Think of the eye as this amazing camera that captures millions of images and records it in our memory. Light bouncing off objects in front of us enters our eye and passes through the iris and pupil to reach the lens. The lens then focuses these rays onto the retina, forming an image that can be interpreted by the brain. However, this image is upside down and must be flipped right side up by the brain.
Here’s the role each part takes in your vision:
The cornea is your eye’s clear, protective outer layer. Along with the sclera (the white of your eye), it serves as a barrier against dirt, germs, and other things that can cause damage. The cornea can filter out some of the sun's ultraviolet light but not much, so for best eye protection, wear a pair of sunglasses.
The pupil is located between the cornea and the lens. The amount of light entering the eye is restricted by the pupil. In a dark room, a person’s pupils are large, perhaps 8 mm (0.3 inch) or more in diameter. When the room is lighted, there is an immediate constriction of the pupils, the light reflex. After a time, the pupils expand even though the bright light is maintained, but the expansion is not large.
The iris is located in front of the lens and behind the cornea. It is bathed in front and behind by a fluid known as the aqueous humour. The iris consists of two sheets of smooth muscle. These muscles control the size of the pupil and thus determine how much light reaches the sensory tissue of the retina. The amount of pigment contained in the iris determines eye colour. When there is very little pigment, the eye appears blue. With increased pigment, the shade becomes deep brown to black.
The retina is a thin layer of tissue that covers approximately 65 % of the back of the eye. It is near the optic nerve. Its job is to receive light from the lens, convert it to neural signals and transmit them to the brain for visual recognition. Because the retina originates as an outgrowth of the developing brain, it is considered part of the central nervous system and brain tissue.
Made of nerve cells, the optic nerve (or second cranial nerve) is located in the back of the eye. It is a bundle of nerve cells that transmits sensory information for vision in the form of electrical impulses from the eye to the brain. The optic nerve has been studied heavily because it is a direct extension of the brain.
The primary function of the human lens is to focus light undistorted onto the retina. While the transmission properties of most of the components of the eye are stable, the transmission properties of the lens change throughout life. It adjusts shape depending on whether the light reflects off something near you or far away.
If you’ve read this, your eyes are hard at work. Take good care of them!