Amblyopia: Effectiveness of visual screening for early detection in a comparative study between urban and rural school children

Abstract

Background: 

Amblyopia an important health problem among young children causing lifelong visual impairment if not treated at correct age. Timely screening of children for amblyopia and its appropriate treatment can prevent the consequences of the problem in their adulthood.

Materials and Methods: 

This study carried out a visual screening of 1234 school children in the age group of 3–12 years of urban and rural schools. All children having vision < 6/6, were called for detailed ophthalmic evaluation at tertiary care Government Hospital. Children who met the inclusion criteria and their best-corrected visual acuity found to be <6/6 on Snellen’s chart even after refractive check-up, were assessed for different amblyopia tests to categorize amblyopia into various types and severity.

Results: 

The prevalence of amblyopia in study group was 2.41% (8) in rural and 1.43% (13) in urban schools of 78 children from urban and 37 children from rural referred for detailed Ophthalmic evaluation which includes dropout rate of 24.35% and 35.13% from urban and rural, respectively. The prevalence of isoametropic amblyopia (38.46%) was maximum in urban whereas in rural it was anisometropic amblyopia (37.5%). Among the strabismic amblyopia, most frequent pattern was exotropia in both the groups, moderate degree amblyopia was more in urban and severe degree in rural. Amblyopia was bilateral in most of urban (61.53%) whereas unilateral in most of rural (75%) children. Hypermetropic refractive error was more prevalent in both urban and rural.

Conclusion: 

The prevalence of amblyopia was found more in rural children. The study highlighted differences in the severity of amblyopia, its types, and common refractive errors in both the groups. On the whole, there was no statistically significant difference in all parameters among both the groups.

INTRODUCTION

Amblyopia is defined as unilateral or rarely bilateral, decrease in best-corrected visual acuity (BCVA) caused by form vision deprivation and or abnormal binocular interaction, for which there is no identifiable pathology of the eye or visual pathway.^[1] The prevalence being 1.75% in an Indian study including children between 6 months and 16 years of age group.^[2] The prevalence of amblyopia is underestimated due to the lack of awareness and knowledge in parents, especially in rural areas and hence there is a late ophthalmological referral for visual assessment. This study aims at detecting such kinds of high-risk children at an early age by visual screening in both urban and rural schools. Timely diagnosis and treatment is likely to reduce the prevalence of amblyopia like in many developed countries which have taken mass education and visual screening at community levels.^[3]

Objectives

1. To compare the prevalence of amblyopia in children of urban and rural schools
2. To determine the frequency of different types of amblyopia in urban and rural school children.

MATERIALS AND METHODS

Study design

Cross-sectional study.

Study setting

The visual screening was conducted in rural and urban schools of Surat which gave permission for the same and detailed ophthalmological examination conducted in the department of ophthalmology of a tertiary care center in South Gujarat.

Study population and sample size

Study conducted in 1234 school children of 3–12 years’ age group.

Study period

Visual screening was carried out in 1234 school children in the age group of 3–12 years of urban and rural schools during September 2019–November 2019 and ophthalmic evaluation of referred patients done during a period of December 2019–March 2020.

Inclusion criteria for screening

All children of 3–12 years of age group in identified schools for screening.

Inclusion criteria for diagnosing amblyopia

1. Children of 3–12 years of age group with abnormal vision and suspected to be amblyopic through screening
2. Children whose parents give consent to come to the ophthalmology outpatient department (OPD) of a tertiary care center.

Exclusion criteria

• Participants who have visual disturbances due to any organic ocular diseases
• Mentally challenged children.

Data collection

Permission to conduct the study was obtained from Human Ethical Research Committee of Tertiary Care Hospital of South Gujarat. Many schools of the city did not give permission for visual screening of children. Schools which gave permission were selected and screening conducted in children of 3–12 years’ age group after the consent of principle and parents. Visual acuity assessment done using LEA symbols, Tumbling E-test, and Snellen’s chart as per age of the child and anterior segment examination (on torchlight) were carried out to rule out obvious ocular comorbidities, and the presence of strabismus. All children whose visual acuity was less than normal were referred to the Ophthalmology OPD of a tertiary care center for detailed ophthalmic evaluation. In OPD, visual acuity assessment was done in darkroom in an illuminated Snellen’s chart, and also the slit-lamp examination was carried out. All patients were given refractive correction if BCVA was found <6/6 they were investigated with various tests for amblyopia and data collection done in Microsoft XL sheet and if a child found to be amblyopic was categorized under different types of it.

Categorization and grading of amblyopic children in the study

As per the American Academy of Ophthalmology, amblyopia can be classified into the following.

Anisometropic amblyopia

Hypermetropic patients with anisometropia of 1 D difference may develop Amblyopia whereas in myopic anisometropes it is 2.5 D difference between two eyes.^[4]

Isoametropic amblyopia

Hyperopia exceeding 4.50 D and myopia exceeding 6.00 Din both eyes carry a risk of inducing isoametropic amblyopia.^[5]

Strabismic amblyopia

Results from abnormal binocular interaction between the two eyes where there is continued monocular suppression of the deviated eye.

