In Depth: Eye
Eyes are approximately one inch in diameter. Pads of fat and the surrounding bones of the skull protect them.
The eye has several major components: the cornea, pupil, lens, iris, retina, and sclera. These work together to capture an image and transmit it directly to the brain’s occipital lobe via the optic nerve.
When we look at an object, light reflected from it enters the eye and is refracted, or bent. This creates a focused, upside-down image of the object that the brain will have to interpret and turn in the correct direction.
Inside the eye are photoreceptors, which create nerve impulses when struck by light. There are two types: cones make color vision possible, and rods specialize in black-and-white images.
Although our eyes can only see in two dimensions, we are able to determine distances and depth in our three-dimensional world. This is because the brain interprets the two slightly different images our left and right eyes see as one. This is called stereoscopic vision. Other visual cues, such as shadows, how objects are blocking each other, and our knowledge about the sizes of different objects also help us determine depth and distance.
A series of muscles helps the eye move. The first set is the superior and inferior rectus muscles, which allow upward and downward motion. The medial and lateral rectus muscles allow the eye to move from side to side while staying level. The superior and inferior oblique muscles let it move up or down and to the side. Most of these muscles are controlled by the oculomotor nerve.
Friction from these movements would quickly damage the eye without lubrication. Tears released by the lacrimal gland are spread around by blinking, and provide lubrication for the eye. Tears also help remove foreign objects and bacteria that could cause damage.