Congenital esotropia in Olmsted County, Minnesota1

Congenital Esotropia County, Minnesota Brian G. Mohney , MD,’

Jay C. Erie, MD,’

in Olmsted

David 0. Hodge, MS,’

Steven J. Jacobsen, MD,

PhD3

Objective: To determine the birth prevalence of and risk factors associated with congenital esotropia. Population-based prevalence study with nested case-control study. Design: Participants: All residents of Olmsted County, Minnesota who were diagnosed with congenital esotropia and born between January 1, 1980 and December 31, 1989 (n = 47). Control subjects were chosen by selecting the next two sequential births to parents residing in Olmsted County, Minnesota (n = 94). Methods: Cases were identified through the Medical Diagnostic Index of Mayo and the Rochester Epidemiology Project. The community medical records were reviewed to confirm case status and ascertain risk factor information. Birth prevalence of congenital esotropia. Main Outcome Measure: Results: Forty-seven cases were identified from 17,536 live births, for a birth prevalence of 27 per 10,000 (95% confidence interval [Cl], 20-35). Congenital esotropia was associated with prematurity (odds ratio [OR], 11.5; 95% Cl, 3.4-39.2), a birth weight less than 2500 grams (OR, 4.6; 95% Cl, 1.7-12.9), a low Apgar score at 1 minute (OR, 4.3; 95% Cl, 1.7-l 1.2) and at 5 minutes (OR, 6.3; 95% Cl, 1.3-30.7) and a family history of strabismus (OR, 3.5; 95% Cl, 1.5-8.3). Conclusions: The birth prevalence of congenital esotropia in Olmsted County, Minnesota is lower than previous estimates. Prematurity, low birth weight, low Apgar scores, and a family history of strabismus are significant risk factors for congenital esotropia. Ophthalmology 7998; 705:846-850

Congenital esotropia is a nonaccommodative disorder of ocular alignment in which the eyes manifest convergent deviation within the first 6 months of life. Unlike accommodative or other acquired forms of esotropia, congenital esotropia requires early surgical correction to facilitate binocular visionlm3 and has a poorer long-term motor and sensory status prognosis.“ Moreover, congenital esotropia is a significant risk factor for amblyopia, the most common cause of decreased vision in the first four decades of life.5 Consequently, knowledge about the risk factors for congenital esotropia and reliable estimates of the prevalence of congenital esotropia are important to healthcare providers. Much of the data on congenital esotropia, however, are from

Originally Revision

received: accepted:

January October

3 Section of Epidemiology, ter, Minnesota.

Mayo

Mayo Clinic Clinic

Clinic

and Mayo

Foundation,

and Mayo

Foundation,

Rochester,

and Mayo

Foundation,

Roches-

This study was supported in part by a grant from the National Institutes of Health (AR30582), Bethesda, Maryland; an unrestricted grant from Research to Prevent Blindness, Inc., New York, New York; and Mayo Foundation, Rochester, Minnesota. Dr. Mohney is currently affiliated East Tennessee State University,

with the Division of Ophthalmology, Johnson City, Tennessee.

The authors have no commercial or proprietary or instruments mentioned in this article.

interest

Address correspondence to Jay C. Erie, MD, Mayo of Ophthalmology, 200 First Street SW, Rochester,

846

Methods Source of Data

7, 1997. 17, 1997.

’ Department of Ophthalmology, Rochester, Minnesota. ’ Section of Btostatistics, Mayo Minnesota.

office-, hospital-, or school-based series.“-” Such surveys do not necessarily reflect prevalence rates in the overall healthcare system. The primary goal of this study was to determine the birth prevalence of congenital esotropia among children residing in Olmsted County, Minnesota who were born during the lo-year period from 1980 through 1989. We also assessed risk factors leading to the development of congenital esotropia in this population using a nested case-control design.

in any products

Clinic, Department MN 55905.

