What an OCT retinal scan shows and why it matters

When patients sit down for their eye examination at Cedar Vision Works, the OCT scan is part of the appointment rather than an optional extra. Most people have seen the machine and accepted the scan without quite knowing what it produces. This article explains what the images show, what we are looking for, and what happens if we find something worth investigating.

How the scanner works ¶

OCT stands for optical coherence tomography. The machine directs a beam of near-infrared light at the back of the eye and measures how long it takes to reflect back from different tissue layers. The result is a cross-sectional image of the retina, accurate to a few microns, showing each layer of tissue in a way that a standard fundus photograph cannot.

The scan takes about 90 seconds per eye and requires no contact with the eye surface. Most patients find it straightforward. We ask you to look at a small fixation target while the machine does its work.

What we are looking for ¶

In a routine examination, we are primarily assessing the macular region and the optic nerve head. The macula is the central part of the retina responsible for detailed vision; the optic nerve head is where the nerve fibres leave the eye on their way to the brain.

Small deposits called drusen can accumulate beneath the retinal pigment epithelium in the early stages of age-related macular degeneration. On a standard examination, early drusen are easy to miss. On OCT, they appear as small bumps beneath the retinal surface and can be measured and monitored over time.

At the optic nerve head, we look at the cup-to-disc ratio and the thickness of the nerve fibre layer. Thinning of the nerve fibre layer is one of the earliest detectable signs of glaucoma, often appearing before any change in the visual field.

• Drusen and early macular changes
• Nerve fibre layer thickness
• Epiretinal membranes
• Vitreomacular traction
• Diabetic macular oedema

What happens if we find something ¶

For most patients, the scan is reassuring and the images go into the record as a baseline for future comparison. If we see something that warrants further investigation, we explain what we have found in plain language, what it might mean, and what the next step is.

If a referral to an ophthalmologist is appropriate, we write the letter the same day. We do not send patients away to wait for a GP referral; we write directly to the relevant clinic.

If you have questions about the scan before your appointment, the questions patients ask before booking page covers the most common ones, or you are welcome to call us on +44 1743 556 210.