Author: Claude (AI), from PubMed abstracts · Reviewed by: Dr Mina Abdelmseih · Reviewed: 2026-11-15 · Review due: 2027-11-15

Educational content only. Not personalised medical advice. Clinical decisions remain the responsibility of the treating clinician.

Acanthamoeba keratitis

Acanthamoeba keratitis (AK) is a rare parasitic corneal infection that can lead to permanent blindness if not diagnosed and treated promptly [S6]. It is linked to contact lens wear in Western countries, but in India most cases follow trauma or contaminated water exposure, and many present with a diffuse infiltrate that mimics herpes simplex or fungal keratitis [S2]. Early diagnosis and anti-amoebic treatment decide the outcome [S2] [S10].

Key points - Delayed diagnosis and corticosteroid use before diagnosis are key poor prognostic factors [S10]. - In vivo confocal microscopy (IVCM) is the most recommended tool for early detection; PCR is the alternative if IVCM is unavailable [S6]. - First-line treatment is a biguanide with or without a diamidine [S2] [S10]; in the ODAK phase 3 RCT, PHMB 0.08% alone was non-inferior to PHMB 0.02% plus propamidine 0.1%, with medical cure rates above 86% [S8]. - Contact lens wearers should avoid any water exposure of lenses and cases [S3]. - Keratoplasty is a salvage or rehabilitation option, not first-line [S5] [S10].

Evidence last checked: 2026-10-17 (PubMed abstracts).

Red flags

• "Keratitis" in a contact lens wearer that is not responding to antibacterial, antifungal or antiviral drops. Anti-amoebic drugs were often prescribed only after other treatments had failed, which may contribute to complications [S7].
• Water exposure with lenses: tap water rinsing, wet hands, showering or swimming in lenses [S3].
• Children using overnight orthokeratology lenses, which may increase the risk of microbial keratitis, especially Acanthamoeba [S4].
• Steroid drops started before the diagnosis is made [S10].
• Ring infiltrate, radial keratoneuritis or pain out of proportion, although in India these were seen in less than a third of cases [S2].

Recognise it

• Burden. Data from 20 countries gave an estimated 23,561 cases a year, highest in India [S6]. AK accounts for 2% of microbiology-proven keratitis in an Indian series [S2].
• Risk factors. Daily contact lens wear in Western countries [S2]; trauma and contaminated water in non-wearers [S2]. In historical case reports (1970 to 1995), contact lens wear was reported in 68.2% and trauma in 31.8% [S11].
• Appearance. Most Indian cases present with a diffuse infiltrate mimicking herpes simplex or fungal keratitis [S2]. AK features are non-specific and easily mistaken for other keratitis or coinfection [S12].
• Delay is common. In historical case reports, mean time from presentation to diagnosis was 7.3 weeks, and only 23.2% were diagnosed within 4 weeks [S11].

Confirm it

• Corneal scraping for microscopy and culture on non-nutrient agar with an Escherichia coli overlay confirms the diagnosis [S2].
• IVCM is the most recommended method for early detection [S6] and helps with deep infiltrates, although its value depends on operator experience [S2].
• PCR has shown sensitivity similar to or greater than culture with high specificity [S12], and is the alternative where IVCM is unavailable [S6].

Manage it

Before acting on this section, check the national and local guidelines, product information and regulatory approvals that apply where you practise. See the medical disclaimer.

Tier A (primary care / no specialist)

• Ask every patient with a red eye about contact lens wear, water exposure and trauma [S2] [S3].
• Do not start steroid drops on a suspected corneal infection; prior steroid use worsens prognosis [S10].
• Advise contact lens wearers to avoid handling lenses with wet hands, rinsing lenses or cases in tap water, showering in lenses and swimming without goggles [S3].

Tier B (general eye clinic)

• Scrape and culture where possible [S2]; refer suspected cases to a cornea service (see "Refer when").
• Medical treatment is successful if the disease is diagnosed early and management starts soon; surgery is rarely needed when definitive treatment begins within 3 weeks of symptom onset [S2].

Tier C (specialist centre)

1. Anti-amoebic therapy. Biguanides with or without diamidines are primary treatment [S2]. A systematic review of 61 studies suggests therapeutic epithelial debridement followed by a biguanide, a diamidine and an antibacterial agent as a strong initial option [S10].
2. ODAK trial (2024). In 135 patients at 6 European centres, the adjusted medical cure rate within 12 months was 86.6% with PHMB 0.02% plus propamidine 0.1% and 86.7% with PHMB 0.08%, as reported in [S8]. Treatment failed in 13.4% and 6.3% needed therapeutic keratoplasty; no serious drug-related adverse events occurred [S8]. The result applies with the trial's treatment protocol and similar disease severity [S8].
3. Older evidence. A Cochrane review found only one RCT (56 eyes): chlorhexidine 0.02% and PHMB 0.02% gave similar resolution (86% vs 78%), but the trial was too small to detect differences [S1].
4. Adjuncts. Topical voriconazole 1% or oral miltefosine may be considered [S10]; voriconazole, rose bengal photodynamic therapy, miltefosine and povidone-iodine showed potential benefit in observational studies and small trials only [S12].
5. Steroids may play a role when indicated, following established protocols [S2]; this conflicts with their association with worse prognosis when used before diagnosis [S10].
6. Keratoplasty. In a review of 359 eyes, clear grafts were seen in 73% after therapeutic penetrating keratoplasty, 84% after therapeutic DALK and 94% after optical keratoplasty; recurrence was 16.8%, 19% and 9.5% [S5]. Optical keratoplasty after 6 to 12 months of medical cure appears best; therapeutic DALK may suit early disease and penetrating keratoplasty later disease [S5] [S10]. The best timing remains uncertain [S12].
7. Complications are uncommon overall: perforation 2.21%, evisceration or enucleation 1% and corneal transplantation 16.68% across 158 reports [S9].

Dosing schedules are not covered by these abstracts: follow local formularies.

Refer when

Pitfalls

• Treating as herpes or fungal keratitis for weeks before considering AK [S2] [S7].
• Steroid drops before the diagnosis [S10].
• Relying on classic signs; they may be absent [S2].
• Assuming daily disposable lenses remove the risk: they have not consistently changed the overall rate of microbial keratitis [S4].

Evidence notes

• Only one high-quality RCT (ODAK) guides first-line drug choice [S8]; the Cochrane review found insufficient evidence [S1].
• Most surgical and adjunct evidence is observational [S5] [S10] [S12].
• Sources conflict on corticosteroids [S2] [S10].
• Complication data come from heterogeneous reports and remain poor [S9].
• Not covered by these sources: drug concentrations available outside Europe, duration of treatment, and pain management.

Related articles

• Contact lens complications and safe wear
• Bacterial keratitis
• Fungal keratitis

References

See the numbered source list below. Each marker [S#] links to its PubMed and DOI record.