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.

Visit the Asia Pacific National Members page of the World Blind Union website for information on the various blindness and low vision support organisations in Japan.