Posterior scleral thickness in perfusion-fixed normal and early-glaucoma monkey eyes

To characterize posterior scleral thickness in the normal monkey eye and to assess the effects of acute (15- to 80-minute) and short-term chronic (3- to 7-week) intraocular pressure (IOP) elevations.

Both eyes of four normal monkeys (both eyes normal) and four monkeys with early glaucoma (one eye normal and one eye with induced chronic elevation of IOP) were cannulated. In each monkey, IOP was set to 10 mm Hg in the normal eye and 30 or 45 mm Hg in the contralateral eye (normal or early glaucoma) for 15 to 80 minutes. All eight monkeys were perfusion fixed, yielding eight low IOP-normal eyes, four high IOP-normal eyes, and four high IOP-early glaucoma eyes. Posterior scleral thickness was measured histomorphometrically at 15 measurement points within each eye, and the data were grouped by region: foveal, midposterior, posterior-equatorial, and equatorial.

Overall, posterior scleral thickness was significantly different in the various regions and among the treatment groups (P < 0.0001). In the low IOP-normal eyes, the posterior sclera was thickest in the foveal region (307 microm) and thinner in the midposterior (199 microm), posterior-equatorial (133 microm), and equatorial (179 microm) regions. In the high IOP-normal and high IOP-early glaucoma eyes, the posterior sclera was thinner both overall and within specific regions, compared with the low IOP-normal eyes.

The posterior sclera in the perfusion-fixed normal monkey eye thins progressively from the fovea to the equator and is thinnest just posterior to the equator. Acute and short-term chronic IOP elevations cause regional thinning within the posterior sclera of some monkey eyes, which significantly increases stresses in the scleral wall.