Stimulus deprivation amblyopia

Occurs due to an eye abnormality which obstructs the central visual axis. Conditions like congenital/early acquired cataract, blepharoptosis, periocular lesions that obstruct visual axis, large corneal opacities, hyphema, vitreous hemorrhage etc. may cause this. If pseudophakia in children after cataract surgery not corrected for a longer period can also lead to deprivational amblyopia.

Meridional amblyopia

Results from image blur in one meridian. It can be unilateral or bilateral and is caused by uncorrected astigmatism (usually >1.5 D)^[4] persisting beyond the period of emmetropization in early childhood.

Occlusional or reverse amblyopia

Patching or pharmacological penalization with atropine^[6] if unsupervised can result in reverse amblyopia of the sound eye.

Grading of amblyopia

• Mild degree – BCVA of 6/9–6/12
• Moderate degree – BCVA-6/18–6/36
• Severe degree – BCVA <6/36.^[7]

RESULTS

A total of 1234 school children in four schools of urban and rural areas were screened. One hundred and fifteen children having uncorrected less vision in mass screening referred to the ophthalmology OPD of a tertiary care Eye hospital. Out of these 115, 78 (8.63%) from urban and 37 (11.17%) from rural were referred to ophthalmology OPD for the detailed ophthalmic evaluation. Out of them 32 did not turn up for further evaluation because of the COVID-19 (coronavirus disease) pandemic which occurred from March 2020 till date. This accounted for a dropout rate of 24.35% in urban and 35.13% in rural. Out of the 83 who attended OPD, 21 were diagnosed to have amblyopia, 13 from urban, and 8 from rural making a prevalence of 1.43% in urban and 2.41% in rural [Table 1]. The test result calculated using the Chi-square test– prevalence was found to be statistically insignificant (P = 0.24). Comparison of types of amblyopia was done between urban and rural in which ametropic amblyopia was more in urban that is five cases (38.46%) and anisometropic type in rural three cases (37.5%) [Chart 1]. Hypermetropic refractive error was more prevalent both in urban (30.76%) and rural (37.5%) amblyopes [Chart 2]. The study found that more number of amblyopes were found in the age group of 7–12 years than in 3–6 years both in urban (76.92%) and rural (87.5%) [Table 2]. Moderate degree amblyopia was more prevalent in urban amblyopes(42.30%) while severe degree in rural (25%) [Table 3].

Table 1: Compilation of data collected from the study

Chart 1: Comparison of types of amblyopia between urban and rural

Chart 2: Type of refractive errors seen in all amblyopes in the study

Table 2: Age distribution of amblyopic patients

Table 3: Comparison of severity of amblyopia between urban and rural

DISCUSSION

In our study, the prevalence of amblyopia in rural children (2.41%) was found to be higher than in urban (1.43%). This is comparable to Jarwal and Singh^[8] study in which 4020 children were screened and the prevalence of amblyopia derived was 0.9% in urban and 1.2% in rural, the result of which was statistically insignificant (P = 0.513). A similar study by Goel et al.^[9] screened 2700 children of the age group of 6–14 years of this 54 were amblyopic. This was more in rural (67.21%) than urban (32.76%). The higher prevalence of amblyopia in rural children is probably because of lack of awareness about regular check-ups and lack of parental awareness about ocular conditions in children. Our study result of the prevalence was analyzed using the Chi-square test and it was found to be statistically insignificant (P = 0.24) due to the low sample size and also the incidence of the studied condition is low in the population.

Among 13 urban amblyopes five cases (38.46%) were having ametropic amblyopia, 2 (15.38%) anisometropic amblyopia, 4 (30.76%) meridional amblyopia, 1 case (7.69%) had strabismic amblyopia, and 1 (7.69%) deprivational amblyopia. Among eight rural amblyopes two cases (25%) had ametropic amblyopia, 3 (37.5%) Anisometropic Amblyopia, 2 (25%) strabismic amblyopia, 1 (12.5%) had deprivational amblyopia, and there were no cases of meridional amblyopia found.

The prevalence of amblyopia was compared between two genders which showed a higher prevalence in males compared to females both in urban and rural. A higher prevalence of amblyopia is found in 7–12 years of age group both in urban (76.92%) and rural (87.5%) indicating late identification and diagnosis of amblyopia.

There was a higher prevalence of hypermetropic refractive errors in amblyopes both in urban and rural comparable to Menon et al.^[10] study in which of total 695 cases 359 (51.65%) had hypermetropia, 236 (33.95%) had myopia, and the remaining (14.32%) had astigmatism and compound refractive error.

In our study, a higher percentage of moderate degree amblyopia (42.30%) in urban and severe degree amblyopia (25%) in rural was found. There were more bilateral cases (61.53%) of amblyopia in urban and unilateral (75%) were more in rural.

CONCLUSION

The present study observed the prevalence of amblyopia to be more in rural than urban schools. Screening programs in school children increased parental awareness about ophthalmic conditions of their children, especially in rural areas. This study emphasizes that regular eye check-ups in urban preschool children and rural Anganwadi children which can help reducing the incidence of amblyopia in community.

Limitation of the study

The dropout rate for examination in our study was 24.35% in urban and 35.13% in rural schools and the difference in sample size between urban and rural schools was due to the COVID-19 pandemic.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.