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.
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 deficiency or rupture is the major complication in cataract surgery as it prevents safe in-the-bag intraocular lens implantation. Pseudoexfoliation syndrome (abnormal fibrillin deposition) weakens the zonules and is the most common cause of zonular instability in cataract surgery. Marfan syndrome produces superotemporal lens subluxation (ectopia lentis) from FBN1 mutation causing zonular weakness. Traumatic zonular dialysis from blunt eye injury produces lens decentration and monocular diplopia. Iris hooks and capsular tension rings are surgical adjuncts to support weakened zonules during cataract 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.
