The burden of blindness and visual impairment according to age and gender: A case study of Emohua local government area, Nigeria

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© 2016 Port Harcourt Medical Journal | Published by Wolters Kluwer ‑ Medknow | May‑Aug 2016 | Vol 10 | Issue 2 | 73‑78 73
The burden of blindness and visual impairment according to
age and gender: A case study of Emohua local government
area, Nigeria
A. A. Onua, C. Tobin‑West1, I. Ojule1
Departments of Surgery and 1Prevenve and Social Medicine, University of Port Harcourt, Port Harcourt, Nigeria
Introduction
According to 2005 estimate, the number of people with visual
impairment (which includes both low vision and blindness)
is 314 million worldwide; 45 million people are blind while
269 people live with low vision.1 Ninety percent of the world’s
blind population live in developing countries, out of which
about 1.2 million people live in Nigeria.2,3 The Nigerian
national blindness and visual impairment survey in 2007
estimated that 1,092,028 Nigerians (0.78%) are blind.4 This
Background: Visual impairment and blindness pose different degrees of public health and social problem
among the different age groups and sex. The problems are worse in the developing countries due to
ignorance and lack of adequate eye care services. Public information systems, epidemiological data, and
funding for blindness programs are often lacking and have hampered comprehensive blindness control
programs in the rural communities, a fact that underscores the importance of this study.
Aim: To estimate the burden of blindness and visual impairment according to age and gender in Emohua
local government area (LGA), Nigeria.
Methods: A population‑based descriptive cross‑sectional study conducted between October 11, and
November 29, 2014, in Emohua LGA. Three hundred and fifty‑three inhabitants were recruited in the study
through a multistage sampling method. Demographic data, detailed ocular examinations were recorded
and analyzed using SPSS version 20.
Results: The study participants were 164 males and 189 females (male:female = 1:1.2). The prevalence
of bilateral blindness is 1.4% (95% confidence interval [CI]: 0.78–2.5%) and unilateral blindness
2.5% (95% CI: 1.2–3.4%). Those who had various degrees of visual impairment in both eyes constituted
6.2% (95% CI: 5.7–8.5%) and 9.1% had unilateral visual impairment (95% CI: 8.7–9.7%). Cataract was the
leading cause of bilateral blindness, accounting for 60% of cases, glaucoma (20%), and corneal opacity (20%).
Conclusion: Blindness and visual impairment are more common in the older age groups and female gender
in Emohua LGA. Government and nongovernmental organizations should step up comprehensive eye health
care programs to realize the goals of Vision 2020.
Keywords: Blindness, burden, Emohua local government area, visual impairment
Abstract
Address for correspondence:
Dr. A. A. Onua, Department of Surgery, University of Port Harcourt, Port Harcourt, Nigeria. E‑mail: onuadr@gmail.com
Received: 25.06.2016, Accepted: 26.06.2016
Original Article
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DOI:
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How to cite this article: Onua AA, Tobin-West C, Ojule I. The burden of
blindness and visual impairment according to age and gender: A case study of
Emohua local government area, Nigeria. Port Harcourt Med J 2016;10:73-8.
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Onua, et al.: Burden of blindness and visual impairment according to age and gender
74 Port Harcourt Medical Journal | May‑Aug 2016 | Vol 10 | Issue 2
places a huge public health and socioeconomic burden on the
populace, often leading to social dependence, lack of access to
education, loss of productivity, and income.
It has been estimated that 60% of blind people are women.5,6
In a population‑based study in India by Venkata
et al.
,7 it was
observed that more than half of the visually impaired (52.7%)
were women; 46.9% were aged 50–59 years, 33.8% were aged
60–69 years, and 19.3% were aged 70 years and above. In all,
71% were illiterate, and 84.6% were residing in rural areas. The
sex distribution of glaucomatous blindness revealed that more
females were affected than their male counterparts.8
The prevalence of blindness in India was associated with age,
sex, literacy, place of residence, and working status; people
aged 70 years and above had a five times higher risk of being
blind compared to those aged 50–59 years and females had a
marginally higher risk.7
In another population‑based, cross‑sectional study involving
3850 subjects aged 40 years and above from Chennai city in
India, the prevalence of blindness was 0.85% and was positively
associated with age and illiteracy.8 The prevalence of blindness
and visual impairment was found to be much higher in the
elderly and most of the people bilaterally blind were 45 years of
age and above.9 In Pakistan, a nationally representative sample
of 16,507 adults using multistage, stratified, cluster random
sampling survey revealed that prevalence varied throughout
the country, being highest in the rural areas than urban areas.
