Sense organs (eye and ear)
Lens
Lens
- Origin
- Biconvex, avascular lens behind the iris, in the hyaloid fossa of the vitreous body
- Insertion
- Suspended from the ciliary body by the zonular fibres (zonule of Zinn)
- Function
- Provides about 15-20 dioptres and changes curvature during accommodation for sharp near vision
- Innervation
- Not innervated itself; accommodation runs through the ciliary muscle (oculomotor nerve, parasympathetic)
- Movement & chain
- Becomes more convex during accommodation as the ciliary muscle contracts and the zonular fibres relax
- Palpation
- Slit-lamp assessment; opacity shows as a grey pupil and a reduced red fundus reflex
- Clinical
- Cataract (age, corticosteroids, diabetes), presbyopia from the fifth decade, lens dislocation in Marfan syndrome
- Segmental innervation
- No segment of its own; accommodation via III (midbrain)
- In clinical practice
- Cataract surgery with intraocular lens implantation is the most frequently performed operation worldwide; watch for infection and visual change afterwards
- Region in the model
- Sense organs (eye and ear)