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What is Blindness

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WHO  defines Blindness as the visual acuity in the better eye to be less than 3/60(Snellen's or equivalent) or in the absence of visual acuity chart, blindness is the inability to count fingers in daylight at a distance of 3 m( to indicate less than 3/60  or its equivalent) 

In simple words the term blindness is the inability to perceive light, there are more than 60 definitions of blindness all throughout the world and they differ widely.



 In clinical practice we consider a person to be blind when his BCVA  is less than 3/60 or visual field is less than 10 degrees in diameter or 5 degrees from the center of fixation.

 A low vision person not fulfilling this criterion shall be not called blind instead, he will be termed as a low vision patient. 


Low vision taken together with blindness represents all Visual impairment now let us classify Visual impairment in some categories:

Let us understand some key features in distinguishing the blind from a low vision person:

Now let us understand some types of blindness:

 Legal blindness-Visual acuity in the better eye is less than 3/60  and/ or visual field is constricted less than 10 degrees( in India)

Economical blindness-Visual acuity in the better eye is less than 6/60 and/ or for the visual field constricted to less than 20 degrees( in India)

Visually handicapped-Visual acuity in the better eye is less than 6/18( in India)

Avoidable blindness-This includes both preventable blindness and curable blindness. 85% of the blindness is avoidable. Under this we have two categories:

  • Preventable blindness- This blindness can be easily prevented by attacking the causative factors example corneal blindness( Vitamin A deficiency, trachoma, infectious keratitis, etc.), industrial blindness (By improving occupational safety conditions), Retinopathy of prematurity, diabetic retinopathy, etc.

  •  Curable blindness- It is almost synonymous with cataract blindness. others are glaucoma, inflammation of ocular tissues, etc.


 The number of visually impaired people is estimated by WHO to be around 285 million(2010)

 wherein the number of blind people was estimated around 39.36 million and low vision where around 246.024 million


Causes of Blindness 

Below is a chart stating the various causes of blindness in the world and in India

(Source- Essentials of Ophthalmology SK Basak)

A pie chart showing the statistical study of the various causes of blindness and their overall impact on world blindness(Source- Essentials of Ophthalmology SK Basak)

Causes of Blindness at different age groups



Prevention of blindness

National Program for the Control of Blindness was launched by the Government of India, Ministry of Health and Family Welfare in the year 1976 and is a 100% centrally sponsored scheme/program with the goal of reducing the prevalence of blindness has come up with the sole motto of extinguishing preventable blindness from India. Let us learn some of its objectives: 

  • Provision of comprehensive eye care facilities for primary, secondary, and tertiary

levels of eye-health care.

  • Substantial reduction in the prevalence of eye diseases in general and reduction in

the prevalence of blindness from 1.40% to 0.3% 

  • To reduce the backlog of blindness through identification of treatment of blind and visually handicapped.

  • To develop eye care facilities in every district.

  • To develop human resources for providing eye care services.

  • To improve the quality of service delivery






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