Blindness from park (psm) summary
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Blindness - Summary from Park's Textbook of Preventive and Social Medicine
Definition
WHO definition: Blindness = visual acuity of less than 3/60 (Snellen) or its equivalent.
India's revised definition (aligned with WHO): A person unable to count fingers from 3 meters (previously 6 meters under the 1976 definition). This revision reduced India's estimated blind population from 1.20 crore to 80 lakh.
ICD-11 Classification of Distance Vision Impairment:
| Category | Visual Acuity |
|---|---|
| Mild | Worse than 6/12 |
| Moderate | Worse than 6/18 |
| Severe | Worse than 6/60 |
| Blindness | Worse than 3/60 |
Near vision impairment: Presenting near visual acuity worse than N6 or M0.8 at 40 cm with existing correction.
Magnitude
Global
- 1 billion people have a vision impairment that could have been prevented or has yet to be addressed.
- Breakdown of unaddressed causes: refractive error (123.7 million), cataract (65.2 million), glaucoma (6.9 million), corneal opacities (4.2 million), diabetic retinopathy (3 million), trachoma (2 million), presbyopia (826 million).
- 80% of all blindness is avoidable (preventable or treatable).
- ~82% of visually impaired are aged 50 years and older.
- 19 million children are visually impaired; 1.4 million are irreversibly blind.
India
- Prevalence of blindness: 0.36% (National Survey 2015-19), down from 1.0% (2006-07) and 1.4% at NPCB launch.
Causes of Blindness in India (National Survey 2015-19)
| Cause | Percentage |
|---|---|
| Cataract (untreated) | 66.2% (leading cause) |
| Cataract surgical complications | 7.2% |
| Non-trachomatous corneal opacity | 7.4% |
| Other posterior segment disease | 5.9% |
| Glaucoma | 5.5% |
| Phthisis | 2.8% |
| Diabetic retinopathy | 1.2% |
| Aphakia uncorrected | 1.7% |
| ARMD | 0.7% |
| Trachomatous corneal opacity | 0.8% |
| Refractive error | 0.1% |
Global causes of blindness: Un-operated cataract (35%), uncorrected refractive error (21%), glaucoma (8%).
Developed countries: Accidents, glaucoma, diabetes, vascular diseases, cataract, retinal degeneration, hereditary conditions.
Childhood blindness: Xerophthalmia, congenital cataract, congenital glaucoma, optic atrophy (from meningitis), retinopathy of prematurity (ROP), uncorrected refractive errors.
Epidemiological Determinants
(a) Age: ~30% of India's blind lose eyesight before age 20, many under age 5.
- Children: refractive error, trachoma, conjunctivitis, vitamin A deficiency
- Middle age: cataract, refractive error, glaucoma, diabetes
- All ages: accidents/injuries (especially 20-40 years)
(b) Sex: Higher prevalence in females - attributed to higher rates of trachoma, conjunctivitis, and cataract.
(c) Malnutrition: Closely linked to low vitamin A intake plus infectious diseases (measles, diarrhea which precipitate PEM). Keratomalacia is most frequent in ages 6 months to 3 years.
(d) Occupation: Factory/workshop workers at risk from dust, flying particles, fumes, radiation (welding flash), UV rays; premature cataracts from X-ray/UV exposure.
(e) Social class: Blindness is twice as prevalent in poorer classes vs. well-to-do.
(f) Social factors: Quackery ("meddlesome ophthalmology"), ignorance, poverty, poor personal hygiene, inadequate health services.
Prevention of Blindness - Components for Action
1. Initial Assessment
Prevalence surveys to assess magnitude, geographic distribution, and causes - essential for setting priorities.
