Acanthamoeba keratitis
Acanthamoeba keratitis is a corneal infection by a free-living amoeba, strongly linked to soft contact lens wear combined with freshwater exposure, diagnosed by microscopic examination of corneal scrapings and treated with prolonged topical antiamoebic/antifungal therapy that often fails to prevent progressive corneal destruction. Any contact lens wearer with a painful, non-healing keratitis that is not responding to antibacterial therapy needs this diagnosis considered and an urgent corneal scraping sent.
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What this article covers
- Overview
Corneal infection by a free-living amoeba: Acanthamoeba causes amebic (amoebic) keratitis, an infection of the corneal epithelium and stroma, distinct in cause and course from bacterial-keratitis…
- Epidemiology
An uncommon but distinct cause of infectious keratitis: the organism and the exposure history are entirely different from the far more common bacterial (chiefly Pseudomonas-associated, contact-lens-related) keratitis.
- Risk factors
Soft contact lens wear: the amoeba causes amebic keratitis specifically in persons who wear soft contact lenses.
- Pathophysiology
A free-living amoeba invades the cornea: Acanthamoeba is a free-living organism, capable of independent existence outside a host, that invades the corneal epithelium and superficial stroma once…
- Clinical features
Painful red eye with corneal involvement, the shared hallmark of all keratitis: severe eye discomfort, difficulty keeping the affected eye open, and circumferential redness around the cornea (ciliary…
- Differential diagnosis
Bacterial keratitis: most often Pseudomonas or Staphylococcus in contact lens wearers; presents identically at first glance (painful red eye, corneal infiltrate) but is discriminated by corneal…
- Diagnosis
Confirmed by microscopic examination of corneal scrapings: this is the stated basis of diagnosis for Acanthamoeba keratitis, distinct from the Gram stain/culture approach used to confirm a bacterial cause.
- Management
First, urgent ophthalmology referral and corneal scraping before definitive therapy: evaluation and treatment begin emergently, and the scraping for microscopic examination is obtained as part of…
- Complications
Progressive corneal destruction: the disease is characterized by a poor response to therapy with ongoing corneal destruction in many patients, the central threat driving the urgency of diagnosis and treatment.
- Prognosis
Often poor despite treatment: patients often respond poorly to therapy and have progressive corneal destruction, a meaningfully worse expected course than typical bacterial keratitis caught and treated early.
- Prevention
Never wear soft contact lenses while swimming in freshwater: this specific combined exposure is linked directly to infection, so lenses should be removed before any freshwater swimming and not…
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Related articles
- Bacterial keratitis
Bacterial keratitis is a corneal epithelial and stromal infection, most often Pseudomonas or Staphylococcus in soft contact lens wearers, that is a sight-threatening emergency treated with same-day corneal culture followed by hourly topical moxifloxacin 0.5% (small ulcer) or alternating fortified vancomycin and tobramycin (large or central ulcer). Delay or misdiagnosis as a benign red eye risks stromal melt, perforation, and permanent vision loss.
- Viral keratitis
Non-herpetic viral keratitis, overwhelmingly adenoviral, produces copious watery discharge, severe irritation, and preauricular lymphadenopathy that starts unilateral and spreads to the second eye. Management is supportive and infection-control focused; chronic subepithelial infiltrates are the vision-affecting sequela that sometimes needs ophthalmology-directed topical corticosteroid.
- Herpes simplex keratitis
Herpes simplex keratitis is reactivation of latent HSV along the trigeminal nerve causing a corneal dendritic ulcer with pain, photophobia, and decreased corneal sensation. Diagnosis is clinical on slit lamp with fluorescein staining; treatment is a topical or oral antiviral, and topical corticosteroids are contraindicated in active epithelial disease.
- Corneal ulcer (microbial keratitis)
Microbial keratitis (infectious corneal ulcer) is the unifying vision-threatening syndrome of a painful red eye with a corneal infiltrate, produced by bacterial, viral, fungal, or amebic invasion of a breached corneal epithelium, managed by the same urgent pathway regardless of organism: emergent scraping for smear and culture before any drug is given, then broad empiric coverage narrowed once results return. Delay, misdiagnosis as simple conjunctivitis, or premature corticosteroid use converts a treatable ulcer into stromal melt, perforation, and permanent vision loss.
- Corneal abrasion
A corneal abrasion is a traumatic or foreign-body-related defect of the corneal epithelium diagnosed by fluorescein uptake under cobalt-blue light. Uncomplicated cases heal in days with lubrication and pain control, but contact-lens wear mandates antipseudomonal coverage and any red flag (rust ring, infiltrate, Seidel sign, hypopyon) demands same-day ophthalmology referral.
- Conjunctivitis
Conjunctivitis is inflammation of the conjunctiva from viral, bacterial, or allergic causes presenting with red eye, discharge, and preserved vision, diagnosed clinically by discharge character and managed with supportive care, targeted topical antibiotics, or topical antihistamine/mast-cell-stabilizer therapy.
- Uveitis
Uveitis is inflammation of the uveal tract, classified by anatomic location as anterior, intermediate, posterior, or panuveitis and by systemic association such as HLA-B27 spondyloarthritis, sarcoidosis, or Behcet disease. Anterior uveitis presents with a painful red eye and photophobia diagnosed at the slit lamp, while posterior uveitis presents with painless floaters or vision loss, and treatment is topical corticosteroid for anterior disease escalating to systemic corticosteroid and steroid-sparing immunosuppression for recurrent, severe, or posterior-segment disease.
- Acute angle-closure glaucoma
Acute angle-closure glaucoma is a pupillary-block emergency in which sudden closure of the iridocorneal angle blocks aqueous outflow, causing severe eye pain, halos, and rapidly rising intraocular pressure that can blind the eye within hours if not treated. Diagnosis is clinical plus tonometry and gonioscopy; treatment is immediate topical and systemic IOP-lowering therapy followed by laser peripheral iridotomy.