Optical Coherence Tomography

Optical coherence tomography (OCT)

Optical Coherence Tomography (OCT) uses a non-invasive safe beam of light with special processing to look at the structures within the retina in very high detail. The anatomic features visible with OCT are much more detailed than that seen by normal examination. Seeing the retina from this cross sectional viewpoint provides a powerful way to detect, diagnose, and treat retinal and uveal diseases as well as glaucoma.

Indications:

Some of the indications for this test include:
- Diabetic macular oedema
- Macular oedema secondary to retinal vein occlusions
- Cystoid macular oedema secondary to intermediate uveitis
- Central serous retinopathy
- Age related macular degeneration
- Polypoidal choroidal vasculopathy
- Secondary Choroidal neovascular membranes (Idiopathic, myopic, inflammatory)
-Macular holes
- Vitreo-macular tractions
-Diagnosis and follow up of Glaucoma

Preparation:

The only requisites for this test include a well dilated pupil and clear media. Eye drops are applied to the eye prior to the test in order to ensure good dilatation.

Procedure:
After dilatation. Patient is asked to place his /her chin on the chin rest and the images are acquired. Ideally the patient must avoid blinking when the images are being acquired OCT not only helps in diagnosis but also helps to make treatment as well as post treatment decisions.

Diabetic macular oedema:
OCT detects macular oedema (thickening). It measures the thickness which aids in treatment decisions. After treatment, reassessment of thickness also helps in monitoring of the disease. Monitoring the nature of vitreo- retinal interface at macula also helps in deciding the nature of treatment ( medical or surgical)

ARMD:
OCT identifies drusen or neovascular membrane. Likewise pathologies like sub retinal fluid (SRF) and sub retinal haemorrhage can be detected which decide whether treatment has to be initiated or not. Retreatment is also decided based on features like SRF, macular thickening or identification sub retinal haemorrhage.

Retinal vein occlusions:
OCT identifies thickness of macula. Both treatment and retreatment decisions are made based on macula thickness in consonance with visual acuity

OCT scan report

OCT Angiography
What is OCT Angiography (OCTA)? Optical Coherence Tomography Angiography (OCTA) provides three-dimensional (3D) imaging of the anterior segment, retina, and optic nerve head. OCT-A technology uses laser light reflectance of the surface of moving red blood cells to accurately depict vessels through different segmented areas of the eye, thus eliminating the need for intravascular dyes.

Indications:
Used to diagnose and manage retinal diseases which are major causes of blindness such as:

• Diabetic retinopathy
• Age-related macular degeneration (ARMD)
• Retinal artery and retinal vein occlusions
• Glaucoma

Advantages over FFA

• A high-speed device- produces images in 10-15 seconds; FFA takes over 10-15 minutes
• Non-invasive; FFA needs injections
• No dye injected, instead uses motion contrast. Hence no leakage, staining and other side effects such as nausea and severe allergic reactions (anaphylaxis)
• Can acquire different scan sizes in the macula and the optic disc in seconds
• Visualizes both the retinal and choroidal vasculature
• Can be used for routine screening examinations for early diagnosis of vascular abnormalities, and for routine follow-up examinations to evaluate the efficacy of treatments such as intra-vitreal injections.
• Since no dye is injected it is safe for patients with kidney problems, those on dialysis or patients with diabetic nephropathy. With OCT angiography, we now have a noninvasive, safe, and effective tool to visualize the earliest pathological changes in the most common diseases that cause blindness, leading to earlier diagnosis and more successful treatments.

OCT Angiogram