**Core Concept**
Glaucoma is a group of optic neuropathies primarily caused by progressive damage to the retinal ganglion cells due to impaired blood flow and axonal injury, most commonly associated with elevated intraocular pressure (IOP). This pressure arises from an imbalance between aqueous humor production and outflow, particularly through the trabecular meshwork.

**Why the Correct Answer is Right**
In primary open-angle glaucoma, the most common form, increased intraocular pressure results from reduced aqueous humor drainage through the trabecular meshwork. This sustained pressure leads to mechanical stress on the optic nerve head, causing irreversible vision loss. While other forms like angle-closure glaucoma also involve elevated IOP, the fundamental pathophysiological mechanism in most cases is raised intraocular pressure.

**Why Each Wrong Option is Incorrect**
Option B: Raised intracranial pressure affects the brain and is associated with conditions like hemorrhage or tumors, not glaucoma.
Option C: Intraocular infection (e.g., endophthalmitis) causes inflammation and vision loss but is not the cause of chronic glaucoma.
Option D: Orbital masses may cause visual disturbances or compressive optic neuropathy, but they are not the primary cause of glaucoma.

**Clinical Pearl / High-Yield Fact**
"Glaucoma is often called the 'silent thief of sight' because it progresses without symptoms until significant vision loss occurs. Early detection through regular eye exams and IOP measurement is critical—especially in patients with family history or high myopia."

✓ Correct Answer: A. Raised intraocular pressure