Visual disabilities range from mild or moderate vision impairment (“low vision” or “partial sight”) to substantial and uncorrectable loss of vision in both eyes (“blindness”). Some people have Color Vision Deficiency (CVD, sometimes called colorblindness) or increased sensitivity to excessive brightness in colors. Color perception can be independent of visual acuity.
When we talk about accessibility issues on the web we often think of visual disabilities first, because they often need the most accommodation to provide access.
Examples of visual disabilities
We often conflate visual disabilities with total blindness, and total blindness with the same sensation as having one’s eyes closed, but it’s important to understand that people who are blind very often are able to see colors and varying levels of light, just not clearly enough to function at the same level as those without visual disabilities.
Similarly, those with low vision may be able to see their full field of view, but require correction, or they may have a constricted view, where part of their field of vision is blocked due to glaucoma, age-related macular degeneration (AMD), or similar issues.
- It is estimated that 10 million Americans are blind or visually impaired.
- As of 2014, 2.3% of the population of the United States ages 16-75+ had a significant visual disability.
- More than 70% of the blind population had a high school diploma or above, but only 40.4% were employed.
- From 2000 to 2010, there were 186,555 eye injuries worldwide in military medical facilities, according to the Vision Center of Excellence.
- Because we cannot detect screen readers or similar technology (nor should we, necessarily), it is impossible to estimate exactly how many users with visual disabilities are using our website.
Impact of aging
Our ability to discriminate between colors reaches full maturity around age 15. At that point a child can tell colors apart about as well as an adult. From around age 30 onward, our ability to discriminate between colors then declines, first losing blues, then greens. This is thought to be due to yellowing of the eye’s lens. Scores on color matching tests show a 70% decline by age 60 and an additional 56% change by age 80.
Find the Invisible Cow is a web-based game that only uses audio to play.
Independence Day by Jennifer Warnick is about a prototype technology that uses wireless beacons and on-bone headphones to help blind participants navigate an area near Reading, UK. The technology is a partnership between Microsoft and Guide Dogs, a local charity.
“For me as a designer of interaction whose focus is always about the quality of the human experience, I found out very early on that if you want to understand something, you go to the extreme cases and try to understand things at the edges. In nearly all cases, what you learn people need while you’re there will also apply to the general population.”
~Bill Buxton, Microsoft
Examples of people using screen readers for various purposes. For screen reader links and instructions, see Testing tools.
Design considerations for screen readers
When designing for users of screen readers we need to:
- Describe images and provide transcripts for vide
- Follow a linear, logical layout
- Structure content using HTML5
- Build for keyboard use only
- Write descriptive links and headings, for example “Contact Us”.
We need to avoid:
- Only showing information in an image or vide
- Spreading content all over a page
- Relying on text size and placement for structure
- Forcing mouse or screen use
- Writing uninformative links and headings, for example, “Click here”.
A good metaphor for what it’s like to use a screen reader can be found in A Tale of Two Rooms by Ryan Jones.
See Color Vision Deficiency (Colorblindness) for a list of tools for that specific condition.
- WebAIM’s Color Contrast Checker will tell you if two colors you enter pass accessibility guidelines
- Eye disease simulators (in the form of pictures) by the National Eye Institute
To be added later.