41 Epidemiology of Pediatric Strabismus
a
1
b
Fig. 1.3 A child with left fourth nerve palsy showing, (a) right head tilt and (b) left hypertropia with left head tilt
hypertropia include primary inferior oblique overaction, Brown syndrome, and CNS-associated hypertropia [14].
included children with CNS disorders or acquired nonaccommodative esotropia, distinct forms of early-onset esotropia that have been shown to occur more frequently than infantile esotropia. Acquired nonaccommodative esotropia, on the other hand, appears to be relatively prevalent and is a form of esotropia that is much more likely to develop fusion and normal stereopsis with treatment [8]. Intermittent exotropia, the most common form of exodeviation, is more prevalent than any other form of strabismus in Asia and, as a result, may be the most prevalent form of strabismus worldwide.
1.4.2Changes in Strabismus Surgery Rates
There have been several reports from the United Kingdom describing a decrease in the incidence of strabismus or strabismus surgery in recent years [21–24]. Explanations for this decline have included the implementation of childhood vision screening programs and the more frequent correction of the full hyperopic refractive error. Contrasting data, however, has come from Louwagie et al.’s population-based cohort study reporting on the incidence of infantile esotropia as well as the incidence of surgery for infantile esotropia in Rochester, Minnesota, US [7]. From 1965 through 1994, there was no significant change in the numbers of children diagnosed with infantile esotropia, and there was no significant change in the number of surgeries performed on these children.
1.3Strabismus and Associated Conditions
A number of studies have demonstrated an association between prenatal and environmental factors and the development of strabismus. Significant independent risk factors for strabismus include: family history, prematurity, low birth weight, low Apgar scores (at 1 and 5min), maternal cigarette smoking, increasing maternal age, retinopathy of prematurity, refractive error, and anisometropia [15–20].
1.4Changing Trends in Strabismus Epidemiology
1.4.1Changes in Strabismus Prevalence
Our understanding of the prevalence of childhood strabismus continues to change. As discussed earlier, congenital esotropia has recently been reported to occur less commonly than once widely believed, comprising only 8.1% of all diagnosed esodeviations [3]. The previously reported higher incidence of infantile esotropia may have
Summary for the Clinician
■Congenital esotropia appears to be less prevalent than previously believed, whereas other forms such as acquired nonaccommodative esotropia are relatively common.
■Intermittent exotropia may be the most prevalent form of strabismus worldwide.
■Therateof pediatricstrabismussurgeryhasrecently been reported to be in decline; however, data from a population-based cohort of children with congenital esotropia in the United States found no change in strabismus incidence or surgical rate over a 30-year period (1965–1994).
1.5Worldwide Incidence and Prevalence of Childhood Strabismus
Recent reports describe the prevalence of pediatric strabismus as ranging from 0.12% in 1.5-year-old Japanese children [25] to 20.1% in a cohort of low birth weight
1.5 Worldwide Incidence and Prevalence of Childhood Strabismus |
5 |
