By Liz Segre; eye illustration by Stephen Bagi
The human eye has been called the most complex organ in our body. It’s amazing that something so small can have so many working parts. But when you consider how difficult the task of providing vision really is, perhaps it’s no wonder after all.
How the Eye Works
In a number of ways, the human eye works much like a digital camera:
Light is focused primarily by the cornea — the clear front surface of the eye, which acts like a camera lens.
The iris of the eye functions like the diaphragm of a camera, controlling the amount of light reaching the back of the eye by automatically adjusting the size of the pupil (aperture).
The eye’s crystalline lens is located directly behind the pupil and further focuses light. Through a process called accommodation, this lens helps the eye automatically focus on near and approaching objects, like an autofocus camera lens.
Light focused by the cornea and crystalline lens (and limited by the iris and pupil) then reaches the retina — the light-sensitive inner lining of the back of the eye. The retina acts like an electronic image sensor of a digital camera, converting optical images into electronic signals. The optic nerve then transmits these signals to the visual cortex — the part of the brain that controls our sense of sight.
Other parts of the human eye play a supporting role in the main activity of sight:
Some carry fluids (such as tears and blood) to lubricate or nourish the eye.
Others are muscles that allow the eye to move.
Some parts protect the eye from injury (such as the lids and the epithelium of the cornea).
And some are messengers, sending sensory information to the brain (such as the pain-sensing nerves in the cornea and the optic nerve behind the retina).