Atrophy of relay neurons in magno- and parvocellular layers in the lateralgeniculate nucleus in experimental glaucoma

PURPOSE. To determine whether in glaucoma there is atrophy of relay neurons in magnocellular and/or parvocellular lateral geniculate nucleus (LGN) lay ers projecting to the visual cortex and to compare the degree of neuronal a trophy in magnocellular layers with that in parvocellular layers. METHODS. Seven cynomolgus monkeys with unilateral experimentally induced gl aucoma and five control monkeys were studied. The left LGN neurons in magno cellular layer I and parvocellular layers 4 and 6, connected to the right g laucomatous eye were examined. Immunocytochemistry with antibody to parvalb umin was used to specifically, label relay neurons connecting to the visual cortex. Neuronal cell body cross-sectional area was estimated using unbias ed point-counting methodology. Experimental and control groups were compare d using t-tests. Analysis of covariance (ANCOVA) tests were used to compare the percentage of decrease in mean neuronal area between layers 1, 4, and 6, as a function of percentage of optic nerve fiber loss or mean IOP. There was significant correlation between percentage of optic nerve fiber loss a nd mean IOP. RESULTS. The mean cross-sectional area of relay neurons in magnocellular la yer 1 and parvocellular layers 4 and 6 were significantly decreased in glau coma compared with controls by 28%, 37%, and 45%, respectively. Neuronal ar ea decreased in a linear fashion, with increasing optic nerve fiber loss or increasing mean IOP for layers 1, 4, and 6. The percentage of neuronal shr inkage in each of parvocellular layers 4 and 6, as a function of optic nerv e fiber loss (P = 0.05; P = 0.001, respectively) or mean IOP (P = 0.046; P = 0.0008, respectively), was greater than that seen in magnocellular layer 1. CONCLUSIONS. Relay neurons in the LGN, which project to the visual cortex, undergo significant shrinkage in glaucoma, and neurons in parvocellular lay ers undergo significantly more shrinkage than neurons in magnocellular laye rs.