In vivo imaging of retinal ganglion cells in the human eye with adaptive optics optic coherence tomography

Abstract

Purpose : Optical coherence tomography (OCT) has greatly improved our understanding of the pathophysiology of the living human retina. However, resolving retinal cells in conventional OCT remains impossible without adaptive optics (AO). Our purpose was to visualize and evaluate human retinal ganglion cells (RGCs) in healthy eyes in vivo by using the prototype AO-OCT system.

Methods : Eight eyes of 8 healthy volunteers (mean age 42 ± 6 years, range 30–82 years) were imaged with the prototype AO-OCT system (Canon Inc., Tokyo, Japan). The AO-OCT system used a superluminescent diode with a center wavelength of 855 nm and a bandwidth of 100 nm, which resulted in an axial resolution of 3.4 μm in the retina. The beam diameter measured 6.7 mm at the pupil of the eye, thus producing a diffraction-limited transverse resolution of approximately 3 μm within the retina. The AO-OCT system was operated with an A-scan rate of 24 kHz, which was translated to a B-scan (comprising 448 A-scans) rate of 45 Hz. A total of 100 B-scans were acquired in 2.2 s. To improve the signal-to-noise ratio, we averaged over 100 consecutive B-scans. The scan range was 728 μm. The fovea, which was located 0.75 mm superiorly from the center of the foveola, was scanned vertically and evaluated as follows. Small hypoeflective dots (HDs) were identified in the ganglion cell layer (GCL). The GCL area, the HD diameter, HD area, HD count, and HD density (HD count divided by GCL area) were measured using ImageJ software.

Results : When the AO system was focused on the outer retinal layers, the HDs were not detected in the GCL, whereas they were clearly detected and delineated in the GCL in all eyes when the AO system was focused on the inner retinal layers, and particularly on the GCL. Within the scanned region, the mean GCL area was 41093 ± 3432 μm². The HD count was 176.8 ± 25.1 and the HD density was 4367 ± 448 count/mm². The mean HD diameter and area were 10.5 ± 0.7 μm and 50.4 ± 5.9 μm², respectively. The HD density was negatively correlated with age (β = -0.860, P= 0.0061). The HDs detected in the GCL were highly concordant with histological investigations of the human eye that have been previously reported.

Conclusions : The HDs, which may represent RGCs, were observed in the GCL by using AO-OCT. Our results indicate that RGC count and features can be evaluated in vivo by using AO-OCT.

This abstract was presented at the 2019 ARVO Annual Meeting, held in Vancouver, Canada, April 28 - May 2, 2019.