Prevalence of amblyopia in primary school children in Qassim province, Kingdom of Saudi Arabia.

PURPOSE: To determine the prevalence and causes of amblyopia in primary school children in Qassim province, Kingdom of Saudi Arabia (KSA).
MATERIALS AND METHODS: In this cross sectional study, 5176 children, aged 6 to 13 years (mean - 9.53 ± 1.88 years) were evaluated. There were 2573 (49.71%) males and 2603 (50.29%) females. Distance visual acuity (V/A) was tested monocularly using a logMAR chart with and without correction. Cycloplegic refraction was performed in children with reduced vision. To determine the etiology of amblyopia, children were enrolled if there was a difference in V/A of two or more lines between eyes or an absolute reduction in acuity <20/30 in either eye, that could not be corrected by refraction. P ≤ 0.05 was considered statistically significant.
RESULTS: There 202 out of 5176 (3.90%) with ambylopia. There are 98 (1.88%) amblyopic females. There was no statistical difference in gender for amblyopes (P > 0.05). The prevalence of amblyopia was statistically significant higher in the older age group (10-13 year) compared to younger age group (6 to 9 years) (P < 0.05). Unilateral amblyopia (3.24%) was more frequent than bilateral amblyopia (0.66%). The most frequent causes of amblyopia were refractive error (94.56%), of which anisometropic amblyopia was present in 77.72%, isoametropic amblyopia in 16.84% and strabismus in 5.44%.
CONCLUSION: The prevalence of amblyopia in Qassim province, KSA, is 3.9% which is similar or higher than other published studies on amblyopia. Anisometropic refractive errors are the most common underlying cause for this population. We recommend implementation of visual screening programs for children with appropriate clinical and social settings for early detection and proper management of amblyopia.

INTRODUCTION

Amblyopia is a unilateral or bilateral condition in which the best corrected visual acuity is below normal, in the absence of any obvious structural or pathologic anomalies but with one or more of the following conditions occurring during visual developmental: Amblyogenic anisometropia, constant unilateral strabismus, amblyogenic bilateral isoametropia, amblyogenic unilateral or bilateral astigmatism.12 Amblyopia is a leading cause of vision impairment in children and usually begins in infancy or childhood.3 Congenital cataract, congenital ptosis and corneal injury or corneal dystrophy can also cause amblyopia but are less common.4 Amblyopia is a public health problem and is relatively common, affecting approximately 2 to 3% of children depending on the population studied and the definition used.56789 Its prevalence is usually underestimated, often due to lack of awareness and detection. The traditional concepts regarding the treatment of amblyopic children in older age groups have been disproven and amblyopia in older children can be treated successfully, although the outcomes may not rival those of children <7 years old.101112131415 In most cases amblyopia is unilateral, hence, even severe cases may not be detected by parents or care givers.16 Screening programs that test monocular visual acuity in children while they are young result in the best treatment outcome.17 With appropriate intervention most vision loss from amblyopia is preventable or reversible.2181920212223

The prevalence of amblyopia in the Kingdom of Saudi Arabia (KSA) varies based on geographic area. In the year 1994, the prevalence of amblyopia in preschool children in Riyadh, KSA was 2.6%. Among school age children it was 1.9% in Abha and 1.6% in Al BahaCity.24252627

Most of studies on the prevalence of amblyopia in KSA were conducted in the early nineties and studied local populations. To our knowledge, there is no published data on the prevalence or incidence of amblyopiain Qassim province, KSA. This is the first study designed to determine the prevalence of amblyopia and identify the causes of amblyopia in Qassim province. Our desire is to contribute to the development of an adequate visual screening program that will lead to early detection, diagnosis and proper management of amblyopia resulting in a decrease in the prevalence of amblyopia in KSA.

MATERIALS AND METHODS

A written request was sent to the general administration for education in Qassim province, seeking permission and selection for school-based vision screening. After approval, 21 schools were selected by the administrative authority for vision examination.

Prior informed consent was obtained from the parents of all children and the administrative officer of every school. Any child found to have ocular disorders was referred for treatment as warranted. Information was provided to the teachers explaining the need to inform the parents for further action.

A cross-sectional study was conducted in the primary schools in different region within Qassim province, KSA. The target population was primary school children. Data were collected from September 2010 to May 2011. The total number of children was 5176, of whom 2573 (49.71%) were males. The mean age was 9.53 ± 1.88 years (range, 6 to 13 years).

The eye examination included an assessment of eye health. It also included the assessment of the visual acuity, fixation pattern, refractive status, ocular alignment, motility, the Bruckner test, pupil examination, anterior and posterior segment examination, cycloplegic retinoscopy/refraction and funduscopic examination.

