|Year : 2014 | Volume
| Issue : 4 | Page : 220-225
Prevalence of amblyopia among children attending primary schools during the amblyogenic period in Minia county
Sahar T Abdelrazik, Mohamed F Khalil
Department of Ophthalmology, Faculty of Medicine, Minia University, Minia city, Egypt
|Date of Submission||17-Apr-2014|
|Date of Acceptance||25-Jul-2014|
|Date of Web Publication||24-Feb-2015|
Sahar T Abdelrazik
MD, Department of Ophthalmology, Minia University Hospital, Minia city 61111
Source of Support: None, Conflict of Interest: None
Amblyopia is one of the most important causes of visual impairments in young children; its incidence varies between 0.14 and 4.7%. An early diagnosis can enable optimal treatment.
Illiteracy and poverty play a major role in preventing individuals from seeking medical advice, and we lack data on the prevalence of amblyopia in Upper Egypt, especially Minia county.
This study aimed to screen for amblyopia in students attending the governmental primary schools in Minia County during the amblyogenic period.
A prospective observational cross sectional study was carried out between March and April 2010.
Patients and methods
Visual acuity and pen light ophthalmic examinations were performed for 1608 students (age range 7-9 years). Overall, 864 students were from urban areas and 744 were from rural areas. Children with defective vision were subjected to a full ophthalmic examination including slit lamp, orthoptic, and fundus examination in addition to cycloplegic refraction to detect the cause of reduced vision.
Of the total number of participants, 14.49% had defective vision; 0.75% had organic causes (5.2% of the patients with defective vision), 12.25% had refractive errors (84.5% of the patients with defective vision), and 1.49% had amblyopia (10.3% of the patients with defective vision). The main cause of amblyopia was anisometropia (54.16%), followed by strabismus (25%), ametropia (12.5%), and finally deprivation (8.33%).
The prevalence of amblyopia in our study is 1.49%, which is higher in rural areas than in urban areas.
Keywords: Amblyopia, Minia, rural, urban
|How to cite this article:|
Abdelrazik ST, Khalil MF. Prevalence of amblyopia among children attending primary schools during the amblyogenic period in Minia county. J Egypt Ophthalmol Soc 2014;107:220-5
|How to cite this URL:|
Abdelrazik ST, Khalil MF. Prevalence of amblyopia among children attending primary schools during the amblyogenic period in Minia county. J Egypt Ophthalmol Soc [serial online] 2014 [cited 2019 Aug 25];107:220-5. Available from: http://www.jeos.eg.net/text.asp?2014/107/4/220/150657
| Introduction|| |
Amblyopia is one of the most important causes of visual impairments in schoolchildren and responds well to treatment if diagnosed at a younger age. Many conditions are considered as predisposing factors for amblyopia including strabismus, refractive error (particularly anisometropia) or, more rarely, media opacification. In population-based studies, the prevalence of amblyopia was between 0.14 and 4.7%, and most of these studies in schoolchildren showed that 2% of students had amblyopia .
According to UNESCO statistics in 2004, the prevalence of illiteracy in Upper Egypt was 41.23% for adult women and 17.94% for adult men; in the same year, poverty increased to 20% nationwide, and in rural Upper Egypt, the poverty rate is as high as 41% .
Illiteracy and poverty play a major role in preventing individuals from seeking medical advice and some traditions prevent parents from seeking treatment for strabismus or allowing their children, especially females, to wear glasses to correct refractive errors.
| Objective|| |
For the above reasons and because of the lack of data on the prevalence of amblyopia in Upper Egypt, especially Minia county, we aimed to carry out this study to screen students in the amblyogenic period attending primary schools, where it is easy to gather the students in one place.
This prospective observational cross sectional study was carried out in the period from March to April 2010.
| Patients and methods|| |
After obtaining the approval of the research ethics committee of the faculty of medicine, Minia University, eight governmental primary schools from Minia County were selected to perform ophthalmic examination of children in grades 1, 2, and 3 for visual functions between March and April 2010.
The rural primary schools were two schools in the north and two schools in the south of the region and one near Minia city, whereas three urban primary schools were studied: one in the north, one in the south, and one in the center of Minia city.
All students had to be in the amblyogenic period (≤9 years); therefore, we chose to examine children from grades 1, 2, and 3 in each school, that is children who were 7, 8, and 9 years old.
A total of 1608 students were examined: 864 students from urban areas (urban group) and 744 students from rural areas (rural group).
In both the urban and the rural group, all the students were examined as follows:
- Anterior segment with a torch pen light.
- Visual acuity using the Kay picture test crowded LogMAR book (Kay Pictures, Tring, UK).
Students with visual acuity less than 6/6 in one or both eyes were referred and subjected to the following examination to detect the cause of reduced visual acuity:
- Anterior segment examination using slit lamp.
- Orthoptic examination.
- Cycloplegic refraction.
- Fundus examination.
After a full examination, the students were categorized into three subgroups:
- Those with organic causes of reduced visual acuity, for example media opacity, retinal lesions, etc: organic subgroup.
