Acanthamoeba Keratitis: Early Diagnosis and Treatment
Last updated: November 2026
Acanthamoeba keratitis is rare but devastating, and it is often treated for weeks as herpes or bacterial keratitis before the diagnosis is made. Think of it in any contact lens wearer with a painful keratitis that does not behave as expected.
Risk factors
- Contact lens wear in about 9 out of 10 cases, especially with tap water exposure, swimming or showering in lenses, poor hygiene or reused solution.
- Corneal trauma with soil or water in non-wearers.
Clinical features by stage
| Stage | Signs |
|---|---|
| Early | Pain out of proportion to the signs, irregular epithelium, pseudodendrites, punctate keratopathy, radial keratoneuritis (perineural infiltrates) |
| Later | Ring infiltrate in the stroma, satellite lesions |
| Advanced | Scleritis, limbitis, ulceration, thinning, cataract, glaucoma |
Diagnosis
- Corneal scrape for culture on non-nutrient agar with an E. coli overlay (look for amoebic tracks), staining with calcofluor white.
- PCR on scrapings: sensitive and fast where available.
- In vivo confocal microscopy: double-walled cysts and trophozoites.
- Send the contact lenses, case and solution for culture.
Treatment
- Topical biguanides: polihexanide (PHMB) 0.02% or chlorhexidine 0.02%, often with a diamidine (propamidine 0.1%), hourly day and night at first, then tapered over months.
- Polihexanide 0.08% (Akantior) became the first licensed treatment in Europe in 2024.
- Steroids only for persistent inflammation once anti-amoebic therapy is established; never as first treatment.
- Pain control and cycloplegics; keratoplasty for perforation or after the infection is eradicated.
Prevention
Tell every contact lens wearer: no tap water on lenses or cases, do not swim or shower in lenses, never top up solution, replace cases monthly.
Where residents slip
- Treating as herpes simplex for weeks: pseudodendrites and pain out of proportion are clues.
- Starting steroids before the diagnosis.
- Not culturing the lens case.
Test yourself: flip cards
Related: Microbial Keratitis: A Workup Approach, Contact Lens Quick Reference: Vertex Table, LARS, RGP and Keratoconus, Fortified Eye Drops and Keratitis Regimens: Concentrations and Preparation.
Key sources
- Dart JK, et al. Polihexanide 0.08% monotherapy vs combination for Acanthamoeba keratitis (ODAK trial). Ophthalmology. 2024
- Carnt N, et al. Acanthamoeba keratitis: risk factors and outbreak. Eye. 2018
- European Commission marketing authorisation for Akantior (polihexanide 0.08%), August 2024
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