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Michael Pircher, Marie Laslandes, Matthias Salas, Andreas Wartak, Christoph K Hitzenberger; Increasing the field of view in high resolution imaging of the retina with adaptive optics optical coherence tomography. Invest. Ophthalmol. Vis. Sci. 2018;59(9):298.
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© ARVO (1962-2015); The Authors (2016-present)
To test the performance of an adaptive optics optical coherence tomography instrument (AO-OCT) that supports a field of view of up to 4°.
Traditional AO systems support only a limited field of view because of the small isoplanatic patch size of the eye and aberrations that are introduced by off axis propagation through the system. For high resolution systems that use the full pupil diameter of the eye (~7mm) this angle typically is around 1°. In this work we increased the angle to up to 4° through the implementation of a second deformable mirror (DM) for field correction. Thereby, the DM is placed at a location that is optically conjugated to a plane anterior to the retina. The first DM is placed traditionally in a plane that is conjugated to the pupil plane of the eye and is driven by the wavefront measurements of a Shack-Hartmann wavefront sensor. The spectral domain OCT system is based on a light source emitting at 840nm (bandwidth of 50nm, corresponding to 4.5µm axial resolution in tissue) with an A-scan rate of 100kHz. The entrance pupil diameter at the eye is 7mm which results in a transverse resolution of ~2.3µm.
Representative images that were recorded with the system are shown in the figure. Figures A and B display en-face images generated by depth integration over the junction between inner and outer segments of cones (IS/OS) (A) and rod outer segment tips (B). The false color image (C) shows the cones color coded in red and the rods in green. In the enlarged region of interest (inset) individual rods and cones can be observed. A representative B-scan of the image data is shown in (D) where discrete spacing corresponding to cone photoreceptors can be observed at both photoreceptor layers. Figure (E) shows a representative B-scan with the focus set to the nerve fiber layer. The corresponding en-face images (F, G) show individual nerve fiber bundles close to the optic disc.
The concept of two DM’s for enlarging the field of view was successfully translated to AO-OCT. Different retinal cells such as cones and rods could be visualized. The extended field of view facilitates the exact determination of the imaging location and may enable acquisition of large patches (>10°) of the retina with cellular resolution via image stitching.
This is an abstract that was submitted for the 2018 ARVO Annual Meeting, held in Honolulu, Hawaii, April 29 - May 3, 2018.
Figure: AO-OCT images retrieved with the instrument
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