**Core Concept**
Romana's sign is a clinical finding associated with a specific condition, characterized by unilateral proptosis and edema of the eyelids, along with conjunctival congestion. This phenomenon is indicative of a particular systemic disease that affects the orbit and surrounding structures.

**Why the Correct Answer is Right**
Romana's sign is specifically seen in Chagas disease, caused by Trypanosoma cruzi. The parasite invades the orbital tissues, leading to inflammation and subsequent edema, proptosis, and conjunctival congestion. This manifestation is a result of the parasite's tropism for the Schwann cells of the autonomic nervous system. The resulting autonomic dysfunction and inflammation contribute to the development of Romana's sign.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because Romana's sign is not typically associated with thyroid ophthalmopathy. While thyroid eye disease can cause proptosis and eyelid swelling, it does not characteristically present with conjunctival congestion.
**Option B:** This option is incorrect because orbital cellulitis would present with more acute symptoms, such as severe pain and fever, rather than the chronic, unilateral proptosis and edema seen in Romana's sign.
**Option C:** This option is incorrect because neurosarcoidosis can cause orbital inflammation, but it does not typically present with the specific constellation of symptoms seen in Romana's sign.

**Clinical Pearl / High-Yield Fact**
Chagas disease, the cause of Romana's sign, is a significant public health concern in Latin America, with an estimated 6 million people infected. Early diagnosis and treatment are crucial to prevent long-term complications, including cardiac and gastrointestinal involvement.

**Correct Answer: D. Chagas disease.**