Intended for healthcare professionals

Clinical Review

Cataract and surgery for cataract

BMJ 2006; 333 doi: (Published 13 July 2006) Cite this as: BMJ 2006;333:128
  1. David Allen, consultant ophthalmologist (,
  2. Abhay Vasavada, director2
  1. 1 Sunderland Eye Infirmary, Sunderland SR2 9HP,
  2. 2 Iladevi Cataract and IOL Research Centre, Raghudeep Eye Clinic, Memnagar, Ahmedabad-380 052, India
  1. Correspondence to: D Allen
  • Accepted 12 June 2006


Cataract surgery is the commonest single surgical procedure carried out in the developed world. In the developing world, cataract remains the commonest cause of blindness. In 1990 an estimated 37 million people were blind worldwide—40% of them because of cataract.1 Every year, an extra 1-2 million people go blind. Every five seconds one person in our world goes blind, and a child goes blind every minute. In 75% of these cases the blindness is treatable or preventable. However, 90% of blind people live in the poorest sections of the developing world, and without proper interventions the number of blind people will increase to 75 million by 2020.

Various aspects of the surgery for age related cataract have changed substantially in the past five years, and the quality of outcome, plus the improved safety of the modern procedure,2 has in part driven the increase in numbers of procedures performed.

What causes cataract

Most cataracts arise because of ageing of the crystalline lens. As new lens fibres continue to be laid down in the crystalline lens, and existing ones are not replaced, the lens is unusual in being one of the few structures of the body that continues to grow during life. The transparency of the lens is maintained by many interdependent factors that are responsible for its optical homogeneity, including its microscopic structure and chemical constituents. With ageing, there is a gradual accumulation of yellow-brown pigment within the lens, which reduces light transmission. There are also structural changes to the lens fibres, which result in disruption of the regular architecture and arrangement of the fibres that are necessary to maintain optical clarity.

Extrinsic factors associated with cataract formation vary with socioeconomic and geographical differences (box 1). In the developing world a multitude of factors—such as malnutrition, acute dehydrating diseases at young age, …

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