Biomechanical Effects of Intraocular Pressure Elevation on Optic Nerve/Lamina Cribrosa before and after Peripapillary Scleral Collagen Cross-Linking

PURPOSE. To evaluate the biomechanical effect of intraocular pressure (IOP) elevation on the optic nerve/lamina cribrosa complex (ON/LC) and peripapillary sclera ( PS) of porcine eyes before and after localized collagen cross-linking. METHODS. Eighteen porcine globes were divided evenly into three groups. The optic nerves were transected to expose the ON/LC, and each globe was infused through an in-line pressure transducer for direct IOP control. Surface wave velocity, a nondestructive measure of tissue stiffness, was measured across the ON/LC and PS before and after collagen cross-linking at IOPs of 10 and 30 mm Hg ( groups 1 and 2) and at each globe's preinflation IOP and 80 mm Hg ( group 3). In group 3, papillary strain was measured by analyzing the displacement of fiducial marks immediately adjacent to the ON/LC by using digital photography. Cross-linking in group 1 was achieved with riboflavin-ultraviolet A (UVA) delivery to the entire ON/LC and PS and, in groups 2 and 3, with an annular sponge soaked in glutaraldehyde (GTA) and applied only to the PS. RESULTS. Native PS was significantly stiffer than the ON/LC across all experiments. Before cross-linking, IOP elevation caused significant stiffening of both the ON/LC and PS. After cross-linking with either technique, IOP elevation stiffened the PS but not the ON/LC region. In group 3, papillary strain during IOP elevation was significantly reduced after PS cross-linking. CONCLUSIONS. Stiffening of the peripapillary scleral ring reduces the biomechanical sensitivity of the ON/LC complex to IOP elevation and may represent a novel mechanism for neuroprotection in glaucoma. (Invest Ophthalmol Vis Sci. 2009; 50: 1227-1233) DOI:10.1167/iovs.08-1960