A look inside your eyes
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A look inside your eyes
من طرف 7oda السبت أغسطس 28, 2010 5:36 pm
Inside your eyes
Here's a look at the various parts of your eye and how they work
together to help you see the world around you. Each part plays an
essential role in your eyes' healthy functioning.
Eyelids
Upper and lower eyelids protect the front of your eyeball (orbit) by
blocking foreign objects and bright light that can damage your eye. Your
eyelids involuntarily open and shut (blink) every few seconds to help
protect your eyeball. You can, of course, blink intentionally as well.
With each blink, a tiny bit of tear fluid comes out of a gland near each
eye. The lubricant washes away germs, dust, eyelashes or other foreign
objects and keeps your eyes from drying.
The front of your eye
Three parts make up the front of your eye, or the part of your eye that's visible to others:
Sclera. The white of your eye is actually a tough, leathery coating that
helps form the spherical shape of your eyeball and protects the
delicate internal structures of your eye.
Pupil. The dark spot at the center of your eye is a hole that allows light to pass into your eye.
Iris. The colored part of your eye contains a ring of muscle fibers that
can expand or contract the size of your pupil, controlling the amount
of light entering your eyeball.
A thin transparent tissue called the conjunctiva covers the sclera of
your eye. The blood vessels that are often visible in the white part of
your eye run through the conjunctiva.
Your inner eye
Behind the scenes, other parts of your eye are working to help you see:
Cornea. Your cornea is a protective dome of clear tissue over the front
of your eye. It functions as a convex surface that helps focus the light
rays before they are fine-tuned by the lens.
Lens. Your lens is a clear, elliptical structure about the size and
shape of an M&M'S candy. The curvature of your lens changes to
sharpen the focus of whatever you're looking at.
Vitreous cavity. The vitreous cavity extends from the back of the lens
to the back of your eyeball. It's filled with a clear, jelly-like
substance that allows light to pass through. It also maintains the shape
of your eyeball.
The back of your eye
Structures at the back of your eye help complete the vision process:
Retina. Your retina is a thin layer of tissue that lines the back inner
wall of your eyeball. Your retina consists of millions of
light-sensitive cells and nerve cells that capture the images focused
onto them by your cornea and lens. When light hits these cells,
electrical impulses are generated and carried to your optic nerve.
Macula. Your macula is a specialized part of the retina. This patch of
densely packed light-sensitive cells is essential to your central vision
and allows you to see fine detail.
Optic nerve. Your optic nerve carries information gathered by your
retina to your brain via a bundle of more than 1 million nerve fibers.
How your eyes move
Each eyeball has six muscles attached to the sclera — five are seen from
this angle — allowing you to move both eyes and track an object without
necessarily turning your head. These eye muscles, working individually
or together, allow you to shift your field of gaze left, right, up, down
and diagonally. Your brain coordinates these eye movements, so your
eyes move together when tracking an object
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