Download Causes of visual impairment - Consortium of Universities for Global

Visual Impairment
Geoffrey C. Tabin, M.D.
John A. Moran Eye Center
University of Utah
Salt Lake City, UT
Kurt H. Kelley, M.D.
Fletcher Allen Health Care
University of Vermont
Burlington, VT
Prepared as part of an education project of the Global Health
Education Consortium and collaborating partners
Learning objectives
1.
2.
3.
4.
5.
To briefly review normal eye anatomy
To be able to define and appreciate the magnitude of
visual impairment
To understand why visual impairment is an important
global health issue
To be able to describe the major causes of visual
impairment worldwide, including background,
epidemiology, and management
To present some of the public health efforts to improve eye
health worldwide
Page 2
Normal eye anatomy
• Before we begin a
discussion of visual
impairment and its causes,
let’s take a moment to
review the normal structures
of the eye (seen here in
cross-section).
Cross-sectional diagram of the human eye. (Image:
National Eye Institute, National Institutes of Health)
Page 3
Normal eye anatomy
• Cornea: the transparent front “window” of the eye, the
cornea serves as an important refractive surface.
• Iris: the colored part of the eye which helps to screen out
and focus incoming light.
• Pupil: the circular opening in the center of the iris.
• Lens: a transparent, biconvex structure behind the pupil and
iris that aids in focusing of images.
• Retina: the neural tissue which lines the back of the eye, it
converts light energy to impulses that travel to the brain via
the optic nerve.
• Macula/Fovea: the area of the retina responsible for fine,
central vision.
Page 4
What is visual impairment?
• Includes both low vision and blindness, as clinically
defined by the World Health Organization (WHO):
– Low vision is the inability, even with corrective
lenses, to clearly see at a distance of 6 meters (20
feet) what individuals with normal vision can clearly
see at a distance of 18 meters (60 feet).
– Blindness is the inability to read the largest letter on
a vision chart at a distance of 3 meters (10 feet).
WHO. International statistical classification of diseases, injuries and causes of death: tenth
revision. Geneva: WHO, 1992.
Page 5
The magnitude of visual impairment
• According to WHO, in 2002 more than 161 million people
were visually impaired. Of those individuals, an estimated
37 million were blind.
• Uncorrected refractive error (near-sightedness, farsightedness, and astigmatism) may account for an
additional 82 to 117 million cases of visual impairment.
• Over 90% of all blind people live in developing countries.
–- Resnikoff S et al. Global data on visual impairment in the year 2002. Bull World Health Organ 2004;
82:844-851.
–- Dandona L, Dandona R. What is the global burden of visual impairment? BMC Med 2006; 4:6.
Page 6
Why is this an important global health issue?
• Blindness and low vision are important global health issues because they
confer increased morbidity and mortality, decreased quality of life, and
substantial economic productivity loss.
• Without additional intervention, the total number of blind people worldwide
has been predicted to increase to 76 million by 2020.
• Remarkably, at least 75% of world blindness is believed to be entirely
treatable or preventable. Let’s discuss the leading causes.
–- Frick KD, Foster A. The Magnitude and Cost of Global Blindness: An Increasing Problem That Can Be
Eliminated. Am J Ophthalmol 2003; 135:471-476.
–- Lee DJ et al. Visual Impairment and Morbidity in Community-Residing Adults: The National Health Interview
Survey 1986-1996. Ophthalm Epidemiol 2005; 12:13-17.
–- McCarty CA et al. Visual impairment predicts 5 year mortality. Br J Ophthalmol 2001; 85:322-326.
–- Lee DJ et al. Visual Acuity Impairment and Mortality in US Adults. Arch Ophthalmol 2002; 120:1544-1550.
–- Wang JJ et al. Visual Impairment, Age-Related Cataract, and Mortality. Arch Ophthalmol 2001; 119:11861190.
–- Knudtson MD et al. Age-Related Eye Disease, Visual Impairment, and Survival: The Beaver Dam Eye
Study. Arch Ophthalmol 2006; 124:243-249.
–- Vu HTV et al. Impact of unilateral and bilateral vision loss on quality of life. Br J Ophthalmol 2005; 89:360363.
Page 7
Causes of visual impairment
Trachoma, 3.6%
Onchocerciasis, 0.8%
Childhood Blindness,
3.9%
Diabetic Retinopathy,
4.8%
Corneal Opacity, 5.1%
Age-Related Macular
Degeneration, 8.7%
Cataract, 47.8%
Glaucoma, 12.3%
Others, 13%
Major causes of blindness as a proportion of total blindness. (Data: Resnikoff S et al. Global
data on visual impairment in the year 2002. Bull World Health Organ 2004; 82(11):844-851.)
