Light-sensitive cells in the retina that work best in darkness or dim illuminations.

Glossary of Terms - R
Common terms to help you learn more about your eyes and vision
Retina
Innermost layer of the eye containing light sensitive nerve cells and fibers connecting with the brain through the optic nerve and nourished by a network of blood vessels; receives image and sends it to the brain.
Refraction
Measurement of the focusing characteristics of the eye to determine refractive error and the need for prescription glasses.