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The inner plexiform layer (IPL) of the retina comprises extremely thin sublaminae with connections between bipolar cells, amacrine cells, and ganglion cells. So far, observations of IPL lamination in near-infrared Optical Coherence Tomography (OCT) images have been anecdotal. Visible light OCT theoretically provides higher axial resolution than near-infrared OCT for a given wavelength bandwidth. Imaging of the human retina with ultrahigh resolution visible light OCT and longitudinal chromatic aberration correction was recently shown, with a focus on the outer retina. Here, we demonstrate in vivo imaging of lamination in the inner plexiform layer using achromatized visible light Optical Coherence Tomography (OCT). To further improve the achievable axial resolution and contrast, we incorporate a grating light valve spatial light modulator (GLV-SLM) spectral shaping stage into our setup. The GLV-SLM rapidly and dynamically shapes the source spectrum to either reduce sidelobes in the axial point spread function, improve axial resolution by reducing the width of the axial point spread function, or switch between red light alignment mode and white light acquisition mode. In vivo retinal OCT images acquired from human subjects show that the IPL consists of 3 hyper-reflective bands and 2 hypo-reflective bands, corresponding well with the standard anatomical division of the IPL into 5 layers. Strategies to improve contrast of the subtle bands representing the IPL sublaminae are investigated. Possible explanations for the ability of visible light OCT to visualize IPL sublaminae, based only on backscattering or backreflection contrast, and implications for glaucoma progression monitoring, are discussed.
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