Optical Coherence tomography (OCT)
OCT is the study of ultrastructure of retinal. In this investigation Laser light in near infra red spectrum (810nm) is used to produce high resolution cross sectional image of retina using coherence inferometry. In coherence inferometry partial reflective mirror is used to split a single laser beam into measuring and reference beam. Measuring beam pass from neurosensory retina upto choriocapillaris. At each optical interface some of light reflected back to OCT photodetector. Reference beam is reflected off the reference mirror at a known distance of beam splitter back to photo detector. Reference mirror can be adjusted to make the path traversed by reference and measuring beam equal, and creates wave pattern in constructive interference. However some of the lights through retinal surface are reflected off deeper layer in the retina. This light will have traversed a longer distance than reference beam and create some degree of destructive interference when the two beams come at photodetector. The amount of destructive interference measured by OCT and translated into measurement of retinal depth and graphically displayed as retinal cross-section.
We can assess the abnormality of layers of retina through this investigation. It is useful in the study of macular edema following diabetic retinopathy, retinal vein occlusions, dry & wet Age related macular degeneration, Choroidal Neovascular membrane and Macular Hole.