Vision is the primary means of integration between individuals and external
environment. It has been estimated that 75-90 % of all learning in the
class room comes to the students either wholly or partially via the visual
pathway (Negrel et al., 2000).
Visual problems have negative effects on learning and social interaction,
thus affecting the natural development of academic and social abilities.
Uncorrected refractive error is recognized as the principal cause of visual
impairment in school aged children.
In the beginning of 1998, a series of visual acuity study in children
were carried out in several geographic areas: a rural district in Eastern
Nepal (Pokharel et al., 2000), the semirural Shunyi district near
Beijing, China (Zhao et al., 2000), the urban La Florida area of
Santiago, Chile (Maul et al., 2000), a rural area near Hyderabad
in Southern India (Dandona et al., 1999), an urban area of New
Delhi, India (Murthy et al., 2002), a semi-rural/urban area of
Durban, South Africa (Naidoo et al., 2003) and most recently in
Guangzhou, China (He et al., 2004). These population based surveys
of school aged children document the wide variation in visual impairment
across different areas of the world. Of the approximately 1.4 million
children with blindness in the world, about 75% live in high poverty areas
in Asia and Africa. The major cause of blindness is refractive errors.
Throughout Africa, the main meal of the day is lunch, which usually consists
of a mixture of vegetables, legumes and sometimes meat (Lentz and Carola.,
1999). However, though different meats are considered staples in many
areas, many Africans are not able to eat meat often, due to economic constraints.
Beef, goat and sheep (mutton) are quite expensive in Africa, so these
foods are reserved for special days. However, fish is abundant in coastal
regions and in many lakes. The combination of various foods is called
stew or soup depending on the region. This mixture is then served over
a porridge or mash made from rice or corn. Regional differences are reflected
in variations on this basic meal, primarily in the contents of the stew.
In urban areas, however, the diet of (black) Africans is increasingly
dependent on meat as well as on empty calories from prepackaged foods.
The result is an unbalanced diet.
The purpose of this study was to investigate the visual acuity in relation
to dietary intake in high school children. Findings from this study will
help to make appropriate recommendations to identify and to treat the
visual impairment in an early stage so that it will not affect the academic
and social development of the students.
MATERIALS AND METHODS
Subject selection: This is a cross sectional study with systemic
sampling done in 2006. A random selection of 10 classes out of 25 totaling
400 students, from one of the schools in Mthatha was requested to participate
in the study. The principal of the school was contacted and informed consent
obtained after a detailed explanation of the purpose, content and benefit
of the study. Each volunteer was interviewed and the procedures as well
as the benefits of doing the study were explained to each subject. Each
subject was required to acknowledge in principle that they fully understood
the reasons for the study and what was required of them. Furthermore they
were required to sign a consent form, which gave permission to use them
Snellen test for visual acuity: US criteria was adopted for
measuring the visual acuity. The subjects in this study were considered
to have visual impairment, if their best visual acuity was below 20/30.
Visual acuity was measured in a quiet room of 10x8 m size, using a properly
illuminated Snellen chart at 6 m to discriminate different letters:
||Each eye was tested separately and was allowed to repeat
the procedure three times
||A child, who wore eye glasses were examined with their glasses appropriately
||Letters in the charts are of a size that can be seen by the normal
eye at a distance of 6 m (20 feet) from the chart
||Letters appear in rows and are arranged so as the normal eye can
see them at distances 9, 12, 15 m (30, 40, 50 feet) and so forth
||A person who could identify the letters of the size 6 at 6 m (20
at 20 feet) was said to have 6/6 (20/20) vision
||The result from the best of the two eyes was used to determine visual
The numerator expressed the distance between the observer and the letters
while the denominator expresses the distance at which they could be distinguished
by the normal eye.
Food frequency questionnaire: The food frequency questionnaire
included three basic food groups: protein rich; carbohydrate rich; and
vegetables and fruits. The protein group comprised of animal products
such as eggs, dairy products, organ meats and fish. Carbohydrate group
comprised of cereals, bread and other commonly used food and a variety
of fruits and vegetables containing beta carotene, which the body converts
into vitamin A were included in the questionnaire. Subjects were asked
to complete the questionnaire.
