FOR PUBLIC HEALTH OPTOMETRY

2. Epidemiology –definition
 is the study of the distribution Determinants &
Control of disease in human populations

3. Visual impairment

 a functional limitation of the eye(s) or visual system
due to a disorder / disease that can result in a visual
disability or a visual handicap.

4.  Purpose in studying the epidemiology of eye disease in
different populations
 is to promote the preservation of healthy eyes and
normal vision
 to prevent blindness and low vision in individuals and
populations

5.  Meaurement of size of the problem of VI
 Describe patterns of eye disease resulting in VI in
different populations
 This quantification is expressed as
Prevalence
Incidence of disease
Causes of blindness

6. Magnitude
 Measure of size of the problem of a condition or
disease
 2 measures used
 prevalence
 incidence

7.  Prevalence =the number of cases or events
the total population at risk
 Incidence = no: of new cases occurring in a given
time period
total population at risk at the beginning of
the period
 This is a proportion and time period is conventionally
taken to be 1 year

8. ACCORDING TO ICD -10
CATEGORY OF
VISUAL
IMPAIRMENT
VISUAL ACUITY
WITH BEST
POSSIBLE
CORRECTION
MAXIMUM LESS
THAN
VISUAL ACUITY
WITH BEST
POSSIBLE
CORRECTION
MINIMUM
EQUAL TO
BETTER THAN
1 6/18 6/60
2 6/60 3/60
3 3/60 1/60
4 1/60 LIGHT
PERCEPTION
5 NO LIGHT
PERCEPTION
NO LIGHT
PERCEPTION
9 UNDETERMINED
OR UNSPECIFIED
UNDETERMINED
OR UNSPECIFIED

9.  Low Vision Categories 1 And 2 Of The Table
 Blindness Categories 3,4 ,5 And 9 Of The Table

10. Factors affecting prevalence of
blindness
1. Demographic factors
2. Service delivery factors
3. nutritional factors
4. environmental factors
5. other factors
Age
Gender
Religion
Residence
socio-economic status

11.  Demographic factors
 2 major demographic events are
 increase in population size
 is the major determinant of blindness in developing
countries
 life expectancy
 In India life expectancy at birth has increased from 46 years
in 1971 to 59 years in 1990

12.  Service delivery factors
 service delivery factors under concern include
 lack of surgical services
 inadequacy and under utilization of available man
power

13.  OTHER FACTORS
 age –prevalence of blindness increases with age
(initial peak at birth due to congenital abnormalities
followed by an exponential increase after 40 years)
 residence –prevalence of blindness is known to be
highest in rural and remote areas all over the world
 Gender
 socio –economic status –universally blindness have a
predilection for the poor
 religion

14. Cause of visual impairment
 Globally principal causes of visual impairment are
 uncorrected refractive errors 42%
 Cataracts 33%
 Other causes are
 glaucoma, 2%
 age related macular degeneration (AMD),
 diabetic retinopathy,
 trachoma
 corneal opacities,(all about 1%)
 A large proportion of causes, 18%, are undetermined

16. Causes of blindness in India(vision
2020)
Cause Percentage
Cataract 62.6
Refractive error 19.7
glaucoma 5.8
Corneal pathologies 0.9
Other causes 11.0

17. Causes of blindness in India

18.  Childhood blindness :
 Childhood blindness and visual impairment is a
public health problem in developing countries with
75% of the world’s blind children
 childhood blindness is the priority of “Vision 2020 -
the Right to Sight,” a global initiative for the
elimination of avoidable blindness..

19.  Indian Scenario :
 In India 3,20,000 children (<16 years) are blind, and
this constitutes 1/5 of the world’s blind children
(Murthy et al.IJO.2008; 56).

20.  Causes :
 Corneal Scar- (Vitamin A deficiency, Measles,
trauma) is the most common cause of childhood
blindness.
 Cataract : 39% childhood blindness
 Trachoma
 Glaucoma
 Source : ORBIS-2010

21.  India has the greatest number and percentage of
Vitamin A deficiency children in the world.
 VAD persists as a public health problem, especially
in rural areas
 The overall prevalence of xerophthalmia among
children is 1.7%, and approximately 0.8% of all
children had Bitot’s spots.

22. Summary
 Population based sample surveys are the most reliable
source of data from which to analyse the magnitude
and cause of blindness and low vision
 Based on these it is clear that total number of people
with blindness and low vision in the world is steadily
increasing

23.  Causes of blindness vary widely from region to region
and within regions and countries
 Cataract is the leading cause of blindness in India

24. references
 Global data on visual impairment
 Low vision manual – A Jonathan Jackson
 The epidemiology of eye disease-Gordon J Johnson
 Epidemiological Overview of Preventable Blindness in
India-A Focus on Vitamin A Deficiency among Pre-
school Children in India-Dr N Arlappa
 Principles and practice of community ophthalmology-
NPCB

25. THANK YOU