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Background: Refractive defects were identified as one immediate priority within the framework of VISION20/20.Uncorrected refractive defects are responsible for academic failure and several cases of amblyopia.
Objective: The basic aim of this study was to assess the status of refractive errors in school population, and their relation with amblyopia.
Method: The study was done on 8715 students aged 11 years to 16years, selected randomly from eight secondary government schools.
Result: Refractive errors were found in 226 (2.6%) children out of which 33 (14.6%) suffer from amblyopia. Astigmatism was the refractive error found more frequently (77%), followed by myopia (11%) and hyperopia (4.5%).
Conclusion:> Ametropias are very present in the school population and it is certain that they influence enormously the school life of children. Ametropias are also important causes of amblyopia, and low vision.
In order to appreciably reduce the problem of blindness in the world, WHO as well as a broad coalition of international organizations, launched on February 16th, 1999 in Geneva a baptized world initiative “VISION 20/20: right to the sight”. The objective of this new initiative is to eliminate avoidable blindness by 2020. Refractive defects were identified as one immediate priority within the framework of VISION 20/20. Ametropia is represented by all the situations where the optical system of the eye does not make it possible to focus the image of an object on the retina (Batterbury & Bowling, 2005). Thus, refractive anomalies have an immediate effect on the perception of objects or images and can also start several issues: cephalgias, tiredness, and pain.
A report of WHO in 1999 had estimated that the overall of refractive disorders in children lay between 2% and 10% 1999. With modernization, the invasion and the development of the digital screens, the statistics change continuously. One even currently speaks about an epidemic of myopia since the figures of this visual disorder are alarming . Recent meta-analyses have suggested that nearly half of the world’s population may be myopic by 2050, with as much as 10% highly myopic . Uncorrected refractive defects are also responsible for several cases of amblyopia. This disorder seems to assign 2 to 5% of the
population according to Flom & Neumaier . Amblyopia is a cortical disorder: the part of the brain which processes the data coming from an eye does not function in an optimal way. If this visual problem is not dealt with in time, that is likely to cause the vision loss. Locating amblyopia as soon as possible in children allows a more effective treatment as Stewart et al.  advise.
In Togo, the real prevalence of the refractive error and amblyopia is unknown. However, a regional study carried out in school in 2011 revealed that 6.5% of the pupils had an ametropia with a vision of the better eye lower than 7/10 (Togolese Red Cross, 2015). One can thus deduce from it, that with a national population of almost seven million inhabitants of which half of them is in school age, Togo would count about two hundred thousand (200,000) people of school age with an ametropia with visual acuity lower than 7/10 of the best eye.
Uncorrected ametropia can have a negative impact on the school output. Indeed, these children have a possible hazard of loss of education and thus an impossibility of finding decent employment. It results a situation from it being able to generate a poor quality of life and a fall of individual and social productivity. It is then, crucial to fight against refractive error in the population especially in young people or scholars.
In this study, we propose to analyze, thanks to the data
collected by the project “optical caravan”, the prevalence of
refractive defects, and their impact on vision in Togo. The first
objective consists in classifying and measuring the frequency of
the three main refractive defects which are myopia, hyperopia and
astigmatism; these data will allow a better estimate of ametropia
in the population and will be used as a basis to effectively follow
the statistics of refractive errors in the population.
The second objective will be examining the cases of
refractive amblyopia. Currently, we do not have of any data on
the frequency of amblyopia in our population whereas it would
be responsible of several cases of low vision and blindness. The
third objective is related to evaluate the impact of the project
and bring out the requirement of medical glasses, equipment
and techniques in order improve the projects which aim at the
correction of ametropia.
Togo, officially the Togolese Republic, is a country in West
Africa bordered by Ghana to the west, Benin to the east and
Burkina Faso to the north. It extends south to the Gulf of Guinea,
where its capital Lomé is located. Togo covers 57,000 square
kilometers, making it one of the smallest countries in Africa, with
a population of approximately 7.6 million. Togo is subdivided in
five regions and thirty-nine prefectures.
The national program of fight against blindness is a state
structure in charge of ocular health of the population. The
national program of fight against blindness, with the assistance
of the NGO Planet Vision, has to initiate since 2016 the project
“optical caravan” which consists of detecting refractive errors
among students and then, offering a pair of adapted glasses to
correct the defect (Figure 1). This project thus made it possible
to gather important information about ametropia in students
The educational system in Togo is organized in three
sections: primary school up to sixth grade, secondary school first
cycle which has four grades, and secondary school second cycle
with three grades. Generally, children begin school at six years
old. The targets of “Optical caravan” are pupils of the secondary
school first cycle between the ages of 12 to 16 years old (Table
This is a transversal study which takes into account eight
(8) secondary schools of the public sector. These schools are
distributed in seven (7) prefectures of the country. The study
unfolded over a period of one year (May 2017 to July 2018).
