What are rods and cones in the eye's retina?

Rods and cones are photoreceptor cells in the retina that help in vision by responding to light.

Rods and cones are specialised cells located in the retina, the light-sensitive layer at the back of the eye. They are named for their distinctive shapes; rods are elongated, while cones are more conical. These cells play a crucial role in vision as they convert light into electrical signals that can be interpreted by the brain.

Rods are primarily responsible for peripheral and low-light vision. They are more sensitive to light and allow us to see in dimly lit environments, but they do not perceive colour. This is why our vision in low light is often monochromatic. There are approximately 120 million rods in the human eye, and they are more concentrated towards the edges of the retina.

Cones, on the other hand, are responsible for our ability to see colour and detail. They function best in bright light conditions. There are three types of cones, each sensitive to a different range of wavelengths corresponding to red, green, and blue light. By responding to these different wavelengths, cones allow us to perceive a wide spectrum of colours. There are about 6 million cones in the human eye, and they are most densely packed in the centre of the retina, an area known as the fovea.

The signals from rods and cones are sent to the brain via the optic nerve. The brain then processes these signals into the images we see. This process, known as phototransduction, is a complex chemical reaction involving a pigment called rhodopsin in rods and photopsin in cones. These pigments undergo a change in structure when they absorb light, triggering a series of events that result in an electrical signal being sent to the brain. Understanding the function of rods and cones is fundamental to understanding how we see the world around us.