QS Study

Accommodation reflex: Convergence of the eyeball with constriction of pupils occurs on looking on a near object called accommodation reflex. The reflex, controlled by the parasympathetic nervous system, involves three responses; pupil accommodation, lens accommodation, and convergence. The change in the shape of the lens is controlled by the ciliary muscles inside the eye.

It refers to a reflex action of the eye to focus on nearby objects after looking at distant objects, and vice versa. It has to do only with the focus of the image, not color or quality.

Pathways of Accommodation Reflex 1

Fig: Pathways of Accommodation Reflex

Pathways of Accommodation Reflex –

The accommodation reflex has its afferent input from the primary visual pathway. The efferent pathway of the reflex starts in visual cortex. Information from light is received by the rods and cones of the retina (receptors) and then sent via the optic nerve (sensory nerve) through the optic chiasm to the optic radiations in the occipital lobe of the brain where it is interpreted as vision.

  • Light,
  • Cornea,
  • Traverse Refractory Media,
  • Rods & cons,
  • Optic nerve,
  • Optic tract,
  • Lateral geniculate body,
  • Optic radiation,
  • Visual cortex,
  • Eye field of the frontal cortex,
  • Internal capsule,
  • Oculomotor nuclei in the midbrain
  • Medial rectus (causes convergence of eyeball)
  • Edinger-Westphal nuclei of third cranial nerve on both sides
  • The oculomotor nerve to the ciliary ganglion on the orbit
  • Short ciliary nerve
  • Ciliary muscle and
  • Constrictor pupillae muscle of the iris,
  • Constrictor pupillae muscle of the iris,
  • Contraction of (Constricts the pupil) ciliary muscle,
  • Relaxation of the suspensory ligament,
  • Lens thickens increases,
  • Refractive power increases.

The ciliary muscle contracts and changes the lens shape to focus the nearby image. At the same time, impulses from sympathetic nerves cause papillary constriction, another form of accommodation.

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