Something to Think About...
Assistive technology supports tasks that would be difficult or impossible for those with disabilities if that technology was not available. Most people that wear glasses or corrective lenses would not consider themselves as having a disability, yet many of them would have difficulty accomplishing everyday tasks if they did not have that technology. Glasses and contact lenses have become so commonplace in society and are so effective at correcting many visual disabilities that most people do not consider them assistive technology in place due to a disability.
Imagine if a web page was designed to be incompatible with glasses or corrective lenses? If this were to occur, then the impacts of that visual disability and the considerations for ensuring the content worked with those technologies would suddenly become very acute. Much of web accessibility is simply ensuring that web content is compatible with various assistive technologies.
Some people have visual disabilities that are not easily corrected. Some have no vision at all. Total lack of vision represents the extreme end of the scale of a condition that we call blindness. Most people who are considered "legally blind" do have some vision. Legal blindness is commonly defined as a condition in which the best corrected visual acuity is 20/200, or less, or the person's visual field is 20 degrees or less. Having visual acuity of 20/200 means the person must stand 20 feet away to see something that can be seen from 200 feet away by someone with 20/20 vision. People who are blind have an amazing array of assistive technologies available to them to support common tasks, such as using the web. We'll take a closer look at some of these technologies.
Another category of visual disability is low vision—typically considered to be vision that cannot be corrected to near 20/20. It is a common condition among the elderly, but younger individuals may also have this disability, whether due to genetics, traumatic injuries, or illnesses.
A third category of visual disability is color-deficiency or color-blindness, though it may be an overstatement to call color-blindness a disability, since the conditions under which color-blindness is a true limitation are few. Still it is helpful to be aware of color-blindness when designing web content.