From the American Academy of Ophthalmology

This prospective, case-control study involved 90 daily contact lens wearers with moderate and severe keratitis, and 1,090 community controls. Both poor contact lens storage case hygiene and infrequent replacement of the contact lens case were independently associated with a higher risk of moderate and severe microbial keratitis. They note that attention to both factors together would remove 62 percent of the disease load. Other risk factors included occasional overnight contact lens use, smoking and higher socioeconomic class. Ophthalmology, August 2012