Deformation of the Normal Monkey Optic Nerve Head Connective Tissue Following Acute IOP Elevation Within 3-D Histomorphometric Reconstructions
Hongli Yang 1*,
J. Crawford Downs 2,
Ian Alejandro Sigal 2,
Mike D Roberts 3,
Hilary Thompson 4,
and
Claude F. Burgoyne 5
1 Optic Nerve Head Research Laboratory, Devers Eye Institute, Portland, Oregon, United States; Biomedical Engineering, Tulane University, 500 Lindy Boggs, New Orleans, Louisiana, 70118, United States; Ocular Biomechanics Laboratory, Devers Eye Institute, Portland, Oregon, United States
2 Biomedical Engineering, Tulane University, 500 Lindy Boggs, New Orleans, Louisiana, 70118, United States; Ocular Biomechanics Laboratory, Devers Eye Institute, Portland, Oregon, United States
3 Ocular Biomechanics Lab, Devers Eye Institute, Portland, Oregon, United States
4 School of Public Health, LSU Health Sciences Center, New Orleans, Louisiana, United States
5 Optic Nerve Head Research Laboratory, Devers Eye Institute, Portland, Oregon, United States
* To whom correspondence should be addressed. E-mail: hyang{at}deverseye.org.
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Abstract |
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Purpose. To characterize optic nerve head (ONH) connective tissue deformation following acute (15 or 30 minutes) intraocular pressure (IOP) elevation within six adult normal monkeys using 3-D histomorphometry.
Methods. Trephinated ONH and peripapillary sclera from both eyes of six monkeys, each perfusion fixed with one eye at IOP 10 mmHg and the other at IOP 30 or 45 mmHg by anterior chamber manometer) were serial sectioned, 3-D reconstructed, 3-D delineated and quantified using standard parameters. For each monkey, inter-eye differences (high IOP eye minus IOP 10 eye) for each parameter were calculated and compared by ANOVA and EPIDmax both overall and regionally. EPIDmax deformations for each parameter were defined to be those statistically significant differences that exceeded the maximum physiologic inter-eye difference within six bilaterally normal monkeys of a previous report.
Results. Regional EPIDmax laminar thinning, posterior bowing of the peripapillary sclera, thinning and expansion of the scleral canal were present in most high IOP eyes and were colocalized in those demonstrating the most deformation. Laminar deformation was minimal and not only posterior but in some cases anterior in the high IOP eyes. No increase in deformation was seen in the IOP-45 versus the IOP-30 eyes.
Conclusion. ONH connective tissue alterations following acute IOP elevation involve regional thinning, stretching and deformation of the lamina cribrosa and peripapillary sclera which are minimal to modest in magnitude. The time-dependent character of these alterations, as well as their compressive, expansile, and shear effects on the contained axons, astrocytes, laminar and posterior ciliary circulations remain to be determined.
Key Words:
glaucoma, optic nerve head, lamina cribrosa, Acute IOP elevation, Neural Canal, Peripapillary Sclera
