Zonular Fibers
As mentioned, the lens is supported by a system of fibers (the zonule) that originate from the basal lamina of the nonpigmented epithelium of the pars plana and pars plicata of the ciliary body. These zonular fibers, which are located in the valleys between the ciliary processes, consist of microfibrils composed of elastic tissue. They insert at discrete points on the lens capsule 1.5 mm anterior to the equator and 1.25 mm posterior to the equator (Fig 2-4). With increasing age, the equatorial zonular fibers regress, leaving separate anterior and posterior layers that appear in a triangular shape on cross section of the zonular ring. The fibers are 5–30 μm in diameter; on light microscopy, they are revealed as eosinophilic structures that have a positive periodic acid–Schiff (PAS) reaction. Ultrastructurally, the strands, or microfibrils, composing the fibers are 8–10 nm in diameter, with 12–14 nm of banding (Video 2-1).
VIDEO 2-1 Endoscopic view of ciliary body, zonular fibers, and lens capsule.
Courtesy of Charles Cole, MD. Go to
www.aao.org/bcscvideo_section11 to access all videos in Section 11.
Excerpted from BCSC 2020-2021 series: Section 11 - Lens and Cataract. For more information and to purchase the entire series, please visit https://www.aao.org/bcsc.