Page 8
Causes of visual impairment:
Cataract
• Background
– An opacity in the lens of
the eye
– Most often age-related,
but can also be genetic,
congenital, or the result
of disease, trauma or
medication use
A mature age-related cataract. (Image: National Eye Institute,
National Institutes of Health)
Page 9
Causes of visual impairment:
Cataract
• Epidemiology
– The most common cause of world blindness, accounting
for almost 50% of cases (18 million people)
– Risk factors: cigarette smoking, UV-B light exposure,
diabetes mellitus, and corticosteroid use; possibly
dehydration (e.g. from severe diarrhea), malnutrition,
and heavy alcohol use
Page 10
Causes of visual impairment: Cataract
• Management
– Surgical removal of the lens, typically
followed by implantation of a synthetic
intraocular lens, is curative and costeffective
– Small-incision cataract surgery (SICS) is a
fast and inexpensive method used in
some developing countries that has been
shown to have excellent visual outcomes
An intraocular lens. (Image: FDA)
–- Baltussen R et al. Cost-effectiveness analysis of cataract surgery: a global and regional analysis. Bull
World Health Organ 2004; 82:338-345
–- Ruit S et al. A Prospective Randomized Clinical Trial of Phacoemulsification vs Manual Sutureless SmallIncision Extracapsular Cataract Surgery in Nepal. Am J Ophthalmol 2007; 143:32-38
Page 11
Causes of visual impairment:
Glaucoma
• Background
– A group of diseases
characterized by optic nerve
cupping and irreversible
vision loss, usually associated
with elevated intraocular
pressure (IOP)
– Two most common forms are
primary open-angle glaucoma
(POAG) and angle-closure
glaucoma (ACG)
Optic nerve cupping consistent with glaucoma. (Image:
National Eye Institute, National Institutes of Health)
Page 12
Causes of visual impairment:
Glaucoma
• Epidemiology
– The 2nd most common cause of world blindness,
accounting for 12.3% of cases (4.4 million people)
– Risk factors: increasing age, African ethnicity (POAG),
Asian ethnicity (ACG), increasing IOP, and genetic
predisposition; possibly diabetes mellitus
Page 13
Causes of visual impairment:
Glaucoma
• Management
– Goal is to maintain normal IOP through the use of a
variety of pharmacologic therapies
– Refractory cases may be treated with laser therapy or
surgically
– Regular eye examinations assessing IOP, visual fields,
and changes in the appearance of the optic nerve are
essential
Page 14
Causes of visual impairment:
Age-related macular degeneration
• Background
– A chronic, degenerative condition common in older
individuals that affects the part of the eye responsible for
central vision
– Classified into two types, dry and wet:
• Dry form accounts for 80% of all AMD
• Wet form involves proliferation of blood vessels
(neovascularization) and accounts for the nearly 80%
of blindness caused by AMD
Page 15
Causes of visual impairment:
Age-related macular degeneration
A
B
A. Dry age-related macular degeneration. The multiple small, yellow deposits in the macula are
called drusen. B. Wet age-related macular degeneration demonstrating neovascular changes
and hemorrhage. (Images: National Eye Institute, National Institutes of Health)
Page 16
Causes of visual impairment:
Age-related macular degeneration
• Epidemiology
– The third leading cause of blindness worldwide,
accounting for 8.7% of cases (3.2 million people), and the
primary cause of blindness in developed countries,
particularly in elderly individuals
– Risk factors: increasing age, cigarette smoking, family
history, low dietary intake of antioxidants and zinc, white
ethnicity, and hypertension; possibly female gender,
cardiovascular disease, and cataract surgery
Page 17
Causes of visual impairment:
Age-related macular degeneration
• Management
– Studies have shown a possible benefit from antioxidants such as
vitamins C and E, beta-carotene, and zinc
– Laser therapy, intravitreally injected medications, and photodynamic
therapy are options for treatment of the wet form
–- Klein R et al. The Epidemiology of Age-Related Macular Degeneration. Am J Ophthalmol 2004; 137:486495.
–Fine SL et al. Age-Related Macular Degeneration. New Engl J Med 2000; 342:483-492.
–- Age-Related Eye Disease Study Research Group. A Randomized, Placebo-Controlled, Clinical Trial of
High-Dose Supplementation With Vitamins C and E, Beta Carotene, and Zinc for Age-Related Macular
Degeneration and Vision Loss: AREDS Report No. 8. Arch Ophthalmol 2001;119:1417-1436.
Page 18
Causes of visual impairment: Corneal
opacity
• Background
– Caused by corneal disease or
trauma with subsequent
scarring and possibly monocular
or bilateral blindness
– Specific causes include trauma,
corneal infection, vitamin A
deficiency, measles, trachoma,
onchocerciasis, leprosy, and
harmful traditional practices
A child with corneal scarring at an outreach clinic
in Nepal. Photo courtesy of The Tilganga Eye
Centre.
