Book Definition:

Photoreceptors in the retina that are especially sensitive to dim light but not to colors. They are rod-shaped.

In Your Own Words

  • photorecptors in retina allowing you to see in the dark
  • rods cause you to see dimness.
  • The companions of cone cells in the eye that interpret dimness of light


  • Getting out of bed at night, turning on a light switch
  • Finding a seat in a movie theather.
  • Seeing during night time
  • Located at the back of the retina
  • Nocturnal creatures have more rods than cones to help them see at night

Additional Resources


used for night vision
used for day vision
very light sensitive; sensitive to scattered light
not very light sensitive; sensitive only to direct light
loss causes night blindness
loss causes legal blindness
low visual acuity
high visual acuity; better spacial resolution
not present in fovea
concentrated in fovea
slow response, to light, stimuli added over time
fast response to light, can perceive more rapid changes in stimuli
have more pigment than cones, so can detect less light
have less pigment than rods, require more light to detect images
stacks of membrane-enclosed disks are unattached to cell membrane
disks are attached to outer membrane
20 times more rods than cones in the retina
one type of photosensitive pigment
three types of photosensitive pigment in humans
confer achromatic vision
confer color vision
Web link for this table and other information on rods:

Information on nocturnal eyes vs. diurnal eyes