Towards wide-field retinal imaging with adaptive optics

In vivo imaging of the retina on humans by means of adaptive optics can lead to a significant gain in resolution. We demonstrate the realization and use of a system made of a Shack-Hartmann wavefront sensor carefully matched to a 13-actuator bimorph deformable mirror sensor, operating at a closed loop frequency of 70 Hz at lambda = 835 nm. Even with this simple but optimized system with 12 degrees of freedom, correcting only aberrations of moderate orders, we routinely and systematically obtain retinal images containing spatial information up to half the diffraction limit frequency of a dilated (7 mm) iris at a lambda = 550 nm wavelength (1.6 mum diffraction spot size). Signal-to-noise ratio on the images is limited by eye safety constraints, but is sufficient to reach the high-frequency information on single, short-exposure (7 ms) images, which clearly show individual cones and capillary details. Correction is highly depending on proper centering of the eye, achieved with an active target. Focusing through the retina is possible with a reduced depth of focus. Variability of moderate order aberrations among dilated subjects has been observed. Using an image fitting algorithm, individual images are used to build a wider field corrected image of the retina (approximate to3degrees), possibly useful for diagnosis and microcirculation analysis. (C) 2003 Elsevier B.V. All rights reserved.