Table 3.
A comparison of the prevalence of amblyopia reported in population studies.
| Authors (year) | Country, Age of Sample, (n) | Amblyopia Criterion |
Equipment to
determine VA |
Amblyopia
Prevalence |
Unilateral
versus Bilateral Ratio |
Refractive Error
among Amblyopes |
Amblyopia
Severity |
Presumed
Amblyopia Aetiology ☖ |
|---|---|---|---|---|---|---|---|---|
| Oliver and Nawratzki (1971). | Israel, 1.5-6 year olds, (n=5232). Population-based study. Random sample of children attending Mother & Child Care Clinics or kindergartens. |
VA difference of ≥2 lines. When VA test could not be performed (young children) diagnosis was established from unilateral strabismus or an obvious difference in the behavior of the child when one eye was covered as compared with the other. |
Equipment included small toys, matching tests, picture charts and illiterate E charts. Different tests used according to age. |
1.2% | --- | Hyperopia of ≥+3D: 46.3% Astigmatism of ≥2D: 13.4% Myopia (any amount): 6% |
--- | Strabismus: 68.7% (Esotropia 89%/Exotropia 11%) Anisometropia (≥2D): 29.9% |
| Lim et al. (2004) | Korea, 3-5 year olds (n=7116). Population-based study (‘Seoul Metropolitan Preschool Vision Screening Programme’). A home vision test kit was sent to the parents of kindergarten children. Children were identified from the Ministry of Health and Welfare database, The enrolled children represented 10.1% of the total same-age group of children who lived in Seoul. |
VA of 20/40 or worse (age ≤3 years) or 20/32 (>3 years), or any case with ≥2 line difference between eyes. |
Picture tests or single optotype tests. |
0.4% | --- | --- | --- | Ametropia 48.3%; Anisometropia 34.2%; Strabismus 12.8%; Unclassified 4.7%. |
| Pai et al. (2012) | Australia, 30 to 72 months, (n=1422). Population-based, cross-sectional study (‘The Sydney Paediatric Eye Disease Study’). |
Unilateral: ≥2-line difference in VA between 2 eyes with VA of 20/32 or below in the worse-seeing eye with 1 or more amblyogenic factor(s) Bilateral: VA of less than 20/50 (children aged <48 moths) or less than 20/40 in children aged ≥48months ,with either past history of bilateral visual axis obstruction, or bilateral significant ametropia |
Most with ‘Electronic Visual Acuity’ system, some using LogMAR chart |
1.9% | 63%/37% | Hyperopia ≥+4D SE: 51.9% Astigmatism of ≥1D: 48.1% Myopia of ≤− 0.50D SE: 7.4% Mean SE refractive error of amblyopic eyes +3.6D, compared to +1.25D in non- amblyopic eyes |
Mean VA of amblyopic eyes 20/50 compared to 20/25 in non- amblyopic eyes |
Amongst the unilateral cases: Anisometropia only, 41.2%; Strabismus only, 29.4%; Strabismus and Anisometropia, 29.4% |
|
Robaei et al. (2005)
Robaei et al. (2006) |
Australia, 6 year-olds (n=1741). Population-based, cross- sectional study (‘The Sydney Myopia Study’). The study area was stratified by socioeconomic status using Australian Bureau of Statistics 2001 National Census data. These data were used to select 34 primary schools across Sydney. |
Unilateral: Corrected visual acuity <0.3 logMAR units (poorer than 20/40) in the affected eye not attributable to any underlying structural abnormality of the eye or visual pathway, together with a 0.2− logMAR difference between the eyes and presence of an amblyogenic risk factor. Bilateral: Visual acuity worse than 0.3 in presence of bilateral hyperopia >+4D, bilateral myopia of −6 or greater or bilateral astigmatism of 2.5D or greater. |
LogMAR) visual acuity measured in both eyes before and after pinhole correction and with spectacles if worn. |
0.7% rising to 1.8% if children with successfully treated amblyopia are included. |
