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Y. Zhang, B. Cense, R. Jonnal, W. Gao, D. Miller; Speckle Reduction in Retina Imaging With Adaptive Optics Optical Coherence Tomography. Invest. Ophthalmol. Vis. Sci. 2007;48(13):2851.
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© ARVO (1962-2015); The Authors (2016-present)
Recent imaging of the in vivo human retina with adaptive optics spectral-domain optical coherence tomography (AO SD-OCT) has revealed the three-dimensional morphology of individual cone photoreceptors. Individuation of other retinal cells, however, has proven more difficult. This is likely because of the lower contrast of these cells in conjunction with masking by high contrast speckle noise that is ubiquitous in OCT images, especially at the 3D resolution limit. To this end, we propose a novel speckle reduction technique and evaluate it for AO SD-OCT imaging of the retina.
A fiber-based, high-resolution AO SD-OCT retina camera was developed for high-speed imaging of retina in vivo. The SD-OCT subsystem included a broadband superluminescent diode (=840 nm, Δ=50 nm) and a linescan detector. The AO sub-system included an AOptix bimorph mirror and a Shack-Hartmann wavefront sensor that operated at closed loop up to 25 Hz and corrected the ocular aberration across a 6.6 mm pupil. A bite bar and forehead rest stabilized the subject’s head. A-scans were acquired at 73,000/s and combined to form volume images. Speckle reduction involved manipulation of the spectrum and optical path length followed by image registration and averaging.
Transverse and axial resolution of the AO SD-OCT instrument were measured at 3 and 5 µm, respectively. The centroid RMS error of the AO system was reduced by a factor of three. Small volume and B-scan images of the living retina were successfully acquired at several retinal eccentricities within a short time to minimize eye motion artifacts. The large stroke of the bimorph mirror was used to focus through the retina and onto specific retinal layers, increasing the local signal to noise. All major layers of retina were clearly observed in the volume images. Application of the speckle reduction technique was found to reduce speckle contrast by 4.1 dB.
A new speckle reduction technique was evaluated for AO SD-OCT retinal imaging. Results indicate the technique can be readily applied to AO SD-OCT and holds promise for elucidating additional retinal cells.
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