Acanthamoeba keratitis

Acanthamoeba is a protozoan which is found ubiquitously, notably in domestic water supplies. Acanthamoeba cysts are resistant to antimicrobial agents, including current lens disinfectant solutions. Cysts may contaminate lens storage cases in asymptomatic users.

Contact lens wearers account for 80% of the cases; poor hygiene, such as failure to disinfect daily wear contact lenses and the use of chlorine release lens disinfection systems (these have little protective effect against the organism) (1,2,3) are all risk factors for infection with acanthamoeba.

Risk of infection is particularly high in users of disposable contact lenses. This is because these lenses have a philosophy of "low care" - however in practice often a "no care" policy is used by ill informed contact lens practioners and users.

The patient will present with:

• severe pain
• corneal ulceration

A corneal ring infiltrate suggests Acanthamoeba keratitis (2)

Confocal microscopy allows accurate diagnosis (3).

The keratitis is refractive to antibiotics but responds to Brolene drops.

Acanthamoeba keratitis should be managed in a specialist unit.

Complications of Acanthamoeba keratitis are dacryoadenitis, corneal scarring, secondary glaucoma, cataract and rarely ischemic retinitis (3).

Reference:

1. Tzanetou K et al. Acanthamoeba keratitis and contact lens disinfecting solutions. Ophthalmologica. 2006;220(4):238-41.7-70.
2. Dahlgren MA et al. The clinical diagnosis of microbial keratitis.Am J Ophthalmol. 2007 Jun;143(6):940-944.
3. Awwad ST et al. Updates in Acanthamoeba keratitis. Eye Contact Lens. 2007 Jan;33(1):1-8.
4. Radford CF et al. Risk factors for acanthamoeba keratitis in contact lens users: a case-control study. BMJ. 1995 Jun 17;310(6994):1567-70.