Acanthamoeba keratitis

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Acanthamoeba keratitis (AK) is a rare eye infection that affects the cornea, the clear front surface of the eye. It’s caused by Acanthamoeba, tiny organisms found in soil and water.

Who is at risk
- Most cases happen in soft contact lens wearers.
- Other risk factors include eye trauma, exposure to contaminated water or lens solution, wearing lenses while swimming or bathing, low socioeconomic status, and living in tropical or subtropical areas.

How you get it
- Contact lenses can pick up Acanthamoeba from contaminated solution, tap water, or dirty cases.
- The organism can get between the lens and the eye and cause infection. It can also enter through eye injuries or exposure to soil or vegetation.

Symptoms
- Eye pain that is more severe than expected from exam findings
- Redness and blurred vision
- Sensitivity to light (photophobia)
- Discomfort or a feeling that something is in the eye
- Early signs can resemble other keratitis (such as viral or bacterial); a ring-shaped corneal infiltrate may appear in about half of cases as it progresses

How it’s diagnosed
- If AK is suspected, a corneal scrapings are taken and tested
- Methods include culture on special plates with bacteria, staining (Gram or Giemsa), and PCR to detect Acanthamoeba
- Confocal microscopy can visualize the organisms in the cornea without more invasive testing

Treatment
- Prompt, aggressive treatment is important to protect vision
- First-line medicines are biguanides (such as polyhexamethylene biguanide or PHMB) and chlorhexidine; these help kill the trophozoite form of the organism
- Often given together with diamidines (like propamidine or hexamidine)
- Drops are usually started very frequently (often hourly) for several days, then gradually reduced over weeks to months
- Steroid eye drops may help inflammation but can worsen infection, so they’re used cautiously and usually only after anti-amoebic treatment has begun
- Surgical options include removing infected tissue (debridement) to reduce organism load and improve drug penetration
- In severe cases, a corneal transplant may be needed; infection can recur, so anti-amoebic therapy is continued around surgery

Outcomes and prognosis
- AK can cause permanent vision loss if not treated early and effectively
- Outcomes are better with early diagnosis and aggressive treatment
- Some people may need corneal transplantation, and recurrences can occur

Prevention
- Don’t expose contact lenses to water (tap, lake, or swimming water)
- Wash and dry hands before handling lenses
- Clean and store lenses and cases as directed; replace cases regularly
- Do not wear lenses while swimming or bathing
- Follow lens/container instructions and replace lenses as advised

Epidemiology
- Globally, about 1.2–3 million people get AK each year
- In the United States, roughly 100 cases occur annually
- About 1 in 10,000 contact lens wearers may develop AK

Notes
- AK is rare but serious; if you wear contact lenses and develop eye pain, redness, or vision changes, seek prompt eye care.