## **Core Concept**
The patient's symptoms, including redness, foreign body sensation, excessive tearing, and corneal ulcers following contact lens use, suggest an ocular infection likely caused by a microorganism associated with contact lens wear. The presence of polygonal cysts in the saline mount preparation of the corneal scraping is key to identifying the causative agent.

## **Why the Correct Answer is Right**
The description of polygonal cysts in the corneal scraping is characteristic of **Acanthamoeba** infection. Acanthamoeba keratitis is a rare but serious eye infection often associated with contact lens wear, especially if the lenses are not properly cleaned and maintained or if tap water is used for cleaning. The polygonal cysts (or cysts with a characteristic polygonal shape) are a hallmark of Acanthamoeba infection when viewed under a microscope. This condition can lead to severe ocular morbidity if not promptly diagnosed and treated.

## **Why Each Wrong Option is Incorrect**
- **Option A:** This option is not provided, but typically, incorrect options might include other causes of keratitis such as bacterial, viral, or fungal infections. These would not typically present with polygonal cysts in a corneal scraping.
- **Option B:** Similarly, without the specific content of Option B, we can infer that any option not describing Acanthamoeba would be incorrect based on the provided clinical scenario and diagnostic findings.
- **Option C:** Again, without specifics, any option not aligning with Acanthamoeba keratitis would be incorrect.
- **Option D:** This option is also not provided, but presumably, it does not match the diagnosis of Acanthamoeba keratitis.

## **Clinical Pearl / High-Yield Fact**
A key clinical pearl is that Acanthamoeba keratitis should be suspected in contact lens wearers presenting with severe eye pain, photophobia, and corneal ulcers, particularly if there is a history of exposure to contaminated water or poor lens hygiene. Early diagnosis and treatment are crucial to prevent vision loss.

## **Correct Answer:** C. Acanthamoeba.