A 24-year-old patient presents with redness, foreign body sensation, excessive tears in the eyes along with corneal ulcers following the use of contact lens. The saline mount preparation of the corneal scrapping shows polygonal cysts. What would be the most probable cause?

The given clinical history and the demonstration of polygonal cysts are suggestive of amoebic keratitis caused by Acanthamoeba. Acanthamoeba culbesoni is a free-living amoeba. It exists as trophozoite form and resistant cystic form. Both these forms are infective. The trophozoite is large and characterized by spine-like pseudopodia (acanthopodia). Human beings acquire by inhalation of cyst or trophozoite, ingestion of cysts, or through traumatized skin or eyes. It presents as two chronic conditions - acanthamoeba keratitis and granulomatous amoebic encephalitis. Diagnosis of amoebic keratitis is made by the demonstration of the cyst in corneal scrapings by wet mount, histology, and culture. Reference: Paniker&;s Textbook of Medical Parasitology 8th edition