Visual Impairment :

Visual Impairment :

v A vision impairment refers to when you lose part or all of your ability to see (vision). The impairment must persist even with the use of eyeglasses, contact lenses, medication, or surgery.

v Visual impairment is the lack, deficiency, or decreased vision. For many people the word blind means total lack of vision, visual impairment but is divided into total blindness or amaurosis, blindness.

v Visual impairment (or vision impairment) is vision loss (of a person) to such a degree as to qualify as an additional support need through a significant limitation of visual capability resulting from either disease, trauma, or congenital or degenerative conditions that cannot be corrected by conventional means, such as refractive correction, medication, or surgery.

Vision Testing

Visual acuity is usually measured with a Snellen chart. The Snellen chart displays letters of progressively smaller size. "Normal" vision is 20/20. This means that the test subject sees the same line of letters at 20 feet that a normal person sees at 20 feet.

20/40 vision means that the test subject sees at 20 feet what a normal person sees at 40 feet. Another way of saying this is that a person with 20/40 vision has vision that is only half as good as normal - or, objects must be at half the normal distance for him to see them.

A person with 20/20 vision is able to see letters 1/10th as large as someone with 20/200 vision. However, 20/15 vision is better than 20/20.

A person with 20/15 vision can see objects at 20 feet that a person with 20/20 vision can only see at 15 feet.

Levels of Vision

·        20/20 - Normal vision. Fighter pilot minimum. Required to read the stock quotes in the newspaper, or numbers in the telephone book.

·        20/40 - Able to pass Driver's License Test in all 50 States. Most printed material is at this level.

·        20/80 - Able to read alarm clock at 10 feet. News Headlines are this size.

·        20/200 - Legal blindness. Able to see STOP sign letters.

Types of Vision Impairments

The way in which vision impairments are classified differs across countries. The World Health Organization (WHO) classifies visual impairment based on two factors: the visual acuity, or the clarity of vision, and the visual fields, the area from which you are able to perceive visual information, while your eyes are in a stationary position and you are looking straight at an object.

Three Types of Vision Impairments

The types of vision impairments are low visual acuity, blindness, and legal blindness (which varies for each country):

1.      Low visual acuity, also known as moderate visual impairment, is a visual acuity between 20/70 and 20/400 with your best corrected vision, or a visual field of no more than 20 degrees.

2.      Blindness is a visual acuity of 20/400 or worse with your best corrected vision, or a visual field of no more than 10 degrees.

3.      Legal blindness in the United States is a visual acuity of 20/200 or worse with your best corrected vision, or a visual field of no more than 20 degrees.

Classification : Partial blindness, when the vision of the person is low or there is insufficient capacity and need to wear glasses to improve it.

Macular degeneration:

loss of peripheral vision and central vision is weak or a black hole.

Cataracts occur when the eye’s lens becomes cloudy; it is the most common cause of low vision in old age.

Tubular or tunnel vision: it is caused by glaucoma. Damage to the optic nerve at the back of the eye leads to a gradual loss of nerve function and can cause loss of peripheral vision.

\Diabetic retinopathy is a common source of low vision in middle age. Diabetes can damage blood vessels in the eye.

Blindness: means there is difficulty distinguishing between colors, especially reds and greens.Cortical blindness is caused by brain damage in the primary visual area of the occipital lobe although the visual organs are in good condition. The vision of the person is vague to light or movement.

Uveitis is swelling and irritation of the uvea, the middle layer of the eye that provides most of the blood flow to the retina. People with uveitis may have one or more symptoms such as blurred vision, perception of flies buzzing, eye pain, eye redness and sensitivity to light.

Trachoma: is an infection caused by the bacterium Chlamydia trachomatis, which affects mostly children in rural areas of developing countries. It begins as an inflammation of the lining of the eyelids, conjunctivitis or pink eye, without treatment can heal. Symptoms may include corneal opacity, eye discharge, swollen lymph nodes just in front of the ears, swollen eyelids and eyelashes reversed.

Treatment

Now a days, we have many devices to help people with visual impairment, ophthalmologic examination, this depends to determine what kind of support they need.Audio books,Braille.