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An OCT scan takes a detailed, cross-sectional image of the back of your eye, showing the layers of the retina and the optic nerve. It can pick up early signs of glaucoma, macular degeneration and diabetic eye disease, often before you notice any change in your vision.
OCT stands for optical coherence tomography. It uses light, not X-rays, to build a cross-sectional image of the back of your eye, a bit like an ultrasound uses sound. Each scan shows the separate layers of the retina and the nerve fibres around the optic nerve, measured in thousandths of a millimetre.
You sit with your chin on a rest and look at a target for a few seconds while the machine scans. There is no puff of air, nothing touches your eye, and you usually don’t need drops.
In a standard eye test I look at the surface of your retina, and a retinal photograph records that surface. OCT shows what is happening underneath: thinning of the nerve fibre layer, swelling, fluid or small deposits that may not be visible from the surface yet.
Just as important, every scan is stored. Next time, the machine compares the new scan with the old one, so even a very small change shows up.
Glaucoma gradually damages the optic nerve, usually without symptoms until a lot of sight has been lost. OCT measures the nerve fibre layer around the optic nerve and can show thinning years before you would notice a change. If glaucoma runs in your family, read glaucoma, family history and what an OCT scan actually shows.
Age-related macular degeneration affects your central vision, the part you use for reading and recognising faces. OCT can show early deposits called drusen, and fluid under the retina that can be a sign of the “wet” form, which needs urgent treatment. Here are the early signs of macular degeneration.
Diabetes can cause swelling at the centre of the retina, called diabetic macular oedema. OCT is very good at showing this, sometimes before it affects your vision.
OCT also helps detect and monitor macular holes, scar tissue on the retina (epiretinal membranes) and pulling on the retina from the gel inside the eye. It is useful for people with high short-sightedness, whose retinas are more prone to these changes.
Test | What it shows | What it can’t show |
Standard eye examination | Your prescription, eye health, how your eyes work together | Detail beneath the surface of the retina |
Retinal photograph | A colour image of the retina’s surface, kept for comparison | Thinning, swelling or fluid in the deeper layers |
Visual field test | Whether you have gaps in your side vision | Early structural damage before sight is affected |
OCT scan | Cross-sections of the retina and optic nerve, measured precisely | Your prescription, or how well you actually see |
The tests work together. OCT doesn’t replace a full eye examination; it adds detail to it.
At Mosspark, OCT is part of our 45-minute eye examination, so you don’t have to decide on the day whether to pay extra. Some practices offer it as a separate paid add-on, so if you’re comparing opticians, it’s worth asking.
Is it worth it? For most people over 40, and anyone with the risk factors below, I think it is. A single scan gives a detailed record of your eye health today. If something changes in five years’ time, that record is what lets us spot it early and act quickly.
Some practices charge a separate fee for OCT on top of the eye test. We’ve made it part of our standard 45-minute examination for private patients, because frankly it should be – the information it provides is too clinically important to treat as an optional upgrade. The scan becomes your personal retinal baseline, which means every future visit can be compared against it. Changes that would be invisible on a one-off look become trackable year to year.
If you’ve never had an OCT scan, or you aren’t sure whether your previous eye tests included one, it’s worth having a baseline. NHS eye tests are free in Scotland. Here’s who qualifies for a free eye test.
To book your eye examination with OCT, call Mosspark Opticians on 0141 427 4040, or visit us at 115 Airth Drive, Bellahouston, Glasgow G52 1JU.
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No. It is completely non-invasive. You rest your chin on the machine and look at a target while it scans. Nothing touches your eye, and it takes around 30 seconds per eye.
Usually not. Most OCT scans are taken without dilating drops, so you can drive afterwards. If your optometrist also needs drops to examine the back of your eye, they will tell you beforehand.
For most people over 40, or anyone with risk factors such as a family history of glaucoma, diabetes or high short-sightedness, once a year alongside their eye test is a sensible baseline. If we are monitoring a change, we may suggest scanning more often.
No. A retinal photograph shows the surface of the retina, like a photo of a wall. OCT shows the layers beneath the surface in cross-section, so it can pick up thinning, swelling or fluid that a photograph cannot show.
Yes - OCT measures nerve fibre layer thickness with precision that can detect glaucomatous thinning years before symptoms or visual field loss occur.
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