Causes of childhood blindness in a school for the visually impaired in Hong Kong

ORIGINAL ARTICLE
CME
DSP Fan

Causes of childhood blindness in a
TYY Lai

EYY Cheung
school for the visually impaired in
DSC Lam

Hong Kong
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Objective. To identify the causes of blindness in children attending a
school for the blind in Hong Kong.
Design. Cross-sectional observational study.
Setting. School for blind children in Hong Kong.
Participants. Eighty-two blind students at the Ebenezer School and Home
for the Visually Impaired were examined between December 1998 and
August 1999.
Main outcome measures. Demographic data were obtained from stu-
dents and a questionnaire assessment made of their medical and ocular
history. Visual acuity was assessed and visual loss classified according to
the World Health Organization classification of visual impairment. Com-
plete ophthalmic assessments were performed in all students including
slit-lamp examination and dilated binocular indirect ophthalmoscopy.
Results. The mean age of the students was 12.2 years. Ten (12.2%) had a
family history of eye disease. Major past medical illnesses were reported in
50% with prematurity and diseases of the central nervous system found in 26.8%
and 11.0% of students, respectively. The most common anatomical site for
visual impairment was the retina (47.6%), followed by diseases of the optic
nerve (14.6%), and diseases of the anterior segment and the lens (14.6%).
Conclusions. The pattern of childhood blindness in Hong Kong is simi-
Key words:
lar to that seen in other developed countries. Preventable causes of child-
Blindness;
hood blindness, such as prematurity and birth asphyxia, were responsible
Cataract;
for a large proportion of cases. Early diagnosis and treatment of such
Child;
conditions may reduce the incidence of childhood blindness in Hong Kong.
Optic nerve diseases;
Retinopathy of prematurity

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Hong Kong Med J 2005;11:85-9
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Department of Ophthalmology and Visual

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Sciences, The Chinese University of Hong
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Argyle Street, Hong Kong
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DSP Fan,
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FRCS (Edin), FHKAM (Ophthalmology)
TYY Lai, MMedSc, MRCS
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EYY Cheung, BSc, MMedSc
DSC Lam, MD, FHKAM (Ophthalmology)

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Correspondence to: Prof DSC Lam
(e-mail: dennislam_pub@cuhk.edu.hk)
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Hong Kong Med J Vol 11 No 2 April 2005 85

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Fan et al
Introduction
Table 1. World Health Organization (WHO) category of
visual loss
Childhood blindness is a major problem throughout
O
H
W
t
a
c
y
r
o
g
e
l
a
u
s
i
V
y
t
i
u
c
a
s
t
n
e
d
u
t
S
the world and results in a substantial life-long burden
.
o
N
%
(
)
of disability. There are approximately 1.5 million blind
o
N
t
n
e
m
r
i
a
p
m
i
<
0
6
/
6
o
t
/
6 8
1
04
)
9
.
4
(
0
V
l
a
u
s
i
i
a
p
m
i
t
n
e
m
r
/
6
<
8
1
o
t
0
6
/
6
07 (
)
5
.
8
0
children worldwide.1 Childhood blindness has been
e
r
e
v
e
S
l
a
u
s
i
v
/
6
<
0
6
o
t
/
3 0
6
6
1 (
)
5
.
9
1
identified as a priority in the World Health Organiza-
t
n
e
m
r
i
a
p
m
i
tion’s (WHO’s) global initiative to eliminate avoidable
d
n
il
B
0
6
/
3
<
o
t
o
n
il
t
h
g
5
5 (
)
1
.
7
6
i
t
p
e
c
r
e
p
n
o
blindness by the year 2020.2 The prevalence of blind-
ness in children is estimated to range from 0.2 to 0.3
per 1000 children in developed countries and 1.0 to
1.5 per 1000 children in developing areas.3 In 2003,
were excluded. Initial ocular examination was carried
the mid-year population aged 15 or under in Hong
out at the school by an ophthalmologist. At the time of
Kong was about 1.1 million.4 Extrapolation of these
examination, the children’s parents or carers were
data produces a figure of approximately 400 to 1000
asked to provide details of the children’s general
blind children in Hong Kong.
medical and eye condition including age of onset of
the eye condition, perinatal period, previous eye
The causes of childhood blindness have been
surgery, and family history. Family members were
studied in various countries including Mainland China,
also examined if the cause of visual impairment was
and vary between undeveloped, developing, and
hereditary or if ocular examination was requested.
developed countries.5-16 Corneal scarring secondary
The main purpose of examining family members
to vitamin A deficiency, measles infection, and oph-
was to provide them with access to specialist ophthal-
thalmia neonatorum are the main causes of childhood
mologist care. The students’ best-corrected visual
blindness in developing countries, whereas in develop-
acuity was assessed, wherever possible, using a
ed countries, retinal diseases and lesions of the central
standard Snellen chart. Visual loss was classified
nervous system (CNS) are more common.16,17 Genetic
according to the WHO classification for visual impair-
and hereditary components also play an important role
ment (Table 1). Slit-lamp examination of the anterior
in these ocular disorders.
segment was performed. Fundi were examined by
binocular indirect ophthalmoscopy after pupillary
Determining the causes of childhood blindness is
dilatation using 0.5% phenylephrine and 0.5%
important because the epidemiological data may be
tropicamide eye drops (Mydrin-P; Santen, Osaka,
used to determine how resources are allocated for
Japan). Some students required further ophthalmic
the prevention and treatment of eye disease.15 These
investigations including ocular examination under
data are nonetheless not readily available in many
sedation, fundus fluorescein angiography, ocular
developed countries, including Hong Kong.2 This study
ultrasonography, automated visual field testing, and
aimed to identify the causes of blindness among
electrophysiological studies. These were performed at
children attending the only school for visually impaired
the Department of Ophthalmology and Visual Sciences,
in Hong Kong.
Prince of Wales Hospital, Hong Kong. The study proto-
col was approved by the ethics committee of the
Methods
Chinese University of Hong Kong.
Students from the Ebenezer School and Home for
Results
the Visually Impaired were recruited between
December 1998 and August 1999 for detailed ophthal-
Demographics of participants
mic examination. The school can accommodate 150
A total of 82 students underwent ocular examination.
students, with space for 120 residential pupils.18 The
This represented a recruitment rate of 78.8% of students.
admission criteria for the school are: (i) Hong Kong
Ocular examination was not performed in 21.2% of stu-
resident, (ii) aged 4 to 18 years, (iii) visual acuity
dents because written consent could not be obtained.
?6/18, or visual field <20? (Education Department
The mean age (standard deviation) of the 82 students
criteria), and (iv) capable of benefiting from a regular
was 12.2 (4.3) years, with a range of 4 to 23 years.
education curriculum.18 Inclusion criteria for the study
included all students enrolled at the school for the
Family and medical history
academic year 1998/99. Students whose informed con-
A family history of eye disease was present in 10
sent could not be obtained from their family members
(12.2%) students. Three had a family history of
86 Hong Kong Med J Vol 11 No 2 April 2005

