Macular degeneration
A blurred or dark patch in the centre of vision, more common after 50.
OCT Scan of the Eye
A cross-section of the eye. An OCT scan images the retina and optic nerve at the back of the eye, and the front of the eye too. Nothing touches the eye.
- Senior Consultant Eye Surgeons
- 50+ combined years in ophthalmology
- Seven clinics in six locations islandwide
Camden (Orchard)Joo ChiatClementiBedokToa PayohJurong
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What an OCT scan is
OCT stands for optical coherence tomography. It is a scan that images the eye in cross-section, using light rather than sound or X-rays.
You will also see it written as ocular coherence tomography, and asked for as an OCT eye test, an OCT eye examination or an OCT eye scan. All of those mean this one test. Optical is the correct word, because it is light the scanner works with.
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A beam of light is scanned across the retina
- Why a cross-section. The retina is about a quarter of a millimetre thick, built of layers stacked on top of one another. From the front, through the pupil, they cannot be told apart. The scan cuts through them, the way a slice through a cake shows what a photograph of the icing cannot.
- What is scanned. The macula, the small patch at the centre of the retina you read with; the optic nerve, where the nerve fibres leave the eye; and the front of the eye.
- Following a change. OCT imaging of the retina is also used where something is already known about: the same spot is measured again months later and the two scans put side by side.
Been told you need a scan? Tell our friendly staff what you have been told and they will arrange the right appointment.
Common reasons for an OCT scan
What you may have noticed, and the conditions the scan helps the doctor look at.
Macular hole or membrane
Straight lines look wavy or bent, or print blurs in the middle.
Diabetic eye disease
Swelling at the centre of the retina, which can come with diabetes.
Glaucoma
Raised eye pressure, or an optic nerve that needs a closer look.
Fluid in or under the retina
A dim, blurred or distorted spot in the centre of vision.
Long-term medicines
Some, such as hydroxychloroquine for lupus or arthritis, are checked for their effect on the retina.
If you have a concern, talk to our friendly eye doctors for peace of mind. They will decide whether a scan is needed.
Scanning the macula
The centre of the retina, and the part of it you read with.
A macular OCT, or an OCT scan of the retina, images the layers under the middle of your vision.
- What it shows. Swelling, fluid, and changes in the thickness of those layers. A photograph taken from the front shows none of it, because from the front the retina looks flat.
- When it is used. Where the complaint is about central vision: blur that glasses do not sharpen, straight lines that look bent, a patch missing in the middle of what you see.
- Who reads it. The eye specialist, alongside the rest of the examination.
Wavy straight lines are one of the things the Amsler grid checks before a scan is arranged.
Scanning the optic nerve
Also written as an OCT RNFL scan, after the layer it measures.
The nerve fibres from across the retina leave the eye together at the optic nerve head. The layer they travel in is the retinal nerve fibre layer, RNFL for short.
- What it measures. How thick that layer is around the nerve head.
- How it is read. In glaucoma, the scan is interpreted together with eye pressure readings and a visual field test.
- Why it is repeated. One scan is a measurement. It is the comparison between scans that shows which way things are moving.
- Where it is done. As part of a consultation.
What a reading means, and what is done about it, is set out under glaucoma and high eye pressure.
Scanning the front of the eye
Also written as an anterior segment OCT.
The same scan, aimed at the front of the eye rather than the back.
- What it shows. The cornea, the clear window at the front of the eye, and the drainage angle between the cornea and the iris, where fluid leaves the eye.
- When it is used. Checking how open the drainage angle is, which is part of assessing some kinds of glaucoma, and measuring how thick the cornea is.
- Where it is done. In our general, diabetic retinal and comprehensive screenings, at our community clinics in Bedok, Clementi, Toa Payoh and Jurong.
How an OCT scan works, and how it is done
The scanner shines a beam of low-power light into the eye and measures what comes back from each layer. Light returning from a deeper layer takes fractionally longer to come back, and it is that difference the machine turns into depth.
- You sit at the scanner and rest your chin and forehead against a frame, the same position as the letter chart and the slit lamp.
