Blindness

What is blindness?

Blindness literally means "deprived of sight". Blindness with respect to web development is a condition whereby users receive no visual cues from the computer interface. This is different from low vision in that users with low vision have some sight and are potentially able to identify large contrast features on the screen.

Blindness does not prevent a person from perceiving information displayed on a web page. Access is generally dependent on being able to convert the information to a non-visual form. Internet users who are blind are interested in text content. Since blind computer users cannot see the screen, they interact with computer applications using screen access software, either applications that translate text on the screen into Braille or synthesized speech, for example JAWS from Freedom Scientific. Blind users use the same computers as everyone else, noting that most screen access software is Microsoft Windows based. Note that blind users are unable to track the movement of non-text cursors and rely on keyboards for navigation and data entry.

Challenges/Barriers on the Internet

Blind users are unable to process any information that can only be obtained visually. That's not to say that blind users are deterred by graphics, just that alternatives to graphical content must be provided. Any application that cannot be interpreted as text must NOT be used as the exclusive source of content for the site.

Blind users use either relatively plain versions of common browsers or text only browsers such as Lynx. Web sites which attempt to take advantage of advanced browser features or plug-ins will NOT be accessible to blind users.

Most screen access software reads text one line at a time. This means that text which has been split up for visual effect will typically be unintelligible to the blind user. This problem is especially pronounced in tables and forms. Table headings might be visually above appropriate columns yet the table data might be hard to understand when read as a stream of continuous text. For example, it is difficult to differentiate between product item number and product serial number when both are read continuously without preamble or headings. Form data fields separated by layout from their labels are equally mysterious.

Finally, blind users tend to process and navigate websites using very different strategies from sighted users. Screen readers do not skip redundant or repetitive text that a sighted person typically ignores. Screen access software will "read" at many different speeds. Timed features or content that periodically updates will be very confusing to a blind user, since the timing of the update may force blind users to re-read entire pages or may prevent blind users from ever knowing that prior information had been displayed. Blind users usually use keyboard shortcuts when navigating, for example, using Tab to quickly review the links on a page. Links with descriptions like "Click Here" will be extremely cryptic.

Key Concerns

The following items should be red-flags to website developers designing for accessibility:

• Graphics without alt text or text-only alternatives
  <img src="myimage.gif">
• Graphs or charts without text representations
  <img src="chart.jpg" alt="this chart has lots of information not revealed by the accompanying text">
• Image maps
  <MAP> <AREA href="somelink.html"/> </MAP>
• Flash animations
  <EMBED src="myflash.swf" TYPE="application/x-shockwave-flash" "></EMBED>
• Java applets
  <APPLET CODE="MyApplet.class"></APPLET>
• Javascript
  <SCRIPT TYPE="text/javascript"><!--do.stuff(here);--></SCRIPT>
• Plug-in applications such as Adobe Acrobat, QuickTime, ActiveX controls, Shockwave, etc.
• Markup text or features specific to a single browser
• Text separated from other text or fields for visual effect
  

  Like
  		Goofy text
  	This

• Timed splash screens
• Periodically updated content
  <META HTTP-EQUIV="REFRESH" CONTENT="5">
• Links whose text is not self-explanatory

Solutions/Guidelines