**Core Concept**
Latanoprost is a synthetic prostaglandin F2-alpha analogue used in the treatment of glaucoma. Prostaglandins play a crucial role in the regulation of intraocular pressure (IOP) by enhancing the outflow of aqueous humor through the trabecular meshwork. By mimicking the action of natural prostaglandins, latanoprost helps to decrease IOP, thereby reducing the risk of optic nerve damage and visual loss associated with glaucoma.

**Why the Correct Answer is Right**
Latanoprost works by activating the FP receptor in the ciliary muscle, leading to relaxation of the muscle and increased outflow of aqueous humor. This results in a decrease in IOP, which is a hallmark of glaucoma. The use of latanoprost has been shown to be effective in reducing IOP in patients with open-angle glaucoma, making it a valuable treatment option for this condition.

**Why Each Wrong Option is Incorrect**
**Option A:** Latanoprost is not used to maintain the ductus arteriosus, which is a blood vessel that connects the pulmonary artery to the aortic arch in fetal life. Maintenance of the ductus arteriosus is typically achieved through other mechanisms, such as prostaglandin E1 (PGE1) infusion.

**Option B:** While latanoprost does affect the cardiovascular system by reducing IOP, it is not used to treat pulmonary hypertension. Pulmonary hypertension is a condition characterized by high blood pressure in the pulmonary arteries, which is typically treated with other medications such as endothelin receptor antagonists or phosphodiesterase-5 inhibitors.

**Option C:** Latanoprost does not have a role in gastric mucosal protection. Gastric mucosal protection is typically achieved through the use of medications such as proton pump inhibitors or histamine-2 receptor antagonists, which reduce gastric acid secretion.

**Clinical Pearl / High-Yield Fact**
It's essential to remember that prostaglandins, such as latanoprost, can cause changes in iris pigmentation, particularly in patients with darker irises. This is a common side effect of prostaglandin analogues and can lead to permanent changes in iris color.

**✓ Correct Answer: D. Glaucoma**