Causes of visual impairment in children with low vision

Abstract

To determine the main causes of visual impairment in children with low vision. To assess the need of spectacles and low vision devices (LVDs) in children and to evaluate visual outcome after using their LVDs for far and near distance.
Observational study.
Khyber Institute of Ophthalmic Medical Sciences, Peshawar, Pakistan, from June 2006 to December 2007.
The clinical record of 270 children with low vision age 4-16 years attending the Low Vision Clinic were included. All those children, aged 4-16 years, who had corrected visual acuity (VA) less than 6/18 in the better eye after medical or surgical treatment, were included in the study. WHO low vision criteria were used to classify into visually impaired, severe visually impaired and blind. Results were described as percentage frequencies.
One hundred and eighty nine (70%) were males and 81 (30%) were females. The male to female ratio was 2.3:1. The main causes of visual impairment included nystagmus (15%), Stargardt's disease (14%), maculopathies (13%), myopic macular degeneration (11%) and oculocutaneous albinism (7%). The percentages of visually impaired, severe visually impaired and blind were 33.8%, 27.2% and 39.0% respectively. Spectacles were prescribed to 146 patients and telescopes were prescribed to 75 patients. Spectacles and telescope both were prescribed to 179 patients while Ocutech telescope was prescribed to 4 patients.
Retinal diseases nystagmus and macular conditions were mainly responsible for low vision in children. Visually impaired children especially with hereditary/congenital ocular anomalies benefit from refraction and low vision services which facilitate vision enhancement and inclusive education.

Full text

88 Journal of the College of Physicians and Surgeons Pakistan 2011, Vol. 21 (2): 88-92
INTRODUCTION
The control of childhood blindness is a priority of "Vision
2020 - the right to sight", a global initiative for the
elimination of avoidable blindness.1The importance of
providing care for children with low vision is recognized
by many initiatives, such as Vision 2020, the 2004 Oslo
Workshop on low vision and the United Nation's global
campaign - 'Education for All'.2
The prevalence and major causes of childhood
blindness vary between countries and over time. The
prevalence of blindness in children ranges from
approximately 0.3/1000 children in affluent regions to
1.5/1000 in the poorest communities.3Reliable
population-based data on the causes of blindness in
children are difficult to obtain in developing countries. In
middle income countries the pattern of causes is mixed,
with retinopathy of pre-maturity emerging as an
important cause in Latin America and some Eastern
European countries.4,5 Currently un-avoidable causes
(the biggest group in affluent countries) include
hereditary retinal dystrophies, disorders of the central
nervous system, and congenital anomalies. Un-
corrected refractive errors cause visual impairment and
blindness in all regions, particularly myopia in south
East Asia.6
The prevalence of childhood blindness was 0.3 per
1,000 children in industrialized countries and 1.2 per
1,000 children in the developing countries in the year
2000. Accordingly, it was estimated that there were
nearly 1.4 million blind children in the world. Each year,
an additional 50,000 children become blind and are
added to this pool.7A population- based cross- sectional
study in India has found low vision to have a prevalence
of 1.05% in the year 2000, with a burden of 10.6 (95%
confidence interval, 8.4-12.8) million people requiring
low vision services.8In another hospital-based study,
the age group < 16 years was the leading age group of
low vision.9
WHO definition for low vision (6/60 < VA < 6/18, 10°
<VF < 20°),10 severe vision impairment (3/60 < VA
< 6/60, 5° < VF < 10°), and blindness or profound
vision impairment (VA < 3/60, VF < 5°) are considered
reliable.10
ABSTRACT
Objective: To determine the main causes of visual impairment in children with low vision. To assess the need of
spectacles and low vision devices (LVDs) in children and to evaluate visual outcome after using their LVDs for far and near
distance.
Study Design: Observational study.
Place and Duration of Study: Khyber Institute of Ophthalmic Medical Sciences, Peshawar, Pakistan, from June 2006 to
December 2007.
Methodology: The clinical record of 270 children with low vision age 4-16 years attending the Low Vision Clinic were
included. All those children, aged 4-16 years, who had corrected visual acuity (VA) less than 6/18 in the better eye after
medical or surgical treatment, were included in the study. WHO low vision criteria were used to classify into visually
impaired, severe visually impaired and blind. Results were described as percentage frequencies.
Results: One hundred and eighty nine (70%) were males and 81 (30%) were females. The male to female ratio was 2.3:1.
The main causes of visual impairment included nystagmus (15%), Stargardt's disease (14%), maculopathies (13%),
myopic macular degeneration (11%) and oculocutaneous albinism (7%). The percentages of visually impaired, severe
visually impaired and blind were 33.8%, 27.2% and 39.0% respectively. Spectacles were prescribed to 146 patients and
telescopes were prescribed to 75 patients. Spectacles and telescope both were prescribed to 179 patients while Ocutech
telescope was prescribed to 4 patients.
Conclusion: Retinal diseases nystagmus and macular conditions were mainly responsible for low vision in children.
Visually impaired children especially with hereditary /congenital ocular anomalies benefit from refraction and low vision
services which facilitate vision enhancement and inclusive education.
Key words: Childhood blindness. Low vision. Low vision devices. Vision 2020. Nystagmus. Stargardt's diseases. Maculopathy.
Myopic macular degeneration.
Department of Ophthalmology, Hayatabad Medical Complex,
Peshawar.
Correspondence: Dr. Mufarriq Shah, Doctor’s Hostel No. 1,
R. No. 12, Hayatabad Medical Complex, Peshawar.
E-mail: mufarriq1@hotmail.com
Received March 17, 2009; accepted January 19, 2011.
Causes of Visual Impairment in Children with Low Vision
Mufarriq Shah, Mirzaman Khan, Muhammad Tariq Khan, Mohammad Younas Khan and Nasir Saeed
ORIGINAL ARTICLE

