SOLUTIONS TO EXERCISES, LESSON 13
Please check your entries in the table with table 13-1 of this lesson.
When you look at an object, light from the right half of the visual field goes to the
left half of each eye. Light from the left half of the visual field goes to the right
half of each eye.
The light ray stimulus chemically changes the visual chemical found in the cones
and rods. The cones of the retina are for acute vision and also receive color
information. Light received by the rods is perceived in terms of black and white.
The stimulus from the cones and rods is transferred to the bipolar cells and then
to the ganglion cells. The axons of the ganglion cells leave the eyeball to
become the optic nerve. Since the circular area where these axons exit contains
neither cones nor rods, this area is called the blind spot. (para 13-3)
The axons from the nasal (medial) halves of the retinas cross to the opposite
sides at the optic chiasma. Thus, if an object is in your right visual field, the
information is carried by your left optic tract. If an object is in your left visual field,
the information is carried by your right optic tract. For conscious perception of
vision, the information enters the occipital lobes of the cerebral cortex. Note that
the right visual field is perceived within the left cerebral hemisphere, and the left
visual field is perceived within the right cerebral hemisphere.
The majority of focusing of light rays is accomplished by the cornea. Fine
adjustments of focusing are provided by the crystalline lens. (para 13-5)
The additional focusing provided by the crystalline lens is one of the processes
involved in accommodation. Accommodation refers to the various adjustments
made by the eye to see better at different distances.
The crystalline lens is kept in a flattened condition by the tension of the zonular
fibers. This tension is released by contraction of the ciliary muscle, resulting in
When both eyeballs move through an equal angle in the same direction, it is
called a conjugate eye movement. When both eyeballs turn toward the midline
to focus upon a nearby object, the result is a convergent eye movement.
During a "searching" eye movement, the eyeballs do not focus on a particular
object until it is located. During a "following" eye movement, the eyeballs
continually fix on an object.
Vestibular control of eye movements is necessary in order to compensate for