Blindess is simply defined as the inability
Total blindness is the inability to percieve light
in any way at all, and is rare.
However, some conditions include the term "blindness" while
actually referring to milder, more specific, and/or temporary visual impairments,
for example colour
blindness, and snow
The World Health Organization (WHO) identifies the following four levels
of visual function:
- Normal vision
- Moderate visual impairment
- Severe visual impairment
- Blindness [that is, zero visual perception].
A further complication in definition is classification of "blindness"
for administrative or statutory purposes. That is, people who are considered
"blind" by their government or other organisations offering
assistance may (depending on where in the world they live) receive specific
types of help relevant to the needs of those with extreme visual impairments.
It is not always necessary to be totally blind in order to qualify to
receive such assistance, which might take the form of help with communication,
special education, healthcare, or even financial assistance.
In the same way, some charities and other voluntary groups provide help
to assist blind and partially-sighted persons in their areas, or whom
they are able to reach to provide care or other help.
Causes of blindness:
According to the WHO the main causes of long-term blindness include cataract,
macular degeneration (ARMD), corneal opacities, diabetic retinopathy,
trachoma, and eye conditions in children (e.g. caused by vitamin A deficiency).
Age-related blindness is increasing throughout the world, as is blindness
due to uncontrolled diabetes.
More about Ophthalmology: This section includes short definitions
of many diseases, disorders, and conditions of the eyes and visual system.
For definitions of other terms in this category, choose from the list
to the left (but note that this is not a complete/exhaustive list).
Other related pages include the diagram
of the eye, and definitions
of parts of the eye, a description
of the human retina, and definitions
of parts of the retina, and the section of short definitions
of clinical and surgical procedures re. eyes and human visual system.
For further information see also our section of Books