Off-axis detection methods in adaptive optics (AO) ophthalmoscopy can enhance image contrast of translucent retinal structures such as cone inner segments and retinal ganglion cells. Here, we propose a 2D optical model showing that the phase contrast produced by these methods depends on the offset orientation. While one axis provides an asymmetric light distribution, hence high phase contrast, the perpendicular axis provides a symmetric one, thus substantially lower contrast. We support this model with in vivo human data acquired with a multi-offset AO scanning light ophthalmoscope. Then, using this finding, we provide a post-processing method, named spatial-frequency-based image reconstruction, to optimally combine images from different off-axis detector orientations, significantly increasing the structural cellular contrast of in vivo human retinal neurons such as cone inner segment, putative rods, and retinal ganglion cells.
