Acanthamoeba keratitis

Acanthamoeba keratitis is a rare disease where amoebae invade the cornea of the eye.

Causes
In the United States, it is nearly always associated with contact lens use, as Acanthamoeba can survive in the space between the lens and the eye. For this reason, contact lenses must be properly disinfected before wearing, and should be removed when swimming or surfing.

However, elsewhere in the world, many cases of Acanthamoeba present in non-contact lens wearers.

Diagnosis
To detect Acanthamoeba on a contact lens in a laboratory, a sheep blood agar plate with a layer (a lawn) of E. coli is made. Part of the contact lens is placed on the agar plate. If Acanthamoeba are present, they will ingest the bacteria, leaving a clear patch on the plate around the area of the lens. Polymerase chain reaction can also be used to confirm a diagnosis of Acanthamoeba keratitis, especially when contact lenses are not involved. Acanthameoba is also characterized by a brawny edema and hazy view into the interior AC. Late stages of the disease also produces a ring shaped corneal ulcer.

Presentation
Signs and symptoms include severe pain, severe keratitis (similar to stromal herpetic disease), corneal perineuritis, ring ulcer (although this is late in the disease process)

Treatment
One treatment used is PHMB.

Propamidine isethionate has also shown some effectiveness.

Another possible agent is chlorhexidine.

Keratoplasty may sometimes be required.

A combined regimen of propamidine, miconazole nitrate, and neomycin has also been suggested.