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Peripapillary Scleral Thickness in Perfusion-Fixed Normal Monkey Eyes

¹ From the Department of Biomedical Engineering, Tulane University, New Orleans, Louisiana; and the ² LSU Eye Center, Louisiana State University Health Sciences Center, New Orleans, Louisiana.

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-µm 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-µm 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 µm, nasal; 201 µm, temporal; 240 µm, inferior; 249 µm, superior), thickened progressively to a maximum in the midperiphery approximately 600 to 1000 µm from the PSCO (326 µm, nasal; 415 µm, superior; 420 µm, temporal; 422 µm, 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 µm, nasal; 369 µm, superior; 372 µm, inferior; and 369 µm, 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.

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