ACANTHAMOEBA KERATITIS

KERATITIS

•It refers to the INFLAMMATION OF CORNEA

•It is characterized by:

•(A) Corneal Oedema

•(B) Cellular Infiltration 

•(C) Ciliary Congestion

Acanthamoeba

•It is a Pathogenic Free Living Amoeba.

•Species:   1)A.castellanii

                     2)A.culbertsoni

                     3)A.polyphagia

                     4)A.astromyx

Acanthamoeba Castellanii is responsible for Acanthamoeba keratitis

Morphology

•It exists in two forms

1.Active Trophozoite form

2.Resistant Cystic form

Life Cycle

•Habitat:  Soil, Fresh water, Well water, Sea water, Sewage, Air

•Infective Form : Both Trophozoites and cysts

•Mode of transmission:  Direct contact with cornea

•Other infections:   Granulomatous Amoebic Encephalitis(GAE)(Inhalation or Ingestion)

ACANTHAMOEBA KERATITIS

•Recently gained importance because of

1.Increasing incidence

2.Difficulty in Dx

3.Unsatisfactory Rx

ETIOLOGY

•Causative agent: Acanthamoeba castellani : a pathogenic free living Amoeba

•Habitat: soil, fresh water, sea water, well water, sewage , air

•Mode of infection: Direct corneal contact with any material or water contaminated with the organism

CLINICAL FEATURES

•Symptoms:

1.Foreign Body Sensation

2.Mild pain to Severe pain ( out of proportion to degree of inflammation)

3.Watering

4.Photophobia

5.Blurring of Vision

6.Blepharospasm

EPITHELIAL LESIONS

•Epithelial roughening and irregularities: often mistaken for Punctate epitheliopathy

•Epithelial ridges

•Radial keratoneuritis:

•Pathognomic of Acanthamoeba keratitis

•Seen in 50% of cases

•It is the inflammatory response of corneal nerves associated with perineural infiltrates.

•These infiltrates are found in the midstroma, beginning paracentrally, and extending to the limbus in a radial pattern.

•This is the cause of severe pain disproportionate to inflammation.

•Trophozoites selectively cluster around corneal nerve fibres

•Also seen in P. aeruginosa ulcerative keratitis

•Psedodendrites:

•mistaken of Herpes simplex keratitis

STOMAL LESIONS

•Patchy and satellite stromal infiltrates

•Ring infiltrates:

•Central or Paracentral

•Overlying epithelial defect

•Underlying Keratic precipitates

•Ring abscess:

•Stromal necrosis+Hypopyon @ later stages

Differential diagnosis

•Viral Keratitis

•Fungal Keratitis

•Suppurative Keratitis

    

DIAGNOSIS

•Clinical Dx:

•Difficult to diagnose due to overlapping features

•Dx by exclusion in non responsive pt.s being treated for herpetic, bacterial and viral keratitis

•Confocal microscopy:

•Direct visualization of cysts in cornea

••Laboratory Dx:

•KOH mount: Detection of cysts

•Calcofluor white stain: Cysts appear Bright apple green.

•LPCB film: Demonstration of cysts in corneal scrapings

•Culture on E.coli enriched non nutrient agar:Trophzoites within 48 hrs which turn into cysts.

•PCR: Amoebic DNA

•Corneal Biopsy: non conclusive cases; cyst detection

TREATMENT

•Quite unsatisfactory.

1.Non specific Rx:

ØCycloplegics: 1% Atropine eye drops     

ØReduce pain from ciliary spasm

ØPrevents formation of post. synechiae from secondary iridocyclitis

ØIncrease blood supply to ant. uvea by relieving pressure in ant. ciliary artery; thereby bringing more antibodies to aqueous humor

ØReduces exudation by decreasing hyperemia and permeability

ØSystemic analgesics: Paracetamol or Ibuprofen

ØVitamins: A,B and C: Helps in healing

2)Specific Rx:

a.Topical antiamoebic agents include:

• Diamidines: Propamidine isethionate (0.1 %), and

   hexamidine (0.1%).

• Biguanides : Polyhexamethylene biguanide

   (PHMB), 0.02% and chlorhexidine, 0.02%.

• Aminoglycosides: Neomycin and Paromycin

•Imidazoles: Clotrimazole and miconazole.

•Multiple drug therapy is needed for a long time (3–4

months) for early epithelial lesions and 6–12 months

for stromal lesions. Any of the following combination

may be choosen:

• Propamidine or hexamidine + PHMB or

• Chlorhexidine + Neomycin or

• Paromycin + clotrimazole or miconazole or

itraconazole.

• Frequency of instillation: hourly for a week, then

taper slowly over 3–4 months for epithelial lesions

and 6–12 months for stromal lesions.

b. Oral ketoconazole 200 mg BID, or itraconazole 100mg BD may be added in advanced cases.

3. Long-term prophylactic therapy with PHMB, twice a day for a year is recommended.

4. Penetrating keratoplasty is frequently required in non-responsive cases. Surgery should be performed after a full course of maximum medical therapy and a quiescent phase of at least six months.