**Core Concept**
Stem cells responsible for corneal epithelial regeneration are located in the limbus, the junction between the cornea and the sclera. These limbal stem cells are essential for maintaining the cornea’s epithelial layer through continuous renewal.

**Why the Correct Answer is Right**
Limbal stem cells reside in the basal layer of the limbus and are the primary source of corneal epithelial cells. They differentiate into epithelial cells that migrate across the corneal surface, ensuring constant renewal. These cells are vital for healing after injury or chemical burns and are the target in conditions like limbal stem cell deficiency.

**Why Each Wrong Option is Incorrect**
Option B: The stroma is the middle layer of the cornea and consists of densely packed collagen fibers; it lacks stem cells and does not regenerate epithelium.
Option C: The epithelium itself is a terminally differentiated layer and does not contain stem cells; it is maintained by limbal-derived cells.
Option D: Descemet’s membrane is a basement membrane underlying the endothelium and serves as a structural support; it does not harbor stem cells.

**Clinical Pearl / High-Yield Fact**
In corneal transplantation, limbal stem cell deficiency is a major cause of graft failure. Patients with limbal stem cell disease often require autologous limbal stem cell transplantation or grafting from a donor limbus.

✓ Correct Answer: A. Limbus