Increasing age and being female were significantly associated
with blindness.10
In Nigeria, Abdull
et
al
.4 observed that increasing age was
associated with increasing prevalence of all major blinding
conditions. Furthermore, in this study, females, illiterate
persons, and residents in the Northeast geopolitical zone
had significantly higher odds of cataract‑induced blindness
and severe visual impairment. In another study in Nigeria
involving 15,122 persons aged 40 years and above, Kyari
et
al
.2 observed that the prevalence of blindness and severe
visual impairment (visual acuity [VA] on presentation)
was 4.2% (95% confidence interval [CI]: 3.8–4.6%) and
1.5% (95% CI: 1.3–1.7%), respectively. Blindness was
associated with increasing age, being female, poor literacy, and
residence in the North. Participants residing in the Southwest
had the lowest prevalence while those in the Northeast had
the highest prevalence of blindness. It is estimated that
4.25 million adults aged ≥40 years have moderate to severe
visual impairment or blindness in Nigeria.2
Cataract, trachoma, uncorrected refractive error, onchocerciasis,
childhood blindness, glaucoma, and diabetic retinopathy are
the identified the leading causes of blindness worldwide.3 In
Nigeria, the major blinding diseases are cataract, glaucoma,
corneal diseases, trachoma, onchocerciasis, and ocular
trauma.2 This is similar to the situation in other developing
countries.6,11
In Southeastern Nigeria, Ezegwui
et
al.
12 observed the varying
causes of blindness in children depending on the anatomical
structure of the eye that was primarily involved. According to
the study, the major causes of visual impairment identified in the
children (aged 15 years or less) were lesions of the lens (30.4%),
corneal lesions (21.7%), whole globe lesions (mainly phthisis
bulbi) (17.4%), and glaucoma/buphthalmos (10.9%). For
all the students (more than 15 years), these lesions accounted
for 31.9%, 21.3%, 23.4%, and 8.5% of visual impairment,
respectively. For all the students, the most common single
diagnoses were cataract (23.5%) and corneal scarring (21.4%),
of which 86.7% were caused by measles. By etiological
classification, childhood factors (38.6%) constituted the
major cause of blindness: 37.0% in the children and 39.4%
in the young adults. In 74.5% of all the students, blindness
was considered avoidable.
The World Health Organization (WHO) Program for the
Prevention of Blindness (PBL) established in 1978 has
definite objectives of making essential eye care available to all
and to eliminate avoidable blindness.3 The target of WHO
Program for PBL is to reduce blindness rates to <0.5% in all
countries and <1% in individual countries.3 This is possible
if all major blinding eye diseases are detected early and treated
or even prevented from occurring. The aim of this study was
to estimate the burden of blindness and visual impairment
according to the age and gender in Emohua local government
area (LGA), Nigeria.
Materials and Methods
This was a population‑based, descriptive cross‑sectional study
conducted between October 11, and November 29, 2014, in
Emohua LGA of Rivers State, Nigeria. Ethical approval for the
study was obtained from the Research and Ethics Committee
of the University of Port Harcourt Teaching Hospital,
Port Harcourt.
Three hundred and fifty‑three residents of Emohua LGA
who verbally consented to ocular examinations were recruited
in the study through a multistage sampling method. Consent
was also obtained from family heads/chiefs on behalf of
children <18 years. The subjects were told that participation
was absolutely voluntary, that they could withdraw from the
screening exercise at any point in time without victimization
and that the survey will be free of charge.

