Acanthamoeba keratitis.

AD Nicholson, S Motwane, A Gogate 
 Department of Ophthalmology, LTM Medical College, Sion, Mumbai.

Correspondence Address:
A D Nicholson
Department of Ophthalmology, LTM Medical College, Sion, Mumbai.

Full Text

::   Introduction

Corneal infection with acanthamoeba should be considered in any patient with a history of soft contact lens use, poor contact lens hygiene (i.e. using non-sterile or improperly stored saline solution to clean or store lenses and/or infrequent disinfection and/or swimming with the contact lenses.

::   Case report

A 22-year-old female medical student was referred with complaints of a left eye corneal ulcer not responding to antibacterial and antiviral treatment. She gave a history of using soft contact lenses for the, last two years. Dis-infection was performed on an irregular basis and she used un-preserved saline to soak and rinse her soft lenses. There was no history of trauma or contamination with vegetable matter. The patient had been initially treated with several different antibiotic eye drops. Later, she was diagnosed as having a suspected viral den-dritic ulcer and treated with antiviral medication but there was no beneficial response.

On examination, the vision in left eye was projection of light in all 4 quadrants and 20/20 in the right eye. The right eye was normal. The left eye showed a large epithelial defect measuring 8 mm vertically and 9 mm horizontally with a prominent ring infiltrate surrounding the epithelial defect. There was marked stromal infiltration and severe hyperemia of the globe. Evaluation of fund-us and examination of anterior chamber were not possible.

A corneal scraping was performed for examination in 10% KOH which demonstrated acanthamoeba cysts. A culture on nonnutrient agar with E. Coli overlay, revealed acanthamoeba. The corneal scraping was repeated at an interval of one week to reconfirm the diagnosis of acanthamoeba. Subspecies isolation revealed it to be Acanthamoeba culbertsoni.

She was subsequently treated with topical Neopolygramin/Andresporin eye drops (Polymxin, Bacitracin and Gramicidin) one hourly, Brolene 0.1 % eye drops (Prompamidine isethionate 0.1 %) every two hours atropine eye drops 1% thrice daily and oral tablet ketoconazole 200 mg twice daily.

[Figure:1] shows the patient one week following institution of therapy. The condition improved over several weeks. The frequency of administration of topical drugs was gradually tapered. The patient's response to medical therapy was excellent.

At present [Figure:2] i.e. 9 months following therapy, the visual acuity is 20/20. The cornea is crystal clear and without any evidence of subepithelial opacification or vascularisation

::   Discussion

Corneal infection with acanthamoeba is believed to result from direct contact of the cornea with contaminated water or other material. At least 22 species of acanthamoeba have been identified. Species including A. culbertsoni, A. castellini, A. polyphaga and A. astronyxis are considered pathogenic to human. The trophozoite undergoes encystation in adverse conditions and this renders it highly resistant to freezing and dessication and a wide range of antimicrobials.

Wet mounting of corneal scraping in 10% KOH solution enables rapid identification of acanthamoeba cysts. Special growth media consisting of nonnutrient agar with an overlay of E coli, enables culture of the trophozoites and identification within 72 hours on the surface of the medium. Later, they begin to change into cysts and can be identified by their double walled structure. Acanthamoeba can also grow on blood agar, chocolate agar or nutrient agar but observation on these media is difficult under the microscope as they are opaque. Cultures of conjunctival scrapings have a very low yield of acanthamoeba, Further separation into subspecies is performed by immunofluorescent technique using monoclonal or polyclonal antibodies.

Current medical treatment for acanthamoeba keratitis includes one or more of the following generally used in combination[3].

1. PolymixinNeomycinGramicidin drops 12 hourly.

2. Propamidine isethionate 0.1% drops 12 hourly.

3. Clotrimazole 1% drops 2 hourly.

4. Ketoconazole 200 mg tablets twice daily.

Alternative therapy to clotrimazole includes miconazole 1 % drops or paramomycin drops 2 hourly.

All patients should discontinue contact lens wear and should use a cycloplegic as atropine drops 1% thrice daily and a nonsteroidal antiinflammatory agent such as ibuprofen or flurbiprofen tablets for relief of pain. The local treatment may have to be continued for 36 months to avoid the reactivation of the encysted form and finally a corneal transplant may be indicated for medical failures and for impending or actual corneal perforation but the graft too can be complicated by recurrent infection.

::   Acknowledgment

We thank Dr. (Smt) S S Deshmukh, Dean, LTM Medical College and LTM General Hospital, Sion, Mumbai 400022 for permission to report hospital and publish the case report.

References