Low vision and blindness

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.

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.

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.


Colorblindness is a specific visual disability where the user may (or may not) be able to clearly see, but they are unable to fully perceive the color in what they see.

Approximately 4.5% of the world population have some form of colorblindness (also called color vision deficiency, or CVD). it affects 1 in 12 men and 1 in 200 women. These figures are higher for white (Caucasian) people or others who have mixed grace genes in their genetic history.  By the math, at least one of your co-workers is color blind.

For the vast majority of people, the condition was inherited from their mother, but others may become colorblind from other diseases such as diabetes and multiple sclerosis, or from aging or certain medications. As many as 3% of the population could be affected by age-related deficiencies.

More than a few kinds of colorblindness exist, each with its own challenges.

  • Protanomaly is a reduced sensitivity to red light (1% of men). Protanopia is the total inability to see red (1% of men).
  • Deuteranomaly is a reduced sense of green light (and the most common form of colorblindness, 5% of men). Deuteranopia is the total inability to see green (1% of men).
  • Tritanomaly is a reduced sensitivity to blue light (and is extremely rare). Tritanopia is the total inability to see blue. (Put together they’re about 1 in 30,000-50,000 people.)
  • Achromatopsia is the extremely rare (1 in 33,000 people) form of colorblindness where there is no color, only monochromatic (shades of grey) vision.

People with either deuteranomaly or protanomaly are collectively known as red-green colorblind because regardless of which of the two types they have, they have difficulty distinguishing between red and greens, as well as browns and oranges.  They may also confuse blues and purples.

Examples of technology for visual disabilities

Design considerations

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
  • Audo 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

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”.

Low vision

When designing for users with low vision, we need to:

  • Use good contrasts and a readable font size
  • Publish all information on web pages (HTML)
  • Use a combination of color, shapes, and text
  • Follow a linear, logical layout and ensure text flows and is visible when text is magnified to 200%
  • Put buttons and notifications in context.

We need to avoid:

  • Using low color contrasts and small font sizes
  • Burying information in downloads
  • Only using color to convey meaning
  • Spreading content all over a page and forcing a user to scroll horizontally when text is magnified to 200%
  • Separating actions from their context

How to design mobile app experiences for the visually impaired by Ayesha Zafar on Invision discusses steps specific to mobile interactions.

Not opening new windows by 30 Days to a More Accessible Website discusses why opening new windows constantly is bad.


Additional resources

What people with low vision or blindness have to say

  • 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.
  • 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.

Design tips and guidelines


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