A population-based study of the prevalence of congenital esotropia combined with a nested case-control study is possible in Olmsted County, Minnesota because the city and county are relatively isolated from other urban centers and because the population is served by a largely unified medical care system that has accumulated comprehensive clinical records for many years. Rochester, Minnesota (1990 population, 69,995) is located 90 miles southeast of Minneapolis and St. Paul. Approximately 70% of the county population resides within the city limits of Rochester. The 1990 population of the county was 96% white and largely middle class, and approximately 82% of adults were high school graduates. Most medical care for residents of Rochester and Olmsted County is provided by the Mayo Clinic, which is a tertiary referral center but also provides comprehensive primary and secondary care for the region. The Mayo Clinic unit record has afforded access to details of the medical care provided to resi-

Mohney et al * Congenital Esotropia dents of Rochester and Olmsted County, Minnesota since the turn of the century. The diagnoses and surgical procedures of all Mayo Clinic patients are indexed, and the original medical records can be readily retrieved for review.“~” The Rochester Epidemiology Project maintains similar indexes of diagnoses made and surgical procedures performed by other providers of medical care to Rochester and Olmsted County residents, including the Olmsted Medical Center (OMC), the Department of Veteran’s Affairs and the University Hospitals in Minneapolis 90 miles northwest of Rochester, all other small hospitals in the surrounding counties, and the few independent medical practitioners in Rochester. The potential of this data resource for population-based studies has been described elsewhere.‘2m’4

Identification of Potential Cases of Congenital Esotropia and Selection of Control Subjects Potential cases of congenital esotropia within this populationbased cohort of infants of Olmsted County, Minnesota were identified by searching the Medical Diagnostic Index of Mayo and the Rochester Epidemiology Project for patients with a diagnosis of “congenital esotropia,” “infantile esotropia,” or “esotropia” between January 1, 1980 and December 3 1, 1989. Prevalence cases were identified as infants who were diagnosed with congenital esotropia and born to residents of Olmsted County during the specified study period. Only those who met our definition criteria were designated as cases for the study. In our study, we defined congenital esotropia by the following: 1. 2. 3. 4.

Documented presence by 6 months of age. Constant, large angle deviation (2 30 prism diopters). Nonaccommodative esotropia. Normal central nervous system.

Only subjects who displayed all four characteristics were included in the study. All patients were examined and diagnosed by an ophthalmologist. The age at onset was also confirmed by an ophthalmologist or by infant photographs in those children who presented after 6 months of age. The angle of deviation was determined by the Krimsky prism technique in infants and young children until the prism and alternate cover measurementswere determinable.All patients received a cycloplegic refraction using topical 1% cyclopentolate. All children with 3 diopters (D) of esotropia or less were not given a trial of glasses.‘“-” Those children with more than 3 D of hyperopia were given a trial of glasses and included in the study if theil esotropia was nonaccommodative. Consistent with most recent definitions of congenital esotropia,4,‘x.‘9 four children with impaired or aberrant neurologic signs, which were confirmed through a referral neurologic evaluation, were eliminated from the study. For each determined case of congenital esotropia, we sought to identify two controls from our population-based cohort of infants in Olmsted County who did not have a diagnosis of esotropia in order to perform a nested case-control study.‘” Controls were identified by using birth certificate information and matched to case by sex and the next two sequential live births of parents residing in Olmsted County. Residence was verified by means of city and county directories or previous medical records.

Data Collection The medical records of the confirmed cases and their matched controls were reviewed by an ophthalmologist for gender, gestational age, birth weight, Apgar scores, and postnatal medical

history. The maternal obstetric records of the esotropic and control patients were also reviewed for the following data: maternal age at delivery, mode of delivery, prenatal use of alcohol or tobacco, and complications of pregnancy, labor, or delivery. To minimize recall bias, the analysis was restricted to risk factor data documented prior to the date on which the case presented. For each of the case’s two controls, data on risk factors must also have been documented within the same time interval used for the case. The prenatal use of alcohol and tobacco was a specifically elicited condition of the obstetric record. Each was recorded as positive if the substance was used throughout the pregnancy or negative in those mothers who denied its use. No attempt was made to further quantify substance abuse. A family history of strabismus, regardless of the deviation type, was recorded as positive if it occurred in the patient’s siblings, parents, or parental siblings. Ophthalmology records of confirmed cases were reviewed for refractive error, age at onset, age at diagnosis, treatment, and presence of amblyopia.

