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Vishnu Eye Clinic - Laser Foundation : Patient Education

How does the eye function?

The human eye is the organ which gives us the sense of sight, allowing us to learn more about the surrounding world than we do with any of the other four senses. We use our eyes in almost every activity we perform, whether reading, working, watching television, writing a letter, driving a car, and in countless other ways. Most people probably would agree that sight is the sense they value more than all the rest.

The eye allows us to see and interpret the shapes, colors, and dimensions of objects in the world by processing the light they reflect or emit. The eye is able to see in bright light or in dim light, but it cannot see objects when light is absent.

Process of vision

Light waves from an object (such as a tree) enter the eye first through the cornea, which is the clear dome at the front of the eye. The light then progresses through the pupil, the circular opening in the center of the colored iris. Next, the light passes through the crystalline lens, which is located immediately behind the iris and the pupil.

Initially, the light waves are bent or converged first by the cornea, and then further by the crystalline lens, to a nodal point (N) located immediately behind the back surface of the lens. At that point, the image becomes reversed (turned backwards) and inverted (turned upside-down).The light continues through the vitreous humor, the clear gel that makes up about 80% of the eyes volume, and then, ideally, back to a clear focus on the retina behind the vitreous. The small central area of the retina is the macula, which provides the best vision of any location in the retina.

The functioning of the eye can be considered like a Sophisticated Camera which has an array of lenses and shutters with a light sensitive film or CCD.
If the eye is considered to be a type of camera, the retina is equivalent to the film inside of the camera, registering the tiny photons of light which interact with it. Within the layers of the retina, light impulses are changed into electrical signals and then sent through the optic nerve, along the visual pathway, to the occipital cortex at the posterior or back of the brain. Here, the electrical signals are interpreted or seen by the brain as a visual image. When the light entering the eyes is bright enough, the pupils will constrict (get smaller), due to the pupillary light response.

Brain is a sophisticated supercomputer that interprets an image obtained and gives it various attributes after analysis. The size , shape, movement, contrast and non visual cues like sound, smell and touch give additional meaning to the object percieved by sight alone.

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