Most of the eye conditions that take sight away don’t announce themselves. Glaucoma erodes peripheral vision so gradually that the brain papers over the gaps and people often reach the point of real nerve damage while still reading the bottom line of the chart without trouble. Early macular degeneration can sit quietly beneath the retina for a year or more before the first straight line starts to look bent. Swelling at the centre of the retina from diabetes doesn’t hurt.
That is the uncomfortable gap in a routine sight test. Your vision can feel completely normal while the retina is already changing.
For a long time, the best an optometrist could do was look at the retina from the outside, through a lens at the slit lamp or on a colour photograph. Useful, but it flattens everything. The retina is about a quarter of a millimetre thick and built from roughly ten layers stacked on top of one another like sheets of paper. A photograph shows you the top sheet.
The Topcon Maestro2 looks through the stack.
Why a retinal photograph only tells half the story
Picture the retina as a lawn. A retinal photograph is the aerial shot. You can see the colour and the bare patches and anything lying on the surface. What you cannot see is the soil underneath: whether the roots are thinning, or whether water has started pooling below them.
Almost everything that matters happens down there. Glaucoma thins the nerve fibre layer and the ganglion cells that feed it. Wet macular degeneration pushes fluid in between the layers. Diabetic maculopathy fills the retina with pockets of fluid, a bit like a sponge. A fine membrane can grow across the surface and wrinkle everything beneath it. On a colour photo, most of this shows up late, faintly, or not at all.
OCT stands for optical coherence tomography. It sends a beam of near infrared light into the eye and measures how that light reflects back off each layer. From those reflections it reconstructs a cross section, so instead of looking down at the retina, your optometrist is looking through a slice of it. The detail is measured in microns: fine enough to pick out individual layers, and fine enough to notice that one of them has lost thickness since your last visit.
What the Maestro2 does differently
A colour photograph and a cross section from the same sitting
The Maestro2 pairs a true colour retinal camera with a spectral domain OCT scanner in a single unit. It captures both in one go and registers them against each other, so a suspicious patch on the photograph can be traced straight down into the layers below it.
That link does a lot of work. Plenty of things look alarming on a retinal photo and turn out to be nothing much, like an old pigment spot or a benign freckle at the back of the eye. The scan settles the question instead of leaving it hanging until next year.
One wide capture that includes the macula and the optic nerve
Older scanners tended to want one scan of the macula and a separate one of the optic nerve head. The Maestro2 takes a wide scan that covers both areas in a single sweep.
That saves a minute or two, which is the least interesting part of it. The more useful point is that glaucoma damage and macular disease live in different parts of the retina, and a capture that includes both leaves less room for a problem to sit just outside the frame.
Numbers, not only pictures
The software measures the thickness of the nerve fibre layer around your optic nerve and the ganglion cell layer at the centre of your retina, then compares those figures with what would be expected for someone your age. Anything falling outside the expected range gets flagged in colour on the report.
This gives your optometrist something objective to weigh alongside clinical judgement. It is one thing to say a disc looks a little unusual. It is another to see that the tissue around it measures thinner than it should on one side only.
What the scan is actually like
Dull, in the best possible sense.
You sit down, rest your chin, and look at a target inside the machine. The Maestro2 finds your eye, focuses, and captures on its own. Nothing touches your eye. There is no puff of air. Each eye takes a few seconds, and most people need no dilating drops at all. The colour photograph uses a brief flash, which can leave a purple blob drifting across your vision for half a minute afterwards, and that is about the worst of it.
Two honest caveats. If your pupil is very small, or a cataract is dense enough to scatter the light, image quality drops and your optometrist may want to use drops to get a clean result. Eyes that drift or move a lot can blur a scan too, though the capture is quick enough that this rarely spoils it.
What your optometrist is looking for in the images
- Thinning of the nerve fibre layer, which is the earliest fingerprint of glaucoma. It shows on OCT long before you would notice a gap in your vision, and usually before a visual field test detects anything. That head start is the strongest single argument for having the scan at all.
- Drusen deposits sitting beneath the retina, along with the outer layer thinning of dry macular degeneration and the fluid or new vessel activity that marks the wet form.
- Swelling at the macula from diabetes, which is the most common reason diabetes affects reading vision. The scan measures the swelling rather than estimating it by eye.
- A membrane wrinkling the retinal surface, a hole opening at the centre, or the vitreous gel tugging on the retina as it separates. These often explain distortion in an eye that looks close to normal in a photo.
- Central serous retinopathy, a blister of fluid under the retina, seen most often in men in their thirties and forties and frequently after a stressful few months.
- Optic discs that just look unusual. Some people are born with crowded, tilted or naturally large cupped discs. Separating that from genuine damage is one of the harder calls in a sight test, and the scan usually answers it in seconds.
The scan you have today is really for you in five years’ time
One OCT is a snapshot. It tells you what is there now. What it cannot tell you is what has changed, and change is where most of the useful information hides.
Retinas vary enormously between people. A nerve fibre layer that measures on the thin side of average may be entirely healthy for that person and always has been. The only way to know is to have measured it before.
