Acanthamoeba Keratitis

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Clinical Presentation

  • Slow, often protracted course; frequently several week long history
  • Typically associated with contact lenses (especially when swimming or cleaning under tap water)
    • Dendritiform corneal lesions + contact lenses = Acanthamoeba until proven otherwise!
  • Ring infiltrate + severe pain with missed/late diagnosis
  • Epithelial pseudodendrites, perineural infiltrates


  • Large corneal abrasion for specimen collection with a hockey knife and tetracaine (few Acanthamoebas in the epithelium), also therapeutic effect by removing any Acanthamoebas + better penetration
  • Consider sending in contact lens for culture
  • Confocal microscopy (with Z-ring): Cysts?


  • Initiate therapy only after a confirmed diagnosis; no immediate therapy needed!
    • Administer consistent therapy without interruption, if not possible logistically it is better to wait 1-2 days before starting
    • Trophozoites can transform into cysts in about 48 hours (after starting therapy) – cysts are much more difficult to treat!
  • Mandatory hospitalisation for therapy, including effective pain management! Outpatient treatment is usually not viable!
  • Before starting therapy: consider repeating extensive abrasion for better drug penetration
  • Therapy options:
    • Combination of
      • Brolene 0.1% gtt hourly, day and night, for 3 days
      • PHMB 0.02% gtt hourly, day and night, for 3 days
        • Alternatively to PHMB: Chlorhexidine gtt hourly
    • Then reduce frequency to every 2 hours during the day and every 4 hours at night for an additional 4-7 days (different reduction scheme possible depending on clinical presentation)
    • Then 3-4 times daily for a minimum of 4 months, usually 6-12 months
    • Combination therapy is crucial: Brolene 0.1% topical acts only on trophozoites, PHMB/Chlorhexidine act on both trophozoites and cysts!
  • consider cycloplegia (Atropine 1% gtt 2x/day depending on anterior chamber cell flare)
  • consider Flagyl or Itraconazole or Ketoconazole p.o. for advanced stages
  • Steroid therapy is controversial as it increases the virulence of Acanthamoeba!
  • Pain management according to the WHO pain ladder


  • Discharge after 3 days (no clinical improvement expected at this point!)
  • Possible follow-up intervals:
    • 1st follow-up 4-5 days after discharge (therapy adherence?)
    • 2nd follow-up after 10-14 days
    • Further check-ups every 2 weeks
  • After 1 month: consider reducing medications
    • Note: no significant improvement is expected in the first month
  • Red eye in follow-ups:
    • Side effects of drops (Brolene not well tolerated) or amoebic infection?
    • Diffuse superficial punctate keratitis: a sign that the patient has administered the drops as prescribed
  • If suspected resistance: increase treatment frequency or dosage
  • If persistent irritation after 2 months: consider differential diagnosis of immune reaction against disintegrating Acanthamoebas
    • Deep corneal stroma with vascular ingrowth?
    • consider initiating steroid therapy, only if the patient is highly compliant!
  • Duration of therapy: usually 4-6 months up to 1 year
  • Avoid corneal transplantation if possible (often requiring multiple grafts)
  • At final visit: take a photo and perform a confocal microscopy for documentation in case of potential recurrence in the future


  • EyeWiki Acanthamoeba Keratitis
  • The Wills Eye Manual: Office and Emergency Room Diagnosis and Treatment of Eye Disease; Nika Bagheri MD, Brynn Wajda MD, et al; Lippincott Williams&Wilkins; 7th Edition (2016)
  • Kanski’s Clinical Ophthalmology: A Systematic Approach; Jack J. Kanski MD, Brad Bowling MD; Saunders Ltd.; 8th Edition (2015)