Human Cone Photoreceptors Investigated in vivo With SLO/OCT and SD-OCT

Abstract

Purpose: : To investigate different features of human cone photoreceptors as observed with transversal scanning (TS) optical coherence tomography (OCT) and high speed Spectral Domain (SD) OCT.

Methods: : Two different experimental instruments were used in this study: A TS OCT/SLO and a SD OCT system. The TS OCT/SLO instrument is operating at a frame rate of 40 fps (transverse frames, imaging area ~300 x 300µm2) and records SLO and OCT images simultaneously. The SLO images are used in a post-processing step to correct for transverse eye motion. Together with an incorporated axial eye tracker the instrument provides nearly motion artifact free 3D data of the retina. The used SD-OCT instrument is operating at ultrahigh speed up to 200000 A-scans per second. Similar 3D data sets of the human retina at different eccentricities from the fovea were recorded in 3 seconds with the TS OCT/SLO and in 0.8 seconds with the SD-OCT instrument, respectively.

Results: : The human cone mosaic could be observed with both instruments within several volunteers as close as ~2 degrees eccentricity from the fovea. Two different layers, the inner outer segments junction and the posterior tips of photoreceptors, show the cone mosaic. In addition highly backscattering intensity spots can be found that are localized between these two layers (within the layer of the cone outer segments) in all measurements. The total number of spots is counted and the ratio between spots to cones was measured with 2-7%.

Conclusions: : Both imaging systems are capable to provide 3D data sets of the human retina in vivo with a resolution that is sufficient to resolve the cone mosaic. The 3D imaging capability of both systems allows the detection of small localized spots within the cone outer segments. However, the underlying anatomy of these spots is still unclear.

Keywords: photoreceptors • imaging methods (CT, FA, ICG, MRI, OCT, RTA, SLO, ultrasound) • macula/fovea