Accessibility Fundamentals- Low Vision

Low vision is the term used to describe significant visual impairment that can’t be corrected fully with glasses, contact lenses, medication or eye surgery. People with low vision can’t see well enough to drive or read most printed text unless they enlarge it.  it includes Blur, Blur with Low Contrast, Cataracts, Diabetic Retinopathy, Glaucoma, Hemianopia, Macular Degeneration, Retinal Detachment.

Most low vision is caused by eye diseases and health conditions such as cataracts, glaucoma, and diabetes. These are more prevalent in older people. Some low vision is from birth defects or injuries.

There are five categories of visual impairment that impact web use, not including total blindness:

  • Visual acuity (clarity) – Visual acuity is the clarity or sharpness of vision. It is generally dependent on the functioning of the retina part of the eye and of the interpretation of the brain.
  • Light sensitivity – Many people with low vision have extreme sensitivity to light (called photophobia). Bright light makes it difficult or impossible to see, and causes eye pain and headaches. For some people, the normal brightness of a computer screen with a light background is not readable and painful. They need to change the background to a darker color.
  • Contrast sensitivity – Contrast sensitivity is the ability to distinguish bright and dim areas of images, for example, to discern text on a background. A common accessibility barrier for people with low contrast sensitivity is gray text on a light background.
  • Field of vision – The area from which a person’s eye is able to gather visual information when looking straight ahead is referred to as the field of vision or visual field. People generally have a field of vision of approximately 180 degrees from left to right and 150 degrees up and down, with the sharpest vision in the central 5 degrees and color vision in the central 20 degrees. Some people have a smaller field of vision, which is called field loss.
web page with center area obscured
central field loss
web page with outer area obscured
peripheral field loss
web page with scattered areas obscured
 Other kinds of field loss
  • Color vision – Some people cannot see certain colors well or at all, usually because of deficiencies in the cone receptors of their eyes which are responsible for color perception. This is commonly called “color blindness”, even though most people who are color blind can see most colors. It is rare that a person cannot see any color at all. 

Web Accessibility for Low Vision

Screen Magnification

A lot of people with low vision will use screen magnification to be able to see text or images on a screen. this make it a bit cumbersome as you can not see the whole screen at once. Though large magnification can help overcome the main challenges of low vision, there are still some issues a user can encounter. For instance, if an image is particularly large, a user may need to scroll around the screen to see the whole thing. If a JavaScript alert pops up to the side of the current visual focus, the alert may actually appear out of the visible area for the user with low vision, so the user may not see the alert at all. It is best to place popups, alerts, error messages, and other similar messages near the visual focus, to make sure users don’t miss them.

Screen Readers

Most people think of blind people when they think of screen readers, but people with low vision can benefit from screen readers too. 

Color Customization

For people with low contrast vision, or low color vision, colors may not be easily visible, and may be hard to distinguish from each other. Text that is too close in color or luminescence (brightness) to the background can be hard to read. Some people may also experience pain when looking at bright lights or bright areas on paper or computer screens. All-white backgrounds can be particularly difficult. To attempt to remedy the effects of low contrast and bright areas, users may modify the colors either in the operating system or in the web browser.

Design Consideration

User needs varying widely across people who have low vision, and one user’s needs may conflict with another user’s needs. For example, an older person might need high contrast but that might be unreadable to a person with light sensitivity; a person with good visual acuity (clarity) and tunnel vision might need to make the text size small so they can see more words at a time to read better, whereas most people with low visual acuity need large text.

The pinch-to-zoom feature must not be disabled (avoid <meta name="viewport" content="user-scalable=no">).

When zooming is disabled on a web page, which the parameter user-scalable=no does, low vision users who use screen magnifiers to read content may be unable to properly see information on a web page.
All text must pass contrast guidelines against the background (verify using Deque’s aXe accessibility browser extension or a similar tool). Some users who have low vision may see in low contrast. So, text, borders, and other elements may appear as the same or similar shades of brightness to them. Textual elements that are too close in brightness to background colors may be extremely difficult to read for these users.
Links, buttons, and controls must have a visible :focus state and should have a visible :hover state.
Some low vision users may use a keyboard or a mouse, or both, as input methods. Having visible :focus and :hover states helps users to know where the keyboard/mouse focus is on a web page. The default browser :focus state is acceptable per the WCAG guidelines, but users with low vision benefit greatly from enhanced CSS :focus and :hover states.
The user interface should provide a clear visual distinction between content (e.g., text) and controls (e.g., buttons, links, etc.). Again, users who may see in low contrast may have difficulty distinguishing whether controls are actionable on a web page because these elements may blend together with surrounding text and background colors.

The users need to be able to adjust user interfaces to meet their needs. An individual’s optimum display for readability often requires very specific adaptations.

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