- You look at a target inside the machine and hold still. Blinking between scans is fine, and you will be told when.
- The scan runs in seconds per eye. Nothing touches the eye, there is no needle and no dye, and the light is bright for a moment rather than uncomfortable.
- The image is ready immediately, so it can be looked at with you in the room rather than sent away.
Drops to widen the pupil are not always needed for an OCT scan. Whether they are used is decided at the visit, and they blur near vision for several hours if they are.
OCT scan or retinal photograph
Both look at the retina. One is flat and one is a cross-section, and that is the whole difference.
| What is compared | Retinal photograph | OCT scan |
|---|---|---|
| What it produces | A flat picture, the way a camera sees the retina. | A cross-section, layer by layer. |
| How it is made | One flash of light through the pupil. | A beam of light scanned across, measuring what each layer reflects back. |
| What it is for | Colour, and the pattern across the whole retina. | Depth and thickness, at the spot being scanned. |
Neither replaces the other, so both are often done at the same visit, and either may be called a retinal scan.
Where to have an OCT scan, and what it costs
Our screening packages carry two kinds of OCT scan, and they scan different ends of the eye.
- Anterior segment OCT. A cross-section scan of the front of the eye. Included in: General · Diabetic retinal · Comprehensive.
- Posterior segment OCT. A cross-section scan of the retina. Included in: Comprehensive.
The screening packages are optometrist-led and every report is reviewed by an ophthalmologist.
| Screening package | OCT included | Price |
|---|---|---|
| General eye screening | Front of the eye | $99 |
| Diabetic retinal screening | Front of the eye | $99 |
| Comprehensive eye screening | Front of the eye and retina | $249 |
Prices shown are for our community clinics at Bedok, Clementi, Toa Payoh and Jurong. All fees shown are nett, and each figure is the price of the whole screening package, not of the scan on its own.
A scan can also be done at a consultation, which is the route for an optic nerve scan and for one repeated over time. No price is published for a scan on its own, so ask our staff when you book.
Common questions
What is an OCT scan?
Optical coherence tomography. A scanner sends a beam of light into the eye and measures what each layer of tissue reflects back, then builds those measurements into a cross-section image of the retina, the optic nerve or the front of the eye. Nothing touches the eye and there is no injection.
Does an OCT scan hurt, and is it safe?
No, and yes. You rest your chin and forehead against a frame and look at a target while the scan runs. The light is bright for a moment, but nothing touches the eye, there is no needle and no dye, and an OCT scan uses light rather than X-rays, so it involves no radiation.
How long does an OCT scan take?
The scan itself takes a matter of seconds for each eye. Allow a few minutes at the machine for being positioned and for the images to be checked before you get up. If dilating drops are used, they add 15 to 30 minutes before the scan while they work.
Can I drive after an OCT scan?
If no dilating drops were used, yes — the scan itself does not change your vision. If your pupils were dilated for it, near vision is blurred and bright light is uncomfortable for several hours afterwards, sometimes longer, so arrange not to drive.
What is the difference between an OCT scan and a retinal photograph?
A retinal photograph is a flat picture of the surface of the retina, the way a camera sees it. An OCT scan images the same tissue in cross-section, so it shows the thickness of each layer rather than the pattern across the whole retina. They answer different questions and are often done at the same visit.
What is an OCT RNFL test?
A scan of the retinal nerve fibre layer, the layer of nerve fibres that gathers at the optic nerve and leaves the eye there. The scan measures how thick that layer is around the nerve head. It is done as part of a consultation, and the reading is read alongside the eye pressure and the visual field rather than on its own.
How much does an OCT scan cost?
No price is published for an OCT scan on its own. At our community clinics in Bedok, Clementi, Toa Payoh and Jurong, a scan of the front of the eye is part of the $99 general and $99 diabetic retinal screenings, and the $249 comprehensive screening adds a scan of the retina. For a scan at a consultation, ask our staff when you book.
Ask about an OCT scan
Send us a message with what you have been told and a time that suits, and our staff will arrange the appointment.
