This is a study of optimal treatments for acanthamoeba keratitis. In the first part of the study, participants will be randomized to chlorhexidine monotherapy or chlorhexidine plus povidone iodine. After four weeks of therapy, participants will be re-randomized to early corticosteroids, later corticosteroids, or placebo.

Acanthamoeba keratitis is a rare eye infection that is difficult to treat. The mainstay of therapy is a biguanide agent such as chlorhexidine, though recent studies have found povidone iodine to be effective for killing acanthamoeba organisms in vitro. Thus, we randomize participants to topical chlorhexidine 0.04% monotherapy (i.e., routine care) versus topical chlorhexidine 0.04% plus topical poviodine iodine 2.5%. The primary outcome is clearance of acanthamoeba from the ocular surface at 4 weeks.

The role of topical corticosteroids in acanthamoeba keratitis is controversial. Topical corticosteroids can promote growth of acanthamoeba, but may also reduce inflammation and vision-threatening complications of infection. Here, we randomize participants who have completed a course of anti-amoebic therapy to one of three groups: early prednisolone sodium phosphate 1% (started at 4 weeks), late prednisolone sodium phosphate 1% (started at 6 weeks) or placebo (started at 4 weeks). The primary outcome will be visual acuity at 6 months.

Trial 1 Inclusion Criteria:

• Smear or culture positive for acanthamoeba
• Age 13 years or greater

Trial 1 Exclusion Criteria:

• Interstitial or viral keratitis on history or examination
• Corneal perforation
• Therapeutic keratoplasty for acanthamoeba keratitis
• Unwillingness or inability to follow-up (e.g., living too far from hospital)

Trial 2 Inclusion Criteria

• Smear or culture positive for acanthamoeba, with 4 weeks of anti-amoebic treatment
• Age 13 years or greater
• Willing to participate in study

Trial 2 Exclusion Criteria

• Interstitial or viral keratitis on history or examination
• Fungus identified on culture and smear after 2 weeks of anti-amoebic treatment
• Corneal perforation
• Therapeutic keratoplasty for acanthamoeba keratitis
• Unwillingness or inability to follow-up (e.g., living too far from hospital)