Acanthamoeba Keratitis

What causes Acanthamoeba keratitis

Acanthamoeba is common in the environment: tap water, well water, swimming pools, hot tubs, lakes, soil and even air. It rarely causes disease, because a healthy cornea is a strong barrier. A contact lens changes that. The lens can carry amoebae against the cornea and hold them there, and tiny surface scratches let them invade.

Risk factors:

• wearing contact lenses while swimming, showering or in a hot tub
• rinsing or storing lenses or cases in tap water
• "topping off" old solution instead of replacing it
• sleeping in lenses or wearing them longer than recommended
• poor case hygiene and not replacing cases every 3 months
• corneal injury with soil or water exposure, in people who do not wear lenses

In some cases, the amoeba forms tough cysts that resist disinfection and many medicines, which is why treatment is long.

Symptoms

Symptoms usually affect one eye and develop over days to weeks:

• eye pain, often severe and out of proportion to what the eye looks like
• red eye
• sensitivity to light
• blurred vision
• a feeling of something in the eye
• excessive tearing

The clinical picture is often mistaken for herpes simplex keratitis or bacterial infection, which delays diagnosis. A ring-shaped infiltrate in the cornea and inflamed corneal nerves seen with a microscope are characteristic, but they appear later.

Diagnosis

An ophthalmologist examines the cornea with a slit lamp microscope. Tests include:

• corneal scraping for culture on special plates and PCR (DNA testing)
• in vivo confocal microscopy, which can show cysts directly in the cornea
• culture of the contact lenses, case and solution
• sometimes a corneal biopsy

Tell your eye doctor if you wear contact lenses, swim or shower in them, or rinse them in water. That history alone raises suspicion.

Treatment

Acanthamoeba keratitis is difficult to treat and needs specialist care:

• Anti-amoebic eye drops: biguanides (such as polyhexamethylene biguanide or chlorhexidine), often combined with diamidines (such as propamidine). Drops are given very frequently at first, including through the night, then tapered over 6 to 12 months or longer. A high-dose polyhexanide drop has been approved in some countries.
• Pain control: with oral pain relievers and drops that relax eye muscles.
• Steroid drops: used cautiously and only under specialist supervision, to control inflammation.
• Corneal transplant: may be needed for scarring or infection that does not respond, usually once the infection is controlled.

Stop wearing contact lenses in the affected eye. Bring your lenses and case to the clinic for testing.

Complications and outlook

When it is diagnosed early, within the first few weeks, most people keep good vision. Delayed diagnosis can lead to corneal scarring, glaucoma, cataract, perforation of the cornea and, rarely, loss of the eye. Many people need months of follow-up, and some eventually need a transplant.

Prevention

• Never let water touch your lenses. Remove them before swimming, showering or using a hot tub, or wear tight-fitting goggles over them.
• Never rinse or store lenses or cases in tap water or saliva.
• Use fresh solution every time; do not top off.
• Rub and rinse lenses as directed with solution, even with "no-rub" products.
• Clean the case with solution, let it air-dry upside down, and replace it every 3 months.
• Do not sleep in lenses unless prescribed for overnight wear.
• Consider daily disposable lenses, which reduce handling and storage risks.

Frequently asked questions

What are the first signs of Acanthamoeba keratitis?

Early signs include eye pain, redness, sensitivity to light, blurred vision and a feeling that something is in the eye, usually in one eye of a contact lens wearer. The pain is often severe compared with how red the eye looks.

Can you get Acanthamoeba keratitis from tap water?

Yes. Tap water can contain Acanthamoeba. Rinsing contact lenses or cases in tap water, or wearing lenses in the shower, is a well-known risk. The amoeba is harmless to drink but dangerous on a contact lens held against the eye.

How long does treatment for Acanthamoeba keratitis take?

Treatment usually lasts 6 to 12 months and sometimes longer, because the amoeba forms resistant cysts. Drops are used very frequently at first and gradually reduced. Regular specialist follow-up is essential.

Is Acanthamoeba keratitis contagious?

No. It does not spread from person to person. It is caught from water or soil when the amoeba reaches the cornea, usually through contact lenses.