Multi-directional optical coherence tomography in the retina

Abstract

Purpose : To investigate the directional reflectivity of retinal layers using multi-beam (MB) optical coherence tomography (OCT). In particular, the photoreceptor layer (optical Stiles-Crawford effect (o-SCE)), Henle’s fiber layer (HFL) and retinal nerve fiber layer (RNFL) are reported to exhibit non-isotropic angular scattering properties. Thus, we evaluate the potential of MB-OCT to extract additional – multi-directional – information out of simultaneously acquired reflectivity-scans.

Methods : A three-beam spectral domain (SD-) OCT prototype – primarily developed for total retinal blood flow investigations in normal and diseased eyes – enables illumination of the retina from three linear independent orientations at the same time. The system features three superluminescent diode sources (center wavelength: λ₀ = 840 nm; spectral bandwidth: Δλ = 50 nm), a joint Michelson interferometer (sharing the same bulk optic components) and three identical spectrometer units (operating frequency of line-scan cameras: 50 kHz). In the sample arm, the three collimated beams are aligned parallel to one another according to the corners of an equilateral triangle. The refractive optics of the eye focuses the three individual beams to a mutual spot on the retina.

Results : We obtained circular reflectivity scans around the optic nerve head (ONH) of a healthy human subject (undilated pupil). The simultaneously acquired circumpapillary scans (diameter corresponding to a field of view (FoV) of ~10°), show intensity differences in the photoreceptor layer (essentially, in the inner segment-outer segment junction (IS/OS) and the end tips of the photoreceptors (ETPR)), which are caused by the o-SCE. Using a color-coded overlay (bottom side of Fig. 1) of the three respective channels (CH 1, CH2, CH 3), the referred layers show a clear color offset.

Conclusions : MB-OCT approaches enable simultaneous image acquisition of the same retinal location at different angles of orientation. Hence, multi-directional OCT allows for investigation of non-isotropic optical scattering properties of the retinal layers. Intensity variations among the reflectivity-scans of the three channels may potentially further be used for investigations of HFL, RNFL or more detailed studies on the o-SCE.

This is an abstract that was submitted for the 2017 ARVO Annual Meeting, held in Baltimore, MD, May 7-11, 2017.