**Core Concept**
Mooren's ulcer is a rare, idiopathic inflammatory condition characterized by progressive corneal thinning and ulceration, often resulting in vision loss. It typically affects young adults, with a slight predilection for females. The exact pathophysiology is unknown, but it is believed to involve an autoimmune component.

**Why the Correct Answer is Right**
Mooren's ulcer is indeed a rare condition that affects the cornea, and its exact cause remains unclear. The condition is thought to be autoimmune in nature, with some studies suggesting a link to HLA-B27 and other genetic factors. Corneal thinning and ulceration are hallmarks of the disease, often leading to severe vision impairment if left untreated.

**Why Each Wrong Option is Incorrect**
**Option A:** Mooren's ulcer is indeed associated with a poor prognosis if left untreated, often resulting in vision loss. However, this statement is true, so it's not the correct answer.
**Option B:** Mooren's ulcer is a unilateral condition, typically affecting one eye, which is a true characteristic of the disease. However, this statement is true, so it's not the correct answer.
**Option C:** Mooren's ulcer is not typically associated with systemic symptoms, unlike some other autoimmune conditions. However, Mooren's ulcer can be associated with systemic symptoms in some cases, making this statement incorrect.

**Clinical Pearl / High-Yield Fact**
Mooren's ulcer is a rare, but potentially devastating condition that requires prompt diagnosis and treatment to prevent vision loss. It is essential to consider Mooren's ulcer in the differential diagnosis of any corneal ulcer or thinning, particularly in young adults.

**Correct Answer: C. Mooren's ulcer is not typically associated with systemic symptoms.**