Zonular fibres
Fibrae zonulares
Fine fibres that hold the lens of the eye in place, running from the ciliary body to the lens capsule around its equator.
At a glance
- English
- Zonular fibres
- Latin (TA2)
- Fibrae zonulares
- System
- Nerve
- Region
- Head
- Side
- Paired, left and right
About the zonular fibres
The zonular fibres, together called the ciliary zonule or suspensory ligament of the lens, are a ring of very fine, transparent fibres that hang the lens behind the iris. They arise from the inner surface of the ciliary body, both from its flat posterior part, the pars plana, and from the valleys between the ciliary processes. They pass inwards to fix onto the lens capsule around its equator: some reach the capsule a little in front of the equator, some a little behind it, and some at the equator itself.
The fibres are made of bundles of microfibrils rich in fibrillin, a protein also found in elastic tissue elsewhere in the body. Between them lie narrow gaps, the zonular spaces, which form part of the posterior chamber of the eye and through which aqueous humour passes. Behind the zonule lies the vitreous body and in front of it the back of the iris.
The zonule carries the pull of the ciliary body to the lens. For distant vision the ciliary muscle is relaxed, the ring of the ciliary body is wide and the fibres are taut, flattening the elastic lens. For near vision the ciliary muscle contracts under parasympathetic control from the oculomotor nerve, relayed through the ciliary ganglion. The ring narrows, the fibres slacken and the lens becomes rounder and more powerful. Weak or faulty zonules let the lens move out of place, a condition called ectopia lentis. In Marfan syndrome, caused by changes in the fibrillin-1 gene, the lens typically shifts upwards and outwards. Weak zonules also complicate cataract surgery, as in pseudoexfoliation syndrome.
Course and supply
- Arises from
- Ciliary body: the pars plana and the valleys between the ciliary processes.
- Ends in
- Lens capsule at, just in front of and just behind the equator of the lens.
- Supplies
- Suspends the lens and transmits changes in ciliary muscle tone to it, allowing accommodation for near and distant vision.
Anthromica
See the zonular fibres where it really sits, with every layer of the body around it.
- Every layer, one body. Peel from muscle to bone, nerve, vessel and organ, and turn it any way.
- English and Latin. Every structure named the way your exam names it.
- Quiz until it sticks. Short drills on the structures you keep missing.
Free to start. No card.