- Those with a refractive error that was correctable with glasses, with no residual amblyopia: refractive subgroup.
- Those with amblyopia: amblyopic subgroup.
Data were collected and the GraphPad Prism, version 4.0 program for Windows (GraphPad Software Inc., San Diego, California, USA) was used for statistical analyses. Differences between results were assessed using the χ2 -test for trend. P less than 0.05 was considered to be significant.
| Results|| |
A total of 1608 students were enrolled in our study: 744 (46.3%) from rural areas and 864 (53.7%) from urban areas.
The students ranged in age from 7 to 9 years, mean age 7.962 ± 0.8155 SD.
In rural areas, the mean age of the students was 7.960 ± 0.8144 SD, whereas in urban areas, the mean age of the students was 7.964 ± 0.8169 SD.
The male to female ratio was 57 to 42.97%, higher in rural (58.2 to 41.8%) than in urban areas (56.01 to 43.98%).
Causes of defective vision
The organic subgroup included 0.75% of the total students in the study and 5.1% of students with defective vision from both rural and urban areas.
For rural areas, the organic subgroup included 0.94% (seven out of 744 cases) of the total rural students and 6.4% of all patients with defective vision from rural areas.
Four children had corneal opacity with encroachment of the central corneal zone (0.54% of the total rural students).
Two children had macular scar (0.27% of the total rural students).
One child had complicated cataract to uveitis (0.13% of the total rural students).
In urban areas, the organic subgroup included 0.57% (five out of 864 cases) of the total urban students and 4% of all patients with defective vision from urban areas.
Two children had corneal opacity with encroachment of the central corneal zone (0.23% of the total urban students).
One child had a macular scar (0.11% of the total urban students).
Two children had albinism (0.23% of the total urban students).
The refractive subgroups
Refractive errors were found in 84.5% of all students with defective vision and 12.25% of the total number of the students in our study.
In rural areas, the refractive subgroup included 11.9% (89 out of 744 cases) of the total rural students and 80% of all patients with defective vision from rural areas.
Only 27 students (30% of those with refractive errors) were already wearing glasses at the time of screening; 21% were males (n = 19) and 9% were females (eight cases).
In urban areas, 12.5% (108 out of 864 cases) of the total urban students had refractive errors and this represented 88.5% of all patients with defective vision from urban areas.
A total of 43.5% of students with refractive errors (47 students) were already wearing glasses; 59.6% (28 students) were male students and 40.4% (19 students) were female students.
The amblyopic subgroup
Amblyopia was found in 1.49% of the total number of students in our study and 10.3% of patients with defective vision.
The prevalence of amblyopia was higher in students from rural areas (2%) than those from urban areas (1.04%).
In rural areas, anisometropia (eight cases out of 15) had the highest prevalence (53.33%), followed by strabismic (four cases = 26.6%), ametropic (two cases = 13.3%), and finally deprivational (one case of corrected severe ptosis = 6.66%), and we considered sensory strabismus cases because of anisometropia as anisometropic cases.
In urban areas, five out of nine cases were anisometropic (55.5%), two cases were strabismic (22.2%), and one case each of ametropic and deprivational amblyopia (pseudophakic) (11.1%).
In both rural and urban groups, anisometropia (54.16%) was at the top list of causes and deprivational amblyopia at the bottom (8.33%)and 15 children with amblyopia out of 24 (62.5%) in both rural and urban areas were females.
| Discussion|| |
The epidemiology of amblyopia in children is still unknown in some parts of the world, and the aim of our study is to report the prevalence of amblyopia in primary schoolchildren in Minia County.
We chose to screen for the prevalence of amblyopia in the amblyogenic period, that is younger than or at 9 years of age; during this period, treatment of amblyopia yields the best results compared with older ages. Thus, the age of the students enrolled in our study ranged from 7 to 9 years, mean age 7.962 ± 0.8155 SD.
In rural areas, the mean age of the students was 7.960 ± 0.8144 SD, whereas in urban areas, the mean age of the students was 7.964 ± 0.8169 SD.
In both urban and rural groups, there were predominantly male participants (57%), more in rural (58.2%) than in urban areas (56.01%). This can be explained by the fact that families still favor education of boys than girls, which is common in rural areas.
In our study, about 14.49% of the total number of participants had defective vision. The prevalence of defective vision among students in rural areas was 14.9% and that among students in urban areas was 14.1%, with no statistically significant difference (P = 0.6502) [Table 1].
|Table 1: Numbers and percentages of children with defective vision in rural and urban schools|
Click here to view
These results were similar to those obtained by Drover et al.  in Canada (14%), but about double the prevalence in Ghana (6.19%)  and much less than that in urban southern China (53.5%) ; this may be attributed to different ethnicities and also, in the Ghana study, only children attending private schools were included. Thus, they represented a specific cross-section of the Ghanaian society and were expected to have a higher socioeconomic level than the rest of the individuals in that particular locality.
About 0.75% of schoolchildren in our study (5.1% of children with defective vision) had organic causes, that is media and fundus abnormalities, and these results are in agreement with those of Kumah et al.  in Ghana (0.65%) and those of He et al.  (0.73%) in urban southern China.
