Suraj Eye Institute · Medical Retina
OCT and OCT-Angiography
EN: The two scans every retina patient gets, explainedहिंदी: ओसीटी और ओसीटी-एंजियोग्राफीमराठी: ओसीटी आणि ओसीटी-अँजिओग्राफी
OCT and OCT-Angiography
OCT (Optical Coherence Tomography) and its newer sibling OCT-Angiography (OCTA) are two of the most powerful tools we have to look at the retina. They are non-contact, painless, dye-free scans — and together they let us see both the structure and the circulation of the retina in seconds. Almost every patient who visits our retina clinic gets at least one of these scans.
What makes OCT special: It works like an “ultrasound with light” — using a beam of safe near-infrared light to create cross-sectional pictures of the retina at a resolution of less than 5 micrometres — the size of a single retinal cell.
What OCT Shows
A standard OCT scan produces two kinds of images:
- A cross-section (“B-scan”) — a slice through the retina, like a CT slice. We can see all the layers separately, measure thickness, and detect fluid, deposits or scars.
- A thickness map (“en-face”) — a colour-coded map of the macula’s thickness, useful for tracking change over time.
An OCT B-scan through the centre of the fovea. The bright orange/yellow bands are hyper-reflective layers (NFL, IPL, OPL, ellipsoid zone, RPE). The dark bands are hypo-reflective (vitreous, INL, ONL). The small central depression — the foveal pit — is where the inner layers thin away, exactly at the point of sharpest vision.
What OCT-Angiography (OCTA) Shows
OCT-Angiography uses the same machine, but a different scanning pattern. By taking multiple scans of the same spot a fraction of a second apart, the computer detects motion — and the only thing that moves inside the retina is blood. The software then maps these moving signals into a picture of the blood vessels — without any dye injection.
- Shows the retinal capillary network in two layers (superficial and deep)
- Shows the choriocapillaris behind the retina
- Detects abnormal new vessels (CNV) without any dye
- Maps the foveal avascular zone (FAZ) — enlarged in diabetic retinopathy
- Identifies areas of poor blood flow in diabetes, vein occlusions, sickle cell disease
OCT vs. OCTA vs. Fluorescein Angiography
| Feature | OCT | OCTA | Fluorescein Angiography (FA) |
|---|---|---|---|
| What it shows | Structure / layers | Blood flow in layers | Blood flow + leakage |
| Dye injection? | No | No | Yes (IV) |
| Time to do | 2–3 minutes | 3–6 seconds per scan | 10–20 minutes |
| Pupil dilation? | Usually not needed | Usually not needed | Needed |
| Safe in pregnancy / dye allergy / kidney disease? | Yes | Yes | Caution |
| Shows leakage? | Indirect (via fluid) | No | Yes (the strength) |
| Frequency of use | Almost every visit | As needed | For specific indications |
What Conditions Are Diagnosed and Followed with OCT/OCTA?
- Diabetic retinopathy and diabetic macular edema
- Age-related macular degeneration (dry and wet)
- Polypoidal choroidal vasculopathy (PCV)
- Retinal vein occlusion (CRVO and BRVO)
- Central serous chorioretinopathy (CSCR)
- Glaucoma — nerve fibre and ganglion cell layer measurements
- Macular hole, epiretinal membrane, vitreomacular traction
- High myopia and myopic CNV
- Choroidal nevus and tumours (selected cases)
- Optic nerve disorders
The Patient Experience
What to expect during the scan
- You sit at the machine and rest your chin on a support.
- You look at a fixation target inside the machine.
- A faint red or green light beam scans your eye for a few seconds.
- The procedure is completely painless.
- Eye drops to dilate the pupil are usually not necessary, though sometimes used.
- Total time at the OCT machine: about 5–10 minutes for both eyes.
Limitations to know about
- OCT cannot see through a dense cataract or severe vitreous haemorrhage.
- OCTA does not show leakage — FA is still needed for some questions.
- Movement during the scan can blur the image; we may repeat it if needed.
- OCTA covers a smaller field of view than ultra-widefield FA.
Why We Use Both OCT and OCTA
Each scan gives information the other cannot:
- OCT tells us where and how much fluid is present, and how the layers are organised.
- OCTA tells us where the abnormal vessels are and where blood flow is poor.
- Together, they give the full picture of a disease in seconds, without any dye injection.
In short: OCT and OCTA are the modern eyes of the retina specialist. Together they let us diagnose, monitor and treat retinal disease earlier and more precisely than ever before — without dye, pain, or risk.
Frequently Asked Questions
Is OCT safe? Can it be done frequently?
Yes. OCT uses very low-power near-infrared light and is completely safe. It can be repeated as often as needed — weekly if necessary.
Do I need eye drops or an injection for OCT?
Usually not. Most OCT and OCTA scans are done without dilating drops and without any injection. We will dilate only if the image is unclear.
Why do I get OCT every visit?
OCT detects fluid and thickness changes before vision changes. By repeating it at each visit, we catch worsening earlier and decide treatment intervals accurately.
Will OCTA replace fluorescein angiography (FA)?
Not entirely. For most macular diagnoses, OCT + OCTA is enough. FA is still needed when leakage information matters or when the disease involves the far peripheral retina or vasculitis.
Can OCT detect glaucoma too?
Yes — the same machine can measure the nerve fibre layer around the optic disc and the ganglion cell layer in the macula, both of which thin in glaucoma.
I have cataract. Will my OCT still be clear?
Mild cataract usually causes no problem. Dense cataract reduces image quality — sometimes the OCT improves dramatically after cataract surgery.
What does it cost?
OCT and OCTA are charged per scan and are routinely covered under most outpatient retinal visits at Suraj Eye Institute. Please ask at the reception for current charges.
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