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I. L. Thornton, W. J. Dupps, J. Ramos Estaban, R. R. Krueger; The Effects of Intraocular Pressure Elevation on Papillary Stiffness Before and After Riboflavin/Ultraviolet-A Induced Collagen Crosslinking. Invest. Ophthalmol. Vis. Sci. 2007;48(13):3307.
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© ARVO (1962-2015); The Authors (2016-present)
To evaluate the biomechanical effect of riboflavin-UVA crosslinking of the lamina cribosa and peripapillary sclera of the porcine optic nerve.
Surface wave velocity (SWV) is a measure of tissue stiffness, and is performed by detecting the velocity of an ultrasonic wave between 2 points (Sonic Eye, Priavision, Menlo Park, CA). 19 porcine eyes were divided into 2 groups. In group 1 (6 eyes), the SWV across the exposed optic nerve/lamina cribrosa complex (ON/LCC) was initially measured at the eyes’ physiologic IOP and at 100 mmHg. The porcine globes were cannulated with IV tubing to facilitate the change in IOP. In group 2 (13 eyes), the pre-treatment SWV was measured across the same region and atop the peri-papillary sclera, after which both regions were treated with riboflavin 1%, Q 5 min x 6, and UVA irradiation (~365 nm at 3 mW/cm2) for 30 min per eye. The SWV was then re-measured in each eye at the pre-treatment IOP and at 100 mmHg.
In group 1, the SWV of the ON/LCC was 27.5 +1.0 m/s (mean +SD) at physiologic IOP and increased to 36.6 +0.9 mm/s at 100 mmHg (p=0.04). In group 2, crosslinking increased the stiffness of the ON/LCC from 26.0 + 1.2 to 32.8 +1.1 m/s (p<0.001), while the peripapillary sclera increased from 29.7 + 1.2 to 55.7 + 1.5 m/s (p<0.001 ). Upon rising the IOP to 100 mmHg, the SWV of the ON/LCC showed no change (p=0.1), while it increased further along the peripapillary sclera to 63.5 + 1.8 m/s (p=0.007).
IOP elevation and riboflavin/UVA crosslinking independently increased the stiffness of the ON/LCC, and the latter increased the stiffness of the peripapillary sclera. However, after crosslinking, the pressure elevation caused increase stiffness in the peripapillary sclera, but not in the ON/LCC. Based on these findings, we hypothesize that the increased stiffness of the crosslinked peripapillary scleral ring limits the impact of increasing IOP along the crosslinked lamina cribosa. This may have indications in the pathophysiology and treatment of glaucomatous optic neuropathy. Further validation of these findings are recommended with human cadaver globes and with independent crosslinking of the peripapillary sclera.
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