RETINAL INPUTS TO THE MONKEYS LATERAL GENICULATE-NUCLEUS IN EXPERIMENTAL GLAUCOMA

1. The large, alpha type retinal ganglion cells (M-cells) that project to the magnocellular layers of the lateral geniculate nucleus (LGN) a re thought to be preferentially damaged in glaucoma. To test this hypo thesis, we employed microelectrode recording techniques to analyze the response properties of individual LGN neurons in both the parvo- and magnocellular layers of nine monkeys with experimental glaucoma. 2. Th e intraocular pressure of one eye of each monkey was elevated by laser trabeculoplasty. The electrophysiological experiments were conducted following survival periods of 20-52 months. 3. We found a reduction in the encounter rate for neurons in LGN laminae innervated by the treat ed eyes that varied as a function of eccentricity. However, in a given animal the relative reduction in retinal inputs was the same for both the parvo- and magnocellular layers. Quantitative investigations of o rientation bias and spatial frequency tuning for individual cells demo nstrated that the surviving LGN neurons had normal response properties , when receptive field eccentricity was taken into account. 4. Our res ults indicate that (1) the visual losses in long-standing experimental glaucoma are due to retinal ganglion cell loss rather than a reductio n in the functional capacity of surviving neurons, and (2) the retinal ganglion cells that project to the magnocellular LGN are not selectiv ely damaged in long-standing experimental glaucoma. It appears that th e larger members of all functional ganglion cell classes are more susc eptible to glaucomatous damage than their respective smaller members.