BY DR. FAIZ-UR-RAB

ASSISTANT PROFESSOR DUHS

LEARNING OBJECTIVES

• Definitions of blindness

• WHO classification of visual impairment

• Causes of blindness in developing & developed countries

• Causes of high prevalence in Pakistan

• Low vision aids

DEFINITIONS

• Legal Blindness: Visual acuity of less than 3/60 or its

equivalent.

• Low Vision: Visual acuity of less than 6/ 18 but ≥ 3/60 or

corresponding to visual field loss to less than 20° in the better

eye with best possible correction.

• Avoidable Blindness: Blindness which could be either treated

or prevented by known cost-effective means.

DEFINITIONS

• Functional Blindness: Loss of vision sufficient to prevent one

from being supporting in an occupation, making the

individual dependent on other persons, agencies or devices

in order to live.

• Industrial Blindness: It is present when a worker can no

longer pursue an occupation because of poor vision

WHO Classification (Visual Impairment)

Category Grade Visual Acuity Best

Corrected

Low Vision

1

2

6/18

20/60

3/10 (0.3)

6/60

20/200

1/10 (0.1)

Blindness

3

4

3/60

20/400

1/20 (0.05)

1/60

5/300

1/50 (0.02)

5 No light perception

THE PROBLEM:

• Worldwide 161 m people are visually impaired- 124m low vision & 37m blind.

• >90% of world’s visually impaired live in low and middle

income countries.

• Except in most developed countries, cataract remains the most common cause of blindness.

CAUSES OF BLINDNESS:

• IN DEVELOPED COUNTRIES:

•

Accidents ,Glaucoma, Diabetes, Vascular

diseases(hypertension), Cataract and Degeneration of Ocular

tissues esp. of the Retina and Hereditary conditions.

• IN DEVELOPING COUNTRIES:

Cataract

Refractive Errors

Glaucoma

Post. Segment Disorder

Surgical Complication

CAUSES OF CHILDHOOD BLINDNESS:

Refractive errors, Trachoma, Conjunctivitis, Xerophthalmia,

Congenital Cataract , Retinopathy of Prematurity.

CAUSES OF AVOIDABLE BLINDNESS: Cataract, Trachoma, Onchocerciasis, Childhood Blindness,

Refractive errors, Glaucoma, Diabetic Retinopathy.

EPIDEMIOLOGICAL DETERMINANTS:

• Age: More than 82% belongs to the group of >50yrs.

• Gender: Higher in females.

• Malnutrition: Vitamin A deficiency ,infectious diseases of

new born

.

• Social Class: Higher in low socio-economic status.

• Geographical: >90% in developing countries.

REASONS FOR HIGH PREVALENCE IN PAKISTAN

• Overall rise in size of population.

• Major population in rural areas have poor access to eye

care facilities.

• Inadequate availability of trained health personnel &

inadequate utilization of available ophthalmic surgeons.

• Poor nutritional status of mother and young children

• Adverse environmental conditions and domestic

unhygienic conditions.

• Lack of community awareness & poor health seeking

behaviour.

• Myths & misconceptions about surgeries.

LOW VISION AIDS

• All low vision aids work by presenting the patient

with

• A magnified view of object. Most are optical

systems

• Which act by increasing the angle subtended by

the

• Object at the eye, thus producing an enlarged

retinal

• Image.

GOALS OF LOW VISION

Increase functionality o Make the most of the remaining vision

Provide link to community resources and support services

Education

FUNCTIONAL EFFECTS OF LOW VISION

• Loss of central vision (visual acuity)

• Loss of peripheral vision (visual field)

• Glare and contrast

Issues Related to Decreased Acuity

• Difficulty reading

• Problems writing/ completing paperwork

• Inability to recognize distance objects and faces

Issues Related to Visual Field Loss

• Location of scotoma important!

• Generalized loss of visual field difficult to compensate for

• Mobility and independent travel

• Reading may require adaptations

Issues Related to Contrast

• Need for additional lighting

• Problems with glare

• Increased adjustment to changes in illumination

• Visual discomfort and fatigue

LIGHTING

GLARE & CONTRAST

Devices To Help Low Vision

STAND MAGNIFIERS

• Video magnifiers are sometimes called “closed-circuit television (CCTV) systems” and generally use stand-mounted or hand-held video cameras to project a magnified image onto a video monitor, a television (TV) screen, or a computer monitor.

COMMUNICATION GOALS

• Educate patient on eye condition

• Help them to understand what options are available and how

to use/ care for tools

– Glasses

– Low vision devices

– Technology

– Community resources

• Educate parents and teachers/ professionals on functional

implications

FUNCTIONAL IMPLICATIONS

• Print size

• Visual efficiency and fatigue

• Mobility issues

• Positioning/ classroom placement

• Lighting/ glare reduction needs