The next generation of OCT from Topcon

Most are us are becoming so accustomed to high resolution cross-sectional images of the retina and other ocular structures taken with modern OCT machines that we somewhat take for granted what a major breakthrough in clinical practice optical coherence tomography offers. The first in vivo OCT images of retinal structures were published way back in 1993. These initial scans, usually presented in bright colour simulation, impressed at the time but in retrospect are grainy and detail difficult to make out.

Swept source OCT

An OCT directs an incident light beam upon a beam splitter so light is diverted to both the tissue to be imaged and a reference mirror. The reflected radiation from the various structures within the tissue and from the reference mirror are then analysed. The earlier units used a time domain technique which analysed the reflected interference pattern from the reference mirror and the tissue in terms of time to reach a detector. This mechanical and fairly slow process limited the number of scans that might be analysed and therefore restricted the resolution of the image. A significant breakthrough came in the early noughties with the introduction of spectral domain OCT. This technique employs Fourian analysis to evaluate the frequency spectrum of the interference between the reflected light and a stationary reference mirror. This non-mechanical process allows a much quicker interpretation of reflected light using a spectrometer and a camera, and led to the much greater detail and resolution we are now used to.