Original Article Prevalence of Amblyopia and Refractive Errors Among Primary School Children Zhale Rajavi1,2,3, MD; Hamideh Sabbaghi4,5, MS; Ahmad Shojaei Baghini2, MD; Mehdi Yaseri6, PhD Hamidreza Moein4, MD; Shadi Akbarian4, MS; Narges Behradfar4, MS; Simin Hosseini4, MS Hossein Mohammad Rabei2,3,4, MD; Kourosh Sheibani2, MD Ophthalmic Epidemiology Research Center, Shahid Beheshti University of Medical Sciences, Tehran, Iran 2 Basir Eye Safety Research Center, Basir Eye Clinic, Tehran, Iran 3 Department of Ophthalmology, School of Medicine, Shahid Beheshti University of Medical Sciences, Tehran, Iran 4 Ophthalmic Research Center, Shahid Beheshti University of Medical Sciences, Tehran, Iran 5 Department of Optometry, School of Rehabilitation, Shahid Beheshti University of Medical Sciences, Tehran, Iran 6 Department of Epidemiology and Biostatistics, Tehran University of Medical Sciences, Tehran, Iran 1
Abstract Purpose: To determine the prevalence of amblyopia and refractive errors among 7 to 12-year-old primary school children in Tehran, Iran. Methods: This population-based cross-sectional study included 2,410 randomly selected students. Visual acuity was tested using an E-chart on Yang vision tester. Refractive errors were measured by photorefractometry and cycloautorefraction. Strabismus was checked using cover test. Direct ophthalmoscopy was used to assess the anterior segment, lens opacities, red reflex and fundus. Functional amblyopia was defined as best corrected visual acuity ≤20/40 in one or both eyes with no anatomical problems. Results: Amblyopia was present in 2.3% (95% CI: 1.8% to 2.9%) of participants with no difference between the genders. Amblyopic subjects were significantly younger than non-amblyopic children (P=0.004). Overall, 15.9% of hyperopic and 5.9% of myopic cases had amblyopia. The prevalence of hyperopia ≥+2.00D, myopia ≤-0.50D, astigmatism ≥0.75D, and anisometropia (≥1.00D) was 3.5%, 4.9%, 22.6%, and 3.9%, respectively. With increasing age, the prevalence of myopia increased (P7.00D or hyperopia>5.00D, these levels of refractive error are characterized on the printout as high myopia or high hyperopia. Therefore, patients with myopia>7.00D or hyperopia>5.00D were excluded 410
based on the photorefractometer printout (out of limits) and thus not calculated in the prevalence of refractive errors, however such cases were not excluded from the prevalence of amblyopia, since amblyopia was defined according to VA testing. At the next step, cycloplegic refraction was performed in all subjects suspected of amblyopia 30-45 minutes after administration of one drop cyclopentolate 1% and tropicamide 1%, 5 minutes apart in each eye using an autorefractometer (RM-8800; Topcon Medical, Oakland, NJ, USA).
Ocular Alignment Assessment Alternate cover test or the Krimsky method was used to assess ocular alignment in subjects with visual acuity more or less than 20/200, respectively. These tests were performed at far (6 m) and near distances (33 cm) with an accommodative fixation target to detect deviation, if present. Ocular motility was checked in all gazes to detect any muscular dysfunction.[30] Journal of Ophthalmic and Vision Research 2015; Vol. 10, No. 4
Prevalence of Amblyopia in Tehran; Rajavi et al
Ophthalmoscopy Examination of the fundus, red-reflex, and anterior segment components such as crystalline lens and its opacities was performed using a direct ophthalmoscope (HEINE BETA 200; US). If the size of central lens opacity was more than 1mm, the subject was suspected of having a cataract.[31] In addition, the optic nerve and macula were examined using direct ophthalmoscopy by the ophthalmologist to exclude possible fundus lesions.
excluded from the study. Overall, 294 subjects showed reduced VA; of these, 64 had pinhole VA≤20/40 and were suspected of amblyopia and referred to Imam Hossein Medical Center, Shahid Beheshti University of Medical Sciences, Tehran, Iran to determine BCVA using cyclorefraction results [Figure 1].
