Spectral-domain (SD) optical coherence tomography (OCT) has emerged as the gold standard noninvasive technique to visualize fine retinal details and to evaluate retinal structural changes for many ocular treatments. Commercially available SD OCT devices achieve axial scanning speeds of 20 000 to 52 000 A-scans per second, with an axial resolution of 5 to 7 μm in the eye, allowing histologic-like cross-sectional images of the vitreoretinal interface and the retinal structures. High image quality may be achieved by the image averaging system; commercially available software averages 8 to 100 images and increases signal-to-noise ratio in proportion to the square root of the number of images averaged. Some SD OCT devices have automated eye tracking as a feature to ensure that all the images to be averaged are obtained from the same retinal location.

For clinical ophthalmic purposes, typical SD OCT instruments use near-infrared wavelengths of approximately 850 nm that penetrate well into the retina and the subretinal space, whereas deeper penetration is limited because of scattering induced by the retinal pigment epithelium and the vascular nature of the choroid. Other reasons for the choice of wavelengths of approximately 850 nm, versus 1000 or 1300 nm, are the better contrast of retinal structures and better axial resolution. Moreover, typically the point of maximum sensitivity on SD OCT (known as the zero delay line ) is located in the vitreous. As a result, with increasing depth into the tissue, the signal is reduced and details of the choroid are not visible.

More recently, the ability to visualize the choroidal anatomic features has been improved with the development of the enhanced depth imaging (EDI) technique on SD OCT and with the new generation of experimental prototypes of swept-source OCT (SS OCT). The EDI acquisition software automatically captures cross-sectional images with the choroid close to the zero delay line to maximize sensitivity on the outer limit of the choroid, using the current 830- to 880-nm probing light of the conventional SD OCT. Alternatively, SS OCT prototypes (not yet commercially available) use a longer center wavelength (1040 to 1060 nm) and higher scan rate (100 000 Hz) of the light source, allowing deeper penetration into the choroid and the sclera. Clearly, these new techniques allow a great detection of the choroidal borders and fine detail; however, detection of the inner retinal surface is reduced using the EDI OCT, and the posterior vitreous is not visible. Moreover, so far no SS OCT device has been approved by the Food and Drug Administration. In addition, the axial resolution and retinal contrast depends on the wavelength; at higher wavelengths, the resolution deceases and retinal contrast reduces.

To overcome this imaging limitation and to obtain a single comprehensive image of both the vitreoretinal interface and choroid, we developed a novel imaging method using a commercially available SD OCT device. The aims of the present study were: (1) to describe in detail this technique, (2) to test its ability to visualize vitreoretinal and choroidal structures in a series of normal eyes, and (3) to evaluate its limitations in eyes with mild to moderate cataract.