A patient who wore extended-wear soft contact lenses (EW-SCL) for 6 days continuously develops acute red eye, severe pain, and a white corneal stromal infiltrate with an epithelial defect. Confocal microscopy of the cornea shows highly reflective round cysts 15–30 μm in diameter with a double-walled appearance. The causative organism is MOST likely:
- A Acanthamoeba spp. ✓
- B Pseudomonas aeruginosa
- C Fusarium solani
- D Herpes simplex virus type 1
Explanation
The confocal microscopy finding of highly reflective round cysts 15–30 μm with a double-walled (endocyst within an ectocyst) appearance is pathognomonic of Acanthamoeba cysts. Acanthamoeba keratitis is strongly associated with contact lens wear (especially EW-SCL) and exposure to contaminated water. It presents with severe, disproportionate pain, ring infiltrate, and stromal disease. Pseudomonas causes bacterial keratitis without cysts on confocal. Fusarium shows fungal hyphae on confocal (linear branching elements). Herpes simplex causes dendritic ulcers with terminal bulbs and confocal shows inflammatory cells, not cysts.
Reference: Khurana Comprehensive Ophthalmology, 7th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.