High-speed volumetric imaging of cone photoreceptors with adaptive optics spectral-domain optical coherence tomography

Abstract

Abstract:We report the first observations of the three-dimensional morphology of cone photoreceptors in the living human retina. Images were acquired with a high-speed adaptive optics (AO) spectral-domain optical coherence tomography (SD-OCT) camera. The AO system consisted of a Shack-Hartmann wavefront sensor and bimorph mirror (AOptix) that measured and corrected the ocular and system aberrations at a closed-loop rate of 12 Hz. The bimorph mirror was positioned between the XY mechanical scanners and the subject's eye. The SD-OCT system consisted of a superluminescent diode and a 512 pixel line scan charge-coupled device (CCD) that acquired 75,000 A-scans/s. This rate is more than two times faster than that previously reported. Retinal motion artifacts were minimized by quickly acquiring small volume images of the retina with and without AO compensation. Camera sensitivity was sufficient to detect reflections from all major retinal layers. The regular distribution of bright spots observed within C-scans at the inner segment / outer segment (IS/OS) junctions and at the posterior tips of the OS were found to be highly correlated with one another and with the expected cone spacing. No correlation was found between the posterior tips of the OS and the other retinal layers examined, including the retinal pigment epithelium.

Measuring retinal contributions to the optical Stiles-Crawford effect with optical coherence tomography

“…The 6.6 μm corresponds to 4.8 μm in retinal tissue assuming a refractive index of 1.38 [29]. Lateral resolution at the focal plane was nominally 8.6 μm, the diffraction-limited spot size for a 2 mm pupil as defined by 1.22 λ f/d.…”

“…Figure 1 shows a schematic of the laboratory SD-OCT instrument that was used to measure reflectivity as a function of (1) depth in the retina and (2) beam location in the subject's pupil. The instrument represents a modified version of that described in detail by Zhang, et al [29]. In short, the instrument employs a fiber-based beamsplitter that optically connects four channels: (1) illumination channel for generating short-temporal coherence light by way of a broadband 10 mW superluminescent diode (SLD) (λ= 842 nm, Δλ= 50 nm); (2) sample channel for scanning a focused beam across the retina, and collecting reflected and backscattered light from the retina; (3) reference channel for matching the optical path of the sample channel; and (4) detection channel for recording the superimposed sample and reference light after being dispersed by a transmission grating.…”

3-D Ultrahigh Resolution Optical Coherence Tomography with Adaptive Optics for Ophthalmic Imaging

“…In 2006, Yan Zhang established an AO-SDOCT (adaptive optics spectral domain optical coherence tomography) system for high-speed volumetric imaging of cone photoreceptors (Yan Zhang, et al, 2006). In order to overcome retinal jitter, the SDOCT components based on a fast line scan camera which's A-scan rate is 75KHz, and a shorter distance of raster scans (38 A-scans per B-scan).…”

Ultra-high resolution adaptive optics: optical coherence tomography for in vivo imaging of healthy and diseased retinal structures

“…In recent years Adaptive optics -optical coherence tomography (AO-OCT) [1][2][3][4][5][6][7][8] has realized an improvement in lateral resolution compared to stand alone Fd-OCT [9][10][11]. We previously reported [12] an ultra-high resolution (UHR) OCT that is capable of real-time imaging with high volumetric resolution (~3 µm in all three dimensions).…”