The zonule of Zinn (ciliary zonule) consists of hundreds of fine collagen fibres running from the ciliary body and pars plana to the equator and anterior and posterior lens capsule, suspending the crystalline lens within the eye and providing the structural basis for accommodation (ciliary muscle contraction relaxes zonular tension, allowing the elastic lens to round up for near focus). The zonular fibres are composed of fibrillin-1, a glycoprotein encoded by the FBN1 gene.
| Origin | Ciliary body (ciliary processes and pars plana) |
|---|---|
| Insertion | Equatorial region of the lens capsule |
Suspends the crystalline lens within the posterior chamber in optical alignment with the visual axis; transmits forces from ciliary muscle contraction to the lens capsule to change lens curvature for accommodation; maintains lens position during eye movements and head acceleration.
Zonular weakness or rupture is a major complication risk in cataract surgery because it prevents safe in-the-bag intraocular lens implantation. Pseudoexfoliation syndrome is the most common cause of zonular instability in cataract surgery. Marfan syndrome (FBN1 mutation) typically produces superotemporal lens subluxation (ectopia lentis), while homocystinuria typically produces inferonasal subluxation. Traumatic zonular dialysis from blunt eye injury produces lens decentration and monocular diplopia, and complete rupture lets the lens dislocate into the anterior chamber or vitreous. Iris hooks, capsular hooks and capsular tension rings support weakened zonules during surgery.
Blunt ocular trauma tears the zonular fibres producing zonular dialysis with lens subluxation visible as iridodonesis (trembling iris) and phacodonesis (trembling lens); the extent of dialysis determines surgical planning for cataract extraction. Small dialysis is supported by capsular tension rings while large dialysis may require iris-fixated or scleral-fixated IOL implantation.
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