Development of a fundus camera with adaptive optics using a pyramid wavefront sensor
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This PhD thesis presents the building of an adaptive-optics system based on a pyramid wavefront sensor applied to the imaging of the human retina (fundus) in vivo. The instrument aims to simultaneaously measure the ocular aberration, and correct it to allow the imaging of the fundus. The adaptive optics system uses a high-stroke magnetically-actuated deformable mirror with 52 elements that presents a correction range best adapted to the refraction in most non-emmetropic eyes and the appropriate surface deformation required for the correction of high-order ocular aberrations. This wavefront correction system is coupled with a sensor originally used in astronomy here selected for ophthalmic use due to its adjustable dynamic range that insures characterization of the ocular measurement and due to its robustness in adaptive optics applications. The retinal imaging is based on a green illumination (530nm) commonly used in commercial fundus cameras in clinical environments but to our knowledge not yet applied in the existing high-resolution systems imaging the retina at the cellular level. The calibration of the instrument response to the ocular aberration is performed using ophthalmic lenses and custom phase plates representing typical patterns. Adaptive optics correction is applied to these complex refractive elements and to typical test objects to estimate the improvement in retinal image quality. Using safe light levels and an experimental protocol agreed by the Research Ethics Committee of the National University of Ireland, Galway, a high-resolution image of the retina was obtained after correction of the refractive error. Use of this system for imaging at the cellular level would require additional changes.