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# Zonular fibres

The zonular fibres are hundreds of fine threads from the [ciliary body](https://durgical.com/en/anatomy/ciliary-body/) to the edge of the lens; they hold the lens in place and pass on the pull that focuses it.

Official name: Ciliary zonule

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## What it is

Hundreds of fine fibres from the ciliary body to the edge of the lens.

## What it does

Hold the lens in place and pass the ciliary muscle's pull to it.

## Key points

- Made largely of fibrillin-1, the protein affected in Marfan syndrome, which is why the lens dislocates in Marfan
- For near vision the ciliary muscle contracts, the zonules slacken and the lens rounds up; for distance the muscle relaxes and the taut zonules flatten the lens (Helmholtz theory)
- Weak zonules (pseudoexfoliation syndrome, trauma, Marfan syndrome, homocystinuria) let the lens and iris wobble and make cataract surgery harder

## Key facts

**Attaches**
Ciliary processes to the lens capsule equator

**Function**
Suspend the lens; transmit ciliary muscle relaxation

**Tight in**
Distance vision (ciliary muscle relaxed): lens flattened

## Relations

**Course**
From the pars plana and the valleys between the ciliary processes, forward and inward to the [lens](https://durgical.com/en/anatomy/lens/) capsule, attaching in front of, at and behind its equator

**In front**
Posterior chamber and, beyond it, the back of the [iris](https://durgical.com/en/anatomy/iris/); aqueous flows between the fibres

**Behind**
Front face of the [vitreous body](https://durgical.com/en/anatomy/vitreous-body/)

## How to find it

Not seen in a normal eye, as they lie behind the iris. They show at the slit lamp through a dilated pupil when the lens is displaced, or on ultrasound biomicroscopy.

## Examination

- Slit lamp: a lens tremor (phacodonesis) or iris tremor (iridodonesis) on eye movement points to zonular weakness
- Dilated exam: the lens edge seen within the pupil means zonular breaks (subluxation)

## On imaging

Ultrasound biomicroscopy shows the zonules and any gaps; B-scan ultrasound finds a lens fully dislocated into the vitreous.

## Clinical notes

- Pseudoexfoliation syndrome deposits flaky material on the lens and zonules: weak zonules plus a higher risk of glaucoma
- In cataract surgery a capsular tension ring can support a lens bag with partial zonular loss
- Blunt trauma can tear zonules (zonular dialysis), tilting or dislocating the lens

## Development

Laid down as the tertiary vitreous, secreted by the ciliary epithelium.

## Memory aid

Close-up: Contract, slacken, round (the ciliary muscle contracts, the zonules go slack, the lens rounds).

## Related conditions

- [Homocystinuria](https://durgical.com/en/conditions/homocystinuria/)
- [Cataract](https://durgical.com/en/conditions/cataract/)

## Test yourself

Think of the answer, then tap the question to see it.

## Which protein makes up the zonular fibres, and why does the lens dislocate in Marfan syndrome?

Fibrillin-1, the protein affected in Marfan syndrome, so the zonules are weak.

## Are the zonular fibres taut or slack for distance vision, and what happens to the lens?

Taut: the ciliary muscle relaxes, the zonules tighten and flatten the lens (Helmholtz theory).

## Which slit-lamp signs point to zonular weakness?

Phacodonesis (lens tremor) or iridodonesis (iris tremor) on eye movement.

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Educational information, not medical advice. For any symptom, see a health professional.

## Its names

**Official Latin (TA2)**
zonula ciliaris TA2 6795

**Official Spanish (DeCS)**
Fibras zonulares

**English (TA2)**
Ciliary zonule

**Also called**
apparatus suspensorius lentis · zonula Zinni · zonule of Zinn

## Related

- [Lens](https://durgical.com/en/anatomy/lens/)
- [Ciliary body](https://durgical.com/en/anatomy/ciliary-body/)

Sources: Terminologia Anatomica (TA2); [Anatomy, Head and Neck, Eye Ciliary Muscles](https://www.ncbi.nlm.nih.gov/books/NBK482132/); [Anatomy, Head and Neck, Eye](https://www.ncbi.nlm.nih.gov/books/NBK482428/).

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Representative model, for educational purposes only.

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Source: https://durgical.com/en/anatomy/ciliary-zonule/
License: CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Cite as: DurgiPedia (durgical.com), https://durgical.com/en/anatomy/ciliary-zonule/