1. Abrams D Duke Elder’s Practice of Refraction. Edinburgh: Churchill Livingstone; 1993. p. 45-7.
2. Khurana AK Comprehensive Ophthalmology. 4th ed. New Delhi, India: New Age International (P) Limited Publishers; 2007. p. 41.
3. Dandona L, Dandona R Revision of visual impairment definitions in the International Statistical Classification of Diseases. BMC Med 2006;4:7.
4. Holden BA, Sulaiman S, Knox K The challenge of providing spectacles in the developing world. Community Eye Health 2000;13:9-10.
5. Ayanniyi AA, Adepoju FG, Ayanniyi RO, Morgan RE Challenges, attitudes and practices of the spectacle wearers in a resource-limited economy. Middle East Afr J Ophthalmol 2010;17:83-7.