Visual accommodation 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 focus of the image, not color or quality.
The
stimulus for accommodation is the recognition by the occipital cortex of a nearbyor
distant image type.
The pathway for accommodation is as
follows:
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. Here the image type (nearby image) constitutes the
stimulus for accommodation. Nearby images are recognized because they are large and
formed of light rays coming in at a wide angle. This perception of nearby image occurs
in the peristriate area of the brain where accommodation signals are sent via the
Edinger-Westphal nucleus along the III Cranial nerve (relay nerve) to the ciliary
muscle. 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.
The effector organs for
accommodation are the ciliary body and lens, and the pupil.
No comments:
Post a Comment