Cornea
Acanthamoeba Keratitis
Also known as: Acanthamoeba keratitis, AK, contact lens keratitis severe, ring infiltrate keratitis, radial keratoneuritis, amoebic keratitis, contact lens swimming infection, tap water contact lens
Filed as: Emergency
Source-cited from the record's own evidence list. Clinical content programme led by Dr Ankit Mathur, PhD, Grad Cert Ocu Thera, B.S. Optom. How the clinical content is governed
Clinical decision support only
Overview
A rare, sight-threatening corneal infection caused by free-living Acanthamoeba. Contact lens wear, poor lens hygiene, and contaminated-water exposure are major risk factors, although infection can occur without contact lenses. Severe pain disproportionate to the visible signs and radial keratoneuritis are important clues but are not present in every case. Early disease can mimic HSV, bacterial, or fungal keratitis, so suspected cases need prompt specialist assessment.
Recognition
Symptoms: what patients report
- Severe eye pain disproportionate to the clinical signs — classic feature; pain is often described as excruciating.
- Photophobia — marked.
- Tearing and redness.
- Blurred vision.
- Commonly associated with contact lens wear, although non-contact-lens cases occur.
- History of: swimming, showering, or using tap water with contact lenses in place.
- History of prolonged or continuous CL wear.
- History of previous treatment for 'herpetic keratitis' or 'bacterial keratitis' that failed.
Signs: what the examination shows
- Radial keratoneuritis: radial branching opacities along corneal nerves in the anterior stroma. This is a high-concern clue but may be absent.
- Epithelial irregularity or pseudodendrites in early disease.
- Ring infiltrate: a central or paracentral stromal ring-shaped infiltrate — indicates later-stage disease with ring abscess.
- Dense stromal infiltrate with satellite lesions.
- Hypopyon in severe cases.
- Scleritis adjacent to the corneal infiltrate.
- Severe anterior chamber reaction.
What OptoGuide™ covers for acanthamoeba keratitis
- Pattern reasoning: what this combination of findings points to, and its differentiators
- Don't-miss risks and escalation triggers
- Management tiers with linked Australian therapeutics
- Referral urgency, specialty, and letter drafting
Sources
- Acanthamoeba keratitis — clinical signs, differential diagnosis and treatment
- Diagnosis of Acanthamoeba keratitis: past, present and future
- Anterior Eye Disease and Therapeutics A-Z (Bruce & Loughnan) — standard reference text
- Infectious Keratitis in 2021. Durand ML, Barshak MB, Chodosh J. JAMA. 2021;326(13):1319-1320.
- Differentiation of acanthamoeba keratitis from other non-acanthamoeba keratitis: Risk factors and clinical features. Alreshidi SO, Vargas JM, Ahmad K, et al. PloS One. 2024;19(3):e0299492.
- The Global Incidence and Diagnosis of Fungal Keratitis. Brown L, Leck AK, Gichangi M, Burton MJ, Denning DW. The Lancet. Infectious Diseases. 2021;21(3):e49-e57.
Standard texts: Kanski's Clinical Ophthalmology: A Systematic Approach, The Wills Eye Manual, Oxford Handbook of Ophthalmology, Oxford American Handbook of Ophthalmology, Signs in Ophthalmology: Causes & Differential Diagnosis.