The epidemiology of visual impairment and ocular disease among preschool children in the United States was recently elucidated by the Multi-Ethnic Pediatric Eye Disease Study (MEPEDS)1 and the Baltimore Pediatric Eye Disease Study (BