In vivo Cellular-Level Visualization of Human Retina Using Ultrahigh-Resolution, Dual-Channel Full-Field Optical Coherence Tomography

Abstract

Purpose: : To visualize a cellular-level human retinal structure in vivo by dual-channel phase-locked full-field optical coherence tomography (FF-OCT).

Methods: : FF-OCT is a horizontal cross-sectional imaging modality using parallel beam illumination and parallel detection without beam scanning. Human retinal imaging was performed using a dual-channel FF-OCT system that employed a pair of CCD cameras (500x500 pixels) for phase-locked detection. A long-working distance water immersion objective suitable for FF-OCT retinal imaging was newly designed and fabricated. A phosphor buffered saline was used as an immersion media. The light source was a supercontinuum source whose output was reshaped to a quasi-Gaussian shape, centered around 800 nm with 80 nm bandwidth. To minimize the interference fringe washout due to eyeball motion, a short duration illumination (1 ms) method was employed. Human eye under measurement was flood-illuminated in an area of ~650 um in diameter. Axial and transverse resolutions were 3 um and 6 um at retina, respectively. Individual eye parameters were measured in advance to help determine the depth of interference plane in human fundus. FF-OCT images were acquired at a 30-Hz video-rate.

Results: : The subject was a healthy volunteer's eye, and the image eccentricity was chosen to ~6 degrees superior. From a series of FF-OCT images, nerve fiber bundles could be observed when the reference position of the interferometer was set to the anterior retina. Meanwhile, by setting the reference position to the posterior retina, a regularly spaced transverse structure which is characteristic of a retinal cone mosaic could be observed as well. The nearest neighbor pixel between the cone cells is measured to be ~7 um and the cell density is counted to be ~11,000 cells/mm².

Conclusions: : FF-OCT imaging was performed, for the first time to our best knowledge, in living human retina. The ultrahigh resolution of FF-OCT in both transverse and depth directions enabled the observation of nerve fiber bundles and cone mosaic without the use of adaptive optics in a healthy volunteer's eye. Our preliminary results give some evidences that FF-OCT may become a useful tool for high-resolution retinal imaging.

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