Inclusive criteria: All the students present, who readily
agreed to be examined
Non-inclusive criteria: Students who refused the examination
and those which were absent at the time of our passage. Pupils
with untreated pathology that affects refraction and VA. Criteria
of correction of refractive defects: pupils who have a vision with
the better eye lower than 8/10.
a) Secretary: It will be in charge of recording and
managing the student’s files.
b) Logistician: He will be in charge of the organization of
c) Drivers: He will take care of the transport of equipment
In order to perform our study, we used the following
a) Visual acuity scale
It is an eye chart that can be used to measure visual acuity.
Illuminated Snellen E chart is used at 5 meters during screenings.
It permits rapid determination of the VA, and it is very easy to use
when we deal with numerous people. VA is recorded as a fraction
corresponding to each line of the scale used. VA is performed eye
per eye and the mark is seized on the investigation card (Figure
3). Important parameters that can affect VA are considered. To
consider a mark of VA, pupils must “read” at least half of all
the symbols on a line. The environment of the room has to be
clear enough to validate each measure. E chart is easy enough
for secondary pupils so that, effects related to experience and
intelligence are reduced when making the measurements.
Attention and fatigue have also been controlled, as we have three
(3) or more technicians who make VA tests simultaneously.
b) Trial frame
Trial frame refraction is made in all the cases (Figure 2 &
5). Trial frame refraction is good for everyone (children, people
with disabilities, people with low vision, illiterate people, those
speaking a different language, elderly, high prescriptions). In
order to use it properly, the trial frame is adjusted for vertex and
inter-papillary distance and it adjusted to be straight on people’s
c) Slit lamp examination
Some conditions can alter the good functioning of the
eyes; and then alter the VA and refraction. The slit lamp is very
important in full examination process. It facilitates observation
of ocular adnexa, monitoring signs and symptoms of anterior
segment conditions and investigating the posterior segment.
Pupils with some pathological conditions which need medical
attention have been removed from the study (Figure 4).
d) Direct ophthalmoscopy
The ophthalmoscope allows seeing inside the eye. It is
done as part of eye examination to detect posterior segment
pathologies (retina, optic disc, and vitreous humour), which can
affect or alter VA (Figure 5).
Retinoscopy, also called skiascopy is a technique to
objectively determine the refractive error of the eye and the
need for glasses. It used when they suspect that auto refractor
measure is not reliable (Figure 5).
A very simple item, but useful to inspect the appendices and
anterior segment of the eye (Figure 5).
AUTOREFRACTOR NIDEK AR 220 is used during students’
screenings. It is known as very accurate; although in some cases
accommodation affects the result. If a case like this is suspected,
accommodation is controlled by fogging technique or cycloplegia
when performing refraction (Figure 2 & 4).
h) Cycloplegic eye drops
Cycloplegic is very useful in children’s refraction. It permits
to relax accommodation and so obtain more accurate refraction
by autorefractometry or retinoscopy (Figure 5). As we deal with
children in school, we have to manage a lot their accommodation,
because they use it all day to read and work at school. During
the screening, accommodative spasm is found in many pupils:
autorefractometry gives high myopia (over 6D), but in subjective
refraction these numbers are rejected, and by efforts they
manage to read up to 7/10 of VA (that is normally impossible
for a high myopia). In these cases, cycloplegiais mandatory.
It consists of inserting eye drops of Cyclopentolate 1% three
times at 10-minute intervals. After 40 minutes retinoscopy or
autorefractometry is repeated and it frequently occurs that
children have hyperopia.
i) Card of investigation
This card bears all the information concerning a pupil:
name and first name, age, sex, religion, class, telephone number
(own or parents), visual acuity, autorefractometry measure,
refraction, eye examination data, diagnosis and treatment. From
this investigation cards we gather information about ametropia,
visual acuity and amblyopia (Figure 6).
a) Make the examination of adnexa and anterior segment
of the eye with the flashlight.
b) Put the trial glasses to the pupil and hide the left eye.
c) Ask the pupil to keep both eyes opened during the test.
d) Begin with the line of VA 1/10 and then higher values
e) Ask the pupil for what he sees and what he can read.
f) Then measure the VA of each eye.
g) Register the data on the investigation card of survey.
h) If far VA is lower than 8/10, the pupil will be referred
i) Try refraction if there is ametropia.
j) Other eye examinations are performed if necessary:
eye fundus, slit lamp, etc.
Classification used in this study. Refractive errors are
classified as follows:
It is the difficulty in seeing distant objects clearly; image of
object in infinite is focused in front of the retina.
In hyperopia, the optical image of an object placed at infinite
is focused in rear of the retina when accommodation is relaxed.
So, accommodation is used to see from far distances, and even
more in order to see well a close object.
Astigmatism is a common vision problem caused by an error
in the shape of the cornea. With astigmatism, the lens of the
eye or the cornea, which is the front surface of the eye, has not
the same curve in all meridians. This can change the way light
passes, or refracts to the retina, and two perpendicular focal
images are formed in regular astigmatism.
