Which term describes the thick central corneal layer providing most of the cornea's strength and optical clarity?

• A. Stress lines
• B. Trephine
• C. Uvea
• D. Stroma

Answer: (D)

The thick central layer of the cornea that provides most of its strength and optical clarity is the stroma. The stroma makes up about 90% of corneal thickness and is built from tightly organized collagen lamellae with keratocytes in a carefully hydrated, highly regular extracellular matrix. This precise arrangement minimizes light scattering, allowing transparency, while the collagen structure gives the cornea its shape and mechanical strength.

Other options don’t fit the description: stress lines aren’t a corneal layer, a trephine is a surgical instrument used to cut circular tissue, and the uvea is the vascular middle layer inside the eye, not part of the cornea.