The human eye is a extremely sophisticated visual anatomical device ( sensory organ) architecturally designed elegantly and efficiently for its purpose. Our eyes are the window to this world that allow us to see its spectacular beauty. Through our eyes we see places, objects, friends, family, our own body, our pets and other living things around us. It allows us to see, interpret, make decisions and conclusions about things we see. Through our eyes we can tell if something is beautiful, ugly, colorful, dull, rough, smooth, glossy, bright, dark, transparent, as dimensions and so on. Also, it allows us to; learn from visual information, compare, contrast and make decisions. Our eyes serve as a protection device that protect us from harm by allowing us to make judgment or prediction of an object or event and to take the necessary action (response) of whether to fight or flee. Through our eyes we also communicate with each other and send message to others about our present state. For example, we use our eyes to send a message to someone if we are in agreement with the action they are doing or about to do by blinking (winking) one of our eyes. We can also use ours eyes tell someone we are interested in them or you can receive a message if someone is interested in you.Through the eyes we can read messages about the persons state or mood such as if they are; sad, tired, stressed, ill, drunk, frustrated, crying, happy, angry, surprised, depress, excited, sleepy and so on. Thus, like most people we depend on our eyes to carry out our busy daily activities but have you ever wondered or stop to think how incredible this wonderful and special designed organ allows you to see and also to read this article? Let's take a look on the anatomy and function of the eye to see how it works and also how important your vision is to you.

How the eye works can be compared to that of a simple camera. Like the eye, a camera creates images by focusing (using the cornea and lens) on an object by allowing certain amounts of light (reflected from the object) to pass through a hole ( iris and diaphragm) that adjusts the amount of light entering which then creates a visual impression (on the retina and on film). The light can originate directly either from the object (e.g. the sun, bulb) or in directly from an object (a chair, book, moon) by the reflected light from its surface. This explains why we can’t see in the dark. Darkness is the absent of light thus, there is no light reflected from the object to enter through our pupil to form an image on our retina in the eye. If there is light we are able to see the object depending on the amount of light present. The limited amount of light in a dark room for example, can also let us see things without colors giving a dull, dark, grayish appearance (see retina section on rods for reason, further down below). The colors we see when we look at objects are due to the light source and also from the light that is reflected from that object to the eye.
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In order to see an object light must first come from the object or bounce off the surface of that object and then enter our eyes. When light reaches our eyes it enters through a transparent layer of tissue called the cornea (the window of the eye). The cornea, responsible for focusing, takes widely diverging rays of light reaching the eyes and converge (bends) them through the pupil. The pupil is the black-appearing round spot (opening) in the center of the colored iris that regulates how much light enters the eye by expanding and contracting its opening. For example, if you are in a room with low lighting, the pupil will expand to allow more light to enter, likewise, if the light is too bright, the pupil will contract (shrink) to allow more light to enter the eye in order to vision the surrounding. Here, the pupil prevent damage to be done to the eyes from excess light entering. You can try this with a friend, spouse or a family remember by staying in the dark for awhile then let some look at your pupil then repeat this the other way around by staying in a bright light or bright sun then let someone looks at your pupil. Do you ever feel a slight pain and temporary blindness when you ever move from a dark surrounding to a well lit surrounding? This happens because too much lights enters the eyes and the pupil quickly adjust the pupil size to limit the amount of light entering the eye - then that temporary blindness will then all go away.

When the light goes through the pupil it then passes through the lens, a transparent structure situated behind the pupil of the eye, then refract the incoming light and fine tune the focused light onto the retina. This it does by changing the focus of the light from distant objects by altering its shape. This change in focus is called accommodation. You can alter the focus of your lens by placing your finger in front of your face and slowly bringing your finger closer to eyes, right up to your nose then move it away again - there you have just altered your focus by altering the lens of your eyes. This focus light will then travel through the vitreous humour (a clear gel) that fills the central core of the eye and helps to maintain the eye spherical shape.
After leaving the lens and traveling through the vitreous humour it will then reach the retina which is at the back of the eye. The retina is a light-sensitive membrane lining the inner wall of the eyeball. This contains millions of photoreceptor nerve cells which react to the presence and intensity of the light image. There are two types of photoreceptors which are called rods and cones. [image here] The rods register shapes and respond to low levels of light which is responsible for night vision while, on the other hand, the cones register (detect) color and only work in bright light. This means when there is less light or as the evening becomes darker the cones will become less responsive and thus, it is more difficult to see colors.
When the light image hits the retina an image will form upside down on its membrane surface containing the photoreceptors cells (light-sensitive cells). The image will then form upside down because the light rays cross while going through the cornea. This will then stimulate the photoreceptors cells (rods and cones) to change the light image into an electrochemical impulse (signals) which then travels along the optic nerve (bundle of retinal fibers )that exits the back of the eye to the vision center (occipital cortex) of the brain. Here the brain interprets the electrical signal and re-adjust the image upward allowing us to “see” the object. Hence, sight (vision) is achieved in the brain.

Did You Know ?

- Human Eye Facts

• A newborn baby sees the world upside down because it takes some time for the baby's brain to learn to turn the image right-side up.

• The eye is the second most complex organ you possess after the brain.

• The average person blinks about 12 times a minute.

- Animal Eye Facts

• An ostrich which has eyes that are two inches across. Each eye weighs more than the brain. In other words, an ostrich's eye is bigger than its brain.

• An eagle can see a rabbit about 1 mile or 1760 yards away while average person needs to be about 550 yards away to see the same rabbit.
  

• The reason cat's and dog's eyes glow at night is because of a silver “mirrors” in the back of their eyes called the tapetum lucidum (meaning "bright carpet") which is a thick reflective membrane. This collects and re-emits light back to the retina a second time thus giving the light-sensitive cell (rods) a second opportunity to absorb the image information again. This a adaptation for night vision and makes it easier for them to see at night by maximizing the limited available light. Hence, the reflected light from the tapetum let the animal's eyes appear to glow in the dark.