Data Analysis The birth prevalence rates were calculated using the Olmsted County birth certificate database from 1980 through 1989.*’ Interval estimates around the point estimates were calculated by assuming a Poisson error distribution.** Data were analyzed as a matched case-control study with two controls per case using conditional logistic regression. The bivariate association was expressed as an odds ratio (OR) with its associated 95% confidence interval (CI). Multivariate logistic regression models were used to assess the independent association between each variable and congenital esotropia. Candidate variables for the multivariable regression models included those that were significantly (P < 0.10) associated with congenital esotropia in the univariate analysis. First order interaction terms were tested with the appropriate set of dummy variables. No interactions were statistically significant and are not reported. However, the power of the study to detect interactions was limited.

Results The population-based study ascertained 47 cases of congenital esotropia from 17,536 live births during the IO-year study period from 1980 through 1989. These findings correspond to a birth prevalence of 27 per 10,000 (95% CI, 20-35), or 0.27%. All 47 children (24 males and 23 females) were white, a reflection of the racial composition of this geographic area. Ninety-four Olmsted County children (49 males and 45 females) born during the period 1980 through 1989 were selected as gender- and birth date-matched controls. All survived the immediate perinatal period and were assumed to be alive at the time of the study. Table 1 shows the characteristics of the study children and their controls. The mean age at delivery for mothers whose children developed congenital esotropia was 27 years (range, 19-35 years) compared to 26 years (range, 15-41 years) for control mothers. The mean birth weight was 2974 g (range, 580-4600 g) for esotropic children and 3466 g (range, 1280-4620 g) for control children. The esotropic children were born at a mean gestational age of 37 weeks (range, 26-42 weeks) compared to 40 weeks (range, 30-43 weeks) for the control children. The mean Apgar scores at 1 and 5 minutes for the esotropic children were 7.1 and 8.7, respectively, and 8.3 and 9.3 for the control children. Among the 47 children who developed congenital esotropia, the mean age at diagnosis was 7 months (range, 1-34 months).

847

Ophthalmology Table

1. Characteristics of Children with Congenital and Birth Date-matched Controls: No. (%)

Volume Estropia

Variable

Cases

Controls

Male Female Maternal age (yrs) <25 25-29 >29 Maternal smoking

24 (51) 23 (49)

49 (52) 45 (48)

12 (26) 19 (40) 16 (34)

39 (41) 27 (29) 28 (30)

16 (34) 31 (66)

20 (21) 74 (79)

2 (4) 45 (96)

I2 (13) 82 (87)

18 (38) 29 (62)

4 (4) 90 (96)

14 (30) 18 (38) 15 (32)

7 (7) 43 (46) 44 (47)

31 (66) 7 (15) 9 (19)

68 (72) 14 (15) 12 (13)

16 (34) 27 (57) 4 (9)

12 (13) 80 (85)

7 (15) 36 (77) 4 (9)

3 (3) 89 (95)

16 (34) 31 (66)

11 (12) 79 (84) 4 (4)

Gender

during

pregnancy YC5 NO Maternal alcohol pregnancy

use during

YCS

No Gestational age (wks) <37 237 Buth weight (g) <2500 2500-3499 23500 Mode of dehvery Spontaneous vagmal Forceps vagmal Cesarean section Apgar score (1 min) 57 >7 Unknown Apgar score (5 min) 57 >7 Unknown Famdy history of strabismus Yes No Unknown

2 (2)

2 (2)

The meanonsetof esotropiawas 3 months(range, 1 week-6 months). The mean refractive error was + 1.25 D (range, -4.00

