How OCT works
The instrument sends a beam of near-infrared light into the eye and measures the light reflected from each depth of tissue, using interference to resolve reflections separated by microns. Scanning the beam across the tissue builds a cross-sectional image, and stacking those builds a three-dimensional map. Nothing touches the eye; you rest your chin on the instrument and look at a target for a few seconds. Most retinal scans work through an undilated pupil.
What it shows in the retina
The ten layers of the retina, individually. Fluid within or beneath the retina, as in macular edema or wet macular degeneration. Drusen and thinning in dry macular degeneration. Holes, membranes and traction at the macula. Swelling of the optic nerve. Retinal thickness measured to the micron and compared with previous scans, which is how treatment of macular disease is guided visit by visit.
What it shows for glaucoma
The thickness of the retinal nerve fiber layer around the optic nerve and of the ganglion cell layer at the macula, the tissues glaucoma destroys, compared with a normal database and tracked over time. OCT can detect glaucoma damage before field loss appears and is a key monitor of progression, alongside visual fields.
What it shows at the front of the eye
Anterior segment OCT images the cornea's layers and thickness, the depth of a scar, the fit of a scleral lens over the cornea, the LASIK flap, the drainage angle in glaucoma, and the position of a lens implant. It is used in the planning of corneal and refractive surgery and in the fitting of specialty lenses.
When it is ordered
At the diagnosis and every monitoring visit of macular degeneration, diabetic eye disease, vein occlusion and glaucoma; before cataract and lens surgery, to check the macula and set expectations for premium lenses; before and after retinal treatment; in the assessment of unexplained blurred vision; and in corneal and specialty lens work. It is usually billed to medical insurance when ordered for a medical reason; our team confirms your coverage.
Is this right for your eyes?
Nothing on this page is a diagnosis. Whether this is the right choice for you is decided by a full examination at one of our 4 offices: Pasadena, Huntington Beach, Woodland Hills and Beverly Hills.
About this content: This page was written with the assistance of AI tools and reviewed for medical accuracy by Dr. Bavand Youssefzadeh, DO. It is general information, not medical advice, and does not replace an eye examination. Individual results vary. Read our medical disclaimer.
