What is the general histology of the iris stroma?

• A. Dense connective tissue with lots of collagen and fibroblasts.
• B. Loose connective tissue with melanocytes, vasculature, and fibroblasts.
• C. Muscular tissue rich in smooth muscle fibers.
• D. Nerve-rich dense tissue.

Answer: (B)

The iris stroma is a loose connective tissue framework that fills the iris. It is not dense and fibrous; instead, it has a loose organization that accommodates a rich network of blood vessels and pigment cells. Melanocytes within the stroma give the iris its color, especially prominent in darker irides. Fibroblasts are present to maintain the extracellular matrix and keep the tissue flexible. This loose, vascular, pigmented connective tissue supports the embedded smooth muscle components of the iris (like the sphincter and dilator muscles) that control pupil size. So the iris stroma is best described as loose connective tissue containing melanocytes, vasculature, and fibroblasts.