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Year : 2015  |  Volume : 7  |  Issue : 2  |  Page : 53-57

Prevalence of manifest horizontal strabismus among basic school children in Khartoum City, Sudan

1 Abdul Fadeel Almaz National Center for Ophthalmology, Khartoum, Sudan
2 Department of Ophthalmology, Khartoum University, Khartoum, Sudan

Date of Web Publication12-Nov-2015

Correspondence Address:
Aalaa Omer Taha
Abdul Fadeel Almaz National Center for Ophthalmology, Khartoum
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Source of Support: None, Conflict of Interest: None

DOI: 10.4103/1858-540X.169437

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Aim: To determine the prevalence of horizontal strabismus, the relationship between the family's socioeconomic factors and their attitude towards the child's eye health, its types, and to determine the attitude and compliance of the patients and their parents towards it among basic school children in Khartoum city between July and December 2010. Materials and Methods: A cross-sectional survey was conducted in Khartoum city among basic school children by questionnaire and eye examination. Sampling was with systematic random sampling for schools, probability proportional to size for children number in each school and systematic random sampling for children after obtaining a written consent from the ministry of basic education and parents. Results: 768 children were interviewed using questionnaire with a response rate of 100%. The questionnaires were analyzed using SPSS version 19 giving prevalence of horizontal squint of 2.8%, significant association between the father's educational level, socioeconomic status and their attitude towards eyes' health. Esotropia is the predominant type with a 2.2% and a slightly acceptable compliance towards regular eye follow up. Conclusion: Most of families didn't show good compliance towards the eye health unless they had a problem but almost all of them had the desire to know more.

Keywords: Children, Khartoum, manifest horizontal strabismus, prevalence, Sudan

How to cite this article:
Taha AO, Ibrahim SM. Prevalence of manifest horizontal strabismus among basic school children in Khartoum City, Sudan. Sudanese J Ophthalmol 2015;7:53-7

How to cite this URL:
Taha AO, Ibrahim SM. Prevalence of manifest horizontal strabismus among basic school children in Khartoum City, Sudan. Sudanese J Ophthalmol [serial online] 2015 [cited 2022 Jun 30];7:53-7. Available from: https://www.sjopthal.net/text.asp?2015/7/2/53/169437

  Introduction Top

With normal vision experience, the eyes gradually adopt their normal convergence angle while fixation reflex develops. [1] Although binocular single vision develops at the age of 2 years, the fixation reflex does not mature until the age of 9 years. Visual acuity remains in a state of flux before then. During this period, the child is vulnerable to strabismus and amblyopia. [2] The prevalence of strabismus and/amblyopia varies in different parts of the world. While studies in African children showed a prevalence of between 0.5% and 4.4%, [3],[4] its prevalence in other parts of the world varies between 0.9% and 7.4%. [5],[6] Monocular visual loss due to amblyopia is the leading cause of visual impairment in childhood and has a higher prevalence than conditions such as glaucoma and diabetic retinopathy in adult population (20-70 years age group). [7] Early detection of strabismus is important for restoration of normal ocular alignment and establishment of binocular single vision. Despite the fact that strabismus is an important cause of visual impairment among children, there are few studies devoted exclusively to it. [8] The objective of this study is to determine the prevalence of manifest horizontal strabismus and its types, and to determine the awareness, attitude, and compliance of patients and their parents among a group of Khartoum basic school children.

  Materials and methods Top

This is a cross-sectional survey conducted in Khartoum City, Khartoum State.

Study area and population:

  1. Khartoum locality in Khartoum City (one of the seven localities in the state, with its three administrative unit)
  2. Twenty-eight out of 288 basic schools in the locality between July and December 2010
    • Inclusion criteria: Age between 5 and 14 years old
    • Exclusion criteria: Age younger than 5 years and older than 14 years old
    • Diagnostic criteria: Rough estimation of a deviation was done by Hirschberg's test (at the school). Refraction, visual acuity, and full orthoptics report for the patients and suspects were done at Abdu-Alfadiel Almaz Eye Centre.

Systematic random sampling was performed for the schools and for the selection of children from the selected schools. While children number in each school was done with probability proportional to size. The sample size was 768 children.

Data were collected by validated self-administered questionnaires. It was analyzed using validated computer database management analysis, using Statistical Package for the Social Science (IBM SPSS Statistics), version 19.

A written consent was obtained from the Ministry of Primary Education. Another written consent was obtained from the parents. The affected children were referred to the strabismus clinic at Abdu-Alfadiel Almaz Eye Centre to receive appropriate management.

  Results Top

Seven hundred sixty-eight children were interviewed with a response rate of 100%. Among them, the prevalence of manifest horizontal strabismus among basic school children in Khartoum was found 28:1000 (2.8%). Esotropia was the predominant type with 2.2%, while exotropia is 0.4%. Routine visual check was done by nearly third of the study population (31.4%). Among those, 38.9% had glasses prescriptions and nearly half of them (48.4%) used it. There was slightly acceptable compliance toward regular follow-up for the glasses wearers with an ophthalmologist with 71.7%. A strike finding that, children with eye problems were 16.5%, were only half of them sought medical or specialized ophthalmological advice.

