The eye is a sensory organ working in pair. It consists of an eyeball, an optic nerve, and auxiliary structures. The eyeball is situated in the eye socket and protected from all sides with skull bones except from the front where it is exposed and open to light so we could see undisturbed. From the front, the only protection to the open active eye is tear film and eye lids that protect it with occasional blinking, quick reflex closing in case of need, or complete closing, as when in a dream.
After the brain, the eye is the most complex organ in a human body, consisting of more than 2 million parts. The eye enables us to understand our surroundings and experience life in full. With our vision we get the information regarding the shape, color, distance, movement, and the depth of the objects we see. The human eye can differ up to 10 million colors!
Eye problems directly affect the quality of our lives: when we want to see what time it is on a blurred alarm clock every morning, when night driving is a problem, or when we have to wear contacts while playing basketball with our friends. A healthy human eye enables us to have better vision and more active and energetic lifestyle. Around 40 million of people worldwide are blind and about 6 times more have some kind of eye damage. A vast majority of eye conditions can be avoided or are curable.
How the Eyes See
When light rays enter a healthy human eye, they refract (bend) through two main curved objects: the cornea and the lens. The cornea is a delicate transparent layer through which 70% of the light entering the eye refracts. The main function of the cornea and the lens is to refract the light so that rays converge directly on the retina, i.e. at the point of the clearest vision – the macula.
An eye lens (crystalline lens) is responsible for only 30% of the refraction but can change the shape from elongated and thin to round and thick. This capability is called accommodation and enables us to quickly shift focus from faraway objects to those close by, and vice versa.
The retina is a photosensitive layer. It is a part of the eye with numerous photosensitive receptors, cones, and rods. Photosensitive receptors enable us to see the world in color, as well as small details, contrasts, and to have clear vision with a low intensity of light.
The retina has a role similar to a photographic film in a camera. It transforms a light stimulus into nerve impulses and sends information via the optic nerve to the cerebral cortex in charge of vision. This way the human eye acts like a camera recording a movie while the brain reads information from our surroundings. In other words, a realistic picture of the world is created in the brain, whereas the eye only gathers the information.