Different ratings were given to these food stuffs based on the frequency
of consumption like 2-3 times daily, daily, 2-3 times a week, once a week,
once a month and never in the order 5 to 0. For each food group, the individual
food item scores were added to derive the aggregate food scores for the
group. The aggregate food scores for carbohydrates, proteins and fruits
and vegetables were 40, 30 and 45, respectively. Subject`s questionnaires
were treated with confidentialities and the subjects were informed as
Anthropometric measurements: A single measurement of height was
taken while the subject was standing with heels together against the stadiometer
with the body held in a maximally erect (stretched) position. Hands were
placed on hips directed posteriorly and anteriorly, respectively. The
head was held in the Frankfurt plane, the eyes and nose were directed
straight forward and a maximum inspiration was taken. The subject was
instructed to put hands on hips, look straight ahead and take a deep breath.
The measurement was taken at the end of the inspiration.
Weight was measured while the subject was standing on the bathroom scale,
minimally clothed (shorts, light weight shirt), feet comfortably spread
with the weight evenly distributed on both feet and the hands-on hip position.
Two readings were obtained. The subject was instructed to step off the
scale between readings and the scale was zeroed between trials.
A single measurement of abdominal girth was measured at the level of
the umbilicus at the end of expiration with the subject supine and breathing
quietly. The hip girth was measured at the level of maximum protrusion
of the gluteal muscles while the participant stood erect and the weight
distributed equally over both feet.
A Lange Calliper (Cambridge Scientific Industries) calibrated to give
a constant pressure (deleted) throughout the full range was used throughout
the study. The skinfold thickness was read to the nearest 0.5 mm. The
skinfold thickness was measured over the biceps (BCP), triceps (TRCP),
subscapular (SSCP) and the suprailiac (SPIL) areas of the non-dominant
side of the body.
Statistical analysis: All statistical analysis were done with
the (STATISTICA), a commercially available statistical analysis software.
The subjects were divided into those with normal vision and those with
poor vision. Anthropometric measurements and dietary intake between the
two groups was compared using the Mann-Whitney test. Correlation between
dietary intake and visual acuity for each eye was done using the Spearman
Rank Correlation test.
Visual acuity was measured in 143 out of a possible 400 subjects (38%
response rate). Of these, eighty one were females and sixty two were males.
22 (16%) subjects showed poor vision. Table 1 shows
that the mean height and weight of males was slightly higher than the
females although the Body Mass Index (BMI) was higher in females. From
the food frequency questionnaire analysis it was revealed that the major
reason for their poor vision was unbalanced food habits.
|| Summary of the participants in the study
|| Food frequency questionnaire: Intake of carbohydrates
|| Food frequency questionnaire: Intake of proteins
|| Food frequency questionnaire: Intake of fruits and
|| Visual acuity in school children studied
The most frequently used carbohydrate rich food among the school aged
children were bread, cereals and rice and the traditional foods like imbila,
umvubo, umqa and isigwampa were less frequently used (Table
From Table 3, it is assumed that the most popular protein
rich foods include chicken, egg and milk but pork and fish were less frequently
Among the fruits and vegetables orange, carrot, pumpkin, spinach and
cabbage were frequently used. The mean score of the fruits and vegetables
were lower than that of carbohydrates and proteins ( Table
Of the 121 children studied, 16% of the males and 14.5% of the females
showed poor visual acuity (Table 5).
|| Association between poor visual acuity and type of
||Anthropometric measurements of the students with good
and poor visual acuity
Table 6 depicts higher mean scores of carbohydrate
(p<0.07)and lower scores of protein, fruits and vegetables for subjects
with poor visual acuity. Subjects with normal visual acuity showed lower
mean scores of carbohydrates and higher scores of , proteins (p<0.019)
and significantly lower mean scores of fruits and vegetables (p<0.00001).
This showed that carbohydrate had no effect on visual acuity but more
Significantly the importance of fruits and vegetables in the diet.