Onua, et al.: Burden of blindness and visual impairment according to age and gender
Port Harcourt Medical Journal | May‑Aug 2016 | Vol 10 | Issue 2 75
The 14 wards in the LGA formed the sampling frame. Eight
wards (>50%) were randomly selected by a simple random
method. In the second stage of sampling, one village per ward
was also selected by the simple random method. In the third
stage, households were further selected by the simple random
method. Already numbered houses by health‑care workers
for immunization purposes were used for the selection of
households as well as for monitoring purposes. The final
stage of sampling involved the selection of individuals from
the selected households. Eligible persons from the households
were recruited and gathered at their various community halls
for medical examination between the hours of 8 am and 5 pm
each day for 8 weeks. When a selected house was locked, and
eligible subjects absent repeat visits were made the same day.
When contact could not be established after two visits; the
household was categorized as a nonresponding and the nearest
household was automatically recruited for the study. Where two
households were equidistant, the one to the right was selected.
Basic eye examinations (which included checking the eyelids for
trichiasis, globe for phthisis, cornea for opacity or pterygium,
and lens for obvious opacity). Special eye examination with pen
torch for cornea opacities, pupil for pupillary light reaction,
and lens for any visible opacities. The anterior chamber depth
was also assessed using pen torch. Fundoscopy was carried out
with direct ophthalmoscope in a chosen dark area. The state of
the lens, vitreous, retina, and optic nerve was assessed in details
with direct ophthalmoscope. Where small pupils prevented
good view of the fundus, dilatation with mydriacyl 0.5% was
employed after refraction and measurement of the intraocular
pressure (IOP).
Objective refractions were done in a darkened area with
streak retinoscope and then subjectively refined by the
optometrist. IOP measurement was done using Perkins
applanation tonometer (MK2‑model), after instilling local
anesthetic agent (1% of tetracaine), and fluorescein dye into
the conjunctival sac. IOPs were measured in both eyes three
consecutive times. The measurements were done with the
subjects in sitting position. The mean IOP value was adopted.
All the measurements were carried out by the lead investigator
to avoid interobservers’ errors.
Presbyopic corrections‑glasses (readers) were given to deserving
subjects while those requiring further management and surgery
were referred to University of Port Harcourt Teaching Hospital.
Minor ocular ailments such as conjunctivitis were treated on
the spot. Subjects with prolonged dilated pupils were treated
with topical pilocarpine and reassured before going home. The
WHO/PBL Eye Examination Record was used to record the
data of subjects. All data were analyzed using SPSS version 20
(IBM Corporation USA, Chicago, Illinois, USA). Results
were presented in tables and charts. Chi‑square tests were
performed between categorical variables to determine their level
of statistical significance. A p‑value of 0.05 or less is accepted
as statistically significant.
Working definitions
• Blindness: VA <3/60 on presentation or corresponding
visual field <10° in the better eye on presentation
• Visual impairment: Is defined as VA on presentation
of <6/18 in the better eye but better than 3/60
• Glaucoma: Optic neuropathy associated with cupping
of the optic disc (cup/disc ratio >0.5) and/or raised
IOP (>21 mmHg) using Perkins applanation tonometer.
Results
The age group 45–54 years had the highest population of
those examined (30.3%) while those of 15–24 years (2.0%)
constituted the least. Participants of 45 years and above (238)
constituted more than half of the survey population [Table 1].
Out of 353 participants examined, males were 164 (46.5%)
while females constituted 53.5% (189). This gives a male to
female ratio of 1: 1.2.
A total of 27 persons were either bilaterally blind or bilaterally
visually impaired while 41 were either unilaterally blind or
unilaterally visually impaired as shown in Table 2. This gives
a total of 68 persons with various categories of the ocular
problem (blindness and visual impairment). Prevalence of
bilateral blindness in the survey was 1.4%, unilateral blindness
was 2.5%, bilateral visual impairment was 6.2%, and unilateral
visual impairment was 9.1%.
Cataract was the leading cause of bilateral blindness, accounting
for 3 (60%) cases. Other causes were glaucoma 1 (20%) and
corneal opacity 1 (20%) as shown in Figure 1.