93.7%/6.3% | Most amblyopic eyes (58.7%) were significantly hyperopic (spherical equivalent > or = +3.00 D); 8.7% were myopic. |
Mean corrected VA in amblyopic eyes was <20/40 compared to 20/25 for overall sample of 6 year olds. |
Strabismus or strabismus surgery history : 37.5%; Anisometropia: 34.4%, both Anisometropia and strabismus: 18.8%; Isoametropia: 6.3% |
| Friedman et al. (2009) | USA. 30-71 month olds (n= 2546). Population-based, cross- sectional study (‘The Baltimore Pediatric Eye Disease Study’) that enrolled subjects from 54 contiguous census tracts in northeastern and eastern Baltimore City and adjacent portions of eastern Baltimore County. |
As in MEPEDS (2008) (see below). |
As in MEPEDS (2008) (see below). |
Caucasian: 1.8% African- American: 0.8% |
94.7%/5.3% | --- | --- | Unilateral cases: Anisometropia only, 31.6%; Strabismus only, 31.6%; Strabismus and Anisometropia, 10.5%. |
| MEPEDS (2008) | USA. 30-72month olds (n= 3817). Population-based, cross- sectional study (‘the multi- ethnic pediatric eye disease study, MEPEDS’) of children in 44 census tracts in Los Angeles County. |
Unilateral: a 2-line inter-ocular difference in best-corrected VA, VA of 20/32 or worse in the worse eye, and ≥1 amblyopia risk factor(s). Bilateral: Best- corrected VA of 20/50 or worse in children aged 30 to 47 months or 20/40 or worse in children ≥48 months) with either bilateral evidence of visual axis obstruction or bilateral ametropia |
Monocular, single- surrounded HOTV VA tested using the Electronic Visual Acuity system and the Amblyopia Treatment Study VA protocol (Holmes et al., 2001) |
Hispanic/ Latin: 2.6% African American: 1.5% |
76.8%/23.2% | --- | --- | Unilateral cases: Anisometropia. only, 73.6%; Strabismus only, 18.9%; Strabismus and Anisometropia, 5.7%. |
|
Preslan and Novak (1996)
Preslan and Novak (1998) |
USA (n=680) (3-6 year old children) USA (n=285) (4-6 year old children) Study of school children from an inner-city elementary school in Baltimore, USA (‘Baltimore Vision Screening Project’). Screening and treatment study. |
Criterion not explicitly stated but children examined if VA at screening was 10/15 or lower or if the motility examination was failed. |
Isolated Snellen-E optotypes presented at 3m. |
3.9% 5.3% |
88%/12% (1996 sample) 100%/0% (1998) |
Refractive error of anisometropic amblyopic eyes evenly split between hyperopia, myopia and astigmatism. (1996 study) |
VA in amblyopic eye ranged from 20/40 to 20/200 (1996) 60% had VA of 20/50 or better; 40% worse than 20/50 (1998). |
Strabismus: 44% (1996) (all but one was esotropic) 33% (1998); Anisometropia: 44% (1996) Anisometropia 33%, Astigmatism 33%. (1998) |
| Flom and Neumaier (1966) | USA, 10 to 50 year olds (n=7017). Not population- based. Records of patients who had presented for free eye examinations at an Optometry clinic. |
Best-corrected VA of 20/40-or worse and more than one line difference between the eyes,. |
---- | 1.7% | ---- | ---- | ---- | ---- |
| Lithander (1998) | Oman, 6/7 and 11/12 year- olds (n=6292). Cross-sectional study of school-children. |
Best-corrected VA of 20/40 or worse |
Snellen E- chart for 12 year olds, Kolt-test for 6 year olds. |
0.92% | 100%/0% | --- | 86.2% of amblyopic eyes had VA of 20/200 or better. |
Anisometropia only was present in 47.8% of amblyopes. Strabismus only was present in 32.2% of amblyopes. Strabismus and anisometropia were found in 20% of children. |
| Faghihi et al. (2011) | Iran, 6-21 years (mean 13.2 years) (n=2150). Cross-sectional study with cluster sampling from schools of district 1 in Mashhad. |
Reduction of BCVA to 20/30 or less in one eye or 2-line interocular optotype acuity differences in the absence of pathological causes. First to 8th grade students underwent auto-refraction following cycloplegia. Older children had subjective refraction. |
