In vivo imaging of the fine structure of rhodamine-labeled macaque retinal ganglion cells

PURPOSE. The extent to which the fine structure of single ganglion cells, such as dendrites and axons, can be resolved in retinal images obtained from the living primate eye was investigated. METHODS. Macaque retinal ganglion cells were labeled with retrograde transport of rhodamine dextran injected into the lateral geniculate nucleus. Fluorescence images of the ganglion cells were obtained in vivo with an adaptive optics scanning laser ophthalmoscope. RESULTS. Axons and dendritic arborization could be resolved in primate retinal ganglion cells in vivo, comparing favorably in detail with ex vivo confocal images of the same cells. The full width at half maximum of the transverse line spread function (LSF) was 1.6 mu m, and that of the axial point spread function (PSF) was 115 mu m. The axial positional accuracy of fluorescencelabeled objects was approximately 4 mu m. CONCLUSIONS. This in vivo method applied to ganglion cells demonstrates that structures smaller than the somas of typical retinal cells can be accessible in living eyes. Similar approaches may be applied to image other relatively transparent retinal structures, providing a potentially valuable tool for microscopic examination of the normal and diseased living retina.