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 blindness 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. These include:
- Blind users, who rely on screen readers and other technology
- Low vision users, who rely on screen magnification and other technology
- Colorblind users
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, 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. 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.
What people with low vision or blindness say about themselves
- The Things You Don't See by a 21-year-old woman going blind is a blog where she discusses her experiences in life and answers questions on tumblr.
- WebAIM Screen Reader User Survey #7 - includes quantitative and qualitative research directly from people using screen readers on how the web is doing (as of 2017)
- What I learned by going blind by Ingrid Ricks on Salon talks about retinitis pigmentosa. I don't condone of her approach to her doctor's advice, but it's her life to live.
- What It’s Like To Be A Legally Blind Illustrator And Graphic Designer by Keith Rosson at Huffington Post.
- Elsa S. Henry wrote a column on Terrible Minds called So You Wanna Write A Blind Character? that covers what it's like to be blind from a blind person's point of view. Elsa explains how she uses Twitter (reading glasses and Dragon Naturally Speaking), social cues, statistics about blind folks, and guide dogs.
- Alexa is a revelation for the blind by Ian Bogost talks about how, for many blind people, being able to communicate with another human being without someone being a passthrough is a service they may have never had until VUI.
- How the Visually Impaired Experience Hubble Images by NASA is a video of Denna Lambert at the Goddard Space Center describing using this book to learn about telescopes and stars and nebula and planets for the first time.
- Losing my sight made me a better designer by Soren Hamby
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.
Examples of technology for visual disabilities
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
- The little-known iPhone feature that lets blind people see with their fingers by David Pogue
- VoiceOver Getting Started Guide by Apple
- Quick guide to using VoiceOver on Mac OS X by Victor on victortsaran.net
When we design for people with vision impairment we provide:
- The ability to enlarge and reduce text size and images
- The ability to communicate the meaning of visual content - pictures, charts, and icons - through a method other than visual display
- The ability to customize fonts, colors, and spacing
- Properly-tagged semantic HTML understood by a screen reader or text-to-speech software
- Audio descriptions of video in multimedia
- The ability to use a Braille reader
- Forms and data tables where the information is easy to scan and understand even at 400x zoom
- Color palettes and iconography that is compatible with colorblind vision
- Content that always relies on more than just color to communicate meaning
- Keyboard navigation
It's also important to recognize that someone with a visual disability may not know when a new window or browser tab is being opened. Not opening new windows by 30 Days to a More Accessible Website explains more.
When designing for users of screen readers we need to:
- Describe images and provide transcripts for video
- 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 video
- 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 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
- Glaucoma simulator
- Blindness statistics by the National Federation of the Blind
- Karwai Pun's Dos and Don'ts on designing for accessibility and the accompanying posters on designing for users of screen readers (image) and designing for users with low vision (image).
- Space Camp for Interested Visually Impaired Students