Snellen E- chart. |
1.9% | 73%/27% | Among myopic, hyperopic, and astigmatic students, 3.7%, 27.8%, and 6.5% had amblyopia, respectively. . |
--- | Anisometropia:65.9 %; Strabismus in 24.4%; Isoametropia: 9.8%. |
| Williams et al. (2008) | United Kingdom, 7 year olds, (n=7825). Participants consistent of children who participated in a birth –cohort study. |
History of patching treatment and/or with an interocular difference in best acuity for each eye of >0.2 logMAR where the worse-seeing eye had a best acuity of worse than 0.3 logMAR, and the eye looked normal on dilated funduscopy. |
VA measured monocularly, using the “2000” series ETDRS charts. |
3.6% | 83.7%/16.6% | 43.3% of those with hyperopia (≥+2D in either eye) had past or present amblyopia. |
--- | --- |
| Yassur et al. (1972) | Rwanda, 10-18 year olds (n=1552). Random sample consisting from six schools in the two main cities of Rwanda. |
VA of 20/40 or worse in at least one eye. |
Snellen chart. | 1.2% | --- | Hyperopia of ≥+2D:23% Astigmatism of ≥2D: 12% Myopia of ≤-2: 33% |
VA worse than 6/60: 44% VA 6/18 to 6/60: 44% 6/12: 12% |
Strabismus: 72% Anisometropia (>2D difference): 28% |
| Chang et al. (2007) | Taiwan, 3 to 6 year olds (n=5232). Population-based vision screening tests conducted in children in eastern Taiwan. |
Diagnosis by senior ophthalmologist. Best- corrected VA of less than decimal 1.0. |
--- | 2.2% | --- | --- | --- | Strabismus: 2.6%; Refractive errors: 62.6%; Anisometropia: 24.3%; Organic 10.4%. |
|
He et al. (2004)
He et al. (2007) |
China, 5 to 15 year olds (n=4364) China, 13 to 17 year olds (n=2400) Population-based study. Cluster sampling was used to select the study sample. Eye examinations were conducted in schools. |
Best-corrected VA of 20/40 or worse, no apparent organic lesion and with one or more amblyogenic factor(s) present. |
Retro- illuminated (LogMAR) chart with tumbling-E optotypes. |
0.87%/1.97 %* 0.50%/1.05 %^ |
--- | --- | --- | Strabismus: 25%; Anisometropia (≥2D SE difference): 66.6%; Anisometropia & Strabismus: 8.3%. |
| Goh et al. (2005) | Malaysia, 7 to 15 year olds (n=4634). Population-based, cross-sectional survey. Random selection of geographically defined clusters was used to identify the study sample. Children in 34 clusters were enumerated through a door-to- door survey and examined in 140 schools. |
Amblyopia was diagnosed when there was no apparent organic lesion but ≥1 from: 1) esotropia, exotropia, or vertical tropia at 4m, or esotropia or vertical tropia at 0.5m (‘strabismic amblyopia’); 2) anisometropia: ≥ 2D difference in SE (‘anisometropic amblyopia’); or 3) bilateral ametropia of ≥+6D SE. |
LogMAR (tumbling-E optotypes). |
0.65%/3.53 %◆ |
80%/20% | --- | --- | Strabismus: 23.3%; Anisometropia (≥2D SE difference): 63.3%; Anisometropia & Strabismus: 10%. |
|
Ohlsson et al. (2001). Ohlsson et al. (2003). |
Sweden, 12 to 13 years olds (n=1046). Population-based study of 12-13 year old children in Gothenburg, Sweden. Mexico, 12 to 13 years olds (n=1035). Population-based study of 12-13 year old children in Monterrey, Mexico. |
VA of 20/40 or worse or ≥2-line VA difference between the eyes and amblyogenic factors. VA of 20/40 or worse, no organic cause. |
Landolt C LogMAR Landolt C LogMAR |
1.1%■ 2.5% |
82.9%/17.1% |
--- --- |
--- 62.1%: logMAR 0.30 - 0.60; 24.1% logMAR 0.7- 0.9; 13.8%: logMAR<0.3 |
Unilateral cases: Anisometropia (56.5%), strabismus (30.4%), mixed strabismus and anisometropia (13.1%), --- |
| Helveston (1965) | USA, 17 to 25 year old males (n=9000). Army recruits??.CHECK |