2. Methods of Intervention
(a) Primary eye care - At grass-root level by village health guides and multi-purpose workers:
- Treat/prevent: acute conjunctivitis, ophthalmia neonatorum, trachoma, superficial foreign bodies, xerophthalmia
- Drugs provided: topical tetracycline, vitamin A capsules, eye bandages
- Refer difficult cases to PHC/district hospital
- 1 village health guide per 1,000 population; 2 multipurpose workers per 5,000
(b) Secondary care - PHCs and district hospitals:
- Management of cataract, trichiasis, entropion, ocular trauma, glaucoma
- Eye camp approach for cataract surgery - highly successful
- Mobile eye clinics for peripheral areas
(c) Tertiary care - National/regional capitals and Medical Colleges:
- Retinal detachment surgery, corneal grafting, complex procedures
- Eye Banks established under Corneal Grafting Acts
- National Institute for the Blind, Dehradun - rehabilitation
(d) Specific programmes:
- Trachoma control: Mass campaigns with topical tetracycline; Trachoma Control Programme (1963) merged with NPCB in 1976
- School eye health services: Screen for refractive errors, squint, amblyopia, trachoma; health education on posture, lighting, reading habits
- Vitamin A prophylaxis: 200,000 IU orally every 6 months for ages 1-6 years; 100,000 IU for 6 months to 1 year - effectively "immunizes" against xerophthalmia
- Occupational eye health: Safety features, protective devices, proper illumination
3. Long-Term Measures
Improving quality of life, sanitation, safe water, diet (vitamin A-rich foods), personal hygiene, and health education for community awareness and participation.
4. Evaluation
Integral to programmes - measures extent of alleviation of ocular disease and blindness.
National Programme for Control of Blindness (NPCB)
- Launched: 1976 as a 100% centrally sponsored programme (incorporated the 1968 Trachoma Control Programme).
- Goal: Reduce prevalence of blindness from 1.4% to 0.3%.
- Result: 0.36% by 2015-19.
- Renamed: National Programme for Control of Blindness and Visual Impairment (NPCBVI).
Key Objectives (12th Five Year Plan):
- 66 lakh cataract operations/year; school eye screening + 9 lakh free spectacles/year; 50,000 donated eyes/year for keratoplasty
- Reduce backlog of avoidable blindness at all levels
- "Eye Health for All" - comprehensive universal eye care
- Strengthen Regional Institutes of Ophthalmology (RIOs) as centres of excellence
- Human resource development for all districts
- Community awareness on eye care
- Research for prevention of blindness
- Involve voluntary organizations and private practitioners
Administrative Structure:
| Level | Body |
|---|---|
| Central | Ophthalmology Section, DGHS, Ministry of Health & FW |
| State | State Ophthalmic Cell / State Health Societies |
| District | District Blindness Control Society |
Service Delivery:
| Level | Facility |
|---|---|
| Tertiary | Regional Institutes of Ophthalmology, Medical Colleges |
| Secondary | District Hospital, NGO Eye Hospitals |
| Primary | CHCs, Mobile Ophthalmic Units, PHCs, Link Workers |
80 central mobile units attached to medical colleges; 341 district mobile units for rural eye camps.
School Eye Screening Programme
- 6-7% of children aged 10-14 years have refractive errors
- Free spectacles distributed to school children from poor backgrounds
Eye Donation
- Eye Donation Fortnight: 25th August - 8th September every year
- 68,409 donated eyes collected in 2018-19
- Leading states: Gujarat, Tamil Nadu, Maharashtra, Andhra Pradesh
Vision 2020: The Right to Sight
A global initiative to eliminate avoidable blindness by 2020. India's plan targets:
- Diseases: Cataract, refractive errors, childhood blindness, corneal blindness, glaucoma, diabetic retinopathy
- Four-tier structure: Centres of Excellence (20), Training Centres (200), Service Centres (2,000), Vision Centres (20,000)
Nutritional (Xerophthalmia-related) Blindness
WHO Prevalence Criteria for Xerophthalmia Problem:
| Criteria | Prevalence threshold |
|---|---|
| Night blindness | >1% |
| Bitot's spots | >0.5% |
| Corneal xerosis/ulceration/keratomalacia | >0.01% |
| Corneal scar | >0.05% |
| Serum retinol <10 mcg/dL | >5% |
Prevention strategies:
- Long-term: Improve diet (vitamin A-rich foods), control PEM and infectious diseases
- Short-term: 200,000 IU vitamin A orally every 6 months (ages 1-6 years); 100,000 IU for 6 months to 1 year - developed by National Institute of Nutrition, Hyderabad
National & International Agencies
- National Association for the Blind (NAB): Since 1952 - welfare services
- Royal Commonwealth Society for the Blind: Since 1950
- International Agency for Prevention of Blindness: Formed in 1974 under WHO invitation
Source: Park's Textbook of Preventive and Social Medicine, Chapter on Eye Health & NPCB
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