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Acanthamoeba Keratitis: Symptoms, Diagnosis, Treatment, and Prevention

Sight-Threatening Corneal Infection in Contact Lens Wearers

Acanthamoeba keratitis (AK) is a rare (<1–2 per million contact lens users/year) but severe corneal infection caused by free-living Acanthamoeba spp. (ubiquitous in soil, water, air).

Risk Factors

  • Contact lens wear (85% of cases) — especially overnight, swimming/showering in lenses, improper disinfection (tap water, saline, "no-rub" solutions)
  • Corneal trauma (minor abrasion)
  • Contaminated lens cases/solutions

Symptoms (Often Disproportionate to Signs Early On)

  • Severe pain (out of proportion to exam findings) — hallmark
  • Photophobia, blurred vision, foreign body sensation
  • Tearing, redness, ring infiltrate (late), perineuritic radial keratopathy
  • Headache, nausea (from pain)

Diagnosis

  1. Clinical suspicion: CL wearer + severe pain + poor response to antibiotics.
  2. Confocal microscopy: Non-invasive; shows cysts/trophozoites (high sensitivity).
  3. Corneal scrape + culture: Non-nutrient agar + E. coli overlay; 3–7 days growth.
  4. PCR: Rapid, sensitive, species ID.
  5. Histopathology (if therapeutic PK): Calcofluor white, H&E.

Treatment (Prolonged, Multimodal)

  • Topical biguanides: PHMB 0.02% (polyhexamethylene biguanide) or chlorhexidine 0.02% — cysticidal.
  • Topical diamidines: Propamidine 0.1% (Brolene), hexamidine 0.1% — trophozoiticidal.
  • Combination therapy (biguanide + diamidine) — standard; hourly day, q2h night initially, then taper over 6–12+ months.
  • Adjuncts: Oral azoles (voriconazole, itraconazole), topical steroids (controversial — only after anti-amoebic control), cycloplegics.
  • Surgery: Therapeutic penetrating keratoplasty (PK) for perforation, failed medical therapy; high recurrence risk.

Prevention (Critical)

  1. Never use tap water on lenses/cases — rinse with sterile saline or MPS.
  2. No swimming/showering/hot tubs in lenses — wear goggles or remove.
  3. Rub & rinse lenses even with "no-rub" solutions.
  4. Replace case monthly; air-dry face down.
  5. Daily disposables lowest risk.
  6. Regular eye exams.

Prognosis

  • Early diagnosis + aggressive therapy → good visual outcome in ~75%.
  • Delayed diagnosis (>3 weeks) → higher PK rate, vision loss.
  • Recurrence possible; cysts resist treatment.

Any contact lens wearer with severe eye pain disproportionate to findings needs urgent ophthalmology referral.

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