Page 19
Causes of visual impairment: Corneal
opacity
• Epidemiology
– The 4th most common cause of blindness worldwide,
accounting for 5.1% of cases in 2002
– Prevalence varies significantly by region and age,
with some studies showing corneal opacity as the
most common cause of blindness in certain
populations
Page 20
Causes of visual impairment: Corneal opacity
• Management
– Corneal transplantation is the treatment of choice for blinding
corneal opacity but is not cost-effective in most developing countries
due to limited resources (corneal surgeons, eye banks) and
availability of long-term care
– Many causes of corneal opacity in developing countries are
preventable or treatable, thus emphasizing the importance of
establishing effective public health programs
•
•
•
- Whitcher JP et al. Corneal blindness: a global perspective. Bull World Health Organ 2001; 79:214-221.
- Garg P et al. The value of corneal transplantation in reducing blindness. Eye 2005; 19:1106-1114.
- Bowman RJC et al. Non-trachomatous corneal opacities in the Gambia—aetiology and visual burden. Eye 2002;
16:27-32.
Page 21
Causes of visual impairment:
Diabetic retinopathy
• Background
– A common complication of diabetes mellitus, there are two
main types, nonproliferative and proliferative,
distinguished by retinal examination:
• Nonproliferative findings include hemorrhage,
microaneurysms, cotton-wool spots, and macular edema
with visual impairment
• Proliferative findings include formation of new blood
vessels (neovascularization) and scarring which may
cause retinal detachment and profound visual loss
Page 22
Causes of visual impairment:
Diabetic retinopathy
Proliferative diabetic retinopathy demonstrating marked
neovascularization. (Image: National Eye Institute, National
Institutes of Health)
Page 23
Causes of visual impairment:
Diabetic retinopathy
• Epidemiology
– In 2002 accounted for almost 5% of blindness worldwide
– Particularly prevalent among working age people in
developed countries
– Duration of diabetes mellitus, particularly after puberty, is
the most important predictor of diabetic retinopathy
Page 24
Causes of visual impairment:
Diabetic retinopathy
• Management
– Annual eye examinations are recommended to assess for
progression of disease
– Strict blood glucose control slows the progression of
retinopathy
– Laser therapy may be helpful for selected patients with
neovascularization
– A surgical procedure called vitrectomy may be helpful in
patients with severe complications of the disease
–- Diabetes Control and Complications Trial Research Group. The effect of intensive diabetes treatment on the progression of
diabetic retinopathy in insulin-dependent diabetes mellitus. N Engl J Med 1993; 329:977-986.
–- United Kingdom Prospective Diabetes Study Group. Intensive blood-glucose control with sulfonylureas or insulin compared
with conventional treatment and risk of complications in patients with type 2 diabetes (UKPDS 33). Lancet 1998; 352:837-853.
Page 25
Causes of visual impairment:
Vitamin A deficiency
• Background
– Vitamin A is necessary for retinal function and ocular
epithelial cell development
– Vitamin A deficiency (VAD) can cause xerophthalmia, or
dry eye, with a spectrum of severity ranging from night
blindness to corneal ulceration and irreversible scarring
– VAD also increases the risk and severity of infections
such as measles
Page 26
Causes of visual impairment:
Vitamin A deficiency
• Epidemiology
– Considered the leading cause of preventable blindness in
children worldwide
– It is estimated that 127 million preschool-aged children
have VAD, with 4.4 million associated cases of
xerophthalmia
– Mortality estimates in preschool-aged children range from
1.3-2.5 million deaths annually
Page 27
Causes of visual impairment:
Vitamin A deficiency
• Management
– Vitamin A supplements are
inexpensive and may decrease
mortality in preschool-aged
children by as much as 55% in
some regions
– Public health initiatives also
promote vitamin A-rich diets,
breastfeeding, and food
fortification
A Rwandan refugee child receives a vitamin A drop. (Image: UNICEF)
–- Sommer A. Vitamin A deficiency and its consequences: a field guide to detection and control. Geneva: WHO, 1995.
–- Hussey GD, Klein M. A randomized, controlled trial of vitamin A in children with severe measles. N Engl J Med 1990; 323:160–4.
–- West KP Jr. Extent of vitamin A deficiency among preschool children and women of reproductive age. J Nutr 2002; 132:2857S-2866S.
–- Humphrey JH et al. Vitamin A deficiency and attributable mortality among under-5-year-olds. Bull World Health Organ 1992; 70:225-232.
Page 28
Causes of visual impairment:
Trachoma
• Background
– Caused by serotypes A-C of the
bacterium Chlamydia trachomatis
– Spread through contact with eye
discharge from infected individuals,
typically carried by flies
– Recurrent infection causes scarring of
the conjunctiva and eyelid deformities,
which in turn can lead to corneal
ulceration, scarring, and blindness
Progression of scarring caused by
recurrent C. trachomatis infection.
