This patient-education article is written by the cornea service at Suraj Eye Institute, Nagpur.

What is Acanthamoeba Keratitis?

Acanthamoeba is a free-living amoeba found in soil, freshwater, tap water and biofilms. It is an uncommon but very serious cause of corneal infection in contact lens wearers, particularly those who use tap water for lens cleaning, rinse cases under the tap, swim in lenses or sleep in them. The infection is notoriously difficult to diagnose early and to treat — both delays in diagnosis and resistance of the cyst form to most disinfectants make it a feared complication of lens wear.

Acanthamoeba Keratitis — Key Features

Acanthamoeba Keratitis — Slit-Lamp Stages

EARLY: epithelial pseudodendrites

Surface pseudodendrites — often misdiagnosed as HSV

ESTABLISHED: perineural infiltrates

Branching radial — infiltrate along corneal nerves

ADVANCED: ring infiltrate

Classical ring — stromal infiltrate in a circular pattern

Severe pain that seems out of proportion to the slit-lamp signs is a hallmark.

Figure 1. Acanthamoeba keratitis evolves over weeks. Early disease shows superficial pseudodendrites — branching epithelial defects that are often misdiagnosed as herpes simplex keratitis. Established disease shows perineural infiltrates, fine linear infiltrates that track along the corneal nerves and produce the disproportionately severe pain that is characteristic of the condition. Advanced disease shows a classical ring infiltrate.

Risk Factors

  • Contact lens wear — the dominant risk factor
  • Tap water — rinsing lens cases under the tap, topping up solution with water, showering or swimming in lenses
  • Overnight lens wear
  • Use of homemade or non-sterile cleaning solutions
  • Outdoor exposure to soil and stagnant water

Symptoms

The classical story is a contact-lens wearer with several weeks of progressively worsening pain, redness and blurred vision. The pain is characteristically severe and out of proportion to the clinical signs — an important diagnostic clue. The eye often has been treated for several weeks with topical antibiotics and / or antivirals without improvement before the correct diagnosis is reached.

How Acanthamoeba Keratitis is Diagnosed

Diagnosis is often delayed. The key investigations are:

  • In vivo confocal microscopy visualises Acanthamoeba cysts in the corneal stroma without scraping — the most useful single bedside test where available
  • Corneal scraping for microscopy (calcofluor white stain), and culture on a non-nutrient agar plate seeded with E. coli (Acanthamoeba feeds on the bacteria)
  • PCR on the corneal scraping

Treatment

Treatment is prolonged — usually several months — and combines drugs targeting the trophozoite and the cyst form:

  • Topical biguanide — polyhexamethylene biguanide (PHMB) 0.02 % or chlorhexidine 0.02 %, hourly initially
  • Topical diamidine — propamidine isethionate 0.1 % or hexamidine
  • Cycloplegic drops and oral analgesia for pain control
  • Topical steroids are usually avoided early; they may be carefully introduced later under specialist supervision to reduce immune-mediated stromal damage
  • Therapeutic corneal transplantation for severe disease unresponsive to medical therapy — with the knowledge that recurrence in the graft is possible
If you wear contact lenses — never use tap water. Acanthamoeba lives in tap-water biofilms. Storage cases must be rinsed only with sterile saline or fresh disinfecting solution, never water. Do not swim or shower in your lenses.
✔ Acanthamoeba Keratitis Care at Suraj Eye Institute

We offer high-resolution confocal microscopy when available, prompt microbiological work-up on corneal scrapings, and intensive long-duration topical biguanide therapy (PHMB or chlorhexidine) combined with propamidine isethionate. For severe disease unresponsive to medical treatment we offer therapeutic corneal transplantation, with the understanding that recurrence in the graft is possible.

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Frequently Asked Questions

Why did this take so long to diagnose?
Acanthamoeba is uncommon and looks very similar in its early stages to herpes simplex keratitis (the pseudodendrites). Standard antibiotics and antivirals have no effect. Once the right diagnosis is suspected, confocal microscopy and microbiology confirm it — but suspicion often comes only after the usual treatments fail.

Will I lose vision in this eye?
Outcomes are very variable. Early disease, diagnosed and treated promptly, often heals with little permanent visual loss. Late disease with established ring infiltrate or perforation often leaves significant scarring and may need transplantation.

How long is the treatment?
Antimicrobial drops are typically continued for several months and tapered very slowly. Premature discontinuation can allow recurrence from the cyst form. Patience and adherence are essential.

Why is the pain so severe?
Acanthamoeba has a particular affinity for corneal nerves (perineural infiltrates). This produces severe, often constant pain that is out of proportion to what the slit-lamp shows. Adequate oral analgesia and cycloplegic drops help while treatment takes effect.

Can I keep wearing contact lenses afterwards?
We strongly recommend a long break from lens wear (often three to six months), excellent ocular surface recovery, and a switch to daily disposable lenses with strict no-tap-water rules. Some patients choose not to return to lens wear; specialty scleral lenses may be considered for visual rehabilitation of significant scarring.

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