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Anatomy and functioning of the eye

Parts of the eye

• Cornea -- the transparent front window of the eye. The cornea transmits and focuses light into the eye.
• Iris -- the colored part of the eye. The iris helps regulate the amount of light that enters the eye.
• Pupil -- the dark center in the middle of the iris. The pupil changes size in response to various degrees of illumination to control the amount of light that is let into the eye.
• Lens -- the transparent structure behind the iris that focuses light rays onto the retina.
• Retina -- the nerve layer that lines the back of the eye. The retina senses light and creates impulses that are sent through the optic nerve to the brain.
• Macula -- a small specialized area in the retina that contains special light sensitive cells. The macula allows us to see fine details clearly.
• Optic Nerve -- the nerve that connects the eye to the brain. It carries the impulses formed by the retina to the brain, where it is interpreted as images.
• Vitreous -- the clear, jelly-like substance that fills the middle of the eye.

Eye as a camera

The function of our eyes is to enable us to see clearly the objects in our surroundings at variable distances and under various conditions of lights. This function is achieved by a very complex arrangement of structures in the eye. Our eye can be thought of as a very advanced camera. There are many similarities between our eye and a camera. Like in a camera the aim is to provide a well-focused image of the object onto the film at the back of the camera. Similarly in the eye, the retina, which is situated towards the back of the eye, works as the photographic film. The image is formed there and then the signal is sent from there to our brain through the optic nerve, and thus we perceive the objects around us. In fact, the retina is much more advanced than a photographic film because it can automatically change its sensitivity depending upon the amount of illumination present.

The rays of light enters the eye and passes through cornea and lens, which converge them so that it gets focused at the retina and a sharp image is formed. This function is akin to that of the lens of a camera. Once again the eye is superior, because the lens of the eye has the property to automatically adjust its power depending upon the location of the object of interest. Therefore, whenever we see from distance to near object, the lens of eye increases its curvature and thus is able to focus the image clearly onto the retina. The aperture (pupil) in the colored part (iris) of the eye is also adjustable according to the illumination of the surroundings. This is akin to the aperture of the diaphragm in a camera.

How does the rays of light get focused in a normal eye?

In a normal eye, the rays of light coming from a distant object gets focused by the cornea and the lens of the eye onto the retina and form a sharp image. When looking at a near object, the lens of the eye becomes more convex (accommodation) and thus its converging power is increased. This helps in focusing the near object clearly on the retina.