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C. F. Burgoyne, H. Yang, I. Sigal, M. Roberts, H. Thompson, J. C. Downs; Deformation of the Normal Monkey Optic Nerve Head (ONH) Connective Tissues Following Acute IOP Elevation Within 3D Histomorphometric Reconstructions. Invest. Ophthalmol. Vis. Sci. 2009;50(13):4897.
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To characterize ONH connective tissue deformation following acute (15 to 30 minutes) IOP elevation (from 10 to 30 or 45 mm Hg) within 6 young adult normal monkeys using 3D histomorphometry.
Trephinated ONH and peripapillary sclera from both eyes of 6 monkeys (perfusion fixed with one eye at IOP 10 mm Hg and the other following IOP elevation to 30 (n=3 eyes) or 45 (n=3 eyes) mm Hg were serial sectioned, 3D reconstructed, 3D delineated and quantified. For each monkey, inter-eye (high IOP eye minus IOP 10 eye) differences for each parameter were calculated and compared by ANOVA overall and regionally. PID maximum deformations for each parameter were defined to be those that exceeded the maximum physiologic inter-eye difference (PID) within a group of 6 previously characterized, bilaterally normal monkeys (Yang, et al, IOVS, in press)
Regional PID maximum deformations compatible with regional outward bowing of the peripapillary sclera and axial contraction and radial expansion of the scleral canal were present in most eyes. Regional thinning of the lamina cribrosa was accompanied by minimal inward (n=3) or outward (n=3) deformation in all eyes. No increase in deformation was seen in the IOP 45 versus the IOP 30 eyes. The one eye subjected to 30 rather than 15 minutes of IOP elevation demonstrated the largest deformations. Inward laminar deformation accompanied radial canal expansion in n=3 eyes and outward laminar deformation accompanied radial canal contraction or stability in n=2 eyes.
ONH connective tissue alterations following acute IOP elevation in the young adult monkey involves regional thinning, stretching and deformation of both the lamina cribrosa and peripapillary sclera (figure). The viscoelastic (time-dependant) character of these alterations as well as their compressive, expansile and shear effects on the contained axons, astrocytes and laminar and posterior ciliary circulations remain to be determined.
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