Optical Coherence Tomography (OCT) is a standard diagnostic and imaging technique in most clinical practices today. It is a fast and noninvasive scan of the macula. By imaging the retinal histological structure, an OCT scan obtains information similar to that from an optical biopsy, but without the need for excision and histopathologic specimen processing. The OCT employs the Michelson interferometry using near-infrared light (820 nm) produced by a super luminescent diode. The light is split, and the machine compares the echo time delay of the light reflected from the retina with the echo time delay of the same light reflected from a reference mirror at a known distance. The reflected light is recombined, and the resulting interference fringe is detected and measured by a photodiode detector. The information obtained is then used to produce an image of the retina.

Patients can expect a brief, comfortable experience with the OCT. Each scan acquisition usually takes slightly more than one second, and the entire test lasts only five to seven minutes.

The Fourier Domain spectral detection (SD) OCT (3D OCT-1000, Topcon Corporation, Tokyo, Japan) has been shown to be 50 times faster than the conventional Time Domain OCT system. More data can also be collected as compare to the conventional TD OCT due to its higher scanning speed. This new system extracts the necessary information from the spectrum of the light signal using its Fourier transform. The increased scanning speed dramatically reduces motion artifacts. In addition, multiple images may be acquired at different points on the retina at the same time thereby providing wider retinal coverage. The resolution of the scan has also improved to 5 to 6 micron axial image resolution, as compared to the 10-micron axial resolution of standard OCT system. In addition, the Fourier domain OCT is able to acquire three-dimensional (3D) data, allowing 3D reconstructions of the retinal image. It also provides precise point-to-point correlation (Topcon 3D OCT-1000 TruMap™ software) between the individual OCT images and the features of the fundus Retinal “histopathologic” images obtained by Fourier domain OCT are accurate enough to locate and identify macular holes, vitreomacular traction, macular schisis, retinal thickening and subretinal fluid. They can be used to elucidate vitreo-retinal relationships and guide the therapeutic approach. Serial imaging can also be used to monitor disease activity, progression and/or resolution, by demonstrating any changes in retinal elevation or thickness, changes in subretinal fluid or in retinal pigment epithelium (RPE) elevation.

The images can also be used to help patients understand their condition. The images give patients a clearer idea of what is going on in their eyes, and can better appreciate the effects of therapy.

The findings of Fourier domain OCTS are objective and quantitative, and are reproducible, making documentation much more reliable.