Table 1.1. Pediatric strabismus prevalence rates by regions of the world
|
Reference |
Categorical |
Number |
|
|
descriptions |
of |
|
|
within the |
children |
|
|
study |
examined |
North America |
|
|
|
Canada |
|
|
|
|
[31] |
|
946 |
|
[32] |
|
1,074 |
|
[33] |
|
2,619 |
USA |
[34] |
Caucasian |
306 |
|
|
Hispanic |
548 |
|
[15] |
All races |
39,227 |
|
|
Caucasian |
17,931 |
|
|
African American |
19,619 |
|
[35] |
Caucasian |
119 |
|
|
Asian |
310 |
|
|
Hispanic |
1,781 |
|
|
Black |
9 |
|
[27] |
Hispanic |
3,003 |
|
|
African American |
3,005 |
|
([3]a, [9]a, [14]a) |
Population-based |
|
Mexico |
[36] |
|
1,035 |
|
[37] |
|
343 |
Europe |
|
|
|
England |
[38] |
|
4,784 |
|
[39] |
|
6,634 |
|
[40] |
|
7,538 |
Ireland |
[41] |
|
1,582 |
Denmark |
[42] |
|
14,107 |
Sweden |
[43] |
|
6,004 |
|
[44] |
|
1,046 |
|
[45] |
|
3,126 |
|
[46] |
|
143 |
Croatia |
[47] |
All children |
20,045 |
|
|
Term |
17,163 |
|
|
Preterm |
2,882 |
Australia |
|
|
|
|
[20] |
|
1,739 |
|
[48] |
|
2,353 |
Asia |
|
|
|
Malaysia |
[49] |
|
650 |
|
[50] |
Near fixation |
4,634 |
|
|
Distance fixation |
4,634 |
Age of |
Strabismus |
Esotropia |
Exotropia |
Hypertropia |
subjects |
prevalence |
prevalence |
prevalence |
prevalence |
(years) |
(%) |
(%) |
(%) |
(%) |
1.6–11.6 |
4.3 |
|
|
|
<3 |
3.2 |
2.0 |
1.0 |
0.09 |
6 |
4.5 |
2.7 |
1.7 |
0.08 |
6–7 |
1.6 |
|
|
|
6–7 |
0.9 |
|
|
|
0–7 |
4.5 |
3.2 |
1.2 |
|
0–7 |
5.4 |
4.1 |
1.3 |
|
0–7 |
3.6 |
2.3 |
1.3 |
|
8–16 |
3.4 |
|
|
|
8–16 |
2.9 |
|
|
|
8–16 |
1.8 |
|
|
|
8–16 |
1/9 |
|
|
|
0.5–6 |
2.4 |
0.9 |
1.5 |
|
0.5–6 |
2.5 |
1.1 |
1.4 |
|
0–19 |
3.9 |
2.3 |
1.3 |
0.3 |
12–13 |
2.3 |
1.2 |
0.8 |
0.4 |
3–6 |
1.2 |
0.6 |
0.6 |
|
5–6 |
4.4 |
3.6 |
0.8 |
|
2 |
1.5 |
1.1 |
0.4 |
|
7 |
2.3 |
1.7 |
0.5 |
0.1 |
8–9 |
4.0 |
3.4 |
0.6 |
|
0–19 |
4.5 |
3.5 |
0.9 |
0.1 |
0–7 |
3.9 |
3.4 |
0.4 |
0.05 |
12–13 |
2.7 |
1.4 |
0.7 |
0.6 |
≤10 |
2.7b |
1.5 |
0.6 |
|
4–15 |
3.5 |
2.8 |
0.7 |
|
Unspecified |
4.0 |
2.1 |
1.8 |
|
Unspecified |
3.3 |
1.7 |
1.6 |
|
Unspecified |
8.0 |
4.7 |
3.3 |
|
6 |
2.8 |
1.6 |
1.2 |
0 |
12 |
2.7c |
0.9 |
1.1 |
|
8 |
2.2 |
0.2 |
1.8 |
0.2 |
7–15 |
0.7 |
|
0.5 |
|
7–15 |
0.7 |
|
0.6 |
|
(continued)
61 Epidemiology of Pediatric Strabismus
Table 1.1. (continued)
|
|
Reference |
Categorical |
Number |
Age of |
Strabismus |
Esotropia |
Exotropia |
Hypertropia |
|
|
|
descriptions |
of |
subjects |
prevalence |
prevalence |
prevalence |
prevalence |
1 |
|
|
within the |
children |
(years) |
(%) |
(%) |
(%) |
(%) |
|
|
study |
examined |
|
|
|
|
|
|
|
China |
[51] |
Near fixation |
4,364 |
5–15 |
1.9 |
|
1.6 |
|
|
|
|
Distance fixation |
4,364 |
5–15 |
3.0 |
|
2.6 |
|
|
|
[52] |
|
1,084 |
6–14 |
2.5 |
0.4 |
2.1 |
|
|
Japan |
[53] |
Study year 2003 |
86,531 |
6–12 |
1.3d |
0.3 |
0.7 |
|
|
|
[54] |
Study year 2005 |
84,619 |
6–12 |
1.0e |
0.2 |
0.6 |
|
|
|
[25] |
Five consecutive |
33,929 total |
1.5 |
0.01–0.1 |
0–0.03 |
0–0.07 |
|
|
|
|
measurements |
|
|
|
|
|
|
|
|
|
between years |
|
|
|
|
|
|
|
|
|
2000 and 2004 |
|
|
|
|
|
|
|
|
|
Five consecutive |
33,193 total |
3 |
0.2–0.3 |
0.02–0.1 |
0.2–0.3 |
|
|
|
|
measurements |
|
|
|
|
|
|
|
|
|
between years |
|
|
|
|
|
|
|
|
|
2000 and 2004 |
|
|
|
|
|
|
|
Taiwan |
[55] |
|
862 |
6, 8, 11 |
1.6f |
0.5 |
0.9 |
|
|
Thailand |
[56] |
|
3,898 |
1 |
0.6 |
|
|
|
|
India |
[57] |
|
6,447 |
5–15 |
0.5 |
0.3 |
0.2 |
0.02 |
|
|
[58] |
|
10,605 |
≤15 |
0.4 |
|
|
|
|
Nepal |
