Optical Coherence Tomography

Mechanism

• Analogous to ultrasound: uses low coherence interferometry to measure optical reflectivity

• A broadband low coherence light source (near the infrared range) is directed at the target

• A beam splitter simultaneously directs the light source at a reference mirror

• The reflected light from the target and the reference mirror are recombined and directed to a detector

• The interference pattern is analysed using low coherence interferometry

• The structures of the target reflect varying amounts of light depending on their distance from the source, producing different interference patterns

• Fourier-domain scanners show more detail and have shorter acquisition time compared to time-domain scanners (which also leads to less motion artefact)

• Ultra-high resolution OCT can achieve 2-3 micrometer resolution

• Degeneration of the RPE (eg. in macular scarring) increases visualisation of the choroid

Limitations

• Requires a transparent media
• Patient co-operation
• Susceptible to motion artefact
• Requires moderate dilation
• OCT-A: cannot view leakage