Surface tension controls capsule thickness and collagen orientation in glaucoma shunt devices.

Surgical implants to shunt aqueous humor from the eyes of glaucoma patients have been used with limited success, due to a buildup of fibrous tissue in the capsule that causes it to fail as a filtration device. Previous studies suggested that fibers orient along the principal stress lines--surface tension on the capsule directs collagen growth in order to strengthen the stretched membrane. The more tension on the capsule, the thicker the fibrous matrix. In the present study, we analyze collagen fibril and fiber bundle structure to determine whether similar stresses were placed on capsules formed around different implants. We used transmission electron micrographs and light microscopy. Results showed similar structure and collagen fiber bundle densities. This confirmed our previous conclusion that choosing a geometry that reduces surface tension minimizes capsule fibrosis and improves filtration.