Here is a situation that plays out constantly. Someone in their fifties has naturally large optic cups. Every new optometrist who examines them looks twice, mentions glaucoma, and eventually refers them. They go through a round of hospital tests, get told all is well, and the same conversation starts again three years later at a different practice. With a baseline scan on file and a few annual repeats showing no movement, that loop disappears.
The reverse case is more important. A scan can come back marked as within normal limits and still be a warning, if it has lost measurable thickness since the last one. Normal for the population is not the same as normal for you, and that comparison only exists if there is an earlier scan to hold it against.
How the scan changes what happens next
Referral is where OCT earns its keep in the UK. Hospital eye clinics are stretched, and a share of the people sitting in glaucoma waiting rooms are there because a disc looked suspicious and nobody could be certain either way. Every one of those appointments takes a slot that someone with active disease needs.
A scan lets your optometrist filter. Some people who would have been referred can be watched in practice instead, with images on file to compare next year. And the people who do need the hospital get there sooner, with their scans travelling alongside the referral, so the clinic begins from something more solid than a few lines on a form.
Wet macular degeneration is the clearest example of why speed counts. Once abnormal vessels start leaking under the centre of the retina, treatment works best when it starts early. Waiting until you notice the distortion, then waiting for an appointment, then waiting for imaging, costs weeks. Finding the fluid at a routine check, before you have noticed anything is wrong, removes that delay.
Who gets the most out of it
- Anyone over 40, since the risk of both glaucoma and macular disease climbs from that point.
- Anyone with a parent or sibling who has glaucoma. Family history raises your risk considerably and lowers the age at which it is worth watching closely.
- People with diabetes. This sits alongside NHS retinal screening rather than replacing it, and it is better at catching swelling at the macula.
- Strongly short sighted people. Myopic eyes carry a higher risk of glaucoma and retinal problems, and their optic discs are notoriously hard to interpret by eye alone.
- Anyone taking a long term medication that calls for retinal monitoring, such as hydroxychloroquine.
- Anyone who has noticed distortion, a smudge or a grey patch in their central vision. That deserves an appointment quickly rather than at the next routine check.
What the scan will not do
Worth being clear about the limits, because OCT sometimes gets described as though it were a full survey of the eye.
It does not measure how well you see, your eye pressure, or your spectacle prescription. It gives only a limited view of the far edges of the retina, where tears tend to happen, so it does not replace a proper dilated examination if you have flashing lights or a sudden shower of new floaters. And it diagnoses nothing on its own. It produces evidence. The person reading it decides what that evidence means in the context of everything else in your examination.
A clear scan today also says nothing about your scan in two years. That is not a flaw in the technology. It is the entire reason for repeating it.
Where this leaves you
The Maestro2 does not change what your optometrist is looking for. It changes when they can find it. A photograph shows the surface of your retina today. The OCT shows what the layers underneath are doing, and once there is more than one scan on file, what they have been doing over time.
That matters most for the slow, painless conditions, because with those, early detection is the whole game. Sight lost to glaucoma does not come back. What you protect is what you still have.
OCT has moved from hospital departments onto the high street in about fifteen years, and it is turning into the normal standard for a thorough eye examination rather than a luxury bolted onto one. The patients who get the most from it are the ones whose first scan was taken years before anything went wrong, sitting in a file, waiting for something to be measured against. So if you are booking a sight test, ask two things: whether the practice has an OCT, and whether your images will be kept for comparison. People remember to ask the first one.
Frequently asked questions
Does the scan hurt, and will I need eye drops?
No. Nothing touches your eye and there is no puff of air. You rest your chin, look at a target, and the machine does the work in a few seconds per eye. Most people need no drops. If your pupil is unusually small or a cataract is scattering the light, your optometrist may suggest drops to get a clearer image. The light used is low powered and safe to repeat, including in pregnancy.
How is this different from the retinal photograph I have had before?
The photograph shows the surface of the retina in colour. The OCT shows a cross section through it and measures the thickness of each layer. Fluid swelling and nerve thinning all happen below the surface which is why they can be well established before a photo shows anything at all.
How often should I have an OCT scan?
For most adults, at each routine sight test, so every one to two years. More often if you are being monitored for glaucoma, macular changes or diabetes. A single scan is useful. A series of them is far more useful, because a series shows movement.
Is OCT included in an NHS sight test?
No. The NHS sight test does not cover it, so practices offer it as an addition, usually for a fee. Hospital eye clinics use OCT routinely once you have been referred. Ask your practice what they charge and whether it is bundled into a private examination.
What happens if the scan finds something?
It depends what it finds. Some things are stable and simply get noted and rescanned next time. Some need checking again at shorter intervals. Anything that looks active, such as fluid at the macula or nerve fibre loss that is progressing, gets referred, and your images travel with the referral so the hospital is not starting from a blank page. Being told something has appeared on a scan is not the same as being told you are losing your sight. Far more often it means someone has found it early enough to do something about it.
