Abstract
Visible light optical coherence tomography (OCT) theoretically provides finer axial resolution than near-infrared OCT for a given wavelength bandwidth. To realize this potential in the human retina in vivo, the unique technical challenges of visible light OCT must be addressed. We introduce three advances to further the performance of visible light OCT in the human retina. First, we incorporate a grating light valve spatial light modulator (GLV-SLM) spectral shaping stage to modify the source spectrum. This enables comfortable subject alignment with a red light spectrum, and image acquisition with a broad "white light" spectrum, shaped to minimize sidelobes. Second, we develop a novel, Fourier transform-free, software axial motion tracking algorithm with fast, magnetically actuated stage to maintain near-optimal axial resolution and sensitivity in the presence of eye motion. Third, we implement spatially dependent numerical dispersion compensation for the first time in the human eye in vivo. In vivo human retinal OCT images clearly show that the inner plexiform layer consists of 3 hyper-reflective bands and 2 hypo-reflective bands, corresponding with the standard anatomical division of the IPL. Wavelength-dependent images of the outer retina suggest that, beyond merely improving the axial resolution, shorter wavelength visible light may also provide unique advantages for visualizing Bruch's membrane.
Highlights
While optical coherence tomography (OCT) is the clinical standard for high axial resolution imaging of retinal layers, important architectural features of the retina, which may play a role in early eye disease, cannot yet be assessed by current OCT instruments.First, in glaucoma [1], loss of retinal ganglion cells (RGCs) [2,3] occurs along with thinning of retinal nerve fiber layer (RNFL), ganglion cell layer (GCL), and inner plexiform layer (IPL), reflecting axonal, somatic, and dendritic losses, respectively
The point spread function (PSF) were calculated as the Fourier transform of the interference spectra between sample and reference mirrors and processed by conventional OCT processing
The PSF acquired with the shaped spectrum demonstrates better sidelobe supression
Summary
In glaucoma [1], loss of retinal ganglion cells (RGCs) [2,3] occurs along with thinning of retinal nerve fiber layer (RNFL), ganglion cell layer (GCL), and inner plexiform layer (IPL), reflecting axonal, somatic, and dendritic losses, respectively. The IPL is a layer of connections, where the dendrites of ganglion cells, axons of bipolar cells, and processes of amacrine cells converge to form 5 nominal bands or strata [5]. Recent fundamental research [9,10,11,12] in various animal models of optic nerve injury and hypertension [13] suggest that ganglion cell dendritic morphology changes early in glaucoma, and these changes may be most predictive in the off sublamina. Aside from a few anecdotal reports [14,15], the in vivo visualization and quantification of IPL sublaminae remains challenging due to insufficient axial resolution
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