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What Does an Ocular Coherence Tomography (OCT) Exam Show?

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a woman has an ocular coherence tomography done at her optometrist

Technology-Driven Eye Care

Consistent eye exams can help prevent vision problems and protect your eye health. You might encounter many types of diagnostic tools or tests during your optometry visit. Some are as simple as the classic cover tests or technology-driven as ocular coherence tomography (OCT).

OCT is a standard diagnostic test used during routine eye exams. But what can you expect during an OCT exam, and what does it show?

What Is an OCT Exam?

Optical coherence tomography (OCT) is a noninvasive scan used for retinal imaging. OCT uses light waves to create 3D color-coded cross-sectional images. The detailed scan can help eye doctors with the early detection or treatment of ocular disease.

Monitoring changes to eye structures is essential to protecting eye health, as some conditions can develop without noticeable symptoms. With OCT, optometrists look deeper at tissue as the light waves can map layers and measure the thickness.

OCT can help diagnose and treat multiple eye problems, particularly conditions or diseases affecting the retina and optic nerve. However, some eye conditions can interfere with how light waves pass through the eye, such as dense cataracts or bleeding in the vitreous humor.

What Conditions Can OCT Detect?

OCT allows eye doctors to monitor changes to tissue at the back of the eye, particularly the retina and optic nerve. OCT can help diagnose various eye conditions, including:


Glaucoma causes progressive damage to the optic nerve, eventually leading to blindness. As the disease often develops slowly, patients may not notice symptoms until some vision is lost.

The signs or symptoms depend on the type:

  • Primary open-angle glaucoma often develops slowly and painlessly, gradually destroying vision with no early warning signs. Over time, changes to the eye’s drainage angle lead to fluid buildup, and eye pressure increases.
  • Acute angle-closure glaucoma results from a sudden blockage of the eye’s drainage channels, causing a rapid pressure buildup. It can cause blurry vision, halos around lights, pain, and eye redness.

Non-contact tonometry and applanation tonometry are common in glaucoma testing as tonometry can measure intraocular pressure (IOP). However, in some forms of glaucoma, optic nerve damage occurs without increased eye pressure. Therefore, OCT testing evaluates changes to the optic nerve to help detect rarer forms of glaucoma.

Diabetic Eye Disease

Diabetes affects the body’s ability to control blood sugar (glucose) levels. Too much sugar in the blood can damage tissue and blood vessels, including the small blood vessels in the eye.

Diabetic eye disease is a general term for eye conditions occurring due to diabetes and typically includes:

  • Cataracts: excess blood sugar contributes to the clouding of the eye’s lens. Maintaining blood sugar levels can prevent worsening vision and the need for cataract surgery
  • Diabetic macular edema: high sugar levels damage blood vessels in the retina (macula). The blood vessels leak, and fluid builds. The buildup leads to swelling and vision problems, including permanent vision loss.
  • Diabetic retinopathy: abnormal blood vessel growth or blood vessels weakened by high blood sugar damage the retina and cause vision problems.
  • Glaucoma: weakened or abnormal blood vessels can block the eye’s drainage system, resulting in increased intraocular pressure (IOP). Diabetes doubles the chance of developing glaucoma.

Macular Degeneration

Age-related macular degeneration (AMD) is the leading cause of severe vision loss in adults over 50. The disease affects the macula, the oval-shaped center layer of the retina.

When the macula deteriorates, it can cause:

  • Distorted shapes
  • Central vision loss
  • Poor color vision

Macular degeneration has 2 forms: 

  • Dry (atrophic): the macula thins and develops tiny protein clumps (drusen). Dry AMD is the most common form and usually develops slowly. Currently, no treatment is available for dry AMD. Still, eye nutrition, UV light protection, and healthy lifestyle habits can reduce risks.
  • Wet (exudative): abnormal blood vessels (growing under the retina) leak and cause macula scarring. Wet AMD is less common but can cause faster vision loss. Wet AMD may be treated with anti-VEGF intraocular injections or laser surgery.

What to Expect During an OCT Exam

The patient is asked to focus on a green light or target during an ocular coherence tomography exam. The process takes a few minutes, and the patient is seated with their chin resting on a support. Patients are instructed to keep their eyes open when the OCT scanner activates. Patients may notice red lines or light moving across their vision.

Each eye is done separately, so take a few good blinks in between (or when instructed to) to keep your eyes fresh for each scan.

How Often Should You Schedule OCT?

An OCT exam is often part of a routine comprehensive eye exam. The recommended eye exam frequency for adults is every 2 years and annually for children ages 6–17. However, how often you should schedule an eye or an OCT exam depends on your unique eye health and risk factors.

Your eye doctor is more likely to recommend an OCT exam if you’re over 25 or at risk of ocular disease.

a woman sits with her optometrist discussing the results of an oct exam

Protect Your Vision with OCT

A detailed, in-depth look at eye health helps your eye care team offer the best possible care and treatment recommendations. An OCT exam is one type of assessment that can help monitor changes over time. Therefore, it’s crucial to book routine eye exams, so your eye care provider can personalize your care based on your long-term eye health and vision needs.

EyeZone Nevada is committed to setting the bar for comprehensive and custom eye care services. Please contact us today to see the difference with our quality eye care.

Written by Daniel Rowan

Reno optometrist, Dr. Daniel Rowan, was raised in Western Canada and attended Norwich University in Vermont on a hockey scholarship. After obtaining a Bachelor of Science degree in both biology and sports medicine, he received his Doctor of Optometry (OD) degree from the New York College of Optometry in 2001. He performed rotations in a Queens VA hospital, specializing in glaucoma care, and an outpatient eye clinic in the Bronx. Immediately after graduating, he moved to Nevada and is now considered a top Reno optometrist. He is a member of the American Optometric Association and is board-certified by the National Board of Examiners in Optometry for the treatment and management of ocular diseases.
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