Many children with incurable visual loss benefit from
low-vision rectification services, which facilitate near
vision and inclusive education. This study aimed to
determine the main causes of low vision in Pakistani
children and to assess their visual outcome after using
low vision devices for distance and near tasks.
METHODOLOGY
This study was conducted at Low Vision Clinic in Khyber
Institute of Ophthalmic Medical Sciences, Hayatabad
Medical Complex, Peshawar, Pakistan. The clinical
record of 270 children, aged 4-16 years, attending
the low vision clinic from June 2006 to December
2007 were included in the study. They were seen first
by ophthalmologists and then referred to low vision
clinic for assessment, where they are refracted and
assessed for LVDs by an optometrist. Optometric
examination included detailed history of the patient, his/
her family history, functional, occupational and
clinical assessment. The anterior segment examination
was performed using a slit-lamp. Posterior segment
examination was performed by direct or indirect
ophthalmoscopy after mydriasis. The diagnosis was
confirmed by at least one ophthalmologist and one
optometrist.
Distance visual acuity was measured using a range of
techniques. Those included Lea symbols, Snellen
charts and logarithm of the minimum angle of resolution
(Log.MAR) chart with five optotypes on each line at 4 m
and, if necessary, at 3, 2 m on each eye separately while
the patient wear his or her current spectacles (if worn).
Feinbloom chart for the partially sighted and Illiterate E
were used for patient who could not read English,
depending on the level of co-operation. If visual acuity
could not be measured with these charts, a sequential
approach was used with fingers counting, hand
movement, and light perception. Visual fields were
assessed by confrontation and arc perimeter. Refraction
with cycloplegia was carried out on all patients, followed
by subjective refraction using standard techniques. The
best corrected distance and near acuity, the refractive
error and eye to chart distance were recorded for each
eye.
For near visual acuity “Near Reading Card for the
partially sighted” by William Feinbloom and Lea Cards
for near visual acuity were used. For the purpose of this
study near acuity was banded in three groups; 1M (news
paper size) or better which would allow access to most
printed materials, < 1M to 3.2 M (display materials)
which would allow only limited access to ink print; and
< 3.2 M.9Low vision devices like telescopes stand and
hand magnifiers, and closed circuit television were used
during the low vision assessment. The category of
visual impairment was classified by vision in the better
eye for all untreatable causes other than uncorrected
refractive error.
All these variables were translated into SPSS version 10
databsae. Mean values and standard deviation were
calculated for continuous variables while proportions
and percentages were calculated for categorical
variables.
RESULTS
Two hundred and seventy children aged 4-16 years were
assessed at low vision clinic. Mean age was 11 + 2.8
years. Among the children examined, 189 (70%) were
males and 81(30%) were females. The leading cause of
low vision amongst this group was nystagmus (15%)
followed by Stargardt's maculopathies (14%). The next
most common cause was maculopathies (other than
Stargardt's disease) (13%) followed by myopic macular
degeneration (11%), oculocutaneous albinism (7%), and
amblyopia (6%). As a whole retinal disease, including
Stargardt's disease and maculapathies, was the major
cause of visual impairment present in 32% children.
Retinitis pigmentosa was found in 3% cases. The
causes of vision impairment are given in Table I.
Based on vision at initial examination, 3 patients (1.1%)
had VA 6/18. Two of them had retinitis pigmentosa while
one had Stargardt's disease. On presentation 116
children (43%) had visual impairment (having visual
acuity < 6/18 to 6/60 in the better eye), and 62 children
(23%) were severely visually impaired (with visual acuity
< 6/60 to 3/60 in the better eye) while 89 children (33%,
95%CI) were blind (having VA < 3/60 in the better eye)
according to the WHO categories of visual loss. With
best correction, 42 (15.6%) children achieved VA 6/18 or
better. One hundred and sixty four (60.7%) were visually
impaired and 31 (11.5%) were severely visually
impaired while 33 (12.2%) of children continued to be
blind. Amongst 270 children, 42 were prescribed only
glasses for distance while the remaining 228 children
were assessed for low vision devices. With low vision
Journal of the College of Physicians and Surgeons Pakistan 2011, Vol. 21 (2): 88-92 89
Causes of visual impairment in children with low vision
Table I: Causes of vision impairment.
Causes Number Percentage
Nystagmus 40 14.8
Stargardt's disease 37 13.7
Myopic degeneration 30 11.1
Maculopathies 36 13.3
Others (< 2%) 32 11.9
Oculocutaneous albinism with
nystagmus 18 6.7
Amblyopia 17 6.3
Retinitis pigmentosa 9 3.3
Marfan's syndrome 6 2.2
Congenital cataract 8 3.0
Optic atrophy 6 2.2
Corneal opacities 6 2.2
Congenital glaucoma 6 2.2
Rod cone dystrophy 6 2.2
Unknown 13 4.8
Total 270 100