105, Number 5, May 1998 which reported a prevalence of 0.67% to 2%.9,‘5,‘8,2”,24 Previous reports may have overestimated the prevalence of congenital esotropia for various reasons. First, many studies either included all forms of strabismus8-‘0*24-28 or evaluated all esodeviations without distinguishing among individual entities, including congenital, acquired, or accommodative esotropia.697 Second, many studiessurveyed young9,” or older children,h-8~‘0~24-26.28making it difficult to accurately distinguish between congenital esotropia and later occurring acquired or mixed forms of esotropia. Third, some earlier surveys included neurologically impaired children in their definition of congenital esotropia, a condition that is specifically excluded from more recent definitions of congenital esotropia.4”8”9 Surveys of congenital esotropia that included neurologically impaired children might be expected to have a higher prevalence of congenital esotropia, as neurologically impaired children

Table

2. Logistic

Regression Analysis of Risk for Congenital Esotropia

Factors

Univariate Analysis Odds Risk Factor Gender Male Female Maternal age (yrs) ~25 25-29 >29 Maternal smoking during pregnancy Yes No Maternal alcohol use durmg pregnancy Yes

No

Ram 1.0 1.1

Multivariate Analysis* Odds

95% Cl

Ram

0.5 1.2 1.0

0.2-1.3 0.5-2.9

2.2 1.0

0.9-5.2

0.3 1.0

0.1-1.4

11.5 1.0

3.4-39.2

17.4 1 .o

4.6 1.1 1.0

1.7-12.9 0.5-2.5

0.4 1.1 1.0

2.5 1.0

samplesize.

Discussion

CI = confidence

mterval

* Only slgmficant analysis.

crude factors (P < 0.10) were included

tional age), low birth weight (less than 2500 g), low Apgar scores at 1 and 5 minutes,and a family history of strabismus,

regardless of the type of deviation,weresignificantly associated with an increased risk of developing

congenital

esotropia (Table

2). Gender, maternalage, maternalcigarette and alcohol consumption during pregnancy, and mode of delivery did not demonstrate a statistically significant association with congenital

esotropia(Table 2). In multivariate

analysis, a low Apgar score at 1 minute and

a family history of strabismusremainedsignificantpredictors of congenital esotropia (Table 2). The confidence intervals about the point estimates of association were wide, reflecting the small

Our population-based birth prevalence of 0.27% for congenital esotropia is lower than most previous studies,

848

1.0 1.2 1.5

95% CI

0.6-2.0

Gestational age (wks) <37 237 Buth weight (g) <2500 2500-3499 23500 Mode of d&very Spontaneous vagmal Forceps vagmal Ccsarean section Apgar score (1 mm) 57 >7 Apgar score (5 min) 57 >7 Famdy history of strabismus Yes No

to +2.75 D). At the time of surgery, the meandeviation was 41 prismdiopters(range,30-80 prismdiopters).Sixteen (34%) of the 47 children had monocular amblyopia at the time of diagnosis. In univariateanalysis,prematurity(lessthan37 weeksgesta-

