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Accommodation reflex
 
 
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The accommodation reflex is a reflex action
Reflex action

A reflex action, also known as a reflex, is an involuntary and nearly instantaneous movement in response to a Stimulus . In most contexts, in particular those involving humans, reflex actions are mediated via the reflex arc; this is not always true in other animals, nor does it apply to casual uses of the term 'reflex'....
 of the eye
Eye

Eyes are Organ that detect light, and send signals along the optic nerve to the visual system and other areas of the brain. Complex optical systems with resolving power have come in ten fundamentally different forms, and 96% of animal species possess a complex optical system....
, in response to focusing
Focus (optics)

In geometrical optics, a focus, also called an image point, is the point where light rays originating from a point on the object converge ....
 on a near object, then looking at distant object (and vice versa), comprising coordinated changes in vergence
Vergence

A vergence is the simultaneous movement of both eyes in opposite directions to obtain or maintain single binocular vision..When a creature with binocular vision looks at an object, the eyes must rotate around a vertical axis so that the projection of the image is in the centre of the retina in both eyes....
, lens
Lens (anatomy)

The lens is a transparent, Lens_#Types_of_lenses structure in the eye that, along with the cornea, helps to refract light to be Focus on the retina....
 shape and pupil
Pupil

The pupil is the sphere that is located in the center of the Iris of the eye and that controls the amount of light that enters the eye. It appears black because most of the light entering the pupil is absorbed by the biological tissue inside the eye....
 size. It is dependent on cranial nerve II
Optic nerve

The optic nerve, also called cranial nerve II, transmits visual information from the retina to the brain....
 (afferent limb of reflex), higher centres and cranial nerve III
Oculomotor nerve

The oculomotor nerve is the third of twelve paired cranial nerves. It controls most of the eye's movements, constriction of the pupil, and maintains an open eyelid....
.

A near object (for example, a computer screen) appears large in the field of vision
Field of view

The field of view is the angle extent of the observable world that is visual perception at any given moment.The range of visual abilities is not uniform across a field of view, and varies from animal to animal....
, and the eye receives light
Light

Light, or visible light, is electromagnetic radiation of a wavelength that is Visible spectrum to the human eye , or up to 380?750 nm. In the broader field of physics, light is sometimes used to refer to electromagnetic radiation of all wavelengths, whether visible or not....
 from wide angles.






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Encyclopedia


The accommodation reflex is a reflex action
Reflex action

A reflex action, also known as a reflex, is an involuntary and nearly instantaneous movement in response to a Stimulus . In most contexts, in particular those involving humans, reflex actions are mediated via the reflex arc; this is not always true in other animals, nor does it apply to casual uses of the term 'reflex'....
 of the eye
Eye

Eyes are Organ that detect light, and send signals along the optic nerve to the visual system and other areas of the brain. Complex optical systems with resolving power have come in ten fundamentally different forms, and 96% of animal species possess a complex optical system....
, in response to focusing
Focus (optics)

In geometrical optics, a focus, also called an image point, is the point where light rays originating from a point on the object converge ....
 on a near object, then looking at distant object (and vice versa), comprising coordinated changes in vergence
Vergence

A vergence is the simultaneous movement of both eyes in opposite directions to obtain or maintain single binocular vision..When a creature with binocular vision looks at an object, the eyes must rotate around a vertical axis so that the projection of the image is in the centre of the retina in both eyes....
, lens
Lens (anatomy)

The lens is a transparent, Lens_#Types_of_lenses structure in the eye that, along with the cornea, helps to refract light to be Focus on the retina....
 shape and pupil
Pupil

The pupil is the sphere that is located in the center of the Iris of the eye and that controls the amount of light that enters the eye. It appears black because most of the light entering the pupil is absorbed by the biological tissue inside the eye....
 size. It is dependent on cranial nerve II
Optic nerve

The optic nerve, also called cranial nerve II, transmits visual information from the retina to the brain....
 (afferent limb of reflex), higher centres and cranial nerve III
Oculomotor nerve

The oculomotor nerve is the third of twelve paired cranial nerves. It controls most of the eye's movements, constriction of the pupil, and maintains an open eyelid....
.

