The challenge of cellular resolution in the living eye

Imaging the human retina in-vivo with high resolution of enormous interest not only in ophthalmology but also in neurology. As the retina can be seen as extension of the brain's neural  tissue, it is straightforward to assume that the retina is equally affected by neurodegenerative diseases-  casting the phrase of “the eye as window to the brain”. Despite the elegance of non-invasive diagnosis of brain diseases, achieving high resolution needs to overcome the significant aberrations introduced by the imperfect ocular optics, as well as motion artifacts. The first issue has only been solved through expensive adaption of adaptive optics methods in ocular imaging. However, mainly two dimensional sections of the retina have been imaged with high resolution. But the  combination of AO with optical coherence tomography (OCT) promises to achieve high isotropic resolution in all three dimensions. In a recent work we demonstrated how to achieve in a pure computational manner aberration correction of retinal images operating on OCT data in 3D. A remaining challenge are motion artifacts, which can only be properly managed through increased acquisition speed. For this task we first demonstrate small field-of-view imaging with a scanning OCT system. We then show how the FOV can be extended by switching to line field illumination and detection. Further gain in speed is achieved by a line field holography method with up to 100Hz en-face image rate. Finally we demonstrate how computational AO also provides high resolution angiography images without the need of contrast agents.