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Causes of childhood blindness
Table 2. Significant medical history
Table 3. Type of ocular surgery among the 32 students
who had previous ophthalmic surgery
l
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* Two students had more than one type of previous surgery
N
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(
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congenital cataract. Other significant family histories
Causes of blindness and onset of eye disease
included glaucoma, optic atrophy, corneal opacity,
The anatomical sites of visual impairment are listed
retinal dystrophy, retinopathy of prematurity (ROP),
in Table 4. The most common was the retina with 39
and high myopia.
(47.6%) cases. Major retinal causes included 21
students with ROP, seven with retinal dystrophies, four
Forty-one (50.0%) students had significant past
with retinal detachment, and three with retinoblastoma.
medical illnesses other than ocular disease (Table 2).
Other causes included myopic and chorioretinal
The two most common, prematurity and diseases of the
degeneration.
CNS, were found in 22 (26.8%) and nine (11.0%)
students, respectively. One student had a history sugges-
Optic nerve and CNS diseases due to optic atrophy
tive of intrauterine infection causing congenital
or cortical blindness were the second most common
toxoplasmosis. Other significant medical history included
anatomical sites for visual impairment with 12 (14.6%)
congenital heart disease, albinism, kidney disease,
cases and two (2.4%) cases, respectively. The known
neurofibro-matosis, measles, mild mental handicap, mus-
causes of optic atrophy included intracranial tumours
culoskeletal disorder, and ectodermal dysplasia.
(two cases), cerebral asphyxia (two cases), intracranial
haemorrhage (two cases), and hydrocephalus (one case).
Previous ocular surgery
Thirty-two (39.0%) students had undergone previous
Disorders of the anterior segment, including
ophthalmic surgery on at least one occasion (Table 3).
diseases of the cornea and the lens, were also signifi-
The most common surgery was cataract extraction
cant causes of visual impairment. Six (7.3%) students
(eight cases), four of which were performed for
had corneal opacity, four (4.9%) had cataract, and two
congenital cataract, three were performed in associ-
(2.4%) had anterior segment dysgenesis (aniridia).
ation with retinal detachment surgery, and one with
penetrating keratoplasty. The majority of cataract
Glaucoma with buphthalmos was diagnosed in 10
surgery did not result in good visual outcome due to
(12.2%) cases. Anatomical abnormality of the whole
other ocular co-morbidities. Enucleation operations
globe contributed to two (2.4%) cases. Vitreous disor-
were performed in three students with a history of
ders caused three (3.7%) cases of visual impairment
retinoblastoma and two who had end-stage glaucoma.
which were due to persistent foetal vasculature.
Other types of ophthalmic surgery were for retinal
detachment and glaucoma.
In 50 (58.5%) students, the onset of eye disease
was at birth and included ROP (21 cases, 42%),
Extent of visual impairment
glaucoma (seven cases, 14%), and optic atrophy
Using the WHO classification, 55 (67.1%) students
(five cases, 10%). Disease onset occurred in the first
were categorised as blind. Severe visual impairment
year of life in a further 11 (13.4%) students.
was present in 16 (19.5%). The best-corrected visual
acuity of the better eye is shown in Table 1. Four
Discussion
students with visual acuity between 6/6 and 6/18
attended the school because their visual field constric-
The pattern of major causes of childhood visual im-
tion due to glaucoma or retinal dystrophy was <20?.
pairment and blindness in Hong Kong is similar to that
Hong Kong Med J Vol 11 No 2 April 2005 87

