Symblepharon - Treating Diseases of the Ocular Surface
The goal of ocular surface reconstruction is to reconstruct a functional ocular surface. Buccal mucosa or preserved amniotic membrane can be employed.
- Mucous membrane grafting has rarely been used as a treatment for unilateral chemical injury and is used in desperate cases of bilateral injury where advancement of Tenon's capsule is not possible and allograft limbal tissue is not available.
- Amniotic membrane transplantation provides a favorable extracellular matrix substrate for epithelial migration and adhesion. This procedure is not effective in replacing the normal stem cells. An amniotic membrane transplant is often one step in a sequence of procedures.
Steps in the surgical technique include:
- Remove scar tissue of the ocular surface
- Perform superficial keratectomy
- Recess the residual conjunctival free border toward the fornix
- Drape the amniotic membrane over the denuded ocular surface
- Suture graft to the free conjunctival tissues
- Perform partial tarsorrhaphy to prevent graft movement
- Use a conformer to prevent the adhesion of mucosal membranes
Mechanisms of Action Recent reports indicate that the potential mechanisms of action may possibly include the following:
- The basement side of the membrane is an ideal substrate for supporting the growth of epithelial progenitor cells by prolonging life span and maintaining clonogenicity . This action supports why amniotic membrane transplantation can be used to expand remaining limbal stem cells and corneal transient amplifying cells during the treatment of partial limbal (stem cell) deficiency . In adds to, it also explains why amniotic membrane transplantation can be used to facilitate epithelialization for persistent corneal epithelial defects with stromal ulceration . In tissue cultures, amniotic membrane supports limbal epithelial cells grown from explant cultures and the resultant epithelial cells-amniotic membrane can be transplanted back to reconstruct the damaged corneal surface . The amniotic membrane can also be used to promote non-goblet cell differentiation of the conjunctival epithelium . Conjunctival goblet cell differentiation is further promoted by coculturing them with conjunctival fibroblasts on the same side of the basement membrane . These data supports why conjunctival goblet cell density is promoted following amniotic membrane transplantation in vivo
- The stromal side of the membrane contains a unique matrix component that suppresses TGF-b signaling, proliferation and myofibroblast differentiation of normal human corneal and limbal fibroblasts . This action explains why amniotic membrane transplantation helps reducing scars during conjunctival surface reconstruction, preventing recurrent scarring after pterygium removal , and reducing corneal haze following PTK and PRK . Although such an action is more potent when fibroblasts are in contact with the stromal matrix, a lesser effect is also noted when fibroblasts are separated from the membrane by a distance, suggesting that some diffusible factors might also be involved in adds to to the insoluble matrix components in the membrane. In line with this thinking, several growth factors have been identified in the amniotic membrane .
- The stromal matrix of the membrane can also exclude inflammatory cells by rendering them into rapid apoptosis , and contains various forms of protease inhibitors . This action explains why stromal inflammation is reduced after amniotic membrane transplantation and corneal neovascularization is mitigated , actions important for preparing the stroma for supporting limbal stem cells to be transplanted either at the same time or later . This action also explains why keratocyte apoptosis can be reduced and hence the stromal haze.