CHEMICAL INJURIES OF THE EYE - CURRENT CONCEPTS IN PATHOPHYSIOLOGY AND THERAPY

Chemical injuries of the eye may produce extensive damage to the ocula r surface epithelium, cornea, and anterior segment, resulting in perma nent unilateral or bilateral visual impairment. Pathophysiological eve nts which may influence the final visual prognosis and which are amena ble to therapeutic modulation include 1) ocular surface injury, repair , and differentiation, 2) corneal stromal matrix injury, repair and/or ulceration, and 3) corneal and stromal inflammation. Immediately foll owing chemical injury, it is important to estimate and clinically grad e the severity of limbal stem cell injury (by assessing the degree of limbal, conjunctival, and scleral ischemia and necrosis) and intraocul ar penetration of the noxious agent (by assessing clarity of the corne al stroma and anterior segment abnormalities). Immediate therapy is di rected toward prompt irrigation and removal of any remaining reservoir of chemical contact with the eye. Initial medical therapy is directed toward promoting re-epithelialization and transdifferentiation of the ocular surface, augmenting corneal repair by supporting keratocyte co llagen production and minimizing ulceration related to collagenase act ivity, and controlling inflammation. Early surgical therapy, if indica ted, is directed toward removal of necrotic corneal epithelium and con junctiva, prompt re-establishment of an adequate limbal vascularity, a nd re-establishment of limbal stem cell populations early in the clini cal course, if sufficient evidence exists of complete limbal stem cell loss. Re-establishment of limbal stem cells by limbal autograft or al lograft transplantation, or by transfer in conjunction with large diam eter penetrating keratoplasty may facilitate development of an intact, phenotypically correct corneal epithelium. Limbal stem cell transplan tation may prevent the development of fibrovascular pannus or sterile corneal corneal ulceration, simplify visual rehabilitation, and improv e the visual prognosis. Advances in ocular surface transplantation tec hniques which allow late attempts at visual rehabilitation of a scarre d and vascularized cornea include limbal stem cell transplantation for incomplete transdifferentiation and persistent corneal epithelial dys function, and conjunctival and/or mucosal membrane transplantation for ocular surface mechanical dysfunction. Rehabilitation of the ocular s urface may be followed, if necessary by standard penetrating keratopla sty if all aspects of ocular surface rehabilitation are complete, or b y large diameter penetrating keratoplasty if successful limbal stem ce ll transplantation cannot be achieved but other ocular surface rehabil itation is complete. (C) 1997 by Elsevier Science Inc.