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Adaptive optics (AO) coupled with ultra-fast spectral-domain optical coherence tomography (SD-OCT) has achieved the
necessary 3D resolution, sensitivity, and speed for imaging the microscopic retina at the cellular level. While this
technology has been rigorously applied to evaluating the 3D morphology of cone photoreceptors, similar detailed studies
of cell-sized structures in the inner retina have yet to be undertaken. In this paper, we improve the technical performance
of our AO ultrafast SD-OCT and investigate its use for imaging the microscopic inner retina, in particular the nerve fiber
layer (NFL) and retinal capillary network. To maximize lateral resolution within the inner retina, focus was controlled
with a high stroke, 37-actuator bimorph mirror (AOptix) that also served as the wavefront corrector of the AO. The AO
system operated at a closed-loop rate of 25 Hz. The SD-OCT sub-system consisted of a superluminescent diode (&lgr;= 842
nm, &Dgr;&lgr;= 50 nm) and a 512 pixel line scan charge-coupled device (CCD) that acquired 72,000 A-scans/sec. Three
different B-scan lengths (36, 60, and 120 A-scans/B-scan), which correspond to B-scan exposure durations of 0.5, 0.83,
and 1.67 ms, were evaluated to determine the maximum B-scan length that could be tolerated without noticeable loss in
image quality due to eye motion in the well fixated eye. Additional technical improvements included sub-pixel
registration to remove instrument error and axial registration of the volume images. Small volume images were acquired
at 2 and 7 degrees retinal eccentricity with focus systematically shifted through the retina. Small capillaries, some
approaching the smallest in the human eye, were readily detected with AO SD-OCT. Appearance of the nerve fiber layer
varied noticeably with depth. The most inner portion (presumably the inner limiting membrane) appeared as a thin
irregular surface with little characteristic speckle noise. Within the NFL, complex striation patterns (presumably NFL
bundles) were observed throughout the entire thickness with pattern density highest in the inner portion (~15 &mgr;m) and
large corrugations (~35 &mgr;m) at the interface with the ganglion cell layer below. Speckle noise was significant throughout
the NFL.
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