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 addition, 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 addition 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.

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