Optical coherence tomography (OCT) is a non-contact scan that uses reflected light to build cross-sectional images of the back of the eye with a resolution of a few thousandths of a millimetre. Around the optic nerve, it measures the thickness of the retinal nerve fibre layer (RNFL) and, at the macula, the ganglion cell layer.
These layers thin as glaucoma and other optic nerve diseases destroy nerve fibres, often before you notice any loss of vision. OCT does not diagnose glaucoma by itself: it must be read together with eye pressure, the appearance of the optic disc and a visual field test, and its colour-coded comparison with a normal database can mislead in very short-sighted eyes.
What OCT Scan of the Optic Nerve and Retina (RNFL Measurement) shows
The RNFL scan gives average thickness and thickness by quadrant and clock-hour, compared with people of your age and flagged green, yellow or red. Thinning that starts in the lower and upper outer sectors is typical of glaucoma. Repeated scans over time reveal the rate of fibre loss, which is the most useful information for deciding whether treatment is sufficient. The macular scan on the same machine shows fluid, swelling, holes, membranes and the changes of age-related macular degeneration and diabetic macular oedema. OCT angiography, where available, maps retinal blood flow without dye. RNFL measurement also helps in optic neuritis and multiple sclerosis, swollen optic discs and compressive lesions.
When OCT Scan of the Optic Nerve and Retina (RNFL Measurement) is recommended
- People with raised eye pressure or a suspicious optic disc
- Monitoring of established glaucoma, usually once or twice a year
- Close relatives of people with glaucoma, from about age 40
- Blurred or distorted central vision, to look for macular disease
- People with diabetes, before and during treatment for macular oedema
- Follow-up of optic neuritis, multiple sclerosis or raised pressure around the brain
- Users of hydroxychloroquine, as part of retinal toxicity screening
Limits and situations where another test is better:
- Advanced glaucoma, where the RNFL has reached a floor and visual fields track change better
- Dense cataract, corneal scars or a very small pupil that degrade the scan signal
- High myopia and tilted discs, where red flags often reflect anatomy and not disease
- It does not measure eye pressure or the drainage angle; other tests are needed for those
How to prepare
- No preparation is necessary; pupil-dilating drops are sometimes used, so bring sunglasses and avoid driving afterwards
- Remove contact lenses if asked
- Bring earlier OCT printouts or files, ideally from the same make of machine, so that change can be judged
What happens during the test
You rest your chin on a support and look at a small target inside the instrument while it scans each eye for a few seconds. Nothing touches the eye, there is no flash of any strength, and no discomfort. With both eyes and both scan types, the test takes 5 to 10 minutes. If drops are used, near vision is blurred for 2 to 4 hours.
Results and next steps
Images are available immediately and the ophthalmologist usually explains them at the same visit. A normal scan with normal pressure is reassuring. A borderline result leads to a visual field test and a repeat scan in 6 to 12 months to look for change. Confirmed progressive thinning prompts starting or stepping up pressure-lowering drops, laser or surgery.
- Test time: 5 to 10 minutes
- Results ready: Immediately
- Back to everyday activity: None, or 2 to 4 hours of blur if drops are used
Safety and risks
- None from the scan itself, which uses harmless low-power light
- Temporary blur and glare if dilating drops are used, and rarely a pressure rise in eyes with narrow angles
- Overdiagnosis from false red flags, or false reassurance from a normal scan in early disease
Arranging OCT Scan of the Optic Nerve and Retina (RNFL Measurement) in Türkiye
An OCT is part of any thorough eye examination and takes minutes, so it is a natural addition when you are in Istanbul for cataract, laser vision or retinal care, or for a general check-up. Glaucoma monitoring depends on comparing scans on the same device year after year, so long-term follow-up is best kept with one clinic near home; ask for your scan files to take with you.
Send your previous reports and the question you want answered and a Clinic-Y coordinator replies within 24 hours with suitable teams and written, all-inclusive proposals side by side. Reviewing your case is free.
Frequently Asked Questions
My scan shows red areas. Do I have glaucoma?
Not necessarily. Red means thinner than most people of your age in the reference group. Short-sightedness, disc shape and scan quality commonly cause this. The pattern and change over time matter.
How often should it be repeated?
Every 6 to 12 months in glaucoma or suspects; more often in the first 2 years to establish your rate of change.
Is OCT the same as an eye angiogram?
No. Standard OCT shows structure. Fluorescein angiography uses injected dye to show leakage. OCT angiography is a dye-free method that shows vessels but not leakage.