Amblyopia
In this population-based cross-sectional survey, a total of 2,417 school children 7 to 12 (mean, 9.4±1.7) years of age were included. 51.2% were girls and 49.8% of participants were boys. Seven subjects (4 girls, 3 boys) who had abnormal conditions such as mental retardation (n=1), retinal colobomas (n=3), organic blindness (n=1), ocular albinism (n=1), and traumatic cataract (n=1) were
Amblyopia was diagnosed in 56 subjects (2.3%, 95% CI: 1.8% to 2.9%) who had BCVA ≤20/40. The percentage of amblyopia in different sexes and age groups is shown in Figure 2. Amblyopia significantly decreased with older age (P=0.014) [Figure 2]. There was no statistically significant difference between boys and girls in the prevalence of amblyopia at different age groups (P=0.079, based on interaction analysis). Thirty-six (64.3%) subjects had unilateral amblyopia while twenty (35.7%) had bilateral amblyopia. There was no significant difference between right (n=43, 56.5%) and left eyes (n=33, 43.5%) in the prevalence of amblyopia. 93.4% of amblyopic eyes had BCVA in the range of 20/40 to 20/100 (71/76 eyes), and the rest had BCVA less than 20/100. The prevalence of amblyopia was 15.6% among subjects using glasses and 1.04% among those with no prescribed glasses [Figure 1]. Figure 3 shows the prevalence of amblyopia with different types of refractive errors and anisometropia. The percentage of amblyopia was 15.9% in hyperopic eyes, 5.9% in myopia and 5.1% in astigmatism. In addition, 16.1% of anisometropic cases were amblyopic. The calculated OR for hyperopia and myopia as risk factors of amblyopia were 11.87 and 3.98, respectively. Amblyopia was found in 34.8% and 15.6% of esotropic and exotropic subjects, respectively, while only 1.8% of orthotropic ones had amblyopia [Table 1]. In addition, amblyopia was observed in 25% of subjects with anisometropia and strabismus (mixed amblyopia).
Figure 2. Amblyopia prevalence according to age and sex of children.
Figure 3. Amblyopia prevalence in different refractive errors and anisometropia. H, hyperopia; M, myopia; Cyl, cylinder; A, anisometropia; SE, spherical equivalent; diff, difference; D, diopter.
Statistical Analysis To determine the rate of amblyopia, direct standardization (for age and sex) was used in addition to assessing crude rates. To present characteristics of the patients, mean ± SD, median (range), frequency, and percent values were employed. To find the effective risk factors and obtain odds ratio (OR), logistic regression was used. Additionally, the simultaneous effect of different variables was obtained using multiple logistic regression analysis. Multilevel analysis was used in all the above calculations to consider design effect. The number of levels varied based on the type of variables. For example, subject-specific variables were evaluated at 3 levels (zone, school and subject) while eye-specific variables were evaluated at 4 levels (zone, school, subject and eye). All statistical analyses were performed using STATA (version 12.0). P-values less than 0.05 were considered as statistically significant.