Pearson's Chi-square was used to find the association between level of education of parents and attitude toward eye check. The test yielded significant association regarding fathers. The higher level of education of the father, the poorer the attitude (P < 0.001). With regards to mothers education, the same test shows no statistically significant relationship (P = 0.017) [Figure 1] and [Figure 2]. It was also used to find the association between occupational status and attitude toward eye check. The test showed that fathers and mothers with good occupational status have a better attitude toward eye check with P = 0.003 and 0.007, respectively [Figure 3] and [Figure 4].
Figure 1: Relationship between father's educational level and good attitude toward the child's eye health among basic school children in Khartoum City

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Figure 2: Relationship between mother's educational level and good attitude toward the child's eye health among basic school children in Khartoum City

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Figure 3: Relationship between fathers' occupational status and attitude toward the child's eye health among basic school children in Khartoum City

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Figure 4: Relationship between mothers' occupational status and good attitude toward the child's eye health among basic school children in Khartoum City

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  Discussion Top

0 Prevalence of manifest horizontal strabismus

The prevalence of manifest horizontal strabismus in this study is 28:1000. This is consistent with prevalence figures in Australia, 2.8%, [9] and also consistent with figures from Western Nigeria where it was 2.6%, [10] 2.5% in North India, [11] 2.3% in the United Kingdom, [12] and 2.5% in Malaysia. [13] A large variation in this prevalence is found throughout the world. A low prevalence of 0.5% is found in Tanzania [4] and Southern Jordan, [14] of 0.9% in the Sultanate of Oman, [15] and of 1.22% in Cameroon. [16]

However, there is a higher prevalence in previous reports compared with this study: Southern Ethiopia [3] 4.4%, United States of America [6] 3.1%, and Ireland [17] 3.98%.

Furthermore, the variation in prevalence is found in different areas of the same country, such as that found in reports from Australia. They found that the prevalence of strabismus in children of 6 years of age in the Sydney Myopia Study was 1.8% (for children without eyestrain symptoms) and 7.3% (for children with eyestrain symptoms), [18] but was as low as 0.3% in another study of children 3 to 12 years in Victoria and New South Wales. [19]

In addition, these variations were found in Nigeria where it was 0.4% in the South, [7] 2% in the North, [20] and 0.06% in the East, [21] which could be due to racial causes.

There is no similar study done in Khartoum or even other parts in Sudan to determine whether there is similar variation like that or not.

Relationship between family socioeconomic status and attitude toward the child's eye health

Child's eye health had a strong association with the father's educational level [Figure 1], while this association was missing with the mother's [Figure 2]. It showed that the less educated the father was, the more careful toward the eye health. It might be due to the health education through the media, specifically the radio which was the favorable media to the illiterate people. It might also show a reflection of the health education which was always targeting the mother forgetting the role of the father in decision-making in the Arab societies.

The parents' occupational status, mainly father, which was an index of socioeconomic status, showed strong association with their attitude toward their child's eye health [Figure 3] and [Figure 4]. It did not make difference what their job was; the majority did not take care about eye health. This was similar to the findings of a study done in rural China, where the majority of parents had never took their children to be examined. The highest-ranked reason they gave that they were too busy with work. [22]

Another striking finding in this study was that a sizable minority (16.5%) of the study population were already having eye problems, while only 50% of them sought medical or specialized ophthalmological advice. These findings went with the suggestion in one Nigerian study where they thought of the variability in the prevalence of strabismus in different regions of the world as being influenced by social and environmental factors on strabismus. [8]

Types of manifest horizontal strabismus and other accidental findings

In this study, esotropia was more common than exotropia with the prevalence of 2.2% and 0.4%, respectively (81.82% and 18.18% of cases, respectively). This was similar to the findings of various studies done elsewhere. In Ilorin, Nigeria, it was found that esotropia constituted 68.75% cases, while exotropia accounted for 31.25%. [8] In Ethiopia, it was found that esotropia and exotropia consisted 78.1% and 20.8% of cases, respectively. [1] Similarly, in Ireland (United Kingdom), it was found that esotropia is 5 times more than exotropia. [17] Some studies showed different results where exotropia was the predominant. In Cameroon, exotropia was found in 75% cases and esotropia in 25% cases. [16]

In addition, in Iran, exotropia accounted 1.30%, while esotropia accounted only for 0.59 %. [23]

Workers in Hong Kong reported exotropia in 65.2% of cases and esotropia in 27.4% with microtropia accounting for 7.4%. [24] This variation in the pattern of esotropia and exotropia in different parts of the world was obvious with the above figures, but the cause was still unknown. Rachael and Jenkins suggest that the duration and intensity of sunlight as well as racial factors may play a major role. They thought that the higher the intensity of light, the higher the frequency of exotropia. [25] The higher prevalence of esotropia in this study, despite a high duration and intensity of sunlight, was not correlated to that suggestion which could be an influence to unknown, yet, factors.

Attitude and compliance of patients and parents toward eye problems

While only 31.4% of the study population did a routine visual check for their children, 38.9% of them had eye glasses prescription and nearly half of them (48.4%) of them really used it. They showed a slightly acceptable compliance toward it with a regular follow-up with the ophthalmologist of 71.7% of cases. Teachers described the principal barriers to eye glasses wear among children are lack of concern and understanding and worry about the appearance of the eyeglasses. [22] With these percentages, it was very striking that there was a major delay in presentation of squint (median delay = 2 years). The delay could be due to poor awareness among people regarding squint and its treatment or due to lack of proper health referral system and paucity of trained workers and eye care services. [26]


We highly recommend encouraging the authority makers to write recommendations to the Ministry of Basic Education about the importance of the preschool vision screening and making it a routine for school registration, and to stabilize the school screening programs for all schools (public and private). There might be a need to have similar study in other parts of the city and the country to make comparison and find any similarity or differences with this study. In addition, we recommend to make a link with the pediatricians to detect early ocular abnormalities which the parents could not notice and to enhance vision screening as early as possible after the 18 th months of age.

Financial support and sponsorship


Conflicts of interest

There are no conflicts of interest.

  References Top

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  [Figure 1], [Figure 2], [Figure 3], [Figure 4]

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