devices, amongst 228 children, 192 children (84.2%)
achieved distance visual acuity 6/18 or better in the
better eye while 13 patients (5.7%) were visually
impaired and 23 (10.1%) remained in the blind category.
The distribution of visual acuities is given in Table II. On
presentation the difference in percentage amongst male
and female was not very significant regarding categories
of visual impairment, severe visual impairment and
blindness (Table III).
The results from near visual acuity measurements are
shown in Table IV. One hundred and thirty four patients
(49.6%) with low vision were able to discern 1 M
(newspaper print) or better in the better eye without near
addition. Sixty two had near visual acuity < 1 M to 3.2 M
and 74 had < 3.2 M. With low vision aids the number of
children with near visual acuity of 1 M (0.8 print size) or
better increased to 239 (88%), and 26 patients (9.6%)
had < 3.2 M.
Spectacles were prescribed to 146 patients and
telescopes were prescribed to 75 patients. Spectacles
and telescope both were prescribed to 179 patients
while Ocutech telescope were prescribed to four
patients. Forty six patients were feeling better with
filters. For near visual acuity, glasses (included prismatic
glasses) were prescribed to 96 patients, stand
magnifiers to 42 patients, hand-held magnifier to 27
patients and CCTV and Ocutech telescope with cap to 2
patients each.
DISCUSSION
Children with low vision can improve their quality of life
through vision rehabilitation services to teach them how
to use their remaining vision more effectively. Using a
variety of visual and adaptive aids may bring them back
or help them keep their independence. Integrated
education of visually impaired children is now preferred
when possible. Various studies have found low vision
devices as an effective means of providing visual
rehabilitation.11-13
In the present study, hereditary / congenital ocular
anomalies (mainly Stargardt's disease and oculocu-
taneous albinism) accounted for 21% of low vision
patients. The reason for the high proportion of
hereditary / congenital anomalies in this study may be
due to inter-family marriages because consanguineous
marriages are common in this part of the world. Most of
these hereditary / congenital conditions are not treatable
but prevention is possible through genetic counselling.
Gothwal has been shown that in the subjects aged < 30
years the leading causes of low vision were genetic.9
Prior to refraction, 3 children had a visual acuity > 6/18,
with 42 (15.6%) more children moving from the group
with low vision, but having useful residual vision,
improving to the no impairment group after accurate
refraction but none of them improved to 6/12 or better in
the better eye. This greater number was due to the fact
that in the retinal diseases, including Stargardt's disease
and maculopathies, vision is good in early childhood but
deteriorate with the passage of time. This also illustrates
the importance of accurate refraction in children with low
vision and shows that, even in the absence of a special
low vision services, many eye units can help many
children with low vision by providing accurate refraction
services. Moreover, children with corrected VA of 6/18 or
better but having obvious cause of visual impairment
should be considered for follow-up as their VA will
deteriorate with age. Refractive error is also one of the
most common causes of visual impairment. Due to
uncorrected refractive error, there are 145 million people
with VA ranging from < 6/18 to 3/60 and 8 million people
who are blind (VA < 3/60).14
In this study the number of male children is more than
twice the number of female children. Other studies
undertaken by the author did show that the number of
male is more than twice the number of female.9,11 Girls
have poorer access to low vision care than boys. Many
factors may contribute towards the fewer females
referral. These include comparatively small number of
female patients examined in the out patients
department; very low literacy ratio in females; long
distances involved for visiting the only low vision clinic in
the province.9Girls may therefore, need to be
approached directly for eye care and not only indirectly
via community leaders.
90 Journal of the College of Physicians and Surgeons Pakistan 2011, Vol. 21 (2): 88-92
Mufarriq Shah, Mirzaman Khan, Muhammad Tariq Khan, Mohammad Younas Khan and Nasir Saeed
Table II: Distribution of presenting distance VA (visual acuity), best
corrected VA and VA with LVDS (low vision devices) (n = 228).
VA Presenting VA Best corrected VA VA with LVDs
n (%) n (%) n (%)
6/18 or better 0 (0.0) 0 (0.0) 192 (84.2)
< 6/18 to 6/60 77 (33.8) 164 (72.0) 13 (5.7)
< 6/60 to 3/60 62 (27.2) 31 (13.6) 0 (0)
< 3/60 89 (39.0) 33 (14.4) 23 (10.1)
Total 228 (100) 228 (100) 228 (100)
Table III: Presenting visual acuity and visual acuity with low vision
devices by gender (n = 228).
VA on presentation VA with low vision devices
Male Female Male Female
n (%) n (%) n (%) n (%)
6/18 or better 0 (0) 0 (0) 137 (87.0) 55 (78.6)
< 6/18 to 6/60 54 (34) 23 (33) 7 (4) 6 (8.6)
< 6/60 to 3/60 41 (26) 21 (30) 0 (0) 0 (0)
< 3/60 63 (40) 26 (37) 14 (9) 9 (12.8)
Total 158 (100) 70 (100) 158 (100) 70 (100)
Table IV: Near visual acuity at presentation and with low vision aids
(n =270).
VA Presenting near VA Near VA with LVDs
n (%) n (%)
1M or Better 134 (53.1) 239 (93.8)
< 1 M to 3.2M 62 (31.3) 5 (0)
< 3.2 M 74 (15.6) 26 (6.2)
Total 270 (100) 270 (100)

