Anatomy and Physiology / Unit 6: The Nervous System and Senses
6.6 The Eye and Vision
Notes
Light enters through the cornea, passes through the aqueous humor, the pupil (opening in the iris), the lens, and the vitreous humor, and focuses on the retina.
- The cornea does most of the bending of light; the lens fine-tunes focus by changing shape (accommodation): ciliary muscles contract and the lens becomes rounder for near vision.
- Retina: rods work in dim light (black and white), cones work in bright light and detect color (three cone types). The fovea has the sharpest vision. The optic nerve carries impulses to the occipital lobe; the point where it leaves has no photoreceptors (blind spot).
- Disorders: myopia (nearsighted; image focuses in front of the retina), hyperopia (farsighted; focuses behind the retina), astigmatism, cataract (clouded lens), glaucoma (high pressure in the eye damages the optic nerve).
- In bright light the pupil constricts; in dim light it dilates.
Practice
Which structure contains photoreceptors?
The retina contains rods and cones.
A student sees nearby objects clearly but distant objects look blurry. This condition is:
In myopia the eyeball is too long (or the lens too curved), so distant images focus in front of the retina.
Walking from a dark movie theater into bright sunlight, the pupils constrict. This helps because:
Constriction of the iris decreases light entering the eye.
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