Acanthamoeba keratitis is most commonly associated with which risk factor, and which investigation is most specific for diagnosis?
- A Swimming in contaminated water + corneal biopsy with periodic acid-Schiff (PAS) staining
- B Soft contact lens wear, especially with tap water/homemade saline exposure + confocal microscopy showing double-walled cysts and/or trophozoites in the corneal stroma ✓
- C Corneal trauma with vegetable matter + culture on Sabouraud's agar
- D HIV infection + PCR from aqueous humor
Explanation
Acanthamoeba keratitis is strongly associated with soft contact lens wear (especially with non-sterile water exposure, tap water rinsing of lenses/cases, swimming in lenses). The classic presentation is severe pain disproportionate to clinical signs, ring infiltrate (Wessely immune ring), and perineural infiltrates. In vivo confocal microscopy (IVCM) is the most useful non-invasive investigation — it demonstrates double-walled cysts (10–25 μm) and/or trophozoites within the corneal stroma at high magnification. PCR of corneal scraping is the most sensitive and specific. Culture requires non-nutrient agar with E. coli overlay (NNA/E. coli medium).
Reference: Khurana Comprehensive Ophthalmology, 7th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.