Zonule of Zinn


The zonule of Zinn is a ring of fibrous strands forming a that connects the ciliary body with the crystalline lens of the eye. These fibers are sometimes collectively referred to as the suspensory ligaments of the lens, as they act like suspensory ligaments.

Development

The ciliary epithelial cells of the eye probably synthesize portions of the zonules.

Anatomy

The zonule of Zinn is split into two layers: a thin layer, which lines the hyaloid fossa, and a thicker layer, which is a collection of zonular fibers. Together, the fibers are known as the suspensory ligament of the lens. The zonules are about 1–2 μm in diameter.
The zonules attach to the lens capsule 2mm anterior and 1 mm posterior to the equator, and arise from the pars plana region of the ciliary epithelium and pass forward closely related to the lateral surfaces of the ciliary process of the pars plicata.
When colour granules are displaced from the Zonules of Zinn, the irises slowly fade. In some cases those colour granules clog the channels and lead to Glaucoma Pigmentosa.
The zonules are primarily made of fibrillin, a connective tissue protein. Mutations in the fibrillin gene lead to the condition Marfan syndrome, and consequences include an increased risk of lens dislocation.

Clinical appearance

The zonules of Zinn are difficult to visualize using a slit lamp, but may be seen with exceptional dilation of the pupil, or if a coloboma of the iris or a subluxation of the lens is present. The number of zonules present in a person appears to decrease with age. The zonules insert around the outer margin of the lens, both anteriorly and posteriorly.

Function

Securing the lens to the optical axis and transferring forces from the ciliary muscle in accommodation. When colour granules are displaced from the zonules of Zinn, caused by friction of the lens, the iris can slowly fade. These colour granules can clog the channels and lead to glaucoma pigmentosa.

Additional images