Monocular distance visual acuity (VA) was tested with and without correction with a logMAR chart by an optometrist from the optometry department at Qassim University. Pinhole acuity was assessed for any child with <20/30 or if there was more than 1-line (5-letter) difference between eyes.

Definitions

Strabismus was defined with any child with tropia at distance or near, with or without spectacles.

Unilateral amblyopia was defined, as a ≥2-line difference in best VA, when <20/30 in the worse eye and with amblyogenic factors such as past or current strabismus, anisometropia (≥1.00 D difference in hyperopia, ≥3.00 D difference in myopia, or ≥1.50 D difference in astigmatism).

Bilateral amblyopia was defined as best corrected VA (BCVA) in both eyes <20/40 in the presence of amblyogenic factors such as hyperopia >5D, myopia >8.00 D or astigmatism >2.50 D.162829

Any organic disease causing decreased vision was excluded by anterior and posterior segment examination and this was considered exclusion criteria.

A cycloplegic refraction was performed at least 20 min after instillation of 2 drops of 1% cyclopentolate hydrochloride and 1 drop of 1% tropicamide (instilled 5 minutes apart) and after corneal anesthesia with 1% amethocaine hydrochloride. The auto refraction was used as a starting point for the cycloplegic refraction.

Statistical analysis

Age and sex-specific prevalence rates for amblyopia were calculated. A P value of 0.05 or less was considered statistically significant. Means and standard deviation were also estimated. All statistical analyses were run on the computer, using the Statistical Analysis System (SAS) program (SAS, 2003).

RESULTS

There were 202/5176 (3.90%) children with amblyopia. Of the amblyopes, 104 (2.02%) were male. There was no gender difference in the prevalence of amblyopia (P > 0.05). Amblyopia was more common in the older age group (10 to 13 years) compared to the younger age group (6 to 9 years-old) in both male and female children and the difference was statistically significant (P < 0.05).

The most common cause of amblyopia was amblyogenic refractive errors (94.56%) [Table 1]. Other causes are presented in Table 1.

Table 1

The various causes of Amblyopia among schoolchildren in Qassim province, Kingdom of Saudi Arabia

Percentages of hyperopic anisometropic and isoametropic amblyopia and myopic anisometropic and isoametropic amblyopia are presented in Table 2.

Table 2

Proportions of hyperopic and myopic amblyopia among schoolchildren in Qassim province, Kingdom of Saudi Arabia

The contributions of anisometropic, isoametropic and strabismic amblyopia are presented in Table 3. There were 168 (3.24%) children with unilateral amblyopia and 34 (0.66%) with bilateral amblyopia.

Table 3

Proportion of various types of amblyopia among schoolchildren in Qassim province, Kingdom of Saudi Arabia

DISCUSSION

The World Health Organization (WHO) included uncorrected refractive errors among the leading causes of blindness and vision impairment worldwide and the most important/significant risk factor for the development of amblyopia. ‘Vision 2020’, a global initiative for the elimination of avoidable blindness, by the WHO; International Agency for Prevention of Blindness (IAPB) and other partner organizations, also included refractive errors as being among the five conditions, are an immediate priority.30 An important objective is to encourage the elimination of the avoidable causes of blindness that are primarily due to uncorrected refractive errors and low vision by the year 2020. Despite many advances both research and treatment of amblyopia, significant change in the current mode of practice has not occurred internationally.31

The results of this study from the entire Qassim Province revealed that 3.90% (202/5176) of schoolchildren were amblyopic. The prevalence of amblyopia varies regionally in KSA, ranging from 1.3 to 3.3%.25262732 Most previous studies were completed in the early 1990s but had design limitations, including, small sample size and/or sample selection problems, such as screening only children of families with higher education [Figure 1].

Figure 1

Outcomes of some studies on the prevalence of amblyopia in the Kingdom of Saudi Arabia

