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Optical coherence tomography (OCT) is a non-invasive imaging test. OCT uses light waves to take cross-section pictures of the retina. Compared to fundus photographs which captures a 2D image of the top layer of the retina, OCT captures a 3D depth-scan of the retina (similarly to an ultrasound).

With OCT, it's possible to distinguish each of the retina’s distinctive layers. This enables an eye care specialist to map and measure each layer's thickness. Anomalies in the thickness of each layer can be used to identify/diagnose diseases and also provide treatment guidance for retinal diseases.

Types of OCT

There are several types of OCT, the most common being Spectral Domain (SD-OCT), Swept Source (SS-OCT) and the newer Angiography (OCT-A). While SD-OCT and SS-OCT focus both focus on providing structural analysis of the layers of the retina, SS-OCT generally provides faster acquisition times and deeper tissue penetration.

OCT-A is used mainly to generate non-invasive non-dye based angiography (analysis of the microvasculature of the retina and the choroid). The technology compares multiple B-scans (from SD-OCT as well as SS-OCT) to detect motion in the vessels. The remainder of this article focuses on SD-OCT and SS-OCT.

Uses of OCT

OCT is used in many fields of medicine, but there are 3 main uses in the field of Ophthalmology specifically:

• Posterior Segment/Retina/Macula

  To detect retinal diseases and conditions including macula holes and retinal detachments

• Optic nerve

  To detect glaucoma and neuritis

• Anterior segment, referred to as ASOCT

  To detect glaucoma in combination with or as a substitute for gonioscopy

Examples of Posterior segment OCT scans

Example of a healthy patient (macula area)

All retinal layers are "flat" with normal thickness and no immediate holes, detachments or lumps due to liquid build-up.

Example of Central Serous Chorioretinopathy (macula area)

Central serous chorioretinopathy, commonly referred to as CSC, is a condition in which fluid accumulates under the retina, causing a serous (fluid-filled) detachment and vision loss.

Example of Diabetic Retinopathy (DR) with DME

Diabetic retinopathy causes damage to the retina, specifically to the blood vessels. The OCT scan below shows these damaged or abnormal blood vessels.

Example of Dry Age-related Macular Degeneration (Dry AMD)

Age-related macular degeneration (AMD) is a disease OCT-scans can help diagnose, often much earlier than fundus imaging. AMD affects the macula, which is the central part of the retina. Signs of advanced dry AMD like drusen (tiny lumps of protein) are present in the scan below.

Example of Wet Age-related Macular Degeneration (Wet AMD)

In the below scan, signs of advanced wet AMD such as abnormal blood vessels and bleeding are present.