Which layer of the cornea is primarily responsible for maintaining fluid balance and transparency?

The endothelium is the layer of the cornea that plays a critical role in maintaining fluid balance and transparency. This single layer of cells lines the posterior surface of the cornea and is essential for controlling the movement of water between the cornea and the aqueous humor. By actively pumping out excess fluid, the endothelium prevents corneal swelling, which would lead to decreased transparency and impaired vision.

Maintaining the proper hydration level within the corneal stroma is vital for preserving its structure and transparency. If the endothelium is damaged or unhealthy, it can result in corneal edema, where excess fluid accumulates in the stroma, causing the cornea to become cloudy and significantly affecting visual clarity.

In contrast, the epithelium serves as a protective barrier for the cornea against environmental factors but is not primarily responsible for fluid regulation. The stroma is the thick, central part of the cornea that provides structural integrity but relies on the endothelium to maintain optimal hydration levels. Descemet's membrane acts as a basement membrane for the endothelium and also does not play a direct role in fluid balance. Therefore, the endothelium is the key player in maintaining corneal transparency and fluid balance.