To our knowledge, this is the first study in KSA that included a large sample size from different areas in the Qassim province. A large sample size was used to avoid selection bias and it may explain the higher prevalence amblyopia reported in the current study. The prevalence of amblyopia worldwide varies. For example, a study by Awan et al.,(2010) in Lahore, Pakistan, reported that 3% of the children were amblyopic.33 In a multi-ethnic pediatric eye disease study (MEPEDS) conducted on African-Americans and Hispanics, amblyopia was detected in 2.6% of Hispanic/Latino children and 1.5% of African-American children.34 Williams et al.,(2008) found that in 7825 -7 year old children, 3.6% (95% CI: 3.3% to 4.1%) had past/present amblyopia.35 Pai et al.,(2012) included a total of 1422 children in their study and found that 1.9% of children had amblyopia.36 Drover et al.,(2008) estimated that 14.0% of the children possessed significant vision disorders, the most common were hyperopia, amblyopia and strabismus (4.8%, 4.7% and 4.3%, respectively).37 A study from Iran (2010) reported the prevalence of amblyopia was 2.32 in boys and 2.26% in girls.38 A study of Singaporean-Chinese children reported the prevalence of amblyopia was1.19%.39 A recent retrospective study in children aged 13 or older at Nepal Eye Hospital (NEH) reported that amblyopia was present in 0.7% (440) of 62,633 children examined and anisometropia was the most common cause. One-third (29%) of the subjects had bilateral amblyopia due to high ametropia.40 The prevalence of amblyopia in some of the countries mentioned above is presented in Figure 2. The prevalence of amblyopia and definitions of amblyopia used in these studies are further explained in table 4. The criteria for diagnosis of amblyopia are almost the same in these studies [Table 4]. The outcomes of the current study show that prevalence was higher in the older age group as compared to the younger age group. Similarly, a Baltimore pediatric eye disease study (BPEDS) showed a slight increase in the prevalence of amblyopia with advancing age41 whereas a Singaporean-Chinese study reported similar prevalence in different age groups.39

Figure 2

Global prevalence of amblyopia from various studies including the current study

Table 4

Prevalence of amblyopia in children from different population based studies

In the current study population, a high proportion of amblyopia cases were related to refractive errors (94.56%). This outcome concurs with findings from other school-based studies.3438394042 Anisometropic amblyopia was more common at low levels of hypermetopic anisometropia as compared to myopic anisometropia. The multi-ethnic pediatric eye disease study conducted on African-Americans and Hispanics and in the Singaporean-Chinese showed the prevalence of refractive amblyopia was 78 and 85% of cases respectively.3439 In studies conducted in Iran38 and China,42 anisometropic amblyopia was found in 58.1% and 67.3% of the amblyopic subjects respectively.3842 A study conducted in Nepal reported that anisometropia was the most common cause of amblyopia (P < 0.001).40

The current study demonstrates that amblyopia is more common in older children and those refractive errors represent the most frequent cause of amblyopia. This and previous studies have shown that anisometropic amblyopia is diagnosed at later ages than strabismic amblyopia because of a lack of obvious visual signs.434445

Historically it was generally accepted that older children respond less favorably to treatment for amblyopia.46 Hussein et al., (2004) stated that age of six years or older at the onset of treatment was a risk factor for failure to achieve functional success.47 Leon et al., (2008) showed that older children had increased risk of amblyopia as compared to younger children for moderate anisometropia. These studies emphasize the importance of early vision screening and improving treatment compliance as a result of timely intervention, meaning that the reduction in visual acuity caused by amblyopia can be completely or partially reversed.4849

However, recent randomized clinical trials have shown that it is possible to treat amblyopia in older children, adolescents and even adults.101112131415 The studies have reported an improvement in visual acuity occurring during amblyopia treatment is sustained in most children aged 7 to 12 years for at least 1 year after discontinuing treatment other than spectacle wear.101112131415 Hence, treatment of amblyopia even in an older age group may prove to have lasting benefit. However, vigilance is urged for any decrease in vision, which can be possible in this age group. Until proven, long term follow up is needed to determine the stability of visual improvement after cessation of therapy. A study by the Pediatric Eye Disease Investigator Group showed that visual acuity improves with optical correction alone in about one fourth of amblyopic patients aged 7 to 17 years, although most patients who are initially treated with optical correction alone will require additional treatment for amblyopia.12

Globally, different population-based studies suggest that screening increases the likelihood of detection of amblyopia and successful treatment.5051 It is suggested that amblyopic children tend to respond better to treatment during early visual development,5253 generally well before 7 or 8 years of age.54555657585960

In summary, the prevalence of amblyopia and suspected amblyopia in this sample population of Saudi school children was 3.9%, which is higher than that reported by other studies from KSA27303132 and higher than studies from other countries.36373839404142 The most common cause of amblyopia was refractive error particularly anisometropia and it was higher in the older age group as compared to the younger age group. The current detection rate for amblyopia for this age category was higher as compared to other studies suggesting that different strategies are required to promote vision screening and detection of amblyopia in schoolchildren with the goal of improving visual outcomes for amblyopic children with earlier treatment.

These types of prevalence studies are warranted in each region/province of Saudi Arabia to determine the national magnitude of visual impairment due to amblyopia. The data from similar studies will aid the “Saudi Ministry of Health” to design an appropriate strategy for effective screening programs and to provide adequate eye care services for school children throughout KSA.