VA of worse than 20/40 in one eye with ‘normal vision’ in the other eye with no detectable organic disease and no history of trauma or disease |
--- | 1% | --- | --- | --- | 52% of cases had ‘no detectable strabismus (i.e. anisometropia or history of strabismus)’®; 40% had esotropia; 8% had exotropia. |
| Chia et al. (2010) | Singapore Chinese, 30 to 72 months, (n=1682). Population- based study. Chinese children were recruited from Housing Development Board townships through a door-to-door recruitment exercise. The study area included a large part of the South-Western region of Singapore. |
Unilateral: ≥2-line difference in VA between 2 eyes with VA of 20/30 or below in the worse-seeing eye with at least one amblyogenic factor Bilateral: VA of less than 20/50 (children aged <48 moths) or less than 20/40 in children aged 48-72 months with either past or present visual axis obstruction, or bilateral significant ametropia |
LogMAR chart. Sheridan- Gardner when logMAR not possible |
1.2% ⊖ | 69.7%/ 30.3% |
Not stated but astigmatism identified as most frequent amblyogenic risk factor. |
--- | Unilateral cases: Anisometropia only, 78.3% Strabismus only, 21.7%, Strabismus and Anisometropia, 0% |
| Wang et al. (2011). | China, Adults aged 30 to 80 years, (n=6830). Population- based, cross-sectional study. Thirteen villages in the Yongnian County of Handan were selected randomly, and residents of these selected villages 30 years of age or older were invited to participate in the Handan Eye Study. |
Unilateral: best- corrected VA of 20/32 or worse, not attributable to any underlying structural abnormality of the eye or visual pathway. Bilateral: best- corrected VA of 20/32 or less in both eyes and a history of form deprivation during the sensitive period of visual development. |
LogMAR chart | Crude: 3% Adjusted: 2.8%◇ |
60.7%/39.3% | Of the amblyopia cases, 47.6% were hyperopic. |
--- | Anisometropia (67.3%), strabismus (5.4%), mixed strabismus and anisometropia (4.4%), visual deprivation (9.8%), astigmatism association (9.8%), and other (3.4%). |
| Rosman et al. (2005). | Chinese, Indian, and Malay men, aged 18 to 19 in Singapore (n=122,596). Population-based, cross- sectional study of all Singaporean men born in the years 1978 to 1983 were measured before enlistment into military service. |
Best corrected visual acuity of 20/40 or worse, not attributable directly to any underlying structural abnormality of the eye or visual pathways. |
--- | 0.35% | --- | --- | --- | Anisometropia: 37.1%; Strabismus 5.7%; Meridional: 14.3% |
| Brown et al. (2000). | Australia, 40-92 year olds (n=4721). The Visual Impairment Project is a population-based study of age- related eye disease in the state of Victoria, Australia. |
Unilateral: Best- corrected visual acuity of 20/30 or worse in one eye, with at least one line difference in VA between the eyes without attributable pathological cause. Bilateral: Best- corrected visual acuity of 20/30 or worse in both eyes with history of form deprivation or high uncorrected ametropia. |
LogMAR chart, using current glasses. Refraction performed if VA found to be less than 20/20. |
Unilateral: 3.1% |
>99% unilateral |
Spherical equivalent hyperopia (>+0.50D) was present in 52%; myopia (more than −0.5D) was present in 38.6% of amblyopic eyes.. |
54% of amblyopic eyes had visual acuity of worse than 20/40; 27.9% had VA of worse than 20/60; 10.9% had VA worse than 20/80. |
53.9% of amblyopes had anisometropia (≥1D difference in spherical equivalent refraction). 46% of amblyopic eyes had astigmatism of 1D or more. Cover test not performed so no strabismus data reported. |
