Fundus Image Obtained by Fourier Domain Optical Coherence Tomography for Glaucomatous Optic Disc

Abstract

Purpose:: To assess the fundus images obtained by three-dimensional Fourier domain optical coherence tomography (FD-OCT) for a glaucomatous optic disc.

Methods:: Using FD-OCT, 22 eyes of 16 patients with open- angle glaucoma were examined. The OCT system used is a prototype standard-resolution spectral domain OCT system similar to TOPCON 3D-OCT-1000. The acquisition speed is 18,700 axial scans per second. A 3D OCT volume is acquired by a raster scanning using fast horizontal and slow vertical scans. The volume contains 256 (horizontal) × 256 (vertical) A-scans; the acquisition time for this is 3.5 s. In this study, we registered a photograph of the fundus and an OCT projection image by using manually selected control points.

Results:: The fundus image obtained using FD-OCT depicted various optic disc structures for which the OCT signal intensity was clearly different. The rim region expressed a low-reflection doughnut shape in the FD-OCT image. For all the eyes, the FD-OCT image showed clearly defined external rim margins. It showed clearly defined internal rim margins in 18 eyes (mean ± SD: 0.14 ± 2.12 diopters) and ill-defined margins in 4 (-1.31 ±2.77 diopters,). A peripapillary atrophy (PPA) in the fundus photograph was depicted as high intensity region by FD-OCT fundus image. Comparison with longitudinal cross-sectional images and color fundus photographs revealed that the external margin of the rim corresponded to the termination of PPA-ß or the retinal pigment epithelium in the area that had no PPA-ß. The internal rim margin was clearly defined when the direction in which the nerve fiber bundle approached the lamina cribrosa was nearly parallel to the probe light.

Conclusions:: With the exception of the internal rim margin in myopic eyes, the margins of optic disc structures are clearly displayed in fundus images obtained using FD-OCT based on the differences in the OCT signal intensities of these structures. The imaging method involving FD-OCT images of the fundus is potentially useful to assess the optic disc topography and provide optic disc parameters for the diagnosis of glaucoma.

Keywords: imaging methods (CT, FA, ICG, MRI, OCT, RTA, SLO, ultrasound) • optic disc • nerve fiber layer