Thanks for asking such an interesting question.
While it's certainly possible to make counts of the number of people
in a given area with some sort of visual impairment, it's much more of
a challenge to compare one category of health problem (such as vision
problems) to another.
To address this issue, health researchers developed a measure called
Disability Adjusted Life Years, or DALYs for short.
The DALY for a disease takes into account both the reduction in
life-span caused by a disease as well as the loss of healthy years.
You can read a bit more about DALYs at the World Heath Organization
Disability adjusted life years (DALY)
DALYs for a disease are the sum of the years of life lost due to
premature mortality (YLL) in the population and the years lost due to
disability (YLD) for incident cases of the health condition. The DALY
is a health gap measure that extends the concept of potential years of
life lost due to premature death (PYLL) to include equivalent years of
'healthy' life lost in states of less than full health, broadly termed
disability. One DALY represents the loss of one year of equivalent
Definition: The Disability Adjusted Life Year or DALY is a health gap
measure that extends the concept of potential years of life lost due
to premature death (PYLL) to include equivalent years of ?healthy?
life lost by virtue of being in states of poor health or disability
(1). The DALY combines in one measure the time lived with disability
and the time lost due to premature mortality. One DALY can be thought
of as one lost year of ?healthy? life and the burden of disease as a
measurement of the gap between current health status and an ideal
situation where everyone lives into old age free of disease and
The purpose of the DALY is to allow broad comparisons of the overall
burden attributed to particular diseases. Because the measure has a
heavy component related to loss of life, the so-called killer diseases
tend to dominate the world health scorecards, as common sense tells us
Nevertheless, vision loss is a significant contributor to overall
health burdens in the world, according to the latest WHO statistics,
published in 2003:
The World Health Report 2003
Annex Table 3 Burden of disease in DALYs by cause, sex and mortality
stratum in WHO regions,a estimates for 2002
TOTAL DALYs in the world amounted to 1,491,416,000 (1.491 billion).
This is a measure of the total burden of diseases (and injuries) in the world.
Of these, the big ticket health problems are things like:
HIV/AIDS 86,072,000 5.8% of the total world health burden
Cancers 75,407,000 5.1%
Depressive (mental health) disorders 67,295,000 4.5%
Diarrhoeal diseases 61,095,000 4.1%
Tuberculosis 35,361,000 2.4%
Overall, sense organ disorders (mostly vision and hearing loss) are
very significant contributors:
Sense organ disorders 69,380,000 4.7%
a portion of which stems from hearing loss:
Hearing loss, adult onset 26,034,000 1.7%
with the remaining 3.0% attributed to vision impairment:
Glaucoma 3,866,000 0.3%
Cataracts 25,251,000 1.7%
Vision loss, age-related and other 14,191,000 1.0%
Thus, vision problems make a contribution to the overall burden of
DALYs of 3% of the total, on par with tuberculosis.
Interestingly, vision problems are well ahead of these other
contributors to total DALYs:
Poisoning 7,519,000 0.5
Falls 16,232,000 1.1
Fires 11,481,000 0.8
Drowning 10,893,000 0.7
Violence 21,427,000 1.4
Self-inflicted injury 20,836,000 1.4
War 6,505,000 0.4
Yep. War...as horrendous as it is...is not nearly as widespread as
violence in general, and neither war nor violence are as widespread as
disease. Thus, they are significant but not overwhelming contributors
to global disease burdens.
For a more straightforward counting of vision problems in the global
population, there is also this factsheet prepared by WHO:
Magnitude and causes of visual impairment
Globally, in 2002 more than 161 million people were visually impaired,
of whom 124 million people had low vision and 37 million were blind.
However, refractive error as a cause of visual impairment was not
included, which implies that the actual global magnitude of visual
impairment is greater.
Worldwide for each blind person, an average of 3.4 people have low
vision, with country and regional variation ranging from 2.4 to 5.5.
[By "refractive error", I presume they mean uncounted millions of
people whose vision could be corrected by glasses]
Importantly, the above fact sheet also estimates that most vision
problems other than age-related blindness are largely preventable:
"Cataract, glaucoma, corneal opacity, diabetic retinopathy,
onchocerciasis, childhood blindness, trachoma, and some other causes
of blindness can potentially all be prevented and/or treated. WHO
estimates that, globally, up to 75% of all blindness is avoidable.
However, the proportion of the specific causes of blindness varies
considerably from region to region, depending on local circumstance.
Only about half the cases of childhood blindness are avoidable..."
I trust this information fully answers your question.
However, please don't rate this answer until you have everything you
need. If you would like any additional information, just post a
Request for Clarification to let me know how I can assist you further,
and I'm at your service.
All the best,
search strategy -- Used bookmarked sites for WHO.