Acanthamoeba keratitis

What it is

Acanthamoeba keratitis infects the clear cornea at the front of the eye. Unlike mild conjunctivitis, it penetrates corneal tissue and can cause ring-shaped ulcers, severe pain and scarring. It is harder to treat than bacterial ulcers and may need months of antiseptic drops.

Who is at risk

Most cases occur in contact lens wearers. Risk rises with:

• Rinsing or storing lenses in tap water, or swimming or showering in lenses
• Sleeping in lenses not designed for overnight wear
• Poor lens hygiene or using contaminated lens cases
• Recent corneal injury or exposure to soil or stagnant water
• Using steroid eye drops without treating infection

Symptoms

Symptoms can mimic other red-eye problems early on, which delays diagnosis.

• Severe eye pain out of proportion to how the eye looks
• Redness, watering and marked light sensitivity
• Blurred or hazy vision
• A feeling of something in the eye
• Sometimes a ring-shaped white-grey area on the cornea

Diagnosis and treatment

Specialists examine the cornea with a slit lamp, may take corneal samples, and sometimes use confocal microscopy. Treatment is with antiseptic drops such as chlorhexidine or polyhexanide, often for many months. Steroids are avoided until infection is controlled. Late cases may need corneal transplant.

Prevention

Never expose contact lenses to tap water, pool water or saliva. Follow replace-and-clean schedules, rub and rinse reusable lenses with fresh solution, and replace lens cases regularly. Remove lenses before swimming or bathing, and seek same-day care for a painful red eye during lens wear.