1. Agreement on minimum requirements for issue and validity of driving permits (APC) (1975 ) United Nations ECE, Geneva.
2. British Standard 4274 (1968 ) Test charts for determining distance visual acuity. British Standards Institution, London.
3. F. M. Council, and J. A. Allen (1974 ) A study of the visual fields of North Carolina drivers and their relationship to accidents . University of North Carolina, Highway and Safety Research Centre, North Carolina.