Beyond the route of inoculation into the eye and external risk factors, host factors are also likely to play a significant role in the development of Acanthamoeba keratitis. In fact, studies of contact lens users in the UK, Japan, and New Zealand found that 400 to 800 per 10,000 asymptomatic contact lens users had lens storage cases contaminated with Acanthamoeba spp.[3] However, the rate of Acanthamoeba keratitis among these patients was only 0.01 to 1.49 per 10,000 contact lens users.[3] Although the exact host factors have not been fully described, it is likely that corneal epithelial defects, tear film composition, eye surface pH, and level of anti-Acanthamoeba IgA antibodies in the tear film.[6][3]