Optical & ultrasound (in vivo) · reads
Retinal optical coherence tomography (OCT) is a non-invasive optical imaging technique that produces cross-sectional images with near-histological resolution and a penetration depth of a few millimeters. It relies on low-coherence interferometry: light from a broadband source is split between a reference arm and the eye, and the interference between light reflected from the reference arm and light backscattered or backreflected from retinal tissue is measured. In spectral/Fourier-domain systems, this interference is captured as a spectrum with a spectrometer and line-scan camera; taking its Fourier transform recovers the echo time delay and magnitude of light returning from each depth in the tissue, without needing to mechanically scan the reference arm. Scanning this measurement across the retina builds up high-resolution two-dimensional cross-sectional images and reproducible three-dimensional volumetric data of the retina and optic nerve head. The axial (depth) resolution is set by the coherence length of the light source, which is inversely proportional to its spectral bandwidth, so broader-bandwidth sources give finer axial resolution. From the resulting volumes, quantitative measurements such as retinal and optic-nerve-head layer thicknesses are extracted, including the inner retinal nerve fiber layer and ganglion cell-inner plexiform layer, which thin in neurodegenerative disease.
Retinal optical coherence tomography (OCT) is a non-invasive optical imaging technique that produces cross-sectional images with near-histological resolution and a penetration depth of a few millimeters. It relies on low-coherence interferometry: light from a broadband source is split between a reference arm and the eye, and the interference between light reflected from the reference arm and light backscattered or backreflected from retinal tissue is measured. In spectral/Fourier-domain systems, this interference is captured as a spectrum with a spectrometer and line-scan camera; taking its Fourier transform recovers the echo time delay and magnitude of light returning from each depth in the tissue, without needing to mechanically scan the reference arm. Scanning this measurement across the retina builds up high-resolution two-dimensional cross-sectional images and reproducible three-dimensional volumetric data of the retina and optic nerve head. The axial (depth) resolution is set by the coherence length of the light source, which is inversely proportional to its spectral bandwidth, so broader-bandwidth sources give finer axial resolution. From the resulting volumes, quantitative measurements such as retinal and optic-nerve-head layer thicknesses are extracted, including the inner retinal nerve fiber layer and ganglion cell-inner plexiform layer, which thin in neurodegenerative disease.
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