Clinical applications of optical coherence tomography: what should I know?

(OCT has revolutionised ophthalmology and optometry practice, allowing non-invasive in vivo optical biopsy of the anterior and posterior ocular structures.

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Introduction 

Since optical coherence tomography (OCT) was first demonstrated in 1991 (Huang et al. 1991), it has rapidly evolved as the only non-invasive diagnostic technique able to provide images of the retinal microstructure. OCT is arguably one of the most innovative and rapidly evolving optical imaging technologies in recent history (Huang et al. 1991). In less than 20 years of development, axial resolution has improved by greater than 10 times, together with imaging speeds increasing over half a million times (Drexler et al. 2014). OCT has certainly revolutionised ophthalmology and indeed optometric practice, allowing in vivo optical biopsy of not only posterior ocular structures, but the anterior segment as well.

OCT generates cross-sectional or three-dimensional (3D) images by utilising low-coherence interferometry to detect and measure the depth and magnitude of back-scattered (reflected) light. Low-coherence infrared light is emitted from a superluminescent diode laser (Guedes et al. 2003) and travels to the interferometer, where it is split into two equal components by a semitransparent mirror (Figure 1). One component is then directed towards the retina through the ocular media (the measurement beam), whilst the other component is directed to a reference mirror (the reference beam). The combination of measurement beam and reference beam light produces characteristic patterns of light interference, depending on the difference between the two beam pathways. The interference pattern provides information on the intensity and depth of the reflected light from the measurement beam (Keane and Sadda 2014).

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