Optical Coherence Tomography

OCT is based on the principles of low coherence interferometry. Low coherent superluminiscent diode light is directed onto a partially reflective mirror (splitter), whereby two beams are created measurement and reference beams. The measurement beam is directed into the subject’s eye. Here it gets reflected from the boundaries between the microstructures and scattered differently from tissues with different optical properties. The reference beam is reflected from the reference mirror at a known, variable position. Both beams are combined resulting in a phenomenon called interference. This interference is measured by the means of a photosensitive detector. The echo time delay of the measurement and reference beams is compared. Several data points over 2 mm of depth are integrated by the interferometer to construct a tomogram of retinal structures. Image thus produced has an axial resolution of <10 microns and a transverse resolution of 20 microns. The operating wavelength of OCT probe beam is typically in the near infrared (800 nm) and thus minimally visible to the patient.