OCT & OCT Angiography (OCTA)

What is OCT and how does it differ from a standard photograph

OCT uses low-power light (with no ionising radiation) to produce high-resolution cross-sections: the layers of the retina, macular thickness, fluid beneath the retina and lesions not always visible on simple examination can be seen.

With modern devices the test is quick and produces multiple slices, so the macular area or the head of the optic nerve and the surrounding nerve fibre layer can be analysed depending on the plan. Choosing the protocol (e.g. central macula vs a circle around the optic nerve) determines exactly what the test "measures" at each visit.

Digital fundus photography remains valuable for documentation and comparing images over time; OCT complements this with structural information (how "thick" or "thin" a spot is, whether there is oedema or changes in the layers). As part of a comprehensive eye examination, combining clinical examination and imaging helps clear questions to be asked before deciding on monitoring or further tests.

What OCT angiography (OCTA) offers

OCTA reproduces, without a dye injection, an image of the vascular architecture in the macula and elsewhere, revealing, for example, areas of reduced perfusion or abnormal vessel networks in selected conditions. It does not always replace classic fluorescein angiography (FA), which remains useful when a dynamic study of leakage and a time sequence of filling is needed; the choice of one method, the other, or both, is made case by case.

In conditions such as age-related macular degeneration or diabetic retinopathy, OCT and OCTA are often combined with the clinical picture and, where indicated, intravitreal treatments; repeat testing helps show whether the condition is stable or progressing.

Indications: macula, retina, optic nerve

In the context of retina and macula diseases, OCT is used to measure macular thickness, detect fluid or changes in the layers, and to monitor before or after treatment. OCTA can contribute to assessment of vascular patterns when clinically indicated.

In glaucoma, analysis of the nerve fibre layer (RNFL) with OCT complements clinical examination and visual fields / OCT RNFL; structural and functional information are combined to detect progression early, before central vision is significantly affected.

• Structural imaging of the macula and peripheral retina
• Monitoring oedema or lesions after treatment
• RNFL and disc analysis for glaucoma (combined with other tests)
• OCTA for a dye-free vascular picture, when indicated

The pace of re-examination is individualised; comparing tests on different dates is often more informative than a single measurement.

Image quality, limitations and common questions

OCT image quality depends on stability during the scan, the clarity of the optical media (e.g. significant cataract haze reduces the signal), and the device protocol. This is why the same test is repeated when comparison with previous series is needed, rather than for "absolute" values without clinical context — interpretation is always combined with the slit-lamp examination and history.

OCT depicts structure and thickness, not always visual field function; in glaucoma, for example, it does not replace perimetry but complements visual fields. OCTA can show motion artefacts or shadows; when the image does not match the clinical picture, complementary tests such as fluorescein angiography or repetition after dilation are discussed, at clinical discretion.

Long-term monitoring of AMD or diabetic retinopathy is often based on regular intervals set by the ophthalmologist, based on risk, response to treatment and current guidelines. Archiving digital results helps compare older and newer scans and reduces uncertainty when symptoms persist without an obvious change in central vision.

Safety, duration and what to expect

OCT is usually quick, with no contact with the eye; dilation may be required in some protocols to fully image the periphery, and instructions are given by the examiner. OCTA also uses no intravenous dye, which matters for patients with allergies or difficult IV access, although it does not eliminate every need for FA when this is judged necessary.

Interpretation of the images is carried out by the ophthalmologist; the results are discussed in the context of your history, vision and goals (e.g. driving, screen work), and where needed combined with refraction and glasses.

For an overview of all tests and services: services; for appointments: contact.