Optical Coherence Tomography (OCT) is a non-invasive imaging technique that uses low-coherence light and interferometry to produce high-resolution, cross-sectional images of biological tissue. It measures the time delay and intensity of light reflected from internal tissue structures at micrometer-scale resolution, giving clinicians detailed views of retinal, vascular, or dermal layers without contact or contrast agents.
What is Optical Coherence Tomography (OCT)?
OCT sits at the intersection of optics, electronics, and signal-processing software. A broadband or swept-wavelength light source splits into two paths: one aimed at the tissue sample, the other at a reference mirror. Light reflected from both paths recombines at a detector, and the resulting interference pattern encodes the depth and reflectivity of tissue at each scan point. Scanning the beam across a surface builds a cross-sectional or volumetric image, similar in concept to B-mode ultrasound but built from light echoes instead of sound.
Ophthalmology adopted OCT first, imaging the retina layer by layer. The same principle now shows up in intravascular catheters for coronary imaging, endoscopic probes for gastrointestinal tissue, and dermatology scanners. Whatever the application, the device is really an interferometer, a light source, a scanning mechanism, and reconstruction software packaged into a diagnostic instrument.
Why Optical Coherence Tomography (OCT) matters in medical device development
An OCT system’s clinical value depends entirely on measurement accuracy. If the reconstruction algorithm misrepresents tissue thickness or a segmentation feature mislabels a structure, a clinician can make the wrong call on a treatment decision. That risk profile is why diagnostic OCT devices typically fall under FDA Class II or an equivalent EU MDR class, with a technical file and clinical evaluation expected before market entry.
Cost and schedule risk run just as high. Optical subsystems are sensitive to component tolerances and thermal effects, so a design that looks fine on the bench can fail reliability testing late in the program. Rework at that stage is expensive and can push a submission timeline by months. Notified bodies also scrutinize the software that turns raw interferometric data into a displayed image, since it carries its own verification burden under IEC 62304. Skipping early risk analysis on the image-review workflow tends to surface as audit findings later.
How Optical Coherence Tomography (OCT) works
The core physics is interferometry, but the engineering spans several subsystems:
- Light source: a superluminescent diode for spectral-domain systems, or a swept-wavelength laser for swept-source systems, chosen for coherence length and tissue safety margins.
- Interferometer: a Michelson configuration that splits light between a reference arm and a sample arm, then recombines the returning signals.
- Scanning optics or catheter: galvanometer mirrors for surface imaging, or a rotating, pullback-driven catheter for intravascular use.
- Detector: a spectrometer with a line-scan camera for spectral-domain OCT, or a photodetector synchronized to the swept laser for swept-source OCT.
- Reconstruction software applies Fourier-domain signal processing to convert raw interference data into a depth profile, then stitches profiles into a full image.
OCT devices combine electrical, optical, and software subsystems, so they draw on more than one standard at once. Electrical safety follows IEC 60601-1, with photobiological safety under IEC 60601-2-22 or, for ophthalmic instruments, ISO 15004-1 and ISO 15004-2. Reconstruction software falls under IEC 62304, and the review interface is subject to IEC 62366-1 usability engineering. Risk management is documented under ISO 14971 inside an ISO 13485 quality system.
Common challenges and best practices
Motion is the most persistent practical problem. Eye movement, breathing, or cardiac motion during an intravascular pullback all introduce artifacts that can be mistaken for tissue features if the reconstruction software does not account for them. Teams that treat motion compensation as a late-stage patch usually end up reworking acquisition timing instead, a much larger change to validate.
Resolution and imaging depth pull in opposite directions. Shorter coherence length improves axial resolution but reduces how deep the signal can penetrate before noise dominates. Choosing a wavelength without mapping it against the clinical use case, retinal layers versus a coronary vessel wall, is a common early misstep.
The classification strategy also needs to be settled early. The same core technology can be classified differently depending on intended use, anatomical site, and whether measurements feed an automated diagnostic claim. Predicate selection done after the design is frozen almost always costs more than doing it in parallel with early architecture work. Good practice treats safety testing, software verification, and human factors testing as parallel streams, not sequential checkboxes.
How SJML helps with Optical Coherence Tomography (OCT)
SJML’s design and engineering teams work across optics, embedded systems, and electromechanical integration, the same disciplines an OCT platform depends on. In-house labs support IEC 60601 electrical safety, EMC, and reliability testing, so optical and imaging subsystems get validated alongside the rest of the device rather than sent out separately. SJML’s QARA group handles device classification, technical file preparation, and IEC 62304 software lifecycle documentation for imaging and diagnostic platforms, including SaMD elements where image analysis features are involved. Manufacturing support extends to precision assembly and system integration for optical and electromechanical instruments.
Talk to SJML’s engineering team →
Frequently asked questions
Both techniques measure echoes to build cross-sectional images, but OCT uses light, and ultrasound uses sound waves. OCT achieves much finer resolution, often in the single-digit micrometer range, but penetrates only a millimeter or two into scattering tissue. Ultrasound trades resolution for depth. The two are complementary, and device selection depends on the target tissue and required depth.
Surface OCT, such as retinal imaging, is non-invasive and contact-free. Intravascular OCT is different: it requires a catheter inserted into a blood vessel, making it an invasive procedure even though the imaging itself does not damage tissue. Classification and risk documentation differ accordingly, since a catheter carries biocompatibility and sterilization requirements, a benchtop retinal scanner does not.
Most diagnostic OCT systems in the US fall under FDA Class II and go through the 510(k) pathway, referencing a predicate device with similar intended use. In the EU, classification under MDR depends on intended use and measurement claims, typically placing OCT devices in Class IIa or IIb. Automated segmentation or measurement features may add SaMD considerations under IEC 62304.
OCT angiography (OCTA) is a variant that visualizes blood flow by detecting motion contrast between repeated scans at the same location, rather than relying on an injected dye. It is used mainly in ophthalmology to assess retinal and choroidal vasculature. Because it relies on signal processing across sequential frames, motion artifact management matters even more than in standard OCT.
Related terms
- Design Verification
- Design History File (DHF)
- IEC 62304
- Class II Medical Device
- Software as a Medical Device (SaMD)
