B4 (classification)

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B4 is a sports classification for athletes with visual impairments. It is used in many sports, including sailing, bowls, swimming, and cycling. B4 is based on visual acuity only, not on the field of vision, and is a medical classification.

Definitions vary by organization:
- BlindSports SA describes B4 as visual acuity from better than 6/60 up to 6/24 (up to 25%), with no visual field consideration.
- USABA defines B4 as visual acuity from better than 20/200 up to 20/70, with a best-eye visual field larger than 20 degrees after correction.

Governance and where it is used:
- In the United States, USABA governs B4.
- In New Zealand, Blind Sport New Zealand governs it.
- In the United Kingdom, British Blind Sport governs the class, and Blind Sailing handles national governance for B4. Blind cricket is governed by BBS, and Scottish Blind Golf covers golf in Scotland.
- The class is used in national competitions in Canada, Australia, the United States, and the United Kingdom.
- B4 cyclists compete on tandem bicycles with a guide.

Sport-specific notes:
- Junior IBSA blind sailing events sometimes allow B4 competitors in international events.
- In blind cricket, B1, B2, B3, and B4 players all take part, but there is a limit on how many B2–B4 players can be on the field at once.
- Scottish Blind Golf sets handicaps, with a maximum of 28 for men and a slightly higher limit for women.
- Bowls governance has moved away from using field of vision as a determining factor.
- In swimming, B4 athletes have competed at national championships such as the 2012 Australian Blind Sporting Association Championships.
- An archery equivalent for more visual impairment is VI Open, open to those with acuity worse than 20 degrees who can use a bow sight.
- Equestrian sport is not open to Paralympic competition under this classification.

History and context:
- The B4 class was developed to keep competition fair across different levels of vision loss.
- IBSA helped create and refine blind sport classifications, building on earlier ISOD systems from 1976 and 1980.
- In 2003, the International Paralympic Committee aimed to improve the accuracy, reliability, and consistency of sport classifications.

B4+:
- In the United Kingdom, there is a B4+ class for people with acuity of 6/24 who can read the top three lines on a Snellen chart at six metres.