Cataract is the single-largest factor for blindness in India, accounting for nearly 63 per cent of the total burden of vision impairment in the country, said an expert here on Friday.

Ramanjit Singh Sihota, Professor of Ophthalmology at All India Institute of Medical Sciences (AIIMS), said after cataract (62.7 per cent), in descending order of prevalence, the causes of blindness were uncorrected refractive error (19.7 per cent), glaucoma (5.8) per cent, posterior segment disorder (4.7 per cent) and corneal blindness (1 per cent).According to a group of ophthalmologists, who were speaking to the media at Rajendra Prasad Eye (RP) Centre for Ophthalmic Sciences at the AIIMS, India currently has the highest numbers of blind and visually impaired people.In this backdrop, aiming to understand the real burden of visual impairment and blindness in children of north India over the last one decade, the AIIMS is conducting nation's first large-scale community-based study in Delhi where 20,000 children will be screened.The study, results of which are expected in a year's time, is currently underway in small clusters of east Delhi's Trilokpuri.

According to the doctors, the clusters have been divided and from every cluster 500 children are being examined.Once the results are out, the study will also be carried out in other parts of India."In India, there are nearly 0.8 crore blind and 5.4 crore visually impaired. Nearly 80-90 per cent blindness is avoidable and more than 90 per cent of it is seen in people aged 50 years and above," said Praveen Vashist, head of Community Ophthalmology at AIIMS."It is an epidemiological study on childhood blindness. The age group being examined is 0-15 years. This is a pilot study and will be implemented in other parts of the country," said Atul Kumar, Chief of Rajendra Prasad Eye (RP) Centre for Ophthalmic Sciences at AIIMS.

Stating that patients were ignorant about various causes which damaged optic nerves, Jeevan S. Titiyal, Professor of Ophthalmology at AIIMS, said that tobacco, betel nut and lime also caused damage to eyes, without the patients having any idea.On being asked if steroids were also a reason behind blindness, Titiyal told IANS: "This is becoming common and nearly 20 per cent of children with blindness is because of the steroids. However, with the advancement in age, chances of people going blind due to steroids become less."The RP Centre is also conducting a "National Blindness Survey 2015-18" with a sample size of 90,000 people, using Rapid Assessment of Avoidable Blindness (RAAB)-6 method.

Blindness surveys have been completed in 23 districts to date and is scheduled to be completed in all 30 districts by June 2018.Doctors said that the survey would provide the most reliable representative current estimates of blindness and visual impairment among those aged 50 and above.It will also generate, for the first time, the burden of diabetic retinopathy and sight threatening diabetic retinopathy in a representative community sample.