| Nowak et al. (2009). | Poland, Military 18-34 year olds (n=969).Retro spectively study of males of European Caucasian origin, most of whom live and have lived in Poland, and who were selected from the original database comprising 105017 subjects examined in the period 1993-2004. |
Distance visual acuity of worse than 20/40 in one or both eyes. |
Retro- illuminated Snellen chart. |
0.8% | 87.5%/12.5% | ---- | ---- | ---- |
| Quah et al. (1991). | Singapore, Males 18-19 year olds, (n=6556). Vision screening of National Service pre- enlistees. |
VA of 20/40 or less in one or both eyes in the absence of ocular pathology. |
Snellen chart. | 0.73% | 98%/2% | 75% of anisometropic amblyopes were myopic, 25% wer e hyperopic. |
Anisometropia: 50%, strabismus: 18.7%; high astigmatism: 14.5%; Other causes/ combination of factors: 16.7%. |
|
| Attebo et al. (1998). | Australia, 49 years and older, (n=3647, of whom 2068 were female). Population-based, cross-sectional study of eye disease in elderly people living in the community (‘Blue Mountains Eye Study’). All identified, eligible residents were invited to attend a clinic appointment. |
Reduced best- corrected visual acuity in the absence of any other cause |
LogMAR chart, using current glasses and pinhole disc. Refraction performed if VA found to be less than 20/20. |
VA of 20/40 or worse: 2.9%. Prevalence was 3.2% for criterion of 20/30 or worse. |
99%/1% | Spherical equivalent hyperopia up to +5D was present in 50% of amblyopic eyes, ~20% had hyperopia >+5D, and 25% were myopic |
19% of amblyopic eyes had VA of 20/200 or worse, 19% had VA of 20/80 to 20/160, 52% had 20/40 to 20/63, and 11% had VA of 20/30. Poorest VA in visual deprivation amblyopes. VA in strabismic amblyopic eyes was poorer than in eyes with strabismus &anisometro pia and poorer than VA in eyes with anisometropi c amblyopia |
Anisometropia (50%), strabismus (19%), mixed strabismus and anisometropia (27%), and visual deprivation (4%). Amongst strabismic amblyopes, 59% were esotropes, 28% were exotropes and 11% were microtropes |
◇
Adj: prevalence figure adjusted so that the sample population matches overall population according to census in that country. ‘Crude’ refers to actual prevalence in the sample under test.
☖
Aetiology is presumed since the studies reported here are cross-sectional in nature not longitudinal.
*
In He et al. (2004) amblyopia was diagnosed in 0.87% of the population but in a further 1.1% of the population amblyopia was considered the principal cause of the “unexplained reduction” in best-corrected visual acuity, even though none of the explicit criteria for amblyopiadiagnosis were met.
^
In He et al. (2007) amblyopia was diagnosed in 0.50% of the population but in a further 0.54% of the population amblyopia was considered the principal cause of the “unexplained reduction” in best-corrected visual acuity, even though none of the explicit criteria for amblyopia diagnosis were met.
◆
In Goh et al. (2005) amblyopia was diagnosed in 0.65% of the population but in a further 2.88% of the population amblyopia was considered the principal cause of the “unexplained reduction” in best-corrected visual acuity, even though none of the explicit criteria for amblyopia diagnosis were met.
■
Ohlsson et al. (2001) make it clear that this is the prevalence of residual amblyopia since they sampled a population that had previously been screened
®
Some of Helveston’s (1965) amblyopia cases without ‘detectable strabismus’ may have been microtropes.
-—-- means this information was not provided in the paper.
⊖
In Chia et al. (2010), 2.8% of the sample met the visual acuity criterion for amblyopia but 58% of these cases were not diagnosed as have amblyopia because insufficient amblyopic risk factors were identified.