In addition to the association between the food intake and poor visual
acuity, the association between anthropometric parameters and visual acuity
was studied. The data was subjected to Mann-Whitney test. Those with high
BMI and more adipose tissue showed poor visual acuity. Skinfold thickness
measurement showed an obvious relationship between excess adiposity and
poor visual acuity, as shown by excess biceps, triceps, subscapular and
suprailiac measurements. However, less significant association between
waist and hip measurements (Table 7).
Although the present study is in line with many of the earlier reports,
this report is the first of its kind in the region of Eastern Cape in
South Africa which is previously disadvantaged in many respects. In addition
some of the food consumed is unique to this region and this may explain
some of the unique findings in the present study. The frequently consumed
carbohydrate rich food among the school children are bread, cereals and
rice. Most of the subjects didn`t even know about the traditional foods
like imbila, umvubo, umqa and isigwampa, which are prepared with grain
products, leafy vegetables and milk, thus rich in carbohydrates, proteins
and vegetables. The mean scores of the fruits and vegetables are comparatively
lower than that of carbohydrates and proteins. These habits lowered the
intake of proteins and vitamins in their diet. High carbohydrate intake
may take care of the energy needs but less likely the vitamin needs. Many
children who experience academic difficulty may have a treatable visual
impairment. Vision problems can interfere with the ability to perform
in the class room or can impair the ability to read with comfort and efficiency.
16% of the subjects in this study showed poor vision and their diet was
poor in protein, fruits and vegetables and also they showed a high score
for carbohydrates. They are probably obese people with higher BMI and
more adipose tissue than the students with good visual acuity. This showed
that carbohydrate had no effect on visual acuity and stresses the association
between obesity and poor visual acuity. This is a novel finding since
exclusion of traditional food in fact led to vitamin deficient diet which
led to poor visual acuity and replacement of traditional food with bread
has in fact led to poor visual acuity although energy needs are catered
for. Even the anthropometric data is quite revealing since the waist and
hip measurement did not have any impact on visual acuity although overall
BMI scores were reflective of obesity. Refractive error could be the major
reason for poor vision. This study did not check the refractive error
of the students, but it only focused on the effects of nutrition on visual
acuity. It could have produced better result, if it could check the refractive
error of the subjects.
There are few data available on the prevalence and type of refractive
errors in children in developing countries, myopia (5.6%) was the most
common refractive error among school children. In the Indian study 5.1%
of the children in school had a visual acuity of less than 20/40 in the
better eye, while 12.5% had a visual acuity of less than 20/30 or worse
in either eye (Kalikivayi et al., 1997). Recent studies in Nepal,
covering 40,000 children over a period of two years revealed high incidence
of xerophthalmia (Pokharel et al., 2000). Vitamin A deficiency
has long been recognized in much of South and Southeast Asia by the common
presentation of clinical cases of xerophthalmia (Quek et al., 2004;
Lin et al., 2001). Subsequent studies in Africa, where it had been
less well recognized, indicated that a large proportion of pediatric blindness
was due to acute deterioration in vitamin A status during measles and
similar childhood infections (Naidoo et al., 2003). Parental education
coupled with enhanced school-based screening may be needed to help identify
children with visual impairment.
CONCLUSION AND RECOMMENDATIONS
Lack of proteins, high carbohydrate diet and negligible fruit and vegetable
intake seem to be one of the causes of poor visual acuity in school children.
Periodic eye screening programmes can identify previously undetected eye
disorders in the school age population. It is suggested that screening
programmes for school age children coupled with immediate referral and
follow up procedures are worth while. Low visual acuity can be treated
easily and such the detrimental impact of visual impairment on a child`s
education and development could be prevented. It is also important to
educate the parents and the youth about the importance of following a
balanced diet. A school based vision screening at least in the rural communities
of South Africa is recommended. It will improve the children`s academic
life and quality of life in general.
The authors acknowledge the technical help given by Ms. Mapele in the
study and thank Mr. Vattakkunnel, Principal, Khanyisa High School , Mthatha
for providing the necessary assistance to carry out this project. Many
thanks for the students and their parents for their tremendous cooperation
in carrying out this project.