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What is Optical Coherence Tomography (OCT)?

A young woman having her eye examined through OCT

During a comprehensive eye exam, your vision is not the only thing tested, an examination of your eye health is needed as well. Your optometrist uses several tools to examine your eyes, and one of these is optical coherence tomography (or OCT). 

If you experience OCT in an exam, you may wonder what exactly this technology is used for, and how does it work? Before your next eye examination, learn more about optical coherence tomography, what it is for, how it works, and the eye conditions it can diagnose. 

What is Optical Coherence Tomography? 

Optical coherence tomography is a technology used for image testing. It captures high-resolution, cross-sectional photos of the back of your eye (or retina). This technology is non-invasive and utilizes a laser to obtain images of the layers of the retina and optic nerve

The layers of the retina can be compared, and retinal thickness can be measured to help identify and diagnose diseases and conditions. Early detection is key in managing many eye conditions and this technology is vital to the process. OCT functions similarly to an ultrasound, though it uses light instead of sound. 

OCT is an effective technology for assessment for several reasons:

  • It is noninvasive 
  • It has no radiation 
  • It is painless 
  • It has minimal health risks

This technology is a useful tool to ensure your ocular health. If your optometrist recommends the use of OCT, how does it work, and what should you expect to happen? 

How Does it Work? 

OCT is an imaging technology similar to ultrasound, but light waves are used instead of sound waves. These light waves reflect off of different depths within the sample and the machine can reconstruct a profile of whatever is being examined. A laterally scanned light beam helps create a three-dimensional image of the eye. 

With this image, your optometrist can see your retina’s different layers, and they can measure the thickness. This helps with diagnosis and treatment planning for different eye conditions

Early detection is critical to treating many eye conditions, and OCT is effectively able to detect conditions usually showing no noticeable symptoms. For this reason, your optometrist may recommend using OCT during your comprehensive eye exam, but what should you expect?

What to expect 

Before your OCT exam, your eye doctor may administer dilating eye drops which make your pupil wider and easier to examine. During your exam, the machine scans your eyes without making contact for approximately five to 10 minutes. You may notice a red line moving across your vision while your eyes are scanned. 

After scanning your eyes and reviewing the results, your optometrist can diagnose any potential eye conditions and recommend a treatment plan.

A young man having OCT used during an eye exam

What Diseases can OCT Diagnose? 

OCT may be used during your annual comprehensive eye exam, or if you are at risk of eye disease due to conditions such as diabetes. Eye examinations can detect more than 200 potential health concerns and optometrists may use multiple eye health tests such as: 

  • Slit-lamp evaluation 
  • Retinal photo screening 
  • Tonometry 

OCT itself can effectively examine the retina, optic nerve, and blood vessels and can identify several different diseases affecting these areas such as: 


Glaucoma is an eye disease with several variations that damage your optic nerve. It is one of the leading causes of blindness and typically presents no symptoms until its advanced stages. Vision loss due to glaucoma is irrecoverable, so regular eye examinations are vital to help ensure your eye health. 

If glaucoma is diagnosed early, treatments can slow or prevent future vision loss. Visit your optometrist if you experience any: 

  • Severe headache
  • Eye pain
  • Blurred vision 
  • Blind spots in your vision 
  • Halos around lights 

Age-related macular degeneration

Age-related macular degeneration (AMD) causes you to lose your central vision while your peripheral vision is unaffected. It is a leading cause of vision loss in people 50+ years of age. There are two variants of AMD: 

Dry AMD occurs when parts of the macula become thinner with age and you slowly begin to lose central vision. Wet AMD happens when abnormal blood vessels grow underneath your retina that may leak fluid or blood and scar the macula. Contact your optometrist if you experience: 

  • Gradual or sudden changes in vision quality 
  • Dark, blurry, or whited-out areas in your central vision
  • Changes in your perception of color
  • Sensitivity to glare
  • Lines that should be straight appearing wavy

Diabetic retinopathy 

Diabetic retinopathy is a complication within the eyes caused by damage to the blood vessels in the retina. This condition may initially present no symptoms and can develop in anyone affected by type 1 or 2 diabetes. Diabetic retinopathy can eventually cause blindness. 

If you have diabetes, you should see your optometrist so they can carefully examine your eyes and ensure they are healthy. You should visit your optometrist right away if your vision suddenly changes or becomes blurry. Other symptoms can include: 

  • Fluctuating vision
  • Impaired color vision
  • Vision loss
  • Spots or floaters in your vision 
  • Dark areas within your vision

Macular edema

Macular edema occurs when fluid accumulates in the macula. This fluid build-up causes swelling and can lead to permanent vision loss without treatment. This condition can be related to diabetic retinopathy due to the blood vessels in the nearby retina being damaged, but any disease affecting the blood vessels in the retina may cause macular edema. 

The primary symptom of this condition is blurry or wavy vision near or in the center of your vision. Some affected by macular edema may have blurry vision to significant vision loss. Colors may look washed-out or faded as well. 

These are just a few samples of the eye conditions and diseases OCT can identify. Many may not initially show significant symptoms, so regular comprehensive eye examinations can help ensure your eye health and vision. 

Ensure a Future of Eye Health

Optical coherence tomography is only one tool in an optometrist’s arsenal. They can identify any potential eye conditions or diseases, and help you treat any problems you encounter. If you are experiencing any eye condition symptoms, or need your regular eye exam, book an appointment

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  • Written by: Bryan MacDonald

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