Purchase this article with an account.
M. Girard, J.C. Downs, C.F. Burgoyne, J.–K.F. Suh; Experimental Surface Strain Mapping of Porcine Peripapillary Sclera Under Intraocular Pressure . Invest. Ophthalmol. Vis. Sci. 2005;46(13):1271.
Download citation file:
© ARVO (1962-2015); The Authors (2016-present)
To experimentally characterize 2–D surface mapping of the deformation pattern of porcine peripapillary sclera following acute elevations of intraocular pressure (IOP) from 5 to 45 mm Hg.
Four porcine eyes were obtained within 48 hours post mortem and dissected to the sclera. After the anterior chamber was removed, the posterior sclera shell was then mounted at the equator on a custom–built pressurization device, which internally pressurized the sclera shell with basic saline at 22°C. IOP was incrementally increased to 5, 10, 30, and 45 mmHg (± .15 mm Hg), and the surface deformation of the peripapillary sclera immediately adjacent to the dural insertion was tracked using black polystyrene microspheres (10 µm in diameter) which were randomly scattered onto the scleral surface and optically tracked at a resolution of 2 µm/pixel one quadrant at a time, for each of four quadrants (superior, nasal, inferior, and temporal).The 2–D displacement data of the markers were extracted using the optical flow equation1, smoothed by a weighting function interpolation2, and converted to the corresponding Lagrangian finite surface strain.
In all four quadrants of each eye, strain was the highest immediately adjacent to the scleral canal and was principally circumferential in trajectory (see figure). Average maximum Lagrangian strain for all quadrants was 1.25% ± 0.35 from 5 mm Hg to 10 mm Hg, 1.38% ± 0.43 from 10 mm Hg to 30mm Hg and 0.34% ± 0.10 from 30 mm Hg to 45 mm Hg. For each shell, scleral stiffness was low between 5 and 10 mm Hg, but dramaticly increased for each elevation increment beyond 10 mm Hg.
Peripapillary deformation following acute IOP elevations from 5 to 45 mm Hg appears to be governed by the underlying scleral collagen microstructure (as characterized by Koktt, Hernandez, Quigley and others) and may be in the high–stiffness region of the stress–strain curve of the sclera.
References:1) BD Lucas and T Kanade, Proc. DARPA Image Understanding Workshop, 121–130, 1981.
2) R. A. Gingold and J. J. Monagham, Mon. Not. R. astr. Soc. 181:375–389, 1977.
This PDF is available to Subscribers Only