Low vision aids. Basic introduction

1. OLD DEFINITION OF LOW
OLD DEFINITION OF LOW
VISION
VISION
Vision loss that cannot be corrected by
ordinary eye glasses, contact lenses,
medication or surgery.
 A person with Low vision has extremely
limited sight that interferes with daily
activities.

2. NEW DEFINITION OF LOW
NEW DEFINITION OF LOW
DEFINITION
DEFINITION
Severely visually impaired after correction but
can increase visual function with the use of
adaptive aids.
 According to WHO, Low vision corresponds
to Visual acuity less than 6/18 but equal to
or better than 3/60 in the better eye with best
correction.

3. When ordinary eye glasses, contact lens or
intraocular lens implant cannot provide
sharp sight , an individual is said to have
Low vision.

4. PROPOSED DEFINITION OF
PROPOSED DEFINITION OF
LOW VISION
LOW VISION
WHO 1992
 A person with Low vision is one who has
impairment of visual functioning even after
treatment, &/or standard refractive correction, and
has a Visual acuity less than 6/18 to PL +ve or a
Visual field less than 10 degrees from the point
of fixation, but who uses, or is potentially able to
use vision for the planning &/or execution of a
task.

5. Lecture - I
Lecture - I
Magnitude
Definition
Classification
Terminologies
Three classes of Vision Loss
Causes
Signs of Low Vision

6. Magnitude of Low Vision
Magnitude of Low Vision
 World wide (WHO 2001)
- Low vision : 124 million
- Blind : 37 million
 World wide (children)
- Low vision : 7 million
- Blind : 1.5 million
 Low vision : Blindness = 3.4:1

7. Indian Scenario
 Indian scenario (APEDS)
- Prevalence of low vision: 1.05%
- 13.3 million for 1168 million in the year 2010
- 16.7 million for 1312 million in the year 2020
 Only 15% of those in need of basic low vision
care are actually being served
 10.6 million in need for low vision care

8. Regional Blindness Burden
Regional Blindness Burden
(RBB)
(RBB)
% of blind in a given region
% of total population in that region
 RBB > 1.0 indicates the region need more attention towards the cause
 India RBB : 1.46

9. Age Blindness Burden(ABB)
Age Blindness Burden(ABB)
% of blind in a given age group
% of total population in that age group
ABB >1.00 is significant
Developing countries : 45 – 59, > 60

10. Need for low vision care
THE RIGHT TO SIGHT
 WHO global initiative for the
elimination of avoidable blindness
through Vision 2020 program has
prioritized low vision care
Global Initiative for the elimination of avoidable blindness. Geneva: WHO; 1997

11. Need for low vision care
 Only 3% of visually impaired children in
developing countries have access to basic low
vision care
 50% of the visually impaired children in
special schools are low vision
 Low vision has enormous social & economic
consequences in terms of productivity losses
and dependency

12. Lack of professional and community
awareness
Lack of good quality low vision training
programs
Very little emphasis on low vision care in
existing eye care programs
Major Challenges in delivery of low
vision care in developing world

13. Blindness
Blindness
Refers to a condition where a person suffers
from any of the following conditions, namely:
– Total absence of sight; or
– Visual acuity not exceeding 6/60 or 20/200
(Snellen) in the better eye even with correction
lenses; or
– Limitation of the field of vision subtending an
angle of 20 degree or worse.

14. Low Vision
Low Vision
The Persons with Disabilities Act, 1995 also
recognizes low vision as a category of disability
and defines it as follows:
“Person with low vision” means a person with
impairment of visual functioning even after
treatment or standard refractive correction but
who uses or is potentially capable of using
vision for the planning or execution of a task
with appropriate assistive device”.

15. Low Vision
Low Vision
The WHO working definition of Low Vision (WHO, 1992)
is as follows:
“A person with low vision is one who has impairment
of visual functioning even after treatment, and/
or standard refractive correction, and has a visual
acuity of less than 6/18 to light perception or a
visual field of less than 10 degrees from the point
of fixation, but who uses, or is potentially able
to use, vision for the planning and/or execution
of a task”.

16. Low vision
Standard Definition (WHO 1992)
 Impairment of visual functioning in better eye even after
treatment and/or standard refractive correction, and VA
of <6/18 to light perception
 or a VF loss of <100
from point of fixation, but who uses,
or is potentially able to use, vision for the
planning/execution of task

17. Visual Impairment
Visual Impairment
Categories
Categories
Category Visual Acuity
(WHO)
Functional
(WHO)
Indian
0 (6/6 – 6/18) Normal Normal Normal
I (<6/18 –
6/60)
Mod. VI Low vision Low Vision
2 (<6/60 -3/60) Sev. VI Low vision Blind (legal)
3 (<3/60-1/60) Blind Low vision Blind (legal)
4 (<1/60 –Pl) Blind Low vision Blind (legal)
5 (NPL) Blind Totally Blind Total (legal)
Blindness

18. Visual Impairment
Visual Impairment
Categories
Categories
Category Better eye Worse eye %
Impairment
0 6/9 -6/18 6/24 - 6/36 20
I 6/18- 6/36 6/20 - nil 40
II 6/40 –4/60
VF 10- 20*
3/60 - nil 75
III 3/60-1/60 VF10* CF.1ft - nil 100
IV CF1 ft-nil VF10* CF.ft - nil 100
One Eyed 6/6 CF1 ft - nil
VF10*
30

19. WHO Disability Sequence
WHO Disability Sequence
Disorder:
- affects tissues level
Impairment:
- Visual function level
Disability:
- Ability to perform tasks
Handicap:
- Activities of life