(Images: WHO)
Page 29
Causes of visual impairment:
Trachoma
• Epidemiology
– The most common
infectious cause of
blindness worldwide
– Most prevalent in
developing countries
where crowding, poor
hygiene, and limited
access to water are
prevalent
An Ethiopian girl covered in flies. The flies are attracted to eye
secretions and aid in the transmission of trachoma. (Image:
Elizabeth Gilbert, International Trachoma Initiative)
Page 30
Causes of visual impairment:
Trachoma
(Image: WHO, http://gamapserver.who.int/mapLibrary/Files/Maps/global%20active%20may%202006.jpg)
Page 31
Causes of visual impairment:
Trachoma
• Management
– Active infection is effectively treated with antibiotics (oral
azithromycin or tetracyline eye ointment) but reinfection is common
– Long-term control requires a multi-faceted approach, as promoted by
the SAFE strategy:
• Surgery for eyelid deformities
• Antibiotics
• Facial cleanliness
• Environmental improvement
Bailey R, Lietman T. The SAFE strategy for the elimination of trachoma by 2020:
will it work? Bull World Health Organ 2001; 79:233-236.
Page 32
Causes of visual impairment:
Onchocerciasis
• Background
– A parasitic disease spread by a
blackfly which breeds near fastflowing rivers (hence the common
name “river blindness”)
– Larvae are transmitted to a human
host, where they mature to adult
worms and release larval worms
(microfilariae) that migrate to the eyes
and skin and cause local damage
An adult Simulium blackfly.
(Image: WHO/TDR/Stammers)
Adult Onchocerca volvulus worms.
(Image: WHO/TDR/OCP)
Page 33
Causes of visual impairment:
Onchocerciasis
• Epidemiology
– WHO estimates that almost 18
million people are infected, with
500,000 cases of visual impairment
and 270,000 cases of blindness
– Over 90% of onchocerciasis is
located in 30 African countries, with
the remainder in Yemen and Latin
America
A young child leads a blind man with the aid of
a stick, a common sight in some West African
villages. (Image: WHO/TDR/OCP/Ward)
Page 34
Causes of visual impairment:
Onchocerciasis
• Management
– Effectively treated with the anti-parasitic agent
ivermectin, typically given every 6 to 12 months in
endemic regions
– Additional efforts include vector control through
insecticidal spraying, avoidance of blackfly-infested
areas, and the use of insect repellant and protective
clothing
WHO. Onchocerciasis and its control. Report of a WHO Expert Committee on
Onchocerciasis Control. WHO Technical Report Series 852, Geneva: WHO, 1995.
Page 35
Causes of visual impairment:
Refractive error
• Background
– Occurs when an image is not focused clearly on the
retina due to some problem with one of the optical
components of the eye
– Includes myopia (near-sightedness), hyperopia (farsightedness), presbyopia (age-related loss of near
focusing), and astigmatism
– Also includes inadequate correction of refractive error in
aphakic patients (i.e. those who have undergone lens
removal for cataract without implantation of a synthetic
intraocular lens)
Page 36
Causes of visual impairment:
Refractive error
• Epidemiology
– May account for an additional 87-102
million cases of visual impairment
worldwide
– A significant problem in both
developing and developed countries
– Natural refractive error typically starts
at a young age, thus causing greater
socioeconomic burden compared to
age-related eye disease
A child undergoes testing for refractive
error. (Image: WHO)
Page 37
Causes of visual impairment: Refractive error
• Management
– Most cases can be easily treated through the use of corrective
lenses (spectacles, contact lenses) or refractive surgery such as
LASIK, LASEK, or PRK
– Availability of these resources is problematic in developing
countries
– Community vision screening programs are essential for identifying
undiagnosed refractive error and are particularly important in
preschool-aged children to prevent the development of amblyopia
–- Dandona R, Dandona L. Refractive error blindness. Bull World Health Organ 2001; 79:237-243.
–- WHO. Refractive errors and visual impairment. 2006. (Accessed April 14, 2007, at
http://www.who.int/blindness/causes/priority/en/index5.html).
Page 38
Global public health efforts
• In the last section of this module,
we’ll discuss some of the public
health efforts that are being made
to address the global burden of
visual impairment.
Patients at a high-volume microsurgical eye camp in Nepal are evaluated for
postoperative complications following cataract surgery. (Image: Kurt Kelley)
–- WHO. State of the world’s sight: VISION 2020: the Right to Sight: 1999-2005. Geneva: WHO, 2005.
–- Foster A, Resnikoff S. The impact of Vision 2020 on global blindness. Eye 2005; 19:1133-1135.
–- Yorston D, Abiose A. Cataract blindness-the African perspective. Bull World Health Organ 2001; 79:257-258.
–- UNICEF. Vitamin A Deficiency: Progress to Date. 2006. (Accessed April 29, 2007, at http://childinfo.org/areas/vitamina/progress.php).
