Visual disabilities
Visual disabilities include:
- A complete absence of vision
- Partial sight
- Colour perception differences.
Each condition has distinct access implications.
Blindness
A person who is blind receives no functional visual information. They rely on non-visual means to access content and navigate the environment.
Example
A blind person using a computer depends on a screen reader to convert text into speech or braille output. Any visual information must have a text alternative for the assistive tools to be useful.
Key point
Legal and medical definitions of blindness vary. "Legally blind" often includes people with some residual vision. In accessibility practice, assume that a screen reader user may have no usable vision.
Low vision
A person with low vision has partial sight that cannot be fully corrected by glasses or surgery. They may use their vision alongside assistive tools, often with significant magnification.
Example
Someone with low vision might enlarge the text in their browser to 300%. They might also use high contrast mode or rely on a screen magnifier. They often use both vision and technology simultaneously, making layout and spacing critical.
Key point
Many low vision users do not use screen readers at all. Visual presentation matters more for this group.
Colour Vision Deficiency (CVD)
Colour vision deficiency reduces the ability to distinguish between certain colours. The most common form impacts red-green discrimination. But this condition exists on a spectrum.
Example
A chart with only red and green lines is hard to read for those with red-green colour vision deficiency. Adding distinct line patterns or labels solves the problem.
Key point
Colour vision deficiency is far more prevalent than most designers assume. It affects approximately 8% of men of European descent. It is not the same as seeing only in grey tones. Most people with CVD see colour, but not as someone without the deficiency does.