Merck Manual

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Amebic Keratitis


Chelsea Marie

, PhD, University of Virginia;

William A. Petri, Jr

, MD, PhD, University of Virginia School of Medicine

Reviewed/Revised Dec 2022

Amebic keratitis is a rare corneal infection with Acanthamoeba species, typically occurring in contact lens wearers.

Various Acanthamoeba species can cause chronic and progressively destructive keratitis Interstitial Keratitis Interstitial keratitis is chronic, nonulcerative inflammation of the mid-stroma (the middle layers of the cornea) that is sometimes associated with uveitis. The cause is usually infectious.... read more Interstitial Keratitis in normal hosts. The main risk factor (85% of cases) is contact lens use, particularly if lenses are worn while swimming or if unsterile lens cleaning solution is used. Some infections follow corneal abrasion.

Acanthamoeba are present worldwide in water, soil, sewage, and dust. They can also be present in tap water, showers, hot tubs, and air conditioning units. The life cycle of Acanthamoeba involves only 2 stages: cysts and trophozoites (the infective form). The trophozoites form double-walled cysts, which resist eradication. Both forms can enter the body through various means (eg, eyes, nasal mucous membranes, broken skin). When Acanthamoeba enter the eye, they can cause severe keratitis. In infected patients, both cysts and trophozoites may be found in the cornea.

Symptoms and Signs of Amebic Keratitis

Lesions in patients with amebic keratitis are typically very painful and produce a foreign body sensation, redness, photosensitivity, excess tearing, and diminished vision, but typically not systemic symptoms. Initially, lesions may have a dendriform appearance resembling herpes simplex keratitis Herpes Simplex Keratitis Herpes simplex keratitis is corneal infection with herpes simplex virus. It may involve the iris. Symptoms and signs include foreign body sensation, lacrimation, photophobia, and conjunctival... read more Herpes Simplex Keratitis . Later, there are patchy stromal infiltrates and sometimes a characteristic ring-shaped lesion. Anterior uveitis is usually also present.

Diagnosis of Amebic Keratitis

  • Examination and culture of corneal scrapings

Consultation with an ophthalmologist is important for diagnosis and treatment of amebic keratitis.

Diagnosis of amebic keratitis is confirmed by examination of Giemsa- or trichrome-stained corneal scrapings and by culture on special media. Viral culture is done if herpes simplex is considered.

Treatment of Amebic Keratitis

  • Corneal debridement

  • Topical chlorhexidine, polyhexamethylene biguanide, or both

Early, superficial amebic keratitis responds better to treatment.

Epithelial lesions are debrided, and intensive drug therapy is applied. The initial choice is

  • Topical chlorhexidine 0.02%

  • Topical polyhexamethylene biguanide 0.02%

  • Both drugs

For the first 3 days, treatment is given every 1 to 2 hours. Other topical medications used as adjunct therapy include the diamidines propamidine (0.1%) or hexamidine (0.1%).

Early recognition and treatment have eliminated the need for therapeutic keratoplasty in most instances, but keratoplasty remains an option when pharmacologic therapy fails. Intensive treatment is required for the first month; it is tapered per clinical response but continued for 6 to 12 months. Recurrence is common if treatment is stopped prematurely.

Prevention of Amebic Keratitis

To prevent amebic keratitis, contact lenses should be cleaned and stored following the recommendations of eye care providers and manufacturers. Hands should be washed thoroughly before handling them. Solution should be kept fresh, not reused, and not topped off; tap water should never be used. Nonsterile homemade contact lens solutions should not be used. Wearing contact lenses while swimming or showering should be avoided.

Key Points

  • Various Acanthamoeba species can cause chronic and progressively destructive keratitis in otherwise healthy hosts, mainly in contact lens users.

  • Consult with an ophthalmologist about management.

  • Diagnose by examining Giemsa- or trichrome-stained corneal scrapings or by culturing the sample using special media.

  • Herpes simplex keratitis can cause similar lesions; if it seems a possible diagnosis, do viral culture.

  • Debride corneal lesions and treat with topical chlorhexidine, polyhexamethylene biguanide, or both, plus possibly a diamidine for 6 to12 months.

More Information

The following English-language resource may be useful. Please note that THE MANUAL is not responsible for the content of this resource.

Drugs Mentioned In This Article

Drug Name Select Trade
Betasept, Chlorostat, DYNA-HEX, Hibiclens, Oro Clense , Peridex, Periogard, PerioRx , Perisol
NOTE: This is the Professional Version. CONSUMERS: View Consumer Version
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