Labelled Diagram of the Eye

Labelled diagram of the structure of the retina

Blindness is simply defined as the inability to see.

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, day blindness, night blindness, and snow blindness.

The World Health Organization (WHO) identifies the following four levels of visual function:

  1. Normal vision
  2. Moderate visual impairment
  3. Severe visual impairment
  4. 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:

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

For further information see also our pages of books about ophthalmology.

The following books may also be of interest:

The Aging Eye (Harvard Medical School)
MCQ Companion to the Eye (Textbook)
The Secret of Perfect Vision: How You Can Prevent and Reverse Nearsightedness
What Your Doctor May Not Tell You About(TM) Glaucoma: The Essential Treatments and Advances That Could Save Your Sight

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