Ophthalmic OCT
Optical Coherence Tomography — non-X-ray imaging using infrared interferometry. OCT is to ophthalmology what MRI is to neurology: a cross-sectional imaging modality that revealed retinal anatomy at micrometer scale and transformed clinical decision-making. Now a standard-of-care exam in every ophthalmology practice managing retinal disease, glaucoma, or anterior-segment anatomy.
Physics
Optical version of ultrasound. Broadband near-infrared light split into sample + reference arms; interferometry measures the phase / amplitude of light reflected at different depths in tissue. Resolves structure at ~5–10 μm axially.
Three generations:
- Time-domain OCT (legacy) — sequential depth sampling, slow
- Spectral-domain OCT (SD-OCT) — full depth profile simultaneously via spectrometer. ~50x faster than TD-OCT, standard since mid-2000s.
- Swept-source OCT (SS-OCT) — tunable laser swept across wavelengths. Faster still, deeper penetration, better choroidal imaging.
Clinical applications
- Retinal disease — age-related macular degeneration (wet + dry), diabetic retinopathy + macular edema, retinal vein occlusion, macular hole, epiretinal membrane. OCT guides anti-VEGF injection decisions.
- Glaucoma — retinal nerve fiber layer + optic disc assessment. Progression tracking over years.
- Anterior segment OCT — cornea, angle, anterior chamber. Pre-operative cataract + corneal surgery planning.
- OCT angiography (OCT-A) — dye-free vascular imaging. Detects choroidal neovascularization, capillary dropout in diabetic retinopathy.
Clinical adoption
OCT is probably the single biggest technology shift in ophthalmology of the past 25 years. Virtually every retina specialist + glaucoma specialist + many general ophthalmologists + optometrists own one. Market is huge + mature.
Key specs
- Axial resolution — 4–10 μm
- Scan rate — 50,000 to 400,000 A-scans/sec (SS-OCT at top end)
- Depth penetration — ~2–3 mm (retina); more for SS-OCT
- Wavelength — 840 nm (SD-OCT typical), 1050 nm (SS-OCT)
- OCT-A — angiography module (licensed feature on most platforms)
Systems
- Zeiss Cirrus OCT — category-dominant
- Heidelberg Spectralis — research-tier, cSLO + OCT hybrid
- Optovue Solix / Angiovue / Avanti (recently acquired by Visionix)
- Topcon Triton / Maestro
- Nidek RS-3000
- Canon Xephilio (rebrand of Optopol)
Regulatory
- FDA Class II (510(k))
- No state radiation registration (OCT uses infrared, not X-rays)
- ACR / AAO accreditation not generally required for reimbursement
- HIPAA for image storage (workstation + cloud)