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Showing posts with label nuerology. Show all posts
Showing posts with label nuerology. Show all posts

The accommodation or near reflex

Accomodation reflex involve a triad of changes when a person looks at a nearby object.
1. Convergence of eye due to contraction of medial and lateral rectus muscle
2. Miosis -constriction of pupils due to constrictor pupillae  muscle contraction.
3. Accomodation is associated with increased refractive power of the lens.This is due to the contraction of ciliaris muscle.

Pathway of accommodation
1. Afferent impulses from retina pass along the normal visual pathway to reach the visual areas in the occipital lobe
2. From the visual areas fibers descend to the oculomotor (3rd cranial nerve) nucleus of both side in the midbrain.
3. Efferent fibers pass along the 3 rd cranial nerve to the eye to supply the following muscle
  Medial rectus muscle
  Constrictor pupillae muscle 
  Ciliaris musle
In accommodation reflex the fibers reach the lateral geniculate body and the occipital cortex but they donot pass through the pretectal nucleus situated in midbrain.

Method of testing accommodation reflex
The patient is asked to look at a distant object and then at the examiners finger which is gradually brought within 5cm of the eyes.When the gaze is directed from a distant object to near one contraction of medial rectus brings about a convergence of of the ocular axis and along with this accommodation occurs by the contraction of ciliaris muscle and pupil constrict  as a part of associated movement .

Significance  of accommodation reflex
Accomodation reflex is absent in 
      Reverse Argyll Robertsons pupil