Spectral domain optical coherence tomography

ABSTRACT

Optical coherence tomography [OCT] allows high-resolution cross-sectional images of the neurosensory retina to be obtained in a non-invasive manner and has become an important tool for the diagnosis and management of vitreoretinal disease. OCT works by measuring the properties of light waves backscattered by tissue [analogous to ultrasonography] using an interferometer. In conventional OCT systems, light traveling in the reference path of the interferometer is reflected from a mobile reference mirror located within the instrument. OCT instruments that adopt this approach are often termed "time domain" as movement of the reference mirror allows assessment of the interference patterns generated as a function of time. Stratus OCT [Carl Zeiss Meditec, Dublin, CA], the most commonly used OCT system worldwide, is based on time domain technology. The requirement for a mobile reference mirror limits the image acquisition speed of time domain systems [Stratus OCT 400 A-scans/second]. As a result, only sparse sampling of the macular area is possible in a single time domain OCT image set for any given patient. More recently however, the next generation of commercial OCT systems, boasting greatly increased image acquisition speed, has been released. These systems, termed spectral domain OCT, are based on the assessment of interference patterns as a function of frequency rather than that of time. With spectral domain OCT, A-scans can be acquired 50-100 times more quickly than in time domain systems, allowing dense sampling of the retina, volumetric rendering, and the generation of OCT fundus images. Spectral domain OCT is likely to supplant time domain OCT as the standard of care for retinal specialists, as it allows earlier detection of morphological changes in disease states and improved monitoring of disease progression over time