Chapter 5 Notes - Part Four

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Accommodation: changes in the thickness of the lens of the eye that focus images of near or
distant objects on the retina
Normally, the length of the eye matches the bending of light rays produced by the cornea
and the lens so that the image of the visual scene is sharply focused on the retina
For some people, these two factors are not matched
People whose eyes are too long (front to back) are nearsighted [need concave lens to correct
the focus]
People whose eyes are too short are farsighted [need convex lens]
Retina: lines the inner surface of the back of the eye and performs the sensory functions of
the eye
Photoreceptors: (over 130 million embedded in the retina)
Specialized neurons that transducer light into neural activity
Info from photoreceptors is transmitted to neurons that send axons toward one point at the
back of the eye: the optic disc.
Optic disc: located at the exit point from the retina of the axons of the ganglion cells that
form the optic nerve
All axons then leave the eye and join the optic nerve, which travels to the brain
There are no photoreceptors directly in front of the optic disc = portion of retina that is
blind
Johannes Kepler (1571 -1630)
Credited with suggestion that the retina contains the receptive tissue of the eye
Christoph Scheiner:
Demonstrated in 1625 that the lens is simply a focusing device
Retina = 3 principal layers
1) ganglion cell layer (front)
2) bipolar cell layer (middle)
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Document Summary

Accommodation: changes in the thickness of the lens of the eye that focus images of near or distant objects on the retina. Normally, the length of the eye matches the bending of light rays produced by the cornea and the lens so that the image of the visual scene is sharply focused on the retina. For some people, these two factors are not matched. People whose eyes are too long (front to back) are nearsighted [need concave lens to correct the focus] People whose eyes are too short are farsighted [need convex lens] Retina: lines the inner surface of the back of the eye and performs the sensory functions of the eye. Photoreceptors: (over 130 million embedded in the retina) Specialized neurons that transducer light into neural activity. Info from photoreceptors is transmitted to neurons that send axons toward one point at the back of the eye: the optic disc.

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