with you. 

Depending on the reason that the optometrist has ordered the OCT, you may be scheduled for repeat testing to monitor for changes to your condition. If you have a condition where vision loss cannot be reversed, repeat testing will determine if vision loss is stable or worsening. 

Optical coherence tomography imaging is done at the Waterloo clinic, located (until the permanent location reopens) at Unit C, 419 Phillip St., Waterloo. Learn more about the construction and interim clinic location.

OCT imaging is done by our Imaging Service, so you will typically need to book separate appointments for the scan and for consultation with the optometrist. OCT imaging is done by our Imaging Service, so you will typically need to book separate appointments for the scan and for consultation with the optometrist.

OCT imaging isn’t a standard part of a comprehensive eye exam, so there is a separate fee. As of 2025, this imaging has an additional cost of $75. OHIP may cover the cost of OCT imaging for patients with conditions such as glaucoma, macular degeneration or other conditions that affect vision. Some private insurance plans may also cover the cost of testing.

If you need multiple tests – i.e. an OCT scan and a visual field test– it is usually possible to book these back to back. For example, the OCT scan might take 15 minutes, and the visual field test might take 15 minutes, with both taking place during one 30-minute appointment.

• What you should know about: Glaucoma
• What you should know about: Macular degeneration
• What you should know about: Diabetic eye disease
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Reviewed by Dr. Sarah MacIver, BSc, OD, FAAO