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Susanna Finn, Cherry Greiner, Nathan Doble, Robert Zawadzki, John Werner, Stacey Choi; AO-OCT Retinal Imaging with 163-Segment Deformable Mirror. Invest. Ophthalmol. Vis. Sci. 2013;54(15):5549.
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© ARVO (1962-2015); The Authors (2016-present)
Adaptive Optics (AO) has enabled vision scientists to directly image single retinal cells in vivo. We have constructed an AO Fourier-domain Optical Coherence Tomography (AO-FD-OCT) system utilizing a high segment count microelectromechanical systems (MEMS) deformable mirror (DM). This DM provides much higher spatial correction over a 7.5mm dilated pupil (Doble et al. Applied Optics 2007), providing diffraction-limited imaging. We describe retinal imaging results obtained on a range of human subjects.
An AO-FD-OCT was designed and constructed at the New England College of Optometry. The AO-OCT system acquires B-scans made up of 600 A-scans at a frame rate of 60 Hz. A Superlum broadband superluminescent diode (SLD) light source is used with a central wavelength of 860nm and a full bandwidth of 135nm. Imaging data are post-processed and analyzed with custom Matlab software. The AO system consists of a Hartmann-Shack wavefront sensor and a 163-segment, 489-actuator Iris AO MEMS DM. The AO-OCT is designed for a 7.5mm pupil, with 13 discrete mirror segments across the pupil diameter. Retinal images were obtained on normal human subjects at 4 and 10 degrees in the nasal retina. The scan size for each B-scan was 0.5°, corresponding to approximately 150µm at the retina.
Distinct retinal layers were visible from the nerve fiber layer, to the inner and outer photoreceptor segments, through to the retinal pigment epithelium. Moreover, individual cone photoreceptors were clearly visible in images at 4 and 10 degrees eccentricity. The lateral spacing of the cones was measured to be 6.4±1.5 microns at 4° nasal, and 10.4±3.8 microns at 10°. The inner segment length of the cones was found to be 32.9±5.7 microns at 4°, and 24.5±3.0 microns at 10°. The outer segment length was correspondingly found to be 26.2±1.9 microns at 4°, and 27.8±1.4 microns at 10°. These results are in good agreement with histology.
The combination of AO with the use of a higher segment MEMS DM with established OCT technology has enabled us to resolve fine retinal structure unseen with conventional OCT technologies and promises to be highly valuable in the study of retinal disease and injury.
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