Page 39
Global public health efforts:
VISION 2020
• Global initiative launched jointly in 1999 by WHO and the
International Agency for the Prevention of Blindness (IAPB)
• Includes numerous government agencies, nongovernmental organizations (NGOs), professional
associations, eye care institutions, and corporations
http://www.v2020.org/
Page 40
Global public health efforts:
VISION 2020
•
•
The goal of VISION 2020 is to eliminate the main causes of
avoidable blindness by the year 2020:
– Cataract
– Trachoma
– Onchocerciasis
– Childhood blindness
– Low vision
In concert with this goal are efforts to increase awareness
of the causes of avoidable blindness and to improve eye
care resources worldwide through human resource and
infrastructure development
Page 41
Global public health efforts:
VISION 2020
• Data from the first 5 years of VISION 2020 have been
encouraging, with an overall reduction in blindness from
ocular infections
• Cataract surgical rates have improved in some countries
but remain low in others, particularly China and much of
Africa
• Morocco, The Gambia, and India are examples of
countries that have instituted successful eye care
programs
Page 42
Global public health efforts:
GET2020
• The WHO Alliance for the Global Elimination of Trachoma by
2020 (GET2020) was established in 1997 to organize efforts
by governments, NGOs, and academic centers toward the
elimination of trachoma
• From 1998 to 2004 the number of cases of active trachoma
infection is estimated to have decreased from 146 million to
84 million
• However, as of 2004 only 19 of 55 endemic countries
reported implementing the SAFE strategy
Page 43
Global public health efforts:
The Vitamin A Global Initiative
• A cooperative network of international organizations created
in 1998 whose partners include UNICEF, the Micronutrient
Initiative, the Canadian International Development Agency
(CIDA), WHO, and USAID
• Three-fold increase from 1999-2004 in the number of
priority countries providing effective coverage (two rounds of
supplementation in at least 70% of children)
• The prevalence of childhood VAD appears to be decreasing,
however maternal VAD and night blindness is becoming
increasingly recognized as a major public health issue
Page 44
Future challenges
• The prevalence of blindness due to age-related eye disease
is expected to continue increasing as the world population
increases in size and age
• Similarly, diabetic retinopathy will require increasingly more
attention and resources as long as the incidence of diabetes
mellitus continues to rise
• Human resource and infrastructure development will remain
a top priority, particularly in developing countries
• The prevalence of refractive error needs to be more
accurately assessed and availability of corrective lenses and
low vision services improved
Page 45
Quiz
• Now we invite you to take the module quiz and test your
recent learning.
• This module quiz includes 12 questions about visual
impairment and its causes.
• After completing the quiz, come back for the summary
of this module presentation.
Page 46
1.
A
B
C
What is visual impairment (as defined by the World Health Organization)?
The inability to read the largest letter on a vision chart at a distance of 3 meters (10 feet).
The inability, even with corrective lenses, to clearly see at a distance of 6 meters (20 feet)
what individuals with normal vision can clearly see at a distance of 18 meters (60 feet).
A broad category encompassing low vision and blindness, entities clinically defined by WHO.
According to WHO, in 2002, how many people were visually impaired?
A
B
C
D
E
9 million
37 million
55 million
84 million
161 million
Page 47
3. Fill in the blanks: ______ is the most common cause of blindness worldwide, accounting for almost ___
of cases.
A
B
C
D
E
Age-related macular degeneration, 8.7%
Cataract, 50%
Corneal opacity, 5.1%
Glaucoma, 12.3%
Trachoma, 3.6%
4. Glaucoma is:
A
B
C
D
the most common ocular complication of diabetes mellitus.
caused by serotypes A-C of the bacterium Chlamydia trachomatis.
a group of diseases characterized by optic nerve cupping and irreversible vision loss, and is
usually (but not always) associated with elevated intraocular pressure.
an opacity in the lens of the eye.
Page 48
5. _____ is the third leading cause of blindness worldwide and the primary cause of blindness in developed
countries, particularly in elderly individuals.
A
B
C
D
Vitamin A deficiency
Onchocerciasis
Diabetic retinopathy
Age-related macular degeneration
6. True or false: Strict blood glucose control has no effect on the progression of diabetic retinopathy.
A
B
True
False
Page 49
7. Which of the following is not a cause of corneal opacity?
A
B
C
D
E
F
G
Trauma
Corneal infection
Vitamin A deficiency
Measles
Trachoma.
Harmful traditional practices
These are all possible causes of corneal opacity.
