Acanthamoeba keratitis is a progressive, sight-threatening comeal disease. Extended wearing contact lens is one of predisposed factors. Early studies mostly focused on "improper contact-lens hygiene", which described that contact lens wearers have more opportunities to contact with pathogens directly and prone to get A. keratitis. However, improper contact-lens hygiene can not explain the phenomenon that Acanthamoeba protozoon were found in normal individuals' lens-cases. So there might be other factors related with A. keratitis. Recently, more attention has been paid on the influence of extended wearing contact lens on the innate immunity of ocular surface. It has been proven that in contact lens wearers the reactivity of polymorphonuclear leucocytes (PMNs) and the concentration of certain inflammatory mediators were significantly altered compared with that in non-lens wearers. Morever, other studies showed the important contributions of innate immunity on occurrence and development of A. keratitis. With the contribution of extended wearing contact lens on immunity and the relation between innate immunity and Acanthamoeba, we suggest that the impaired innate immunity of ocular surface may be a key bridge between extended wearing contact lens and A. keratitis. With the impaired innate immunity caused by extended contact-lens wearing, the Acanthamoeba trophozoites and cysts could not be easily killed, therefore A. keratitis was occurred and aggravated. Understanding the immunological mechanism of extended contact tens wearing on the A. keratitis may give more contributions on the research of the disease, and facilitate the production of contact tens with much higher biocompatibility. (C) 2007 Elsevier Ltd. All rights reserved.