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 changes in the position of the optic disc and nerve fiber layer during acute and chronic experimental conditions simulating glaucoma in monkey eyes. Methods: The positions of the surface of the optic disc and peripapillary nerve fiber layer were imaged in cynomolgus monkey eyes with the Glaucoma-Scope. Acute intraocular pressure change was produced by anterior chamber cannulation. Chronic change was induced by trabecular laser scarring leading to chronic experimental glaucoma and by orbital transection of the optic nerve, Results: Mean backward movements of the disc surface of 50-60 μm were detected when intraocular pressure 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 pressure 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 deeper excavation of the disc than experimental optic atrophy, but peripapillary atrophy was similar in the two conditions with the index, nerve fiber layer area, whose values correlate well with the number of nerve fibers in an eye that is estimated histologically (r² = 0.75, p = 0.003, n = 9). Conclusion: The optic disc behaves in a visco-elastic manner with change in intraocular pressure. Composite data indices that represent the mean surface topography of the disc and peripapillary region can be used to estimate the degree of glaucoma damage.