2020–2021 BCSC Basic and Clinical Science Course™
2 Fundamentals and Principles of Ophthalmology
Part I: Anatomy
Chapter 2: The Eye
Iris
Vessels and Nerves
Blood vessels form the bulk of the iris stroma. Most follow a radial course, arising from the major arterial circle and passing to the center of the pupil. In the region of the collarette (the thickest portion of the iris), anastomoses occur between the arterial and venous arcades to form the minor vascular circle of the iris, which is often incomplete. The major arterial circle is located at the apex of the ciliary body, not the iris (see Chapter 1, Fig 1-20).
The diameter of the capillaries is relatively large. Their endothelium is nonfenestrated and is surrounded by a basement membrane, associated pericytes, and a zone of collagenous filaments. The intima has no internal elastic lamina. Myelinated and unmyelinated nerve fibers serve sensory, vasomotor, and muscular functions throughout the stroma.
Excerpted from BCSC 2020-2021 series: Section 2 - Fundamentals and Principles of Ophthalmology. For more information and to purchase the entire series, please visit https://www.aao.org/bcsc.