RELATIONSHIP OF OPTIC DISC TOPOGRAPHY TO OPTIC-NERVE FIBER NUMBER IN GLAUCOMA

Objective: To assess the relationship between in vivo measurements of optic disc topography and histomorphometric measurements of optic nerv e fiber number in glaucoma. Methods: Both eyes of 10 monkeys (Macaca f ascicularis) with laser-induced glaucoma in the right eye were studied . Optic disc topography was measured in vivo with a confocal scanning laser ophthalmoscope. Histomorphometry was performed on optic nerve cr oss sections using bright-field microscopy with camera lucida. Nerve f iber density was estimated by unbiased random sampling. Nerve fiber nu mber was estimated for each sector by multiplying nerve fiber density with neuroglial area. Nerve fiber count was compared with each of 13 g lobal optic disc topographic parameters. Results: For neuroretinal mea surements in the glaucomatous eyes, rim area, retinal nerve fiber laye r (RNFL) cross-sectional area, rim volume, and RNFL thickness correlat ed significantly with optic nerve fiber number. Differences in nerve f iber count between control and glaucomatous optic nerves showed the st rongest correlation with differences in mean height contour; this was followed by RNFL cross-sectional area, RNFL thickness, rim volume, and differences in rim area. For cup measurements in the glaucomatous eye s, cup volume below reference, cup area, mean cup depth, the ratio of cup area to disc area, and cup shape correlated significantly with ner ve fiber number. Differences in nerve fiber number between control and glaucomatous optic nerves showed the strongest correlation with diffe rences in cup shape; this was followed by mean cup depth, cup volume b elow reference, the ratio of cup area to disc area, cup area, and diff erences in cup volume below surface. No association was found between optic nerve fiber number and optic disc area in glaucomatous eyes. Con clusions: In experimental glaucoma, most optic disc topography measure s correlated significantly with optic nerve fiber number. The results of this histomorphometric study support the use of confocal scanning l aser ophthalmoscopy to evaluate optic nerve damage in glaucoma.