8. What is the leading cause of preventable childhood blindness worldwide?
A
B
C
D
Trachoma
Vitamin A deficiency
Refractive error
Cataract
Page 50
9. Promotion of the SAFE strategy has been successful in several countries in the treatment of this disease:
A
B
C
D
E
Onchocerciasis
Leprosy
Vitamin A deficiency
Trachoma
Measles
10. What is the vector by which onchocerciasis is spread to humans?
A
B
C
D
E
The Simulium blackfly
The Anopheles mosquito
The tsetse fly (Glossina Genus)
The phlebotomine sandfly
The deer tick (Ixodes scapularis)
Page 51
11. True or false: Refractive error (near-sightedness, far-sightedness, presbyopia, or astigmatism) occurs
when an image is not focused clearly on the retina due to some problem with one of the optical components
of the eye.
A
B
True
False
12. VISION 2020: The Right to Sight is a global joint initiative that was launched in 1999 by WHO and the
International Agency for the Prevention of Blindness (IAPB) to eliminate these avoidable causes of
blindness by 2020:
A
B
C
D
Cataract, glaucoma, age-related macular degeneration, diabetic retinopathy, and corneal opacity
Glaucoma, diabetic retinopathy, onchocerciasis, childhood blindness, and refractive error
Age-related macular degeneration, trachoma, onchocerciasis, childhood blindness, and low vision
Cataract, trachoma, onchocerciasis, childhood blindness, and low vision
Page 52
Now, check your answers against those
provided in the next slides. A summary and
references are in the final slides.
Page 53
1.
What is visual impairment (as defined by the World Health Organization)?
A
The inability to read the largest letter on a vision chart at a distance of 3 meters (10 feet).
Incorrect. (This is the WHO definition of blindness. By definition, visual impairment includes
both low vision and blindness.)
B
The inability, even with corrective lenses, to clearly see at a distance of 6 meters (20 feet)
what individuals with normal vision can clearly see at a distance of 18 meters (60 feet). -- Incorrect. (This
is the WHO definition of low vision. By definition, visual impairment includes both low vision and
blindness.)
C
A broad category encompassing low vision and blindness, entities clinically defined by WHO.
Correct. – (Visual impairment includes both low vision and blindness, as clinically defined by
WHO. Low vision is the inability, even with corrective lenses, to clearly see at a distance of 6 meters (20
feet) what individuals with normal vision can clearly see at a distance of 18 meters (60 feet). Blindness is
the inability to read the largest letter on a vision chart at a distance of 3 meters (10 feet).
Page 54
According to WHO, in 2002, how many people were visually impaired?
A
9 million Incorrect.
B
37 million Incorrect.
C
55 million Incorrect.
D
84 million Incorrect.
E
161 million Correct. -- According to WHO, in 2002 more than 161 million people were visually
impaired. Of those individuals, an estimated 37 million were blind. Including the estimated 82-107 million
people with uncorrected refractive error, the total number of people with visual impairment increases to
approximately 250 million.
Page 55
3. Fill in the blanks: ______ is the most common cause of blindness worldwide, accounting for almost ___
of cases.
A
Age-related macular degeneration, 8.7% -- Incorrect. -- AMD is the third leading cause of
blindness worldwide, accounting for 8.7% of cases (3.2 million people), and the primary cause of blindness
in developed countries, particularly in elderly patients.
B
Cataract, 50% -- Correct. Cataract is the most common cause of world blindness, accounting
for almost 50% of cases (18 million people).
C
Corneal opacity, 5.1% Incorrect. -- Corneal opacity is the 4th most common cause of blindness
worldwide, accounting for 5.1% of cases in 2002. Its prevalence varies significantly by region and age, with
some studies showing corneal opacity as the most common cause of blindness in certain populations.
D
Glaucoma, 12.3% -- Incorrect. -- Glaucoma is the 2nd most common cause of world blindness,
accounting for 12.3% of cases (4.4 million people)
E
Trachoma, 3.6% -- Incorrect. -- Notably, trachoma is the most common infectious cause of
blindness worldwide.
Page 56
4. Glaucoma is:
A
the most common ocular complication of diabetes mellitus. -- Incorrect. -- Diabetic retinopathy is the
most common ocular complication of diabetes mellitus.
B
caused by serotypes A-C of the bacterium Chlamydia trachomatis. -- Incorrect. -- Trachoma is
caused by serotypes A-C of the bacterium Chlamydia trachomatis. It is the most common infectious cause of
blindness worldwide.
C
a group of diseases characterized by optic nerve cupping and irreversible vision loss, and is usually
(but not always) associated with elevated intraocular pressure. -- Correct. -- The two most common forms of
glaucoma are primary open-angle glaucoma (POAG) and angle-closure glaucoma (ACG). Risk factors include
increasing age, African ethnicity (POAG), Asian ethnicity (ACG), increasing IOP, and genetic predisposition.
The goal of treatment is to maintain normal IOP through the use of a variety of pharmacologic or surgical
interventions. Regular eye examinations assessing IOP, visual fields, and changes in the appearance of the
optic nerve are essential.
