1. DEFINITION OF BLINDNESS- REVIEW
Ayesha Abdullah

2. LEARNING OBJECTIVES
By the end of this lecture the students should be able to:
Define blindness, visual impairment & low vision according to the WHO- ICD-10 classification
Critically evaluate the definition & its implications
Describe the global burden of blindness & visual impairment.
Identify the major causes of blindness at global and national level.

3. Definition of blindness
Which system of classification is used to define blindness
1. International Statistical Classification of Diseases & related health problems, 10th revision (ICD-10)

5. Definitions
There are 4 levels of visual function, according to the International Classification of Diseases -10
Normal vision
Moderate visual impairment
Severe visual impairment
Blindness
“low vision”
Visual
Impairment

6. Definition of blindness
(ICD-10,Visual impairment (VI) categories 3, 4 & 5)
Blindness is defined as a visual acuity (VA) of less than 3/60 (20/400) in the better eye with best possible correction Or
A visual field in the better eye to less than from fixation
Key words?

7. 6 5 4 3 2 1
visual acuity
less than 3/60

8. Which one is the better eye?
in the better eye
6/12
1/60
1/60
2/60

9. best possible correction

10. visual field loss
Better eye
less than 100

14. ICD VA VF (degrees) What it defines 6/6 – 6/18 > 20 Normal 1
Category VA VF
(degrees)
What it defines
6/6 – 6/18
> 20
Normal 1
<6/18-6/60
< 20
MVI 2
<6/60-3/60
SVI 3
<3/60-1/60
<10 B 4
<1/60-PL 5
NPL

15. Let’s examine a few scenariosVA
Visual Field
Rt eye (OD)
Lt eye (OS) 1
6/24
2/60 2
6/12
6/9
150
100 3
6/6
1/60 4
6/60 PL 5

16. EPIDEMIOLOGY OF BLINDNESS AND VISUAL IMPAIRMENT MAGNITUDE AND CAUSES

17. Global distribution

18. Causes of blindness, Global level

19. Distribution of causes of blindness
DEVELOPED COUNTRIES
DEVELOPING COUNTRIES
Age-related macular degeneration (AMD)
Cataract
Diabetic retinopathy & glaucoma
Glaucoma & corneal opacity
Diabetic eye disease
( emerging) & AMD

20. “ Avoidable & unavoidable blindness”
That can be either treated or prevented by known, cost-effective means
Cataract
Refractive errors
Diabetic retinopathy
Unavoidable blindness
Retinal causes of childhood blindness
ARMD

21. Cataract

22. Glaucoma

24. Corneal opacity

25. Childhood blindness mortality & morbidity
Vitamin A deficiency
Normal
Keratomalacia

26. Trachoma

27. Age-related macular degeneration