This study showed that even with low vision aids in
female, 8.6% had visual impairment and 12.8% were
blind while in male 4.0% were visually impaired and
9.0% were still blind. However, there was none in the
category of severe visual impairment in both male and
female after low vision aids. Hence the percentage of
visually impaired and blind remained greater in female
as compared to male even with low vision aids. This
finding shows that females have significantly higher
odds of having severe impairment and blindness which
may be reflective of their relatively disadvantaged social
status.
In this study, out of 16 patients with amblyopia, 12 had
visual impairment and 3 were in the blind category. VA
was enhanced to 6/18 or better with LVDs in all cases.
In our other studies amblyopia is a major cause of visual
defects in children.9,15 It is estimated that amblyopia
affects between 1-4% of the world’s population.16
Amblyopia develops during the sensitive period of visual
maturation, which continues until about 8 years of age.17
In this study we found that about 50% children had
normal near visual acuity. These children thus had
sufficient near vision to read the print used in school
books. Most visually impaired children have useful sight
but there is under provision of visual aids, inadequate
training in their uses, specially use of stand magnifiers,
and poor understanding of simple methods of visual
function for daily living. For low vision devices to be used
effectively by children, support, follow-up, training and
motivation is needed. With higher power devices,
specially stand magnifiers, more supervised practice
and greater motivation is required.
The overall visual function of a child has four major
components; communication, mobility, daily living
activities and sustained near vision tasks like reading
and writing, including colour vision and contrast
sensitivity assessment.18 Changes in environment do
not cost much and should be an integral part of the low
vision care of these children.
Comparison of causes of severe visual impairment (SVI)
and blindness in this age group needs to be interpreted
cautiously, as the data are not population-based and
only a small proportion of low vision children who
attended the Low Vision Clinic are presented in this
study. The study results are, therefore, likely to differ
from whole population studies.
Though the need for low vision aids may have been
underestimated in the present study (due to the use of
high addition plus / microscopic lenses and prismatic /
Fonda glasses), which is affordable and easily available
option in our setting. High powered near spectacles can
be readily manufactured using conventional aspheric
lenses.
CONCLUSION
The present study shows that hereditary / congenital
ocular anomalies (mainly Stargardt's disease and
oculocutaneous albinism) were more common in these
children. On the basis of the analysis made in the study
we concluded that visually impaired children especially
with hereditary / congenital ocular anomalies benefit
from accurate refraction and low vision services which
facilitate vision enhancement and inclusive education in
these children.
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92 Journal of the College of Physicians and Surgeons Pakistan 2011, Vol. 21 (2): 88-92
Mufarriq Shah, Mirzaman Khan, Muhammad Tariq Khan, Mohammad Younas Khan and Nasir Saeed
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