Proliferation and apoptosis in the corneal stroma in longterm follow-up after photorefractive keratectomy

Stem Cells in the Limbal Stroma

The corneal stroma contains a population of mesenchymal cells subjacent to the limbal basement membrane with characteristics of adult stem cells. These 'niche cells' support limbal epithelial stem cell viability. In culture by themselves, the niche cells display a phenotype typical of mesenchymal stem cells. These stromal stem cells exhibit a potential to differentiate to multiple cell types, including keratocytes, thus providing an abundant source of these rare cells for experimental and bioengineering applications. Stromal stem cells have also shown the ability to remodel pathological stromal tissue, suppressing inflammation and restoring transparency. Because stromal stem cells can be obtained by biopsy, they offer a potential for autologous stem cell treatment for stromal opacities. This review provides an overview of the status of work on this interesting cell population.

Apoptosis in the initiation, modulation and termination of the corneal wound healing response

Stromal keratocyte apoptosis has been well-characterized as an early initiating event of the corneal wound healing response, triggering subsequent cellular processes that include bone marrow-derived cell infiltration, proliferation and migration of residual keratocyte cells, and, in some circumstances, generation of myofibroblast cells. Recent studies, however, have suggested a more general role for apoptosis in the overall stromal wound healing response that includes modulation and termination functions. This review article highlights, and ties together, recent studies that have demonstrated the important role apoptosis likely plays in weeks to months following an initial insult to the cornea-depending on the type and extent of corneal injury.