Force and geometry determine structure and function of glaucoma filtration capsules.
OBJECTIVE
Glaucoma shunts vent aqueous humor to orbital tissue across a fibrous capsule. The capsule consists of collagen and fibroblasts, and its formation was assumed to be a cicatricial process. Capsule fibrosis remains the leading cause of device failure. We tested the wound healing hypothesis using morphometry and polarization microscopy and found the capsule consists not of scar tissue but rather highly organized extracellular matrix.


METHODS
Polarization microscopy reveals collagen orientation within the extracellular matrix. Rotation of the specimen in the plane of polarized light reveals collagen bundle orientation with respect to capsule surface geometry. Capsule thickness was measured and correlated with device dimension.


RESULTS
Capsule collagen is highly organized and not scar tissue. Relative orientation is predictable from simple engineering principles and shows tissue deposits reinforcing collagen parallel to its principle stress axes along the capsule surface. Capsule thickness and collagen orientation correlate with device dimension and surface geometry.


CONCLUSIONS
The corollary is true. Geometry can be used to manage the amount, distribution and orientation of collagen and thus control hydraulic conductivity and surface area of the filtration capsule.
Wilcox
Michael
M
Biology Department, United States Air Force Academy, 2355 Faculty Drive 2N224, HD USAFA/DFB, Colorado Springs, CO 80840, USA. mike.wilcox@usafa.af.mil
Kadri
Omar A
OA
D000818:Animals; D001082:Aqueous Humor / Q000378:metabolism; D001485:Basement Membrane / Q000378:metabolism / Q000648:ultrastructure; D001768:Blister / Q000378:metabolism / Q000473:pathology*; D003094:Collagen / Q000378:metabolism / Q000648:ultrastructure; D005109:Extracellular Matrix / Q000378:metabolism; D005355:Fibrosis; D020327:Glaucoma Drainage Implants; D008251:Macaca; D008855:Microscopy, Electron, Scanning; D008859:Microscopy, Polarization; D011817:Rabbits; D014945:Wound Healing
D003094:Collagen