Cataract was also the leading cause of unilateral blindness
4 (44.5%), followed by glaucoma 3 (33.3%), corneal opacity
1 (11.1), and pterygium 1 (11.1%) [Figure 2].
The leading cause of bilateral visual impairment was
refractive error 12 (54.6%), followed by cataract 5 (22.7%),
Table 1: Age and gender distribution of the sample population
Age group (years) Male (%) Female (%) Total (%)
15-24 6 (1.7) 1 (0.3) 7 (2.0)
25-34 9 (2.5) 13 (3.7) 22 (6.2)
35-44 32 (9.1) 54 (15.3) 86 (24.3)
45-54 55 (15.6) 53 (15.0) 108 (30.6)
55-64 27 (7.7) 27 (7.7) 54 (15.3)
65-74 29 (8.2) 33 (9.3) 62 (17.6)
75 and above 6 (1.7) 8 (2.2) 14 (4.0)
Total 164 (46.5) 189 (53.5) 353 (100)

Onua, et al.: Burden of blindness and visual impairment according to age and gender
76 Port Harcourt Medical Journal | May‑Aug 2016 | Vol 10 | Issue 2
glaucoma 3 (13.6%) and age‑related macular degeneration
2 (9.1%) [Figure 3].
Cataract was the leading cause of unilateral visual impairment
accounting for 12 (37.5%), others were glaucoma 6 (18.7%),
refractive error 4 (12.5%), corneal opacity 4 (12.5%),
optic atrophy 3 (9.4%), and pterygium 3 (9.4%) [Figure 4].
The prevalence of blindness and visual impairment was higher
in the older age groups. All the five persons who were blind
in both eyes were 55 years of age and above [Table 3]. This
difference was statistically significant (
P
= 0.03). Eighteen
persons (81.8%) out of 22 persons that were visually impaired
in both eyes were 55 years old and above. This difference was
also statistically significant (
P
= 0.01). Among the population
found with unilateral visual impairment, the differences in the
prevalence was statistically significant (
P
= 0.02). However, the
differences in the prevalence of unilateral blindness among the
various age groups were not statistically significant (
P
= 0.06)
[Table 3].
The highest prevalence of bilateral blindness (14.3%)
was observed among those who were 75 years and above,
followed by those in the 65–74‑year age group (3.2%)
while those of 55–64 years’ age group constituted 1.9% as
shown in Table 3.
The female gender was more affected by visual impairment
and blindness more than their male counterparts. Out of
the five bilaterally blind persons, 2 (40%) were males, and
3 (60%) were females as shown in Table 4. However, this was
not statistically significant (
P
= 1.00). The male/female ratio
of bilateral blindness was 1:1.5. Out of the 22 persons that
were with bilateral visual impairment, 9 (40.9) were males, and
13 (59.1) were females giving a male/female ratio of 1:1.4.
This difference was also not statistically significant (
P
= 1.00).
The male/female ratio for unilateral blindness was 1: 1.3
and for unilateral visual impairment was 1: 1.5 [Table 4].
Bilateral and unilateral blindness, as well as bilateral and
unilateral visual impairment, were more common among the
female folk although these differences were not statistically
significant (
P
= 0.097) [Table 4].
