Peripapillary scleral thickness in perfusion-fixed normal monkey eyes.

PURPOSE To characterize the thickness of the peripapillary sclera in perfusion-fixed normal monkey eyes so as to build accurate computational models of intraocular pressure (IOP)-related stress and strain within these tissues. METHODS Nine rhesus monkeys were perfusion fixed, each with one normal eye set to an IOP of 10 mm Hg by manometer. A 6-mm-diameter specimen containing the optic nerve head and peripapillary sclera was trephined from each scleral shell and cut into 4-microm serial sagittal sections across the scleral canal opening, either horizontally (four eyes) or vertically (five eyes). The thickness of the peripapillary sclera was measured on every 24th section at 100-microm intervals from the posterior scleral canal opening (PSCO) to the peripheral edge of the specimen. The data were pooled by quadrant (superior, inferior, nasal, and temporal), regions within each quadrant, and distance from the PSCO, overall and for individual eyes, and subjected to analysis of variance. RESULTS In terms of distance from the PSCO, the peripapillary sclera was thinnest nearest the PSCO (201 microm, nasal; 201 microm, temporal; 240 microm, inferior; 249 microm, superior), thickened progressively to a maximum in the midperiphery approximately 600 to 1000 microm from the PSCO (326 microm, nasal; 415 microm, superior; 420 microm, temporal; 422 microm, inferior), and thinned again peripherally in all quadrants. The peripapillary sclera was thinner in the nasal quadrant when compared with the other quadrants superiorly, inferiorly, and temporally (central region means of 291 microm, nasal; 369 microm, superior; 372 microm, inferior; and 369 microm, temporal; P < 0.0001). CONCLUSIONS In the normal monkey eye, peripapillary scleral thickness varies significantly with distance from the posterior scleral canal opening and is thinner in the nasal quadrant than in the other quadrants. These differences are substantial and are likely to affect the magnitude of IOP-related stress and strain within these tissues for a given level of IOP.