**Core Concept**
Posterior staphyloma is a condition characterized by a bulging of the sclera and choroid due to weakening of the ocular wall. It often results from increased intraocular pressure or trauma, leading to the formation of a full-thickness defect in the sclera. The posterior staphyloma is most commonly associated with conditions that compromise the integrity of the sclera.

**Why the Correct Answer is Right**
The most common cause of posterior staphyloma is a result of chronic angle-closure glaucoma, which leads to increased intraocular pressure. The elevated pressure causes thinning and weakening of the posterior sclera, ultimately resulting in the formation of a staphyloma. The pathophysiology involves the collapse of the posterior sclera due to the increased pressure, which compromises the structural integrity of the eye.

**Why Each Wrong Option is Incorrect**
**Option A:** High myopia is not the most common cause of posterior staphyloma, although it can contribute to the development of staphylomas due to the thinning of the sclera.
**Option B:** Posterior staphyloma is not typically associated with retinal detachment, although the two conditions can coexist.
**Option C:** Trauma is a possible cause of posterior staphyloma, but it is not the most common cause.

**Clinical Pearl / High-Yield Fact**
Posterior staphyloma is often associated with chronic angle-closure glaucoma, which can be a complication of conditions such as hyperopia or anatomically narrow angles.

**Correct Answer: C. Trauma.**