What measurement principle does OCT rely on to detect retinal structures?

What measurement principle does OCT rely on to detect retinal structures?

• A. Interferometry
• B. Doppler shift
• C. Photoacoustic effect
• D. Ellipsometry

Answer: (A)

OCT detects retinal structures through interference of light, using a low-coherence interferometry principle. A broadband light source is split into a sample beam that interrogates the retina and a reference beam. Light reflected from different retinal layers returns and combines with the reference light at the detector. Interference occurs only when the path length difference is within the light’s coherence length, so the detected signal encodes how strongly tissue reflects light at a particular depth. By scanning along the depth (in time-domain OCT) or by measuring a spectrum and applying a Fourier transform (in spectral-domain OCT), you obtain a depth-resolved reflectivity profile (an A-scan). Collecting many A-scans across the image plane builds up a 3D map of retinal structures. The axial resolution is set by the coherence length of the light source—the shorter the coherence length, the finer the depth resolution. Doppler, photoacoustic, and ellipsometry describe different physical effects or modalities and are not the fundamental measurement principle behind OCT.

OCT detects retinal structures through interference of light, using a low-coherence interferometry principle. A broadband light source is split into a sample beam that interrogates the retina and a reference beam. Light reflected from different retinal layers returns and combines with the reference light at the detector. Interference occurs only when the path length difference is within the light’s coherence length, so the detected signal encodes how strongly tissue reflects light at a particular depth. By scanning along the depth (in time-domain OCT) or by measuring a spectrum and applying a Fourier transform (in spectral-domain OCT), you obtain a depth-resolved reflectivity profile (an A-scan). Collecting many A-scans across the image plane builds up a 3D map of retinal structures. The axial resolution is set by the coherence length of the light source—the shorter the coherence length, the finer the depth resolution. Doppler, photoacoustic, and ellipsometry describe different physical effects or modalities and are not the fundamental measurement principle behind OCT.