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Zhuolin Liu, Omer Kocaoglu, Qiang Wang, Donald Miller; Photoreceptor imaging with in-the-plane adaptive optics optical coherence tomography using toroidal mirrors. Invest. Ophthalmol. Vis. Sci. 2013;54(15):5547.
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© ARVO (1962-2015); The Authors (2016-present)
Recent technological advances in adaptive optics (AO) and high-resolution ophthalmoscopy have resulted in sharper images of the cellular retina than previously possible. As part of these ongoing developments, we have re-engineered the Indiana AO-OCT system to improve imaging performance. In this study, we assessed system performance for imaging the 3D structure of photoreceptors.
The 2nd generation Indiana AO-OCT system is based on a novel in-the-plane design of an off-axis ophthalmic AO system realized with toroidal mirrors. Unlike conventional designs that rely on all spherical mirrors, the inclusion of toroidal mirrors avoids accumulation of system astigmatism and unwanted beam displacement at pupil conjugate planes. As part of the new design, the AO system was upgraded with a 97-magnetic-actuator ALPAO wavefront corrector to improve stroke and fidelity, and a Shack-Hartmann wavefront sensor configured with an Andor Neo scientific CMOS camera to improve sensitivity and speed. To assess performance, volume images of the retina with focus at the photoreceptor layer were acquired at retinal eccentricities ranging from the fovea to 6 degrees in human subjects. Power spectra were computed of en face images at different depths in the photoreceptor layer. Each spectrum was radially averaged to increase signal to noise.
Ray trace analysis of the in-the-plane design predicts diffraction-limited imaging across the entire 3.6°x3.6° field of view of the AO-OCT system. Beam displacement of less than the pitch of the SHWS lenslet array is also predicted, thus enabling the full sensitivity of the SHWS to high spatial frequencies. Measured beam displacement and wavefront root-mean-square error of the system confirmed the theoretical predictions. Cone photoreceptors were routinely observed at retinal eccentricities as small as 0.2 degrees. This corresponds to cones narrower than that detected with the previous Indiana AO-OCT system. Analysis of power spectra at the inner segment / outer segment junction, and posterior tip of the outer segment revealed more energy at high spatial frequencies.
The 2nd-generation Indiana AO-OCT system provides a more detailed view of the photoreceptor optical signature than the previous generation system.
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