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the Human eye..

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tasneem rashed

on 15 December 2013

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Transcript of the Human eye..

the Human eye..
Tasneem rashed ..
Maha Ghiberti ..

by :
how we see the world??
The way we see things depends on the light that your eyes reflect from objects.
Now watched this video
Some human eye vision problems

is a vision condition that causes blurred vision due either to the irregular shape of the cornea, the clear front cover of the eye, or sometimes the curvature of the lens inside the eye..

“Color Deficiency”
“color blindness”.
is the inability to distinguish certain shades of color or in more severe cases, see colors at all. The term "color blindness" is also used to describe this visual condition..

is a condition in which distant objects are usually seen clearly, but close ones do not come into proper focus..
Causes of myopia:
the eyeball is too long.
the cornea and/or lens being too curved for the length of the eyeball.
Symptoms of myopia:
• Headache.
• Eyestrain

• Squinting or fatigue.

Signs of myopia:
• difficulty reading road signs.
• difficulty seeing distant objects clearly.
• able to see well for close-up tasks.

Diagnosing of myopia:
Myopia can be easily diagnosed using standard eye exams given by an eye doctor
• Refractive surgery.
• is easily corrected with eyeglasses, contact lenses or surgery.

• Is the most common refractive error of the eye.
• myopia or nearsightedness have difficulty seeing distant objects, but can see objects that are near clearly.
What is myopia
or nearsightedness?

Convex or converging lens (thicker in the middle ,thinner (edges at the

Concave or diverging lens ( thicker at the edges , thinner in the middlr )
Plano convex lens

Convex lens

Biconcave lens (double concave )

Plano concave lens

Concave lens
types of contact lenses
Several different types of contact lenses are available to treat vision problems. Consult an eye doctor who is willing to work with you to select the best type of lens for your needs and lifestyle

Hard contact lenses:
Most hard (rigid) lenses are made of gas-permeable materials that allow oxygen to reach the cornea . This reduces problems that may occur when the cornea does not get enough oxygen. They correct refractive errors, including astigmatism, with no distortion.
Conventional hard lenses (PMMA.
Rigid gas-permeable (RGP) lenses

Soft contact lenses:
Soft (silicone hydrogel) lenses are made of soft, very flexible plastics that absorb water (up to 90% of the lens weight). Many people find them more comfortable to wear than hard lenses, but hard lenses usually provide sharper vision. Soft lenses are more fragile than hard lenses and require more intensive cleaning. Soft lenses that can correct astigmatism are called toric lenses.
Daily-wear lenses.
Extended-wear lenses.
Disposable lenses.

There are two types of disposable lenses:
Daily-wear disposable lenses are removed and cleaned daily, just like conventional lenses. They are worn for 2 to 4 weeks and then discarded.

Most extended-wear disposable lenses are designed to be worn day and night for 1 week and then discarded. some lenses for 30-day use

Why do pupils dilate??
pupil is a circular hole in the middle of the iris which regulates the amount of light passing through to the retina. In dark conditions the pupil expands - or 'dilates' - to allow as much light as possible pass through. In bright conditions the pupil shrinks, limiting the amount of light passing through.

What happens when light reaches the retina??
retina is a complex part of the eye, but only the very back of it is light-sensitive. This part of the retina has roughly the area of a 10p coin, and is packed with photosensitive cells called rods and cones. These allow us to see images in colour and detail, and to see at night.

Sending the image to the brain

Once the image is clearly focused on the sensitive part of the retina, energy in the light that makes up that image creates an electrical signal
What is the blind spot
he blind spot is the point in the eyeball at the head of the optic nerve. This is where nerve fibres and blood vessels leave the eye, and as a result there are no photosensitive cells. Any images, therefore, that are projected onto the blind spot are simply not registered by the brain.

• glasses.
• Contact lenses.
now which this video...
now which this video...
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