Which thin clear mucosal membrane contains blood vessels, nerves and glands and attaches at the limbus?

• A. Cornea
• B. Descemet's membrane
• C. Cilia
• D. Conjunctiva

Answer: (D)

This question tests ocular surface anatomy and the properties of the conjunctival membrane. The conjunctiva is a thin, transparent mucous membrane that lines the inside of the eyelids and covers the sclera up to the limbus. It contains blood vessels, nerves, and glands (notably goblet cells that secrete mucus to keep the eye moist). It attaches at the limbus, the border where the cornea meets the sclera. The cornea, by contrast, is avascular and lacks glands; Descemet's membrane is a basement membrane inside the cornea, and cilia are eyelashes, not a membrane. So the membrane described—the one with vessels, nerves, and glands that attaches at the limbus—is the conjunctiva.