RESULTS
Journal of Ophthalmic and Vision Research 2015; Vol. 10, No. 4
411
Prevalence of Amblyopia in Tehran; Rajavi et al Table 1. Basic characteristics and amblyopia risk factors among participants Associated factor Age (years) Sex Gestational and pediatric factors Prematurity Twin Seizure Ocular factors Anisometropia (SE difference≥1D) Strabismus
Mixed§ Ptosis Parental factors Parents sanguinity Family glasses
Level
Total (%)
Nonamblyopia (%)
Amblyopia (%)
Crude OR
Lower
95% CI of OR Upper
Crude P*
Mean±SD Median (range) Boy Girl
9.4±1.7 9 (7-12) 1199 (49.8) 1211 (50.2)
9.5±1.7 9 (7-12) 1171 (97.7) 1183 (97.7)
8.8±1.7 8 (7-12) 28 (2.3) 28 (2.3)
0.81
0.7
0.93
0.004†
1.04 1
0.66
1.63
0.873
Yes No Yes No Yes No
4 (.2) 2405 (99.8) 45 (1.9) 2364 (98.1) 47 (2.0) 2362 (98.0)
3 (75.0) 2350 (97.7) 41 (91.1) 2312 (97.8) 43 (91.5) 2310 (97.8)
1 (25.0) 55 (2.3) 4 (8.9) 52 (2.2) 4 (8.5) 52 (2.2)
14.05 1 4.26 1 4.07 1
2.72
72.65
0.002
1.47
12.37
0.008†
1.43
11.6
0.009†
Yes
93 (3.9)
78 (83.9)
15 (16.1)
12.87
8.16
20.31
Abstract Purpose: To determine the prevalence of amblyopia and refractive errors among 7 to 12-year-old primary school children in Tehran, Iran. Methods: This population-based cross-sectional study included 2,410 randomly selected students. Visual acuity was tested using an E-chart on Yang vision tester. Refractive errors were measured by photorefractometry and cycloautorefraction. Strabismus was checked using cover test. Direct ophthalmoscopy was used to assess the anterior segment, lens opacities, red reflex and fundus. Functional amblyopia was defined as best corrected visual acuity ≤20/40 in one or both eyes with no anatomical problems. Results: Amblyopia was present in 2.3% (95% CI: 1.8% to 2.9%) of participants with no difference between the genders. Amblyopic subjects were significantly younger than non-amblyopic children (P=0.004). Overall, 15.9% of hyperopic and 5.9% of myopic cases had amblyopia. The prevalence of hyperopia ≥+2.00D, myopia ≤-0.50D, astigmatism ≥0.75D, and anisometropia (≥1.00D) was 3.5%, 4.9%, 22.6%, and 3.9%, respectively. With increasing age, the prevalence of myopia increased (P7.00D or hyperopia>5.00D, these levels of refractive error are characterized on the printout as high myopia or high hyperopia. Therefore, patients with myopia>7.00D or hyperopia>5.00D were excluded 410
based on the photorefractometer printout (out of limits) and thus not calculated in the prevalence of refractive errors, however such cases were not excluded from the prevalence of amblyopia, since amblyopia was defined according to VA testing. At the next step, cycloplegic refraction was performed in all subjects suspected of amblyopia 30-45 minutes after administration of one drop cyclopentolate 1% and tropicamide 1%, 5 minutes apart in each eye using an autorefractometer (RM-8800; Topcon Medical, Oakland, NJ, USA).
Ocular Alignment Assessment Alternate cover test or the Krimsky method was used to assess ocular alignment in subjects with visual acuity more or less than 20/200, respectively. These tests were performed at far (6 m) and near distances (33 cm) with an accommodative fixation target to detect deviation, if present. Ocular motility was checked in all gazes to detect any muscular dysfunction.[30] Journal of Ophthalmic and Vision Research 2015; Vol. 10, No. 4
Prevalence of Amblyopia in Tehran; Rajavi et al
Ophthalmoscopy Examination of the fundus, red-reflex, and anterior segment components such as crystalline lens and its opacities was performed using a direct ophthalmoscope (HEINE BETA 200; US). If the size of central lens opacity was more than 1mm, the subject was suspected of having a cataract.[31] In addition, the optic nerve and macula were examined using direct ophthalmoscopy by the ophthalmologist to exclude possible fundus lesions.
excluded from the study. Overall, 294 subjects showed reduced VA; of these, 64 had pinhole VA≤20/40 and were suspected of amblyopia and referred to Imam Hossein Medical Center, Shahid Beheshti University of Medical Sciences, Tehran, Iran to determine BCVA using cyclorefraction results [Figure 1].