Focus in An Eye
A near object (for example, a computer screen) appears large in the field of vision
Field of view

The field of view is the angle extent of the observable world that is visual perception at any given moment.The range of visual abilities is not uniform across a field of view, and varies from animal to animal....
, and the eye receives light
Light

Light, or visible light, is electromagnetic radiation of a wavelength that is Visible spectrum to the human eye , or up to 380?750 nm. In the broader field of physics, light is sometimes used to refer to electromagnetic radiation of all wavelengths, whether visible or not....
 from wide angles. When moving focus from a distant to a near object, the eyes converge. The ciliary muscle
Ciliary muscle

The ciliary muscle is a muscle in the eye that controls the eye's accommodation for viewing objects at varying distances....
 contracts making the lens
Lens (anatomy)

The lens is a transparent, Lens_#Types_of_lenses structure in the eye that, along with the cornea, helps to refract light to be Focus on the retina....
 more convex, shortening its focal length. The pupil
Pupil

The pupil is the sphere that is located in the center of the Iris of the eye and that controls the amount of light that enters the eye. It appears black because most of the light entering the pupil is absorbed by the biological tissue inside the eye....
 constricts in order to prevent diverging light rays from hitting the periphery of the retina
Retina

The vertebrate retina is a light sensitive tissue lining the inner surface of the eye. The optics of the eye create an image of the visual world on the retina, which serves much the same function as the film in a camera....
 and resulting in a blurred image.

Pathway

Information from the light on each retina is taken to the occipital lobe
Occipital lobe

The occipital lobe is the Visual perception of the mammalian brain containing most of the anatomical region of the visual cortex. The primary visual cortex is Brodmann area, commonly called V1 ....
 via the optic nerve
Optic nerve

The optic nerve, also called cranial nerve II, transmits visual information from the retina to the brain....
 and optic radiation
Optic radiation

The optic radiation is a collection of axons from relay neurons in the lateral geniculate nucleus of the thalamus carrying visual information to the visual cortex along the calcarine fissure....
, where it is interpreted as vision. The peristriate area 19 interprets accommodation, and sends signals via the Edinger-Westphal nucleus
Edinger-Westphal nucleus

The Edinger-Westphal nucleus is the accessory parasympathetic nervous system cranial nerve nucleus of the oculomotor nerve , supplying the constricting muscles of the Iris ....
 and the 3rd cranial nerve
Oculomotor nerve

The oculomotor nerve is the third of twelve paired cranial nerves. It controls most of the eye's movements, constriction of the pupil, and maintains an open eyelid....
 to the ciliary muscle
Ciliary muscle

The ciliary muscle is a muscle in the eye that controls the eye's accommodation for viewing objects at varying distances....
, the medial rectus muscle and (via parasympathetic fibres) the sphincter pupillae muscle..

See also

  • Accommodation (eye)
    Accommodation (eye)

    Accommodation is the process by which the :eye increases optical power to maintain a clear image on an object as it draws near the eye. The young human eye can change focus from distance to 7 cm from the eye in 350 milliseconds....
  • Ciliary muscle
    Ciliary muscle

    The ciliary muscle is a muscle in the eye that controls the eye's accommodation for viewing objects at varying distances....
  • Presbyopia
    Presbyopia

    Presbyopia describes the condition where the eye exhibits a progressively diminished ability to focus on near objects with age. Presbyopia's exact mechanisms are not known with certainty, however, the research evidence most strongly supports a loss of elasticity of the Lens , although changes in the lens's curvature from continual growth and...


External links

  • at Georgia State University
    Georgia State University

    Georgia State University is an Urban area research university in downtown Atlanta, Georgia , USA. Founded in 1913, it serves over 28,000 students, and is one of the University System of Georgia four research universities....