Ocular Coherence Tomography (OCT)
Optical coherence tomography (OCT) is an optical signal acquisition and processing method. It captures micrometer-resolution, three-dimensional images from within the patient eye. Optical coherence tomography is an interferometric technique with the use of relatively long wavelength light allows it to penetrate into eye.
Optical coherence tomography is one of a class of optical tomographic techniques. A relatively recent implementation of optical coherence tomography, frequency-domain optical coherence tomography, provides advantages in signal-to-noise ratio, permitting faster signal acquisition. This diagnostic procedure is very useful to obtain detailed images from within the retina.
It is effectively ‘optical ultrasound’, imaging reflections from within tissue to provide cross-sectional images. OCT delivers high resolution because it is based on light, rather than sound or radio frequency. An optical beam is directed at the eye, and a small portion of this light that reflects from sub-surface features is collected. Note that most light is not reflected but, rather, scatters off at large angles. In conventional imaging, this diffusely scattered light contributes background that obscures an image. However, in OCT, a technique called interferometry is used to record the optical path length of received photons allowing rejection of most photons that scatter multiple times before detection. Thus OCT can build up clear 3D images of thick samples by rejecting background signal while collecting light directly reflected from surfaces of interest. Within the range of noninvasive three-dimensional imaging techniques that have been introduced to the medical research community, OCT as an echo technique is similar to ultrasound imaging.