These are string-like attachments that suspend the lens inside your eye. The zonules run around the periphery of the lens/cataract like trampoline springs and attach to the ciliary body muscle. Muscle contraction of the ciliary body changes the tension on the zonules, and this controls the lens shape to help with visual focus. Certain conditions like Marfan syndrome can cause a weakness to the zonules and make the eye prone to lens dislocations as the zonules break. Pseudoexfoliation syndrome can cause the zonules to become brittle and delicate, making cataract surgery challenging because of the resulting zonular weakness.