There are four broad categories of vision impairment. The following descriptions are loose guidelines, and it should be noted that the individual will hold the information you require so always have that conversation. In general, though, the following are a useful starting point:

• Color blindness: red-green impairment is the most common, affecting 5% of the male population and 1% of the female. One in twelve people using the web are color blind.
• Mild vision impairment: may require larger font size, possibly a different background style and/or color.
• Moderate vision impairment: may require the aid of screen magnification software.
• Blind/severe vision impairment: may require the aid of a screen reader.

For more information on types of vision impairment, eye health and local support services, visit the Canadian National Institute for the Blind (CNIB) and Vision Loss Rehabilitation Canada websites.