Accommodation reflex
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accommodation reflex
(ə′käm·ə′dā·shən ′rē·fleks)
(physiology) Changes occurring in the eyes when vision is focused from a distant to a near object; involves pupil contraction, increased lens convexity, and convergence of the eyes.
American Heritage Stedman's Medical Dictionary:
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accommodation reflex
n.
The coordinated changes that occur in the eye when viewing a near object, including constriction of the pupil, convergence of the eyes, and increased convexity of the lens.
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Accommodation reflex
The accommodation reflex is a reflex action of the eye, in response to focusing on a near object, then looking at distant object (and vice versa), comprising coordinated changes in vergence, lens shape and pupil size. It is dependent on cranial nerve II (afferent limb of reflex), superior centres and cranial nerve III.
A near object (for example, a computer screen) appears large in the field of vision, and the eye receives light from wide angles. When moving focus from a distant to a near object, the eyes converge. The ciliary muscle contracts making the lens more convex, shortening its focal length. The pupil constricts in order to prevent diverging light rays from hitting the periphery of the retina and resulting in a blurred image.
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Pathway
Information from the light on each retina is taken to the occipital lobe via the optic nerve and optic radiation, where it is interpreted as vision. The peristriate area 19 interprets accommodation, and sends signals via the Edinger-Westphal nucleus and the 3rd cranial nerve to the ciliary muscle, the medial rectus muscle and (via parasympathetic fibres) the sphincter pupillae muscle.[1]
See also
References
- ^ Bhatnagar SC. Neuroscience for the study of communicative disorders. p 185-6. | http://books.google.com/books?id=d0D0ghp2fSAC&pg=PA185&lpg=PA185&dq=accommodation+reflex+cranial+nerve+iii&source=bl&ots=JWF1lLVjYt&sig=-rQh6t8JPfSUapV8yiIvBuBcqNw&hl=en&ei=02_LS4ftEsP-8Ab60NX8BA&sa=X&oi=book_result&ct=result&resnum=10&ved=0CC4Q6AEwCQ#v=onepage&q=accommodation%20reflex%20cranial%20nerve%20iii&f=false
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