The Fox Center for Vision Restoration launches an exciting lecture series focusing on ocular regeneration and new therapies.
Distinguished national and international speakers will present their innovative and multidisciplinary approaches to finding cures for vision impairment. The objective of this lecture series is to accelerate research through knowledge sharing, partnership building and out of the box thinking.
Dr. Virender Singh Sangwan has made innovative contributions in ophthalmic research, particularly in having perfected the method of limbal stem cell culturing. He was able to thus produce transparent, stitchable epithelium and transplant it on needy human patients who had their vision substantially restored. He has been able to restore vision to over 600 patients, whose eyesight was lost due to burns and damage of the ocular outer surface.
Virender Singh Sangwan completed his basic medical education from Maharshi Dayanand University, Haryana, in 1986 and MS Ophthalmology in 1991. He did a fellowship in Cornea & Anterior Segment at L V Prasad Eye Institute, and another in Immunology & Uveitis Services at Harvard Medical School, USA, before joining LVPEI.
He has worked as Field Medical Director at ORBIS International, Inc., New York, and chief fellow, immunology & uveitis service of Harvard Medical School, Boston. He is also Adjunct Associate Professor of Ophthalmology, University of Rochester, New York, USA.
The surface of the human eye is covered by a diverse population of stratified non-keratinized epithelial cells namely the columnar cells of the conjunctiva and the squamous cells of the limbus and the cornea. The limbal region is of particular importance because of the presence of adult stem cells which divide slowly throughout life continuously replenishing the multiple layers of mature differentiated epithelium of the cornea. Similarly stem cells for the conjunctival epithelium have been found to be present in the fornix and throughout the bulbar conjunctiva.
Several diseases, acute and chronic, lead to destruction of the ocular surface epithelium in general and the stem cells in particular. Acute damage to the ocular surface occurs commonly in chemical or thermal burns or rarely in Stevens Johnson syndrome (SJS) or Toxic Epidermal Necrolysis (TEN). Whereas chronic smoldering inflammatory disorders like severe ocular allergy in Vernal Keratoconjunctivits (VKC) and Ocular Cicatricial Pemphigoid (OCP) causes progressive damage to the ocular surface epithelium.
If the damage is limited to the limbal stem cells and corneal epithelium it manifests clinically as loss of transparency of the epithelium, vascularization, frequent epithelial breakdown and persistent epithelial defects. When the damage is more extensive there is associated scarring of the conjunctiva, symblepharon formation, forniceal shortening, and loss of the mucin producing goblet cells and lacrimal glands leading to a rough irregular ocular surface and a scanty unstable tear film. In most severe cases losses of both the limbal and conjunctival stem cells leads to dermalization of the entire ocular surface.
Reconstruction of the ocular surface in such conditions involves regeneration of the destroyed epithelial surface, conjunctiva for conjunctiva and cornea for cornea. Needless to say a source of stem cells is required which can be transplanted onto the affected eye to achieve not only repopulation of the surface epithelium but to create a reserve for continuous replenishment. If the affection is unilateral, which is common in cases of chemical injury, the fellow eye can serve as the donor. If both eyes are damaged then there can be two approaches: either a living donor (related or unrelated) may be chosen or a cadaveric donor may serve as the source of these stem cells. The problem with this approach is that the recipient’s immune system must be suppressed life-long to prevent allograft rejection.
The other approach is based on the ability of adult stem cells to transdifferentiate and produce mature epithelial cells similar to the tissue they are transplanted into rather than that from which they are derived. Autologus oral mucosal or nasal mucosal stem cells can also be used as an alternative to allogenic limbal stem cells in eyes with bilateral limbal stem cell deficiency (LSCD) based on this principle.
The current standard in treating eyes with LSCD is obtaining a small biopsy from the donor limbus (autologus or allogenic) and cultivating it ex-vivo on a scaffold and transplanting the cultivated cells onto the affected eye either with or without the scaffold. This technique of cultivated limbal epithelium transplantation (CLET) allows a large population of cells to be generated from a small amount of tissue and avoids any chance of iatrogenic damage to the donor eye. The clinical results of variations of this technique have been widely reported. Our own results (57% cumulative survival in those with a minimum of 1 year follow-up) compare well with those of others (6 out of eight patients; 12 out of 16 patients with chemical burns, and 73 out of 107 chemical burns, 4 out of 9 chemical burns).
The results of allogenic CLET are not very encouraging and success in limited despite long-term immunosuppresion. Cultivated oral mucosal epithelium transplantation had shown initial promising results but late peripheral vascularization is of serious concern in these eyes. Additionally many of these eyes require an allogenic corneal transplantation after successful surface stabilization to reestablish corneal transparency. In our experience only about 50% of these allogenic corneal grafts survive to provide near normal vision. Thus whereas the treatment of unilateral LSCD has been made relatively simple with the success of autologus CLET, treatment of bilateral LSCD and especially those with bone dry eyes still remains unconquered territory for the ocular surface surgeon.
Future challenges include developing techniques to circumvent the laboratory and making limbal stem cell transplantation accessible to every corneal surgeon, developing better substrates to be used as scaffolds for CLET, and the ultimate dream of regenerating the entire cornea layer for layer with autologus cells.
Location and Address
Biomedical Science Tower South, S123
Eye and Ear Institute, 203 Lothrop Street
Pittsburgh, PA 15213