Correspondence Address:
Pulkit Gupta
Department of Ophthalmology, JSS Medical College and Hospital, Mysore-570015, Karnataka
India

Full Text

Sir,

We applaud Kawano et al. for the path breaking surgical modality devised by them to combat the ever dogging degenerative condition 'pterygium'. [1] We take this opportunity to share our enthusiasm in the worth of stem cell transplantation in the management of similar and other disorders.

Stem cells are undifferentiated cells that possess self-renewing capacity and have the ability to give rise to multiple cell types. They exist throughout the body of adult organisms and can be generated from the patient's own tissues, thus breaching the immunological barrier to their acceptance. [2]

The current stem cell research in ophthalmology focuses on isolation, purification, expansion and differentiation of embryonic stem cells, or trans-differentiation of adult stem cells, into target cells e.g. differentiation of retinal stem cells from human retinoblastomas. This is followed by tissue engineering of ocular surface tissues by 3-dimensional dynamic culture and construction of natural animal models of eye diseases.

Limbus at the ocular surface forms a habitat for basal stem cells which are stimulated to divide and undergo differentiation to form transient amplifying cells (TACs) to post-mitotic cells (PMCs) and finally terminal differentiated cells (TDCs). Their presence allows continued replacement and regeneration of tissues. Identification is done by markers e.g. titrated thymidine, p63, Lucifer yellow etc.

Stem cell deficiency occurs as a sequel to various disorders e.g. cicatricial pemphigoid, stevens-johnson syndrome, epidermal necrolysis, chemical and thermal trauma etc. which leads to invasion of the cornea by vascularized conjunctival epithelium leading to functional blindness. [2],[3] Limbal stem cell transplantation involves replacing the lost cell population in such eyes with a hope to restore vision. It can be performed by various modalities as Limbal autograft transplantation (first described by Kenyon and Tseng, transplantation of 2 four clock hour segments), Allograft transplantation (360° annulus from cadaveric donor eyes). Amniotic membranes have also gained popularity as these potentiate epithelial migration, possess growth factors and anti-inflammatory properties. [3],[4] Bio-engineered ocular surface equivalents and serum-free conjunctival tissue equivalents are the newest developments with promising results, formed by ex-vivo expansion of limbal cells on substrates (fibrin based or amniotic membranes) in-vitro followed by transplantation. These cause minimal iatrogenic trauma to donor eye, elimination of chances of immunological rejection and faster rehabilitation, thus possess all the merits of prior techniques minus the demerits and represent the future for replacement and regeneration of ocular tissues. [3] Retina is another exciting milestone in stem cell research. Stem cells can be derived from retinal pigment epithelium and muller glial cells. When cultured in the presence of mitogens, neural cells show differentiation into photoreceptors i.e. display a possibility for initiation of stem cell potential. Such cells selectively target neovascularization and gliosis and provide neurotrophic effects. In animal models of retinitis pigmentosa and macular degeneration, transplantation has produced clinical improvements. [5] Corroborated by the countless exemplifications in the literature it will not be erroneous to state that stem cells represent the future of management of ocular surface, retinal and other disorders in ophthalmology.

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