Daily exposures to relatively small suberythemogenic fluences of UVA (50-200 kJ/m2) for 8 days resulted in cumulative morphological skin alterations indicative of early tissue injury. Histologically, irradiated skin revealed epidermal hyperplasia, inflammation and deposition of lysozyme along the dermal elastic fiber network. Sunburn cells were also present within the epidermis. These changes were quantified by image analysis and were found to be related to the cumulative UVA fluence. A long UVA waveband (UVAI, 340-400 nm) was as effective as a broad UVA band (320-400 nm), suggesting that these changes are induced by longer UVA wavelengths.

Epithelial stem cells play a central role in tissue homeostasis, wound repair, and carcinogenesis. Corneal epithelial stem cells have been demonstrated to reside in the limbal epithelium, while the fornical zone of the conjunctiva appears to be a predominant site of conjunctival epithelial stem cells. Stem cells of the corneal and conjunctival epithelia, as well as the hair follicle and interfollicular epidermis share important features: they are capable of self renewal; they are relatively quiescent (slow-cycling); they can be induced to proliferate; and they are multipotent. Its becoming apparent that a certain degree of flexibility exists between corneal and hair follicle keratinocytes. Eye (2003) 17, 937-942.