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1 From the Department of Ophthalmology and Visual Science, University of Texas Medical School at Houston; and the 2 College of Optometry, University of Houston.
PURPOSE. To evaluate the differential effects of ganglion cell depletion from experimental glaucoma on the relative metabolic activities of neurons in the parvo (P)- and magno (M)-cellular visual pathways of the macaque visual system.
METHODS. Monocular experimental glaucoma was induced in monkeys (Macaca mulatta and M. fascicularis) by applying a laser to the trabecular meshwork to increase intraocular pressure (IOP). After other behavioral and electrophysiological studies, the lateral geniculate nuclei (LGNs) and the primary visual cortices were analyzed for functional afference from surviving ganglion cells, indicated by cytochrome oxidase (CO) histochemistry.
RESULTS. CO reactivity (COR) indicated a general reduction in neural metabolism
with increasing severity of glaucoma. COR in the LGNs was reduced to
the same degree in both the P- and M-cellular layers. In layer 4Cß of
the V1 cortex, the reactivity was always reduced more than in the layer
4C
division.
CONCLUSIONS. Experimental glaucoma in monkeys reduces visual afference to the
central nervous system, thereby reducing the metabolic drive as
indicated by COR. The detrimental effect of glaucoma did not appear to
be any greater for the M-cell, rather than the P-cell pathway in the
LGN or in the visual cortex. Both are affected by the duration and
severity of the experimental glaucoma. Overall, the alterations in
metabolism of neurons in the parallel visual pathways supplied by the
P and Pß ganglion cells do not suggest that tests based on the
functional properties of one or the other would provide optimal
assessment of glaucoma.
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