D
an opacity in the lens of the eye. -- Incorrect. -- Cataract is an opacity in the lens of the eye. It is
most often age-related, but can also be genetic, congenital, or the result of disease, trauma or medication use.
Page 57
5. _____ is the third leading cause of blindness worldwide and the primary cause of blindness in developed
countries, particularly in elderly individuals.
A
Vitamin A deficiency -- Incorrect. -- VAD is considered the leading cause of preventable blindness
in children worldwide.
B
Onchocerciasis -- Incorrect. -- Onchocerciasis accounts for 0.8% of blindness worldwide. Over
90% of onchocerciasis is located in 30 African countries, with the remainder in Yemen and Latin America
C
Diabetic retinopathy -- Incorrect. -- Diabetic retinopathy accounts for almost 5% of blindness
worldwide and is particularly prevalent among working age people in developed countries .
D
Age-related macular degeneration Correct. -- AMD is a chronic, degenerative condition common
in older individuals that affects the part of the eye responsible for central vision. It is classified into two main
types, dry and wet. Studies have shown a possible benefit from antioxidants such as vitamins C and E, betacarotene, and zinc. Laser therapy, intravitreally injected medications, and photodynamic therapy are options
for treatment of the wet form
Page 58
6. True or false: Strict blood glucose control has no effect on the progression of diabetic retinopathy.
A
True -- Incorrect. -- The Diabetes Control and Complications Trial (DCCT) and United Kingdom
Prospective Diabetes Study (UKPDS) showed that intensive blood glucose control significantly reduced the
rate of progression of retinopathy in type I and type II diabetics, respectively.
B
False -- Correct. -- The Diabetes Control and Complications Trial (DCCT) and United Kingdom
Prospective Diabetes Study (UKPDS) showed that intensive blood glucose control significantly reduced the
rate of progression of retinopathy in type I and type II diabetics, respectively.
7. Which of the following is not a cause of corneal opacity?
A
Trauma
Incorrect.
B
Corneal infection -- Incorrect.
C
Vitamin A deficiency -- Incorrect.
D
Measles -- Incorrect.
E
Trachoma -- Incorrect.
F
Harmful traditional practices -- Incorrect.
G
These are all possible causes of corneal opacity. -- Correct. -- Trauma, corneal infection, vitamin
A deficiency, measles, trachoma, onchocerciasis, leprosy, and harmful traditional practices are all possible
causes of corneal opacity. Corneal transplantation is the treatment of choice for blinding corneal opacity but is
not cost-effective in developing countries due to limited resources (corneal surgeons, eye banks) and
availability of long-term care. Many causes of corneal opacity in developing countries are either preventable
or treatable, thus emphasizing the importance of establishing effective public health programs.
Page 59
8. What is the leading cause of preventable childhood blindness worldwide?
A
Trachoma Incorrect. -- Trachoma is the most common infectious cause of blindness worldwide
but is not the leading cause of preventable childhood blindness.
B
Vitamin A deficiency -- Correct. -- It is estimated that 127 million preschool-aged children have
VAD, with 4.4 million associated cases of xerophthalmia. Mortality estimates in preschool-aged children range
from 1.3 to 2.5 million deaths annually.
C
Refractive error -- Incorrect. -- Refractive error is an important cause of visual impairment
worldwide but is not considered the leading cause of preventable childhood blindness.
D
Cataract Incorrect. -- Cataract is the most common cause of blindness worldwide. Several
types of cataract may occur during infancy or childhood (such as congenital or traumatic cataract) but it is not
the leading cause of preventable childhood blindness.
9. Promotion of the SAFE strategy has been successful in several countries in the treatment of this disease:
A
Onchocerciasis
Incorrect.
B
Leprosy
Incorrect.
C
Vitamin A deficiency Incorrect.
D
Trachoma Correct. -- The SAFE strategy was developed to aid in the elimination of trachoma as
a blinding disease. Starting in 1997, promotion of the WHO-developed SAFE strategy has been successful in
several countries, such as Morocco and Oman. The components of the strategy are: Surgery for eyelid
deformities; Antibiotics; Facial cleanliness; Environmental improvement
E
Measles Incorrect.
Page 60
10. What is the vector by which onchocerciasis is spread to humans?
A
The Simulium blackfly -- Correct. -- Onchocerciasis is spread by the Simulium blackfly which
breeds near fast-flowing rivers (hence the common name “river blindness”). Larvae are transmitted to the
human host, where they mature to adult worms and release larval worms (microfilariae) that migrate to the
eyes and skin and cause local damage. The infection can be effectively treated with the anti-parasitic agent
ivermectin, typically given every 6 to 12 months in endemic regions
B
The Anopheles mosquito -- Incorrect. -- The Anopheles mosquito is the vector for malaria.
C
The tsetse fly (Glossina Genus) -- Incorrect. -- The tsetse fly is the vector for African
trypanosomiasis (“sleeping sickness”).
