The International Classification of Diseases 11 (2018) classifies vision impairment into two groups, distance and near presenting vision impairment.
Distance vision impairment:
Mild –visual acuity worse than 6/12 to 6/18
Moderate –visual acuity worse than 6/18 to 6/60
Severe –visual acuity worse than 6/60 to 3/60
Blindness –visual acuity worse than 3/60
Near vision impairment:
Near visual acuity worse than N6 or M.08 at 40cm.
For International comparison, WHO has defined blindness at the level of 3/60 or inability to count fingers at a distance of 3 meters or 10 feet.
Definition of blindness under National Programme for Control of Blindness
Presenting distance visual acuity less than 3/60 (20/400) in the better eye or limitation of field of vision to be less than 10 degree from centre of fixation.
Presenting visual acuity < 3/60 in better eye with available correction
Severe visual impairment (SVI)
Presenting visual acuity < 6/60 – 3/60 in better eye with available correction
Moderate visual impairment (MVI)
Presenting visual acuity < 6/18 – 6/60 in better eye with available correction
Early visual impairment (EVI)
Presenting visual acuity < 6/12 – 6/18 in better eye with available correction
Moderate severe visual impairment (MSVI)
Presenting visual acuity <6/18-3/60 in better eye with available correction
Visual impairment (VI)
Presenting visual acuity < 6/18 in better eye with available correction
Functional low vision
A person with impairment of visual functioning even after treatment and/or standard refractive correction, and a visual acuity of less than 6/18 to light perception, or a visual field of less than 10 degree from the point of fixation, but who uses, or is potentially able to use, vision for planning and/or execution of a task.
the estimated prevalence in overall population of blindness was 0.36%, severe visual impairment was 0.35%, moderate visual impairment was 1.84%, early visual impairment was 2.92%. Estimated moderate severe visual impairment in overall population was 2.19% and that of visual impairment was 2.55%. Estimated prevalence of pinhole blindness in overall population of India was 0.32%.
The prevalence of blindness and visual impairment was lowest in Thrissur district (Kerala) and in Thoubal district (Manipur) respectively. Bijnor district (Uttar Pradesh) had the highest prevalence of both blindness and visual impairment.
Maximum prevalence of blindness was seen in 80+ age group (11.6%), followed by 70-79 age group (4.1%), 60-69 age group (1.6%) and 50-59 age group (0.5%)
Blindness was higher among illiterates (3.23%) compared to literate population. It was only 0.43% among 10th pass and above.
Reasons for prevalence of blindness in India
The major reasons for prevalence of blindness in India are:
The overall increase in the size of the population
The life expectancy for both males and females has steadily increased
A major proportion of aged population in rural areas have poor access to eye care facilities in India
Inadequate availability of trained health personnel. Further, the services of available ophthalmic surgeons in the country are not being adequately utilized. Many ophthalmologists are purely working in administrative jobs and similar proportion is posted at peripheral units with no ophthalmic equipments.
The poor nutritional status of mothers and young children predisposes the pre-school children to nutrition blindness. However, it is heartening to note that prevalence of nutritional blindness has decreased tremendously over the past few years
Adverse environmental conditions and domestic unhygienic conditions predispose to high infection rates
Lack of community awareness and poor health seeking behavior
The prevalence of myths and misconception about surgeries
Main causes of blindness in India
Cataract was the principal cause of blindness (66.2%), severe visual impairment (80.7%), and moderate visual impairment (70.2%)
The other important causes of blindness were corneal opacity (7.4%), cataract surgical complications (7.2%), posterior segment disorders excluding DR and ARMD (5.9%) and glaucoma (5.5%).
Principal causes of severe visual impairment other than cataract were cataract surgical complications (8.3%) and other posterior segment diseases excluding DR and ARMD (3.4%).
For early visual impairment, the most important cause was refractive error (70.6%).
Most of the blindness and visual impairment were due to avoidable causes (92.9% and 96.2% respectively). Among avoidable causes, treatable causes of blindness and VI were 68.1% and 85.7% respectively.