3.3 Vision

Notes

• Light enters through the cornea, passes the pupil (opening controlled by the iris) and the lens, which focuses it onto the retina at the back of the eye.
• The retina has rods (dim light, black and white, peripheral vision) and cones (color and fine detail, mostly in the fovea).
• Signals travel through the optic nerve to the brain's occipital lobe. The spot where the optic nerve leaves the eye has no receptors: the blind spot.
• Trichromatic theory: three cone types (red, green, blue) combine for color. Opponent-process theory: color cells work in pairs (red/green, blue/yellow), which explains afterimages.
• Color blindness is most often caused by a missing or altered cone type and is more common in males.