Discussion
The prevalence of bilateral blindness in Emohua LGA, Niger
Delta, Nigeria was found to be 1.4% from this study. The
Table 2: Blindness and visual impairment in study population
Categories of visual impairment Number of persons
(bilateral)
Prevalence (%)
(bilateral)
Number of persons
(unilateral)
Prevalence (%)
(unilateral)
Blindness (VA<3/60 – NLP) 5 1. 4 9 2.5
Visual impairment category I (VA<6/18≥6/60) 16 4.5 18 5.1
Visual impairment category II (VA<6/60≥3/60) 6 1. 7 14 4.0
Total 27 7.6 41 11.6
VA: Visual acuity, NLP: No light perception
Figure 1: Causes of bilateral blindness (%) Figure 2: Causes of unilateral blindness in percentage
Figure 3: Causes of bilateral visual impairment (%) Figure 4: Causes of unilateral visual impairment (%)

Onua, et al.: Burden of blindness and visual impairment according to age and gender
Port Harcourt Medical Journal | May‑Aug 2016 | Vol 10 | Issue 2 77
prevalence of blindness in Emohua LGA is higher than the
national average of 0.78%.2 Other community‑based studies
done in Nigeria showed prevalence ranging between 0.78%
and 6.6%.2,12 Different independent population studies done
in Rivers State showed the prevalence of blindness between
1.26% and 2.8%.13‑15 In Ahoada East LGA, Pedro‑Egbe
et
al
.13
estimated a prevalence of blindness of 2.8%. Ejimadu and
Pedro‑Egbe,14 found that the prevalence of blindness in Ikwerre
LGA was 1.26%. Although Emohua, Ahoada East, and Ikwerre
LGAs share common sociocultural, health‑care system, level
of development and geopolitical similarities, the differences
in the prevalence of blindness in these areas could probably be
attributed to the differences in sample sizes. One thousand five
hundred and thirteen subjects participated in the prevalence of
blindness study in Ikwerre LGA, 866 people were recruited in
the Ahoada East study while 353 subjects participated in this
study. In Oyorokotor village in Andoni LGA of Rivers State,
the prevalence of blindness was 2.5%.15 The studies with larger
sample population had relatively lower prevalence of blindness
compared to those with smaller sample population. However,
further investigations need to be conducted to explain these
differences.
The Nigeria national blindness and visual impairment
survey (2007) had noted that the prevalence of blindness
increases significantly with increasing age, from 0.8% at 40–
49 years to 23.3% among those aged ≥80 years.2 This study
corroborates the findings of the national blindness and visual
impairment survey (2007). The highest prevalence of bilateral
blindness (14.3%) was observed among those who were
75 years and above, followed by those in the 65–74 years age
group (3.2%) while the prevalence of bilateral blindness among
participants of 55–64 years age group constituted 1.9%. This
high prevalence is due to senile cataract and chronic glaucoma
seen more in the elderly than in the younger population.
This finding also validates the findings of Ejimadu and
Pedro‑Egbe,14 Pedro‑Egbe
et
al
.13 which showed that prevalence
of visual impairment was higher in the elderly.
Bilateral and unilateral blindness, as well as bilateral and
unilateral visual impairment, were more common among
the female folk (1.6% vs. 1.2%) although these differences
were not statistically significant. This finding compares well
with the Nigerian national blindness and visual impairment
survey, 2005–2007 where females had a higher prevalence
of blindness than males (4.4% vs. 4.0%).2 The findings of
Ejimadu and Pedro‑Egbe14 in Ikwerre LGA also supports our
assertion. However, our finding contrasts with the finding
of Ajibode16 in Ogun State, where more males were visually
impaired than their female counterparts. Blindness and visual
impairment were observed more among the females than their
male counterparts, probably because women are prohibited
by some traditions from leaving their homes even when they
need medical help. Furthermore, women are expected to take
care of their homes and raise children while the men go out
to fend for the families. The observed difference could also be
due to gender and socioeconomic differences in health‑seeking
behavior and barriers to uptake of services.
The prevalence of blindness in this study (1.4%) is closer to
the WHO estimate of 1% for Nigeria than those obtained
in Ahoada East LGA and Oyorokotor in Andoni LGA. This
study compares well in methodology with the nationally
representative sample of 16,507 adults using multistage
stratified random sampling survey in Pakistan. More so, in
both studies, blindness was defined on the basis of presenting
VA. However, in the Pakistan blindness survey, a prevalence
of 2.7% was observed.10 This difference could probably be
accounted for because of the difference in the sample size
and different geographical and sociocultural settings.