The refractive errors
In the current study, among all children with defective vision (80% in rural areas and 88.5% in urban areas), 84.5% had refractive errors, and these children accounted for 12.25% of the total number of children in our study (11.9% from rural areas and 12.5% from urban areas), with a statistically insignificant difference between the two groups (P = 0.8514) [Table 2].
|Table 2: Numbers and percentages of children in organic, refractive errors, and amblyopic subgroups in rural and urban schools|
Click here to view
Our results were in the middle of the results reported by other studies in different parts of the world as shown in [Table 2], in which the prevalence of refractive errors ranged from 63.6 to 97.6% among children with defective vision and from 4.5 to 50.7% of the total number of children in each study.
Interestingly, El Bayoumy and colleagues reported a much higher prevalence (22.1%) of refractive errors than that in our study (12.25%) and this may be because their study included a higher age group; they also reported that the prevalence of low vision was greatest among the preparatory schoolchildren aged 12+ years [Table 3]. Also, their study was carried out in Cairo, whose socioeconomic status is different from our region .
|Table 3: Results of our study and other studies on the prevalence of refractive errors|
Click here to view
In our study, about 70% of rural schoolchildren and 55% of urban schoolchildren with refractive errors did not wear glasses at the time of screening; 90% of these children were females in rural areas and 60% were females in urban areas.
Prevalence of amblyopia
The overall prevalence of amblyopia in our study was 1.49% as shown in [Table 2].
A review of the results of other studies on the prevalence of amblyopia among children from different parts of the world is summarized in [Table 4]; the prevalence ranged from 0.14 to 4.7% in different age groups.
In our region, the Middle East, the prevalence of amblyopia in children ranged from 0.5% in Saudi Arabia  to 2.6% in Turkey , whereas the prevalence was 0.92% in the Sultanate of Oman  and 1.9%  and 2.29%  in Iran.
In Africa, Kumah et al.  reported a prevalence of amblyopia of 0.61% among private schoolchildren in Ghana, whereas in South America, Maul et al.  reported a prevalence of 1.57% in their study in Chile.
Interestingly, in the Far East and South Asia, the prevalence of amblyopia was almost the same, and it was around 1% in China, Tibet, and India ,,,.
However, in the developed countries, the prevalence varied from 0.14% in Japan  to 1.8% in Australia  and was as high as 4.7% in Canada .
In our study, the prevalence of amblyopia was higher in rural areas (2%) than in urban areas (1.04%), with a ratio of 5: 3, but the difference is statistically insignificant (P = 0.1082) [Table 2].
The main reason for this disparity could be the high incidence of anisometropic and strabismic amblyopia in rural than in urban areas, and this can be attributed to the fact that in rural areas, traditionally, strabismus is still considered by many as a congenital anomaly that does not necessitate therapy and if the parents are convinced with treatment they think they should wait later on till their child grew up.
In agreement with our results, Ganekal et al.  in their study, reported no statistical difference in the prevalence of amblyopia between rural (1.2%) and urban areas (0.9%), P = 0.5 [Figure 1].
In our study, anisometropia was the leading cause of amblyopia (54%), whereas 25% of children were strabismic, and the rest had ametropic (12.5%) and deprivation alamblyopia (8.5%). The distribution of the four types of amblyopia in both rural and urban groups was similar [Figure 2].
Both anisometropia and strabismus were responsible for about 80% of cases of amblyopia, and these results were similar to those reported in other countries.
In Iran, Yekta et al. and Faghihi et al. carried out two separate studies and reported that the causes of amblyopia were anisometropia (58 and 66%), strabismus (27.5 and 24.5%), and ametropia (14.5 and 9.5%), respectively ,.
In Turkey, Caca et al.  reported that 46% of cases were anisometropic, whereas 34% were strabismic.
In China, Fu et al.  reported that anisometropia was responsible for 48% of cases and other causes were strabismus, 14.8%, ametropia, 26%, mixed, 3.7%, and deprivation, 7.4%.
In another two studies, anisometropia and strabismus were equal causes of amblyopia and both represented 100% of the causes in sultanate Oman and 90% of causes in Australia ,.
In two other studies, anisometropia was second in the list of causes. In Japan, 60% were of unknown cause, 22% were anisometropic, 10% were ametropic, 7.5% were strabismic, and there was no case of deprivational amblyopia, whereas in India, ametropia represented 50%, anisometropia 40%, strabismus 6.8%, deprivational 4.5%, and mixed causes 2.2% ,.
In this study, 62.5% of the amblyopic patients were females, and this difference was statistically insignificant (P = 0.1265); the reason for this result might be that both anisometropia and strabismus represented about 80% of amblyopic cases in our study and as mentioned previously, there is a tendency for late correction of strabismus by parents in our locality also other studies had reported high incidence of anisometropia in females .
| Acknowledgements|| |
Conflicts of interest
There are no conflicts of interest.
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[Figure 1], [Figure 2]
[Table 1], [Table 2], [Table 3], [Table 4]
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