In this study, astigmatism is those regular ones with a
cylinder value of 0.75 diopters or more. Astigmatism is also
a) Direct (0-30°), (180° -150°)
b) Inverse (60°-120°), (240º-300º)
c) Oblique (30°-60°), (120°-150°)
Myopic, hyperopic and mixed Ametropia is also classified by
a) Low myopia (0.5 to 3D), Medium myopia (3.25 to 6D),
High myopia (6.25 D or more)
b) Low hyperopia (0.25 to 3D), Medium hyperopia (3.25
to 5D), High hyperopia (5 D or more)
c) Low astigmatism (0.50 to 1.75) and high astigmatism
(2.00 or more)
We call amblyopia difference in two lines between the VA of
both eyes; VA with the best correction doesn’t increase with pin
hole, and there is not any pathology which can explain the visual
Data were seized in tables and analyzed in the software
Excel 2010. The dynamic cross table, the functions of sorting of
this software made it possible to emphasize the most important
information for our study. We have to count manually some
characteristics. Calculator is used also to do some calculation
and determine percentage. Word tables are used to present the
results of analysis.
The screenings permit to control 8715 pupils in secondary
school. 226 pupils had ametropia with VA in both eyes inferior
to 8/10. The prevalence of refractive errors is about 2.6%(Table
2). Astigmatism was the refractive error found more frequently
(average of 77%), followed by myopia (11%) and hyperopia
(4.5%)(Table 3). Direct or with the rule astigmatism is the
present in majority with 55%, followed by indirect (against
the rule) and oblique astigmatism, 38%; 8% (Table 4). High
refractive error is found in astigmatism (30% of them) and
myopia (9.5%)(Table 5). 33 cases of refractive amblyopia were
found. This represents a prevalence of 0.38%. Low and bilateral
amblyopia is 64% of amblyopia cases. Severe amblyopia is seen
in 3 children(Table 6). Most of the time, astigmatism of 2D or
more is responsible of refractive amblyopia (26 of the 33 cases
found). It is worth to notice that moderate hyperopia is also an
amblyogenic factor (Table 7).
A study done on visual impairment in school children in
southern India by Kalikivayi et al.  in 1990 reported prevalence
rate of myopia to be 8.6%; hyperopia 22.6%; astigmatism 10.3%.
So, hyperopia seems to be the most frequent found in children.
But in this study proportions are different. The great proportion
of astigmatism is explained by the fact that accurate methods are
used to refract pupils: Retinoscopy and autorefractometry. Often
many practitioners don’t correct astigmatism if they consider
VA is good enough with the sphere; but we know well that even
0.25 of astigmatism can change the vision of the patient. In this
study, even astigmatism of O.5D is corrected because we know
that these refractive errors are often causes of symptoms such
as headaches, eye pain, visual fatigue; which can influence the
school performance. Another factor which could influence the
statistics is the refractive errors of those who were not included
in the study. Among them there could be no negligible quantity
of hyperope and myope. So, we have to precise that these results
have to be considered together with the criteria of the study.
Garcia et al. (2005) in their study about the prevalence of
refractive errors in students in North-eastern Brazil showed
that hyperopia was the most common with 71%, followed by
astigmatism (34%) and myopia (13.3%). The resultant on the
studies of prevalence of ametropia vary in various studies,
because their criteria are often not the same, but it is necessary
to indicate that certain refractive errors can be characteristic of
certain ethnic groups or regions. There is also difference in rural
and cities populations .
High ametropia is an important risk factor for amblyopia.
The study showed us that they are responsible for 88% of the
cases of refractive amblyopia. High astigmatism is present for
the greater part; but in most cases it causes low amblyopia. High
hyperopia is a cause of severe amblyopia even if it is rarer. It is
important to note that even uncorrected moderate hyperopia
In this study, the prevalence of amblyopia is about 0.4%,
a figure which is not very far from those published in other
studies. In fact, several studies which were made on prevalence
of the amblyopia gave the following results  (Table 8). The use
of Cycloplegic in screenings is very important, since often many
cases of hyperopia are not reported. Indeed, many children
who reach 10/10 visual acuity could have low and moderate
hyperopia. As they are young, this hyperopia is not manifest in
decreasing VA, but instead it causes nonspecific symptoms such
as fatigue, pain in or around the eyes or episodic blurred vision
Ametropias are very present in the school population in
Togo, and it is certain that they influence enormously the school
life of the children and by consequence the whole society [11-
15]. Astigmatisms affect a lot of people, thus in the projects
which fight against ametropia, it is necessary to plan a large
number of cylindrical glasses. Ametropias are also important
causes of amblyopia, and low vision. Amblyopia is a real social
plague whose origins can be multiple. The only remedy is early
A school screening program is an effective way to detect the
causes of visual impairment in school children. It is worthy to
use for these screenings an objective and accurate technique that
reflects the real refractive status of children [16-18]. Though we
have to be careful in extrapolating the results of this study to
the entire population of school children in Togo, but these data
validate the need for vision screening of school children. School
screening programmes should be mandatory by the government