Amblyopia
In this population-based cross-sectional survey, a total of 2,417 school children 7 to 12 (mean, 9.4±1.7) years of age were included. 51.2% were girls and 49.8% of participants were boys. Seven subjects (4 girls, 3 boys) who had abnormal conditions such as mental retardation (n=1), retinal colobomas (n=3), organic blindness (n=1), ocular albinism (n=1), and traumatic cataract (n=1) were
Amblyopia was diagnosed in 56 subjects (2.3%, 95% CI: 1.8% to 2.9%) who had BCVA ≤20/40. The percentage of amblyopia in different sexes and age groups is shown in Figure 2. Amblyopia significantly decreased with older age (P=0.014) [Figure 2]. There was no statistically significant difference between boys and girls in the prevalence of amblyopia at different age groups (P=0.079, based on interaction analysis). Thirty-six (64.3%) subjects had unilateral amblyopia while twenty (35.7%) had bilateral amblyopia. There was no significant difference between right (n=43, 56.5%) and left eyes (n=33, 43.5%) in the prevalence of amblyopia. 93.4% of amblyopic eyes had BCVA in the range of 20/40 to 20/100 (71/76 eyes), and the rest had BCVA less than 20/100. The prevalence of amblyopia was 15.6% among subjects using glasses and 1.04% among those with no prescribed glasses [Figure 1]. Figure 3 shows the prevalence of amblyopia with different types of refractive errors and anisometropia. The percentage of amblyopia was 15.9% in hyperopic eyes, 5.9% in myopia and 5.1% in astigmatism. In addition, 16.1% of anisometropic cases were amblyopic. The calculated OR for hyperopia and myopia as risk factors of amblyopia were 11.87 and 3.98, respectively. Amblyopia was found in 34.8% and 15.6% of esotropic and exotropic subjects, respectively, while only 1.8% of orthotropic ones had amblyopia [Table 1]. In addition, amblyopia was observed in 25% of subjects with anisometropia and strabismus (mixed amblyopia).
Figure 2. Amblyopia prevalence according to age and sex of children.
Figure 3. Amblyopia prevalence in different refractive errors and anisometropia. H, hyperopia; M, myopia; Cyl, cylinder; A, anisometropia; SE, spherical equivalent; diff, difference; D, diopter.
Statistical Analysis To determine the rate of amblyopia, direct standardization (for age and sex) was used in addition to assessing crude rates. To present characteristics of the patients, mean ± SD, median (range), frequency, and percent values were employed. To find the effective risk factors and obtain odds ratio (OR), logistic regression was used. Additionally, the simultaneous effect of different variables was obtained using multiple logistic regression analysis. Multilevel analysis was used in all the above calculations to consider design effect. The number of levels varied based on the type of variables. For example, subject-specific variables were evaluated at 3 levels (zone, school and subject) while eye-specific variables were evaluated at 4 levels (zone, school, subject and eye). All statistical analyses were performed using STATA (version 12.0). P-values less than 0.05 were considered as statistically significant.
RESULTS
Journal of Ophthalmic and Vision Research 2015; Vol. 10, No. 4
411
Prevalence of Amblyopia in Tehran; Rajavi et al Table 1. Basic characteristics and amblyopia risk factors among participants Associated factor Age (years) Sex Gestational and pediatric factors Prematurity Twin Seizure Ocular factors Anisometropia (SE difference≥1D) Strabismus
Mixed§ Ptosis Parental factors Parents sanguinity Family glasses
Level
Total (%)
Nonamblyopia (%)
Amblyopia (%)
Crude OR
Lower
95% CI of OR Upper
Crude P*
Mean±SD Median (range) Boy Girl
9.4±1.7 9 (7-12) 1199 (49.8) 1211 (50.2)
9.5±1.7 9 (7-12) 1171 (97.7) 1183 (97.7)
8.8±1.7 8 (7-12) 28 (2.3) 28 (2.3)
0.81
0.7
0.93
0.004†
1.04 1
0.66
1.63
0.873
Yes No Yes No Yes No
4 (.2) 2405 (99.8) 45 (1.9) 2364 (98.1) 47 (2.0) 2362 (98.0)
3 (75.0) 2350 (97.7) 41 (91.1) 2312 (97.8) 43 (91.5) 2310 (97.8)
1 (25.0) 55 (2.3) 4 (8.9) 52 (2.2) 4 (8.5) 52 (2.2)
14.05 1 4.26 1 4.07 1
2.72
72.65
0.002
1.47
12.37
0.008†
1.43
11.6
0.009†
Yes
93 (3.9)
78 (83.9)
15 (16.1)
12.87
8.16
20.31
