Jason Porter

We demonstrate here a method to image individual primate retinal neurons in vivo. Following the method of Dacey et al. 2003, we injected the LGN of healthy monkeys with rhodamine dextran, which is retrogradely transported to retinal ganglion cells. The monkey was sedated and in vivo images were acquired with a custom built, high resolution fluorescent scanning laser ophthalmoscope sampling the retina as finely as 512 pixels/deg. For fluorescence imaging, an argon/krypton laser provided 530 nm excitation light, and direct reflectance images could be obtained simultaneously with light from an 808nm laser diode. Estimated resolution of 2–5?m was achieved in reflectance and fluorescent images despite the small numerical aperture and higher order aberrations of the eye. Ganglion cells at 25 degrees eccentricity were resolved in individual frames. Extended light exposure with a small intense patch of light produced enhanced fluorescence (“fireworks”) similar to that observed in vitro by Dacey et al. 2003. Individual dendrites were not resolved, in part because of retinal image blur caused by the eye's aberrations. Future experiments will include the use of adaptive optics to reduce aberrations. In vivo imaging of primate ganglion cells may be useful in a number of future applications. For example, the phototoxicity of rhodamine can be exploited to create spatially localized lesions in individual classes of ganglion cell, allowing the visual significance of these classes of cells to be revealed in psychophysical experiments.