**Core Concept**
Chronic simple glaucoma, also known as primary open-angle glaucoma (POAG), is a type of glaucoma characterized by a slow and progressive loss of vision due to increased intraocular pressure (IOP) without any visible damage to the drainage angle of the eye.

**Why the Correct Answer is Right**
The correct answer is open-angle glaucoma because it is the most common form of glaucoma and is characterized by a gradual loss of vision due to a slow increase in IOP. This type of glaucoma is called "open-angle" because the drainage angle between the iris and the cornea remains open, but the trabecular meshwork, the spongy tissue through which the aqueous humor drains, becomes clogged, leading to a buildup of fluid and increased pressure.

**Why Each Wrong Option is Incorrect**
* **Option A:** Closed-angle glaucoma is a different type of glaucoma where the drainage angle between the iris and the cornea becomes blocked, leading to a sudden and severe increase in IOP.
* **Option B:** Congenital glaucoma is a rare form of glaucoma that occurs in infants and young children due to a developmental abnormality in the eye.
* **Option C:** Acute angle-closure glaucoma is a medical emergency where the drainage angle becomes blocked suddenly, leading to a severe increase in IOP and potentially causing vision loss.

**Clinical Pearl / High-Yield Fact**
Chronic simple glaucoma (POAG) is often asymptomatic until late stages, making regular eye exams crucial for early detection and treatment.

**Correct Answer: C. Congenital glaucoma is a rare form of glaucoma that occurs in infants and young children due to a developmental abnormality in the eye.