The following was written by Bill Evans and published in the Coolum and North Shore News, Ask the Professionals page on Friday, 25th January 2013.
Q: What are the rods and cones of our eyes?
A: The rods and cones are the photoreceptors in our retina, the cells first responsible for receiving and reacting to light to produce a signal that eventually travels along our optic nerve to our brain. The rods are designed to work in low light; when we look at faint stars at night we are using our rods. In fact, they are so sensitive they can respond to a single photon of light. The cone photoreceptors require much more light to respond, but they work very quickly to respond to rapid changes or movement in images, and let us perceive finer detail. The cones are at their highest concentration at the fovea, the area of retina responsible for high acuity. We have cones of three different pigment colours in our retina, each responding to a different part of the colour spectrum. Conversely, our rods have only one pigment colour; on a dark night our vision is absent of colour.