**Core Concept**
Satellite nodules are a characteristic feature of certain corneal ulcers, representing an extension of the infectious process beyond the primary site of infection. They are a diagnostic clue to the underlying etiology, particularly in cases of fungal corneal ulcers.

**Why the Correct Answer is Right**
Fungal corneal ulcers, caused by fungi such as Aspergillus, Fusarium, or Candida, are characterized by the formation of satellite nodules. These nodules are a result of the spread of fungal hyphae from the primary site of infection, leading to the formation of new, smaller lesions. The presence of satellite nodules is a key diagnostic feature of fungal corneal ulcers, distinguishing them from bacterial or viral ulcers. The formation of satellite nodules is thought to be due to the extension of fungal hyphae through the corneal stroma, leading to the development of new, smaller areas of infection.

**Why Each Wrong Option is Incorrect**
**Option B:** Tuberculosis typically presents with a characteristic "tree-bud" appearance, but it is not associated with satellite nodules.
**Option C:** Sarcoidosis can affect the eye, but it typically presents with granulomatous inflammation and not with satellite nodules.
**Option D:** Viral ulcers, such as those caused by herpes simplex virus, typically present with a dendritic or geographic pattern of ulceration, but not with satellite nodules.

**Clinical Pearl / High-Yield Fact**
Remember that satellite nodules are a characteristic feature of fungal corneal ulcers, and their presence should prompt a thorough investigation for fungal infection, including a corneal scraping for culture and histopathological examination.

✓ Correct Answer: A. Fungal corneal ulcer