Table 4: Gender distribution of blindness and visual impairment
Gender Bilateral
blindness,
n (%)
Unilateral
blindness,
n (%)
Bilateral visual
impairment,
n (%)
Unilateral visual
impairment,
n (%)
Male 2 (40) 4 (44.4) 9 (40.9) 13 (40.6)
Female 3 (60) 5 (55.6) 13 (59.1) 19 (59.4)
Total 5 (100) 9 (100) 22 (100) 32 (100)
Pearson’s
Chi-square
value
0.000 0.000 0.000 0.000
P1.00 1.00 0.994 0.970
Table 3: Age‑specific prevalence of blindness and visual impairment
Age group (years) Number
examined (%)
Bilateral
blindness, n (%)
Unilateral
blindness, n (%)
Bilateral visual
impairment, n (%)
Unilateral visual
impairment, n (%)
15-24 7 (2.0) 0 (0) 0 (0) 0 (0) 0 (0)
25-34 22 (6.2) 0 (0) 0 (0) 2 (9.1) 3 (13.6)
35-44 86 (24.3) 0 (0) 1 (1.2) 0 (0) 5 (5.8)
45-54 108 (30.6) 0 (0) 3 (2.8) 2 (1.9) 7 (6.5)
55-64 54 (15.3) 1 (1.9) 2 (3.7) 6 (11.1) 9 (16.7)
65-74 62 (17.6) 2 (3.2) 2 (3.2) 8 (12.9) 6 (9.7)
75 and above 14 (4.0) 2 (14.3) 1 (7.1) 4 (28.5) 2 (14.3)
Total 353 (100) 5 (1.4) 9 (2.5) 22 (6.2) 32 (9.1)
95% CI 0.78-2.5 1.2-3.4 5.7-8.5 8.7-9.7
CI: Confidence interval

Onua, et al.: Burden of blindness and visual impairment according to age and gender
78 Port Harcourt Medical Journal | May‑Aug 2016 | Vol 10 | Issue 2
In general, a prevalence of 1.4% blindness as found in this
study is high. This could be attributed to ignorance, poverty,
harmful traditional practices, and inhibitions that restrict
seeking prompt medical attention. This, however, need further
investigation.
The prevalence of bilateral visual impairment in this study
was 6.2%. In the study by Omoni15 in a fishing community
in Rivers State, the prevalence of visual impairment was 7.5%
while Pedro‑Egbe
et
al
.13 reported a prevalence of 8.2% in a
similar study in Ahoada East LGA also in Rivers State. The
reason (s) for this difference need further investigation.
Refractive error was the most common cause of bilateral
visual impairment in this study, constituting 54.6%. This
may be because most of the study participants were farmers
who reject glasses, claiming that it makes them uncomfortable
while working in their farms. Some believe that people wearing
eyeglasses or having one form of eye problem or the other have
some spiritual problems. This group of people would, therefore,
not seek ophthalmic assistance.
It is worthy of note that 80% of blindness and 77% of visual
impairment in this study are due to avoidable causes. This is
similar to the findings of Stevens
et
al
.17 and Pascolini
et
al
.18
in their global update of available data on visual impairment.
Other comparative studies done elsewhere in Rivers State also
lend support to this finding. Pedro‑Egbe
et
al
.13 reported 80%
of blindness and 90% of visual impairment while Omoni15
in her study noted that 90% of blindness and 75% of visual
impairment were avoidable.
This study was conducted in the respondents’ houses and did
not include slit lamp and visual field assessment. Therefore,
the study was likely to have underestimated the prevalence of
glaucoma and possibly other ocular diseases where VA was
maintained until the late stage of the diseases. Subsequent
surveys should be done with detailed ocular examinations
including slit lamp and visual field assessment to accurately
diagnose ocular disorders.
Conclusion
This study provided important epidemiological data with
regards to the burden of blindness and visual impairment
in Emohua LGA. Blindness and visual impairment are more
common in the older age groups and female gender in Emohua
LGA. Eighty percent of the causes of blindness and 77% of the
causes of visual impairment in Emohua LGA are preventable.
Most of the cases of blindness and visual impairment could
have been prevented or even cured if there were good health
education and effective eye care service delivery in the LGA.
Government and nongovernmental organizations should as
a matter of urgency step up comprehensive eye health‑care
programs to realize the goals of Vision 2020 in Emohua LGA.
Financial support and sponsorship
Nil.
Conflicts of interest
There are no conflicts of interest.
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