• Class B1 Possessing no light perception in either eye up to light perception, but inability to recognize the shape of a hand at any distance or in any direction.
• Class B2 From ability to recognize the shape of a hand up to visual acuity of 20/600 and/or a visual field of less than five degrees in the better eye with the best practical eye correction.
• Class B3 From visual acuity above 20/600 and up to visual acuity of 20/200 and/or a visual field of less than 20 degrees and more than five degrees in the better eye with the best practical eye correction.

CIM Guidelines for the Blind/Visually Impaired

1. Athletes must bring to the designated booth at the CIM Expo a physician's or optometrist's verification of status as visually impaired according to the above classifications.
2. Athletes bring their own guides to the competition. The athlete pays one entry fee as the guide is only the runners "eyes."
3. Athlete and guide are regarded as a team. The guide must wear on the front and back of his/her shirt singlet or bib the GUIDE Runner. Guide(s) are not scored.
4. As the blind or visually impaired runner crosses the finish line, the guide must be behind the athlete.
5. The method of guidance is the choice of the athlete. He or she may choose to use an elbow lead, or a tether, or run free. Strapping or tying the hands of athlete and guide to one another is not permitted. The tether used must provide at least 5 cm (2 inches) length between the respective hands of guide and athlete. In addition, the runner may receive verbal instruction from the guide.
6. Guides may not use a bicycle or other mechanical means of transport.
7. The guide cannot pull the athlete, or propel the athlete forward by pushing. 

For more information on the United States Association of Blind Athletes and information regarding guide running go to usaba.org.