D
The phlebotomine sandfly -- Incorrect. -- The phlebotomine sandfly is the vector for
leishmaniasis.
E
The deer tick (Ixodes scapularis) -- Incorrect. -- The deer tick (Ixodes scapularis) is the vector for
Lyme disease.
Page 61
11. True or false: Refractive error (near-sightedness, far-sightedness, presbyopia, or astigmatism) occurs
when an image is not focused clearly on the retina due to some problem with one of the optical components
of the eye.
A
True -- Correct. -- Refractive error may account for an additional 87-102 million cases of visual
impairment worldwide and is a significant problem in both developing and developed countries.
Most cases of refractive error can be easily treated through the use of corrective lenses (spectacles, contact
lenses) or refractive surgery such as LASIK, LASEK, or PRK. However, availability of these resources is
problematic in developing countries. Community vision screening is particularly important in preschool-aged
children to prevent the development of amblyopia.
B
False -- Incorrect.
Page 62
12. VISION 2020: The Right to Sight is a global joint initiative that was launched in 1999 by WHO and the
International Agency for the Prevention of Blindness (IAPB) to eliminate these avoidable causes of blindness
by 2020:
A
Cataract, glaucoma, age-related macular degeneration, diabetic retinopathy, and corneal opacity
Incorrect.
B
Glaucoma, diabetic retinopathy, onchocerciasis, childhood blindness, and refractive error
Incorrect.
C
Age-related macular degeneration, trachoma, onchocerciasis, childhood blindness, and low vision
Incorrect.
D
Cataract, trachoma, onchocerciasis, childhood blindness, and low vision -- Correct. -- Additional
goals of the VISION 2020 initiative are to increase awareness of visual impairment and to improve eye care
infrastructure and human resources worldwide. Numerous government agencies, non-governmental
organizations (NGOs), professional associations, eye care institutions and personnel, and corporations are
involved in this effort.
Page 63
Summary
• Visual impairment, which includes low vision and blindness,
is a significant global health problem.
• The major causes of visual impairment are cataract,
glaucoma, diabetic retinopathy, age-related macular
degeneration, corneal opacity, vitamin A deficiency,
trachoma, onchocerciasis, and refractive error.
• At least 75% of the causes of visual impairment are thought
to be entirely treatable or preventable.
• A number of encouraging global public health initiatives and
organizations are working to address the causes of visual
impairment with some success, though much work remains
to be done.
Page 64
Credits
Geoffrey C. Tabin, M.D.
John A. Moran Eye Center
University of Utah
Salt Lake City, UT
[email protected]
Kurt H. Kelley, M.D.
Fletcher Allen Health Care
University of Vermont
Burlington, VT
[email protected]
2007
Page 65
General References
• Books
Yanoff M, Duker JS, editors. Ophthalmology, 2nd ed. St. Louis, MO: Mosby, 2004.
• Web links
1. WHO. Blindness: www.who.int/topics/blindness/en/
This is an excellent website that includes an enormous amount of information on the
epidemiology of visual impairment, priority eye diseases, and public health efforts,
as well as a variety of associated publications.
2. IAPB. VISION 2020: The Right to Sight: http://www.v2020.org/
This is the official website for VISION 2020 and includes background information on
the initiative as well as news, information on upcoming training and workshops,
general information about the major causes of avoidable blindness, and links to
member organizations.
3. NEI/NIH. Health Information: http://www.nei.nih.gov/health/
The “Health Information” section of the National Eye Institute website is a good
resource for more information on eye anatomy and a variety of eye diseases and
disorders.
Page 66
References
Visual impairment: definition, magnitude, and significance
1.
WHO. International statistical classification of diseases, injuries and causes of death: tenth revision. Geneva: WHO,
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Frick KD, Foster A. The Magnitude and Cost of Global Blindness: An Increasing Problem That Can Be Eliminated. Am
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16:27-32.
Diabetic retinopathy
12.
Yanoff M, Duker JS, editors. Ophthalmology, 2nd ed. St. Louis, MO: Mosby, 2004.
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References
Vitamin A deficiency
13.
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Humphrey JH et al. Vitamin A deficiency and attributable mortality among under-5-year-olds. Bull World Health Organ
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Onchocerciasis
18.
WHO. Onchocerciasis and its control. Report of a WHO Expert Committee on Onchocerciasis Control. WHO
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Global public health efforts and future challenges
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WHO. State of the world’s sight: VISION 2020: the Right to Sight: 1999-2005. Geneva: WHO, 2005.
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Page 68
Acknowledgements
The Global Health Education Consortium gratefully acknowledges the support
provided for developing these teaching modules from:
Margaret Kendrick Blodgett Foundation
The Josiah Macy Jr. Foundation
Arnold P. Gold Foundation
This work is licensed under a
Creative Commons Attribution-Noncommercial-No Derivative Works 3.0
United States License.