Evaluated

0.7-9.4

0.8-394.2

0.03-6.2 0.3-3.6

0.4-3.6 0.6-3.7

4.3 1.0

1.7-11.2

4.9 1 .o

6.3 1.0

1.3-30.7

0.4 1.0

3.5 1.0

1.5-8.3

4.2 1.0

1.1-22.3

0.03-4.8

1.3-12.9

m m&variate

Mohney et al * Congenital have been shown to have an increased prevalence of strabismus.“.lX,26,2” Our findings, however, are consistent with Archer et al,” who, using a similar definition of congenital esotropia, estimated the frequency to be between 0.09% and 0.5% based on variable follow-up of 3324 infants whose initial examination occurred in the newborn nursery, Many previous studies that provided prevalence estimates or evaluated risk factors associated with congenital esotropia were not population-based but were instead clinic-, hospital-, or academic center-based surveys.‘-” Such series do not necessarily reflect rates in the overall healthcare system and may be difficult to generalize. With the exception of a higher proportion of the working population employed in the healthcare industry, the characteristics of the population of Rochester and Olmsted County are similar to those of United States whites. The results of previous population-based studies from Rochester and Olmsted County have demonstrated that the data from our present study should be applicable at least to the white population of the United StatesI Extrapolating findings from this study to other groups not represented within the county, however, is problematic. A birth prevalence study requires the complete and accurate ascertainment of all cases. As regards the current investigation, incorrectly low numerical estimates of children coming to medical attention are unlikely because the resources of the Rochester Epidemiology Project provide access to all medical records for care provided to Rochester and Olmsted County residents and in nearby areas, including community-based hospitals, emergency rooms, and outpatient ophthalmic, medical, and pediatric clinics. Missing potential cases of congenital esotropia that either were miscoded as another diagnosis or did not come to medical attention may result in our prevalence estimates being low. However, the usefulness of the Rochester Epidemiology Project in providing accurate birth prevalence data and supporting population-based analytic studies of disease causes and outcomes has been described previously. IZ- 14,30-34 The association of prematurity and various types of strabismus has previously been recognized. Nordlow’ found that 7% of strabismic patients were born premature. Cats and Tan35 reported a 25% incidence of strabismus in premature children by the first decade of life. Specifically concerning congenital esotropia, Robb and Rodier36 noted that 9 (12%) of 75 children with congenital esotropia were born at a gestational age of 36 weeks or less. Our case-control study nested in the population found that prematurity (less than 37 weeks gestational age) was associated with a 11.5-fold excess risk of developing congenital esotropia. Low birth weight and low Apgar scores have been associated with various forms of strabismus.28~37~38Although these studies provide limited information specific to congenital esotropia, our study also identifies low birth weight and low Apgar scores as significant risk factors associated with congenital esotropia. The association with low birth weight was statistically significant only for infants weighing less than 2500 g. In the multivariate

Esotropia

model, low birth weight did not contribute to predicting congenital esotropia after adjusting for confounding variables. Thus, the significance observed for low birth weight may be attributable to the associated prematurity. In univariate analysis, low Apgar scores at 1 and 5 minutes were associated with congenital esotropia. Only the lminute Apgar score was significant after adjusting for other factors. Hereditary factors have long been recognized among patients with strabismus. In our study, a positive family history was associated with a 3.5-fold excess risk of developing congenital esotropia. It is not known what factor is inherited nor the mode of inheritance. Transmission in some families has been explained by both Mendelian dominant and codominant models.39,40 We found a weak association between maternal cigarette smoking during pregnancy and the development of congenital esotropia. Although the odds ratio was elevated at 2.2, this increase may be due to chance, given the width of our confidence interval. Also, previous studies have suggested that medical record data on prenatal use of tobacco may be imprecise. This adds to the difficulty in interpreting our nonsignificant results. More recent studies, however, have found maternal cigarette smoking during pregnancy to be a risk factor for the development of esotropia.28’4’ These reports included all esodeviations, however, without evaluating the exposure specific to each of the various forms. Some limitations of this study deserve mention. First, we studied a racially homogeneous population of a single geographic area. We caution the validity of extrapolating findings from this study to groups not represented within our community until similar data are available from other populations. Second, congenital esotropia is an uncommon disorder in our relatively small community. As a result, the cohort size of 47 patients limits our ability to detect small changes that may occur over time. Further, small sample size may hinder our ability to examine the role of potential confounders. This may explain why maternal cigarette smoking, which has been associated with esotropia in other studies, was not found to be a significant factor in our study. Our classification of smoking status or gestational age, however, is unlikely to be systematically related to case or control status. Therefore, the presence of such a misclassification would most likely bias results to the null hypothesis. Third, exclusion of neurologically impaired children may effectively lower our birth prevalence estimates as well as have an impact on the significance of certain risk factors. Fourth, we were unable to examine for congenital esotropia among controls. Given the low incidence of disease, however, the probability of its occurrence in the control patients is extremely small, and its presence would also tend to bias the odds ratio toward unity. In conclusion, our population-based study quantifies the birth prevalence of congenital esotropia in a predominantly white population and identifies prematurity, low birth weight, low Apgar scores, and a family history of strabismus as significant risk factors.

849

Ophthalmology

Volume 105, Number 5, May 1998

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