Evaluation of a broadband OCT light source for retinal layer segmentation and image quality

Abstract

Spectral domain optical coherence tomography (SD-OCT) allows high-resolution visualization of retinal lamination. In SD-OCT, there is an inverse relationship between the bandwidth of the source and the axial resolution in tissue. A number of research instruments have been developed using broadband sources that provide “ultrahigh” resolution. However, the cost and complexity of these systems have, for the most part, kept them out of a clinical setting. The purpose of this study was to examine the possible practical improvement in image quality using broadband light source in a clinical setting. Here we examined a commercially available OCT system, the Bioptigen system, which was configured with a standard source (central wavelength 860 nm, 53.7 nm bandwidth) as well as an external broadband light source (central wavelength 878.4 nm, 186.3 nm bandwidth). We matched the power of the two sources as close as possible using a 50/50 power splitter on the broadband source. The measured power at the cornea was 755 µW for internal source and 746 µW for the broadband configuration. Theoretically, one would expect a factor of 3.28 improvements in axial resolution when using the broadband source; however this does not take into account the deleterious effect of chromatic aberration, and absorption and scattering properties of tissue. Scattering appeared greatly reduced when using the broadband source. We imaged two subjects every four hours for 48 hours and found that these metrics varied by no more than 11%. The local contrast and peak-to-trough ratio of all the layers under evaluation improved when using broadband light source. Broadband source images also displayed sublamination of the inner plexiform layer (IPL). In most spectral domain OCT images it is possible to discriminate the nerve fiber layer from the ganglion cell layer and the ganglion cell layer from the IPL, however, IPL sub lamination was only visualized with the external broadband source that allowed for better axial resolution.

Footnotes

 Supported by NIH EY1931, E. Matilda Zeigler Foundation for the Blind, and Research to Prevent Blindness.