OCT Technologies: Which Machine Do You Want to Own?

Optical coherence tomography (OCT) has evolved over the past decade to become one of the most important ancillary tests in ophthalmic practice. This non-invasive ocular imaging technique provides high-resolution, crosssectional images of the retinal nerve fiber layer (RNFL), macular volume (MV), ganglion cell layer (GCL), and optic nerve head. With OCT, we can learn much about axonal-neuronal integrity in the anterior aspect of the afferent visual pathway. Spectral domain OCT (SD-OCT) techniques provide an axial resolution in the range of 5 to 7 microns (?m), thus images derived from SD-OCT have been likened to an in-vivo optical biopsy of the retina [1]. Optical coherence tomography uses light from a broadband source, which is divided into a reference and a sample beam, to obtain a reflectivity versus depth profile of the retina. The light waves are backscattered from the retina to interfere with the reference beam, and this interference pattern is used to measure light echoes. Initially, time-domain detec on (TD-OCT) was the technique employed by commercially available OCT systems. Previous TD-OCT systems featured scan rates of 400 A-scans per second with an axial resolution of approximately 8 to 10?m in tissue. In 2006, the first commercially available spectral domain (also known as Fourier domain) OCT (SDOCT) system was introduced. In contrast to TD-OCT, SDOCT employs detection of the light echoes simultaneously by measuring the interference spectrum, using an interferometer with a high-speed spectrometer. This technique provides scan rates of 20, 00052, 000 A-scans per second to achieve a resolution of 5to 7?m. This is approximately 50-fold faster than the previous generations of TD-OCT.