CHANGE IN THE OPTIC DISC AND NERVE-FIBER LAYER ESTIMATED WITH THE GLAUCOMA-SCOPE IN MONKEY EYES

Purpose: The purpose of this research was to measure quantitatively ch anges in the position of the optic disc and nerve fiber layer during a cute and chronic experimental conditions simulating glaucoma in monkey eyes. Methods: The positions of the surface of the optic disc and per ipapillary nerve fiber layer were imaged in cynomolgus monkey eyes wit h the Glaucoma-Scope. Acute intraocular pressure change was produced b y anterior chamber cannulation. Chronic change was induced by trabecul ar laser scarring leading to chronic experimental glaucoma and by orbi tal transection of the optic nerve. Results: Mean backward movements o f the disc surface of 50-60 mu m were detected when intraocular pressu re was elevated to 45 mm Hg for 45 min. The disc position reverted in viscoelastic fashion toward its original location on normalization of pressure. Loss of nerve fibers induced by elevated intraocular pressur e was more closely related to change in the mean position of the disc (MPD) than to change in cup/disc ratio. Chronic glaucoma led to much d eeper excavation of the disc than experimental optic atrophy, but peri papillary atrophy was similar in the two conditions with the index, ne rve fiber layer area, whose values correlate well with the number of n erve fibers in an eye that is estimated histologically (r(2) = 0.75, p = 0.003, n = 9). Conclusion: The optic disc behaves in a visco-elasti c manner with change in intraocular pressure. Composite data indices t hat represent the mean surface topography of the disc and peripapillar y region can be used to estimate the degree of glaucoma damage.