19 , 20 , 21 , 22The last decade saw massive innovative applications of OCT in ophthalmology. 15 , 16 , 17 , 18With the evolution of OCT, new clinical entities have been identified, and innovative OCT-guided surgical techniques are being performed. 5Emergence of OCT in anterior-segment evaluation has opened the new world of using OCT for corneal surgeries, especially refractive surgeries. 5 , 14In 1995, Schuman and associates showed that the thickness of the retinal nerve fiber layer as measured by OCT demonstrated a high degree of correlation with the functional status of the optic nerve as measured by visual field examination. 9 , 10 , 11 , 12 , 13In analysis of the optic nerve head, OCT was initially used for determination of the thickness of the retinal nerve fiber layer, which is an important parameter for glaucoma assessment. Quantification of macular edema, diagnosis of central serous retinopathy, grading of macular holes, assessment of age-related macular degeneration, and determination of epiretinal membrane are some of the widely applied fields of macular OCT. Since the introduction of OCT in ophthalmology, this imaging method has been used extensively for the diagnosis of various clinical disorders of the retina. 7It had the advantages of better penetration through sclera as well as real-time imaging at eight frames per second. Izatt et al first introduced micrometer-scale resolution imaging of the anterior eye with OCT in 1994. OCT imaging of the anterior segment with a longer wavelength of 1310 nm was developed later. 3 , 4 , 5 , 6The wavelength of light used for retinal study was 830 nm however, this wavelength was not adequate for imaging the anterior ocular structures, such the cornea, anterior-chamber, angles, and lens. Initially, OCT was used for the evaluation of retinal structures and the optic nerve head. 2OCT gained popularity in ophthalmology as a result of the transparent nature of the ocular media and the ease in evaluation of anterior and posterior segments of the eye.

Puliafito, that led to the conversion of the interferometry principle to a widely used imaging modality in the eye. It was the effort and vision of the physical scientists and ophthalmologists, namely, Doctors David Huang, Joel Schumann, James Fujimoto, Eric Swanson, and Carmen A. OCT was also used in cadaver eyes for ex vivo imaging of the retina and optic nerve head. Their images were displayed as false color scale, depending on the magnitude of the backscattering. 1They reported OCT correlation with the histologic appearance of the retina. In 1991, Huang and associates demonstrated the OCT evaluation of the retina using infrared light of ~ 800-nm wavelength and axial resolution 10 µm.

OCT was first used for in vitro imaging in the peripapillary area of the retina and in the coronary artery, two clinically relevant examples that are representative of transparent and turbid media, respectively. The noninvasive nature and higher resolution compared with other imaging techniques, such as ultrasound, magnetic resonance imaging, and computerized tomography, have made OCT one of the standard diagnostic tests for many ocular disorders. OCT uses low-coherence interferometry to produce a two-dimensional image of optical scattering from internal tissue microstructures in a way that is analogous to ultrasonic pulse-echo imaging.

Although it has been used in other medical fields, the ophthalmologic specialty has used this application widely for the diagnosis, prognosis, and management of ocular pathologies. It performs real-time, high-resolution, micrometer-scale, cross-sectional imaging of ocular tissues in less time. Optical coherence tomography (OCT) is a newer medical investigational modality that has been widely used in ophthalmology.

Optical coherence tomography basics