**Core Concept**
Sympathetic ophthalmia is a rare but serious autoimmune-mediated bilateral uveitis that occurs after trauma to one eye, leading to inflammation and potential vision loss in the unaffected eye. It results from immune system activation due to tissue damage, with the second eye being attacked due to cross-reactive immune responses.

**Why the Correct Answer is Right**
Sympathetic ophthalmia is the most serious and potentially vision-threatening complication following ocular trauma. It typically develops weeks to months after injury to one eye and involves inflammation of the uveal tract in the contralateral eye. The pathophysiology involves activation of autoreactive T-cells that recognize ocular antigens, leading to bilateral uveitis, which can cause permanent vision loss if untreated. This condition is not vision loss due to trauma itself but a systemic immune reaction.

**Why Each Wrong Option is Incorrect**
Option A: Subconjunctival hemorrhage is common after trauma but is benign and self-limiting, not a serious systemic complication.
Option B: Corneal edema occurs in the injured eye and may impair vision, but it is a local, reversible issue and not a complication in the other eye.
Option D: Sudden loss of vision in the unaffected eye is not a typical or direct consequence of trauma; it is more likely due to other causes like stroke or retinal detachment, not sympathetic ophthalmia.

**Clinical Pearl / High-Yield Fact**
Sympathetic ophthalmia is a rare but life-altering condition requiring prompt diagnosis and steroid therapy. It should be suspected in any patient with trauma to one eye who develops vision loss or inflammation in the other eye — early intervention is critical to prevent blindness.

✓ Correct Answer: C. Sympathetic ophthalmia