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Fan et al
Table 4. Anatomical sites and causes of visual impairment in 82 students
a
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seen in other developed countries. Optic atrophy,
A large percentage of children in this study were
cataract, retinal dystrophies, and ROP are responsible
blind at birth, and genetic and prenatal factors were im-
for a large proportion of cases.3,15,16
portant aetiological factors. Ophthalmic examination of
parents and family members of the affected children
Perinatal factors, including prematurity and birth
would enable the provision of informed genetic
asphyxia, accounted for approximately 10% of cases
counselling. Research is being carried out in order to
and resulted in ROP and optic atrophy. Intrauterine
build up an extensive database for genetic eye diseases
infections or drugs ingested during early pregnancy
and gene therapy for the eye is a future possibility.21
may also have caused significant visual impairment
in these children. These causes of visual impairment
One of the weaknesses of the current study is
are potentially preventable through better antenatal
the small sample size. Nevertheless, this study recruited
and perinatal care: high-risk neonates can be identi-
over 75% of students attending the blind school and
fied to allow treatment commenced early on in the dis-
thus the results should be representative of the school
ease process.
population. Another limitation of this study is the
selection bias that arises because a school for the blind,
Congenital cataract, glaucoma, ROP, and retinal
rather than the general population, was used for sub-
detachment are potentially preventable and treatable
ject recruitment. Blind students not attending the school
and accounted for one third of cases in this study.
are thus excluded. Because a substantial proportion of
This finding emphasises the importance of early
children with other disabilities including deafness and
detection and treatment of paediatric eye diseases
mental handicap also have visual impairment, students
by screening (eg screening for ROP). Primary pre-
in special schools for the deaf or mentally handicapped
ventative measures should also be carried out where
were also excluded from this study. Despite these
appropriate. Rubella immunisation in pubertal girls
disadvantages, blind school studies are widely accepted
and non-immune women contemplating pregnancy
because a large number of children with visual loss
can prevent congenital cataract. An epidemic of ru-
can be examined in a short period of time.7,10,13
bella in the United Kingdom in 1996 caused two
cases of congenital cataract.19 Advances in surgical
In conclusion, the causes of childhood blindness in
techniques for various paediatric eye conditions, for
Hong Kong are similar to those identified in other
example, paediatric cataract surgery with contact
developed countries. Retinopathy of prematurity, birth
lens or intra-ocular lens implantation combined with
asphyxia, and potentially treatable causes of visual
aggressive treatment of amblyopia, may reduce the
impairment in children, such as cataract and retinal
severity of childhood visual impairment.20
detachment, accounted for a substantial proportion of
88 Hong Kong Med J Vol 11 No 2 April 2005

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Causes of childhood blindness
cases. Because the risk of amblyopia is high in visu-
8. Rahi JS, Sripathi S, Gilbert CE, Foster A. Childhood
ally impaired children, early detection and diagnosis
blindness in India: causes in 1318 blind school students in
is of paramount importance to reduce the severity of
nine states. Eye 1995;9:545-50.
9. DeCarlo DK, Nowakowski R. Causes of visual impairment
visual impairment. Genetic studies and counselling will
among students at the Alabama School for the Blind. J Am
also play a significant role in the future when more
Optom Assoc 1999;70:647-52.
become known about hereditary eye disease.
10. Hornby SJ, Xiao Y, Gilbert CE, et al. Causes of childhood
blindness in the People’s Republic of China: results from 1131
Acknowledgements
blind school students in 18 provinces. Br J Ophthalmol 1999;
83:929-32.
11. Wedner SH, Ross DA, Balira R, Kaji L, Foster A. Prevalence
This project is funded by the Ebenezer School and
of eye diseases in primary school children in a rural area of
Home for the Visually Impaired. We would like to
Tanzania. Br J Ophthalmol 2000;84:1291-7.
thank all the students and their family members for
12. Alagaratnam J, Sharma TK, Lim CS, Fleck BW. A survey of
their participation in this study as well as the staff
visual impairment in children attending the Royal Blind
members for their support. We would also like to thank
School, Edinburgh using the WHO childhood visual impair-
ment database. Eye 2002;16:557-61.
Dr Simon Leung for commenting on the manuscript.
13. Ezegwui IR, Umeh RE, Ezepue UF. Causes of childhood
blindness: results from schools for the blind in south
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