Definition: Defining the Meaning of Vision Disability
Visual impairment (vision impairment, vision disability) is defined as a decreased ability to see to a degree that causes problems not fixable by usual means, such as glasses or medication. Visual impairment can be due to disease, trauma, or congenital or degenerative conditions. In the United States, the terms "partially sighted", "low vision", "legally blind" and "totally blind" are used by schools, colleges, and other educational institutions to describe students with visual impairments.
The number of different vision conditions that can affect a person's eyesight are varied in the way they do affect the person's daily life. Some of these conditions have a minor affect, while others may have a larger affect.
Various conditions require only eyeglasses or contact lenses in order to correct the person's vision. Other conditions may require surgery. Additional health concerns can affect a person's vision as well, such as Diabetes or Glaucoma.
There are a number of eye problems and conditions that may make it more difficult for a person to see things clearly, yet do not cause loss of vision. An example of this is, 'Myopia,' or, 'Near-sightedness,' where a person sees nearby objects clearly, but has difficulty focusing on objects that are more distant.
'Hyperopia,' or, 'Far-sightedness,' is another example of a vision condition; this one involves the ability to see distant objects clearly, with difficulty focusing on nearby objects.
A third example of an eye condition that does not cause loss of vision is, 'Astigmatism,' where the person's vision appears blurred at any distance. These conditions are common and can often be corrected with eyeglasses or contact lenses.
The term, 'Low Vision,' sometimes also referred to as, 'Vision Loss,' means that even though a person may use eyeglasses, contact lenses, medication, or surgical techniques to improve their vision; they still have difficulty seeing.
Most persons develop low vision due to eye disease or health conditions. There are some common causes of low vision among adults in America.
- 'Diabetic Retinopathy,' is a condition in which Diabetes has damaged tiny blood vessels inside the person's retina, causing low vision.
- 'Age-Related Macular Degeneration,' is a condition in which the cells in a person's retina that allow them to see fine details have died.
- 'Glaucoma,' is a condition in which the fluid pressure in a person's eyes slowly rises, damaging their optic nerve.
- 'Cataracts,' are a condition that involves a clouding of the lens in a person's eye.
Receiving prompt treatment for these conditions may prevent them from getting worse, making regular eye exams crucial.
As many as 10 million people around the world suffer from cataracts.
In Germany alone, more than 600,000 cataract operations are performed each year.
Cataracts can be either congenital or acquired; age-related opacification of the lens is the most common type. The main symptom of cataract is slowly progressive worsening of vision, but glare disability and nearsightedness can also be signs of the disease.
Cataract operations are now usually performed on an outpatient basis. The eye is anesthetized, pretreated with antibiotics, and surgically opened. New approaches permit the operation to be performed through an incision smaller than 2 mm.
In the phacoemulsification technique, the lens is emulsified and aspirated away through a vibrating hollow needle. The surgeon then implants an intraocular artificial lens. Patients without any other diseases of the eye can achieve a visual acuity of 1.0 or even better.
Special optical designs for the artificial lens can further optimize the quality of vision and thereby improve patient satisfaction.
According to the International Classification of Diseases There are 4 levels of visual function:
- normal vision
- severe visual impairment
- moderate visual impairment
Moderate visual impairment combined with severe visual impairment are grouped under the term low vision: low vision taken together with blindness represents all visual impairment.
There are some different terms used to describe levels of vision disability. These terms include, 'Partially-Sighted,' 'Low-Vision,' 'Legally Blind,' and, 'Totally Blind.'
- Partially-Sighted means the person has some form of visual disability that may require special education.
- Low-Vision usually is used to refer to persons who experience a more severe loss of vision that is not necessarily limited to distance vision. Persons with low-vision may be unable to read a newspaper at an average distance with eyeglasses or contacts, and may need large print or Braille.
- Persons who are legally blind have less than 20/200 vision in their better eye, or a very limited field of vision, often 20 degrees at its widest point.
- Persons who are totally blind are unable to see and often use Braille or other non-visual forms of media.
Eye disorders lead to vision loss; visual impairment is a consequence of a functional loss of vision rather than the eye disorder itself. Retinal degeneration, muscular problems, albinism, corneal disorders, congenital disorders, and infections can also lead to vision impairment.
Approximately one in twelve men, and one out of every two-hundred women, experience a form of colorblindness.
One misconception that many people have is that persons with colorblindness see only black and white. In actuality, there are many types and degrees of colorblindness.
- Monochromasy is the form most associated with colorblindness, where people see no colors.
- Protanomaly is referred to as, 'red-weakness,' and the person views a shift in the hue of red colors towards green and additional affects.
- Deuteranomaly is also referred to as, 'green-weakness,' and the person has difficulty telling differences in the red, orange, yellow and green regions of the color spectrum.
- Persons with Dichromasy cannot tell the difference between red, orange, yellow and green.
- Persons with Protanopia find that the brightness of colors such as red, orange and yellow is greatly reduced; they may appear as black or dark gray.
- Persons with Deuteranopia experience the same vision issues as persons with Protanopia, but the dimming is not as great.
Persons with low vision or other visual disabilities have a number of adaptive technologies available for their use.
A list of available screen readers can be found here:
There are also a range of screen magnifiers available; you can learn about them on this page:
Curious about designing websites that are accessible to persons with vision disabilities? You can learn about this subject on this page:
Vision Impairment Awareness
Approximately 285 million people worldwide live with low vision and blindness. The white awareness ribbon represents blindness.
October is Blindness Awareness Month - World Blindness Awareness Month was established for every October to help people understand the realities of living without sight. As part of Eye Care Awareness Month people are encouraged to have an annual eye exam. October has also been declared Children's Vision Month to encourage parents to book annual eye exams for their children to ensure their eye health.
World Sight Day - A global event that focuses on bringing attention on blindness and vision impairment. It is observed on the second Thursday of October each year.
Quick Facts: Vision Disability Causes &
Eye disorders which can lead to visual impairments can include retinal degeneration, albinism, cataracts, glaucoma, muscular problems that result in visual disturbances, corneal disorders, diabetic retinopathy, congenital disorders, and infection." Visual impairment can also be caused by brain and nerve disorders, in which case it is usually termed cortical visual impairment (CVI).
Statistics: Vision Disability Facts &
Key Vision Facts from WHO
- 80% of all visual impairment can be prevented or cured.
- 82% of people living with blindness are aged 50 and above.
- About 90% of the world's visually impaired live in low-income settings.
- 285 million people are estimated to be visually impaired worldwide: 39 million are blind and 246 have low vision.
- The number of people visually impaired from infectious diseases has reduced in the last 20 years according to global estimates work.
- Globally, uncorrected refractive errors are the main cause of moderate and severe visual impairment; cataracts remain the leading cause of blindness in middle and low-income countries.
Facts About Blindness
- Every seven minutes someone in America loses their sight permanently (Research to Prevent Blindness).
- There are an estimated 15 million blind or visually impaired people in the United States (Prevent Blindness America).
- Nationally, among persons ages 21 to 64 who are visually impaired, defined as any difficulty or inability to see words and letters even when wearing glasses or contact lenses, only 41.5% are employed; among individuals unable to see words and letters, this figure decreases to 29.9% (J.M. McNeil, 2001).
- Leading causes of new cases of blindness are, in order, age-related macular degeneration, glaucoma, diabetic retinopathy, cataracts and optic nerve atrophy (Prevent Blindness America).
- In 2000, 1.7 million of 10.5 million California residents age 45 or older, and 755,000 of 3.5 million who are 65 or older, had a self reported vision problem (Arlene R. Gordon Research Institute of Lighthouse International).