Cones are cone-shaped nerve cells on the retina that can distinguish fine details in images. They are located predominantly around the center of the retina called the fovea. The cones are also responsible for color vision. Some cones respond to blue light, being most sensitive to 440-nanometer wavelengths. A second kind has peak sensitivity in the green: 530-nanometer light. The third is sensitive to a wide band of wavelengths from cyan through red. Its sensitivity peaks in the yellow, 560 nanometers.

As the distance grows from the fovea, rod-shaped nerve cells replace the cones. The rods are responsible for a general image over a large area, but not fine details. This explains why we look at objects straight on when examining something carefully. The image will be focused around the fovea, where the majority of cones pick up the fine details of the image. The rods, being much more sensitive in low light levels, are used a lot for night vision.