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Shape. Colour. Depth. Brightness. Distance. Which single organ in the human body allows one to perceive these entities? The human eye. The eye is the most important organ in discovering the world around us. Although the eye measures only 2.5 centimeters in diameter, it can see as far away as a star and as tiny as a grain of sand. It can quickly adjust its focus between distant and near points, even while the head is moving. We use our eyes in everything we do- from reading and working to watching movies and playing games. Therefore, sight is a very precious, and fragile, sense. Though many do not ponder it, the ability to see and see clearly is quite a phenomenon. Here is an explanation of the structure of the human eye, how the eye sees, and some deficiencies that impair proper vision. THE HUMAN EYE: When compared to the eye of various other species that can only differentiate between light and dark, the human eye is a fairly complex organ. Capable of distinguishing minute variations in shape, colour, and more, this light-sensitive organ is comprised of many different components. The entire eye, often referred to as the eyeball, is safely shielded inside the head. The spherical structure is approximately 2.5 centimeters in diameter with a pronounced bulge on the front surface. The outer part of the eyeball is consists of three tissue layers. The outermost layer, the sclera, acts as a protective covering. Also located near the sclera in the front of the eyeball are the iris, the pupil, and the cornea. The middle layer is known as the choroid, while the innermost layer is the light sensitive retina. For light to enter the eye and be directed towards the retina, it must pass through the cornea and then the lens. The lens is a flattened sphere compiled of numerous transparent layers of fibers. It is connected to the ciliary muscle. This muscle changes the lens’ focal length by flattening the lens or making it more spherically shaped. HOW WE SEE: Though it is the organ associated with vision, the eye does not actually do the seeing.
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