[59] |
|
1,100 |
5–16 |
1.6 |
0.09 |
1.5 |
|
|
|
[60] |
|
1,816 |
5–16 |
1.3 |
|
|
|
|
Middle East |
|
|
|
|
|
|
|
|
|
Israel |
[61] |
|
38,000 |
1–2.5 |
1.3 |
0.9 |
0.3 |
0.06 |
|
Oman |
[62] |
|
6,292 |
6–7, 11–12 |
0.6 |
0.4 |
0.2 |
|
|
|
[63] |
|
143,112 |
6–7 |
0.5 |
|
|
|
|
Africa |
|
|
|
|
|
|
|
|
|
Cameroon |
[64] |
|
11,230 |
≤26 |
1.2 |
0.5 |
0.8 |
|
|
Nigeria |
[65] |
|
1,144 |
4–24 |
0.3 |
|
|
|
|
Ghana |
[66] |
|
957 |
6–22 |
0.2 |
|
|
|
|
Tanzania |
[67] |
|
1,386 |
7–19 |
0.5 |
|
|
|
|
Madagascar |
[68] |
|
1,081 |
8–14 |
0.7 |
0.5 |
0.3 |
|
aStudy of incidence rather than prevalence
bStrabismus prevalence includes 19 cases of microtropia cStrabismus prevalence includes 16 cases of microtropia
dStrabismus prevalence includes 245 cases of “unknown” and 20 cases of “other” types of strabismus eStrabismus prevalence includes 110 cases of “unknown” and 23 cases of “other” types of strabismus fStrabismus prevalence includes two cases of “other” strabismus
English children [26]. Prevalence studies, reporting on the number of people with a specific disease at a prescribed point in time, are found most commonly in the pediatric strabismus literature. However, this type of study may only capture a snapshot of childhood ocular deviations. Incidence reports, on the other hand, by including the number of new cases diagnosed during a
specific period of time, may survey any number of characteristics and their changes over time.
Table 1.1 includes recent strabismus prevalence and incidence data organized by regions of the world. One overarching trend is that strabismus prevalence rates differ based on racial and ethnic background. Esodeviations are found with a relatively higher prevalence among
Caucasian populations, while exodeviations are more commonly reported among Asian and African children. As shown, North American, European, and Australian data contrast with epidemiologic information gathered from multiple studies in Asia and Africa. This trend is additionally evident among non-Caucasians in the US. In the Multi-Ethnic Pediatric Eye Disease Study group’s work describing strabismus prevalence among Hispanic and African-American children, for instance, exotropia was diagnosed more commonly than esotropia [27]. The basis of this di erence may be in part linked with popula- tion-based di erences in refractive error. Esotropia is commonly associated with hyperopia, whereas exotropia is more often diagnosed in children with myopia [28].
Summary for the Clinician
■The prevalence of strabismus subtypes varies based on racial and ethnic background; Asians are primarily diagnosed with exotropia whereas Europeans, Australians, and Americans are predominantly diagnosed with esotropia.
1.6Incidence of Adult Strabismus
Although there is substantially less epidemiological information regarding adult strabismus, its prevalence has been reported as approximately 4% in the United States [29]. In a study of strabismus patients over 60 years of age, 29% developed their ocular deviation in childhood [30]. Beauchamp and colleagues similarly found that a minority, or 38%, of strabismus patients between 17 and 92 years of age developed their deviation before visual maturation [29]. Common causes of adult strabismus in descending order include neuroparalytic, restrictive, and sensory factors [30].
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