20. Explanation of Various Terms
Explanation of Various Terms
as Adopted by WHO
as Adopted by WHO
 Impairments:
– Abnormalities of body; structure and appearances; organs or system
functioning
– Disturbances at organ level
 Disabilities:
– Impairment in terms of functional performance and activities
– Disturbances at personal level performance
 Handicaps
– Disadvantages resulted from impairment and disabilities
– Interaction with and adaptations to individual surroundings
Source: WHO Classification of Impairments, Disabilities & Handicaps

21. Disorder
Impairment
Disability
Handicapped
ARMD
sed Central Vn
Diff in reading and recognizing
faces
Social Impact
Example

22.  Diseases affecting the optical media (overall
blurred vision)
 Diseases affecting the macula (central vision)
 Diseases affecting the peripheral retina and
visual pathway
The Three Classes of Vision
Loss

23. Major causes of low vision
Diseases of the optical media:
 Corneal Dystrophy
 Keratoconus
 Microcornea
 Congenital glaucoma
 Cataract
 Vitreous Opacities
 Dislocated lens (Marfan’s syndrome)

24. Major causes of low vision
Diseases affecting the macula
Hereditary :(Dominant or recessive)
 Best’s disease
 Stargardt’s
 Achromatopsia
 Albinism
 Macular coloboma

25. Major causes of low vision
Diseases affecting the macula
 AMD
 Myopic Maculopathy
 Diabetic macular edema
 Chorioretinitis of macula
 Retinal Vascular Disease

26. Major causes of low vision
Diseases of Peripheral retina and Visual pathways
 Diabetes
 Retinitis Pigmentosa & LCA
 Glaucoma
 Optic Atrophy
 Retinopathy of pre maturity (ROP)
 Intra cranial lesions (vascular,
tumors,head injury)

27. Low vision Perception
Cataract and corneal
pathologies
Macular degeneration

28. Signs of low vision
Diabetic retinopathy Retinitis pigmentosa

29. Diagnosis ?
Diagnosis ?

33. REFERENCES
REFERENCES
1. Light house hand book on Vision Impairment & Vision
Rehabilitation by Barbara Silverstone et al., 2000
2. Low Vision Care by Edwin. B. Mehr & Allen. N. Freid,
1975
3.Clinical Low Vision by Eleanor. E. Faye, 1976

34. 3. Dandona R, Dandona L, et al. Design of a population
based study of visual impairment in India: the Andhra
Pradesh Eye Disease Study. Indian J Ophthmol 1997;
45:251-7
4. Moderate visual impairment in India : the Andhra
Pradesh Eye Disease Study [APEDS]. British J
Ophthalmol 2002;86:373-377

35. 5. Dandona L, Dandona R, Srinivas M, et al.
Blindness in the Indian State of Andhra Pradesh,
Invest Ophthalmol Vis Sci 2001;42:908-16
6. Dandona L, Dandona R, Naduvilath TJ, et al. Burden of
Moderate visual impairment in an urban population in
southern India. Ophthalmology 1999;106:497-504
7. Highlights of Ophthalmol, No.12, Vol 21, 1993

36. 8. Kalkivayi V, Naduvilath TJ, et al. Visual Impairment in
School Children in Southern India. Indian J Ophthalmol
1997;45:129-134
9. Weih L, Van Newkirk MR, McCarty C A, et al. Age
Specific causes of bilateral visual impairment. Arch
Ophthalmol 2000;118:264-9
10. Low Vision and Rehabilitation, Ophthalmology Clinics of
North America, A. Colenbrander & D.C.Fletcher;
Vol.7,June 1994

37. Indian Scenario
Cataract : 44%
Refractive error : 16.3%
Retinal disease : 10.3%
Glaucoma : 8.2%
Corneal disease : 7.1%
Optic atrophy : 6%
Amblyopia : 4.3%
Congenital anomaly : 1.1%
Others : 2.2%

38. Indian Scenario – Moderate
Indian Scenario – Moderate
Visual Impairment
Visual Impairment
Refractive error : 45.8% Corneal disease : 2.3%
Cataract : 39.9% Optic atrophy : 1.8%
Retinal disease : 3.4% Glaucoma : 1%
Amblyopia : 2.7% Others : 3.1%

39. Indian Scenario – School
Indian Scenario – School
children
children
Best corrected Visual
Acuity in the better eye
6/5, 6/6, 6/9 : 99.2%
6/12, 6/18 : 0.6%
6/24, 6/36 : 0.2%
< or = 6/60 : 0%
Best corrected Visual
Acuity in the worse eye
6/5, 6/6, 6/9 : 98.5%
6/12, 6/18 : 0.8%
6/24, 6/36 : 0.5%
6/60 : 0.05%
< 6/60 : 0.1%
*
[n = 3987]

40. Indian Scenario - School
Indian Scenario - School
children
children
Amblyopia : 1.1%
Corneal scar : 0.1%
Cataract : 0.05%
Optic atrophy : 0.05%
Keratoconus : 0.03%
HMD : 0.03%
Indeterminate : 0.03%
*
Best corrected visual acuity of < 6/9 in worse eye

41. Distribution according to
Distribution according to
age
age
No.of blind
[In million]
% of total
blind
population
Prevalence
[in %]
ABB
0-14 1.43 3.8 0.08 0.12
15-44 2.47 6.5 0.1 0.14
45-49 12 31.7 1.9 2.68
Developed 2.45 6.5 1.2 1.68
Developing 19.55 51.5 6.8 9.51
Total 37.9

42. Thank you