Ocular Cicatricial Pemphigoid

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OCP is a chronic progressive inflammatory disease that causes bilateral progressive subconjunctival fibrosis eventuating in a blind scarred eye in untreated cases. It is characterized by autoantibodies, most commonly IgG, that bind to corneal epithelial basement membrane zone (BMZ) autoantigens, namely ^4 protein of the a6^4 integrin [21] and epiligrin [22]. The autoantibody formation may be triggered in genetically predisposed individuals by environmental triggers such as ocular exposure to epinephrine, idoxuridine, and phos-pholine iodide [23]. The HLA-DQB1*0301 gene (DQw7) confers an increased genetic predisposition to OCP possibly by having a role in T cell recognition of basement membrane antigens, resulting in anti-BMZ autoantibody production [23]. Binding of autoantibody to the target autoantigen at the epithelial BMZ leads to the development of a type II hypersensitivity reaction involving complement activation, deposition and inflammatory cell infiltration [23]. The conjunctiva of OCP patients has been shown to be infiltrated with predominantly T cells (activated phenotype; surface IL-2 expression), with a 3-fold increase in the epithelium and a 20-fold increase within the substantia propria [24], along with an increased number of macrophages, dendritic cells and neutrophils [24].

The infiltrating macrophages and conjunctival fibroblasts have been implicated in subepithelial fibrosis, which is a key event in the extensive conjunctival cicatrization seen in this disease. Fibrogenic and angiogenic cytokines, such as TGF-p, platelet-derived growth factor, and basic fibroblast growth factor are produced by the conjunctival macrophages which leads to fibroblast migration and proliferation, as evident by the abnormally hyperproliferative conjunctival fibroblasts of patients with OCP [25]. These activated fibroblasts produce an abnormal new extracellular matrix and collagen, thus causing the subepithelial fibrosis that characterizes OCP [23].

Progression of subepithelial conjunctival fibrosis in OCP leads to the formation of symblepharon (fibrotic bands between palpebral and bulbar conjunctiva) and ankyloblepharon (fusion of the lower eyelid to the bulbar conjunctiva) resulting in restriction of ocular mobility. Scarring also causes trichiasis and distichiasis due to alterations in eyelash follicle orientation, and this together with severe dry eye due to scar-induced blockage of tear gland openings causes damage to the corneal epithelium. Advanced OCP is hence accompanied by blinding keratopathy, corneal neovascularization, pseudopterygium formation, and progressive thinning and perforation. Bacterial superinfection follows due to several factors including use of topical steroids, bandage contact lenses, chronic irritation due to trichiasis, meibomitis and lagophthalmos. OCP is an example of an immune-mediated disorder with the primary pathology in the conjunctiva with collateral damage to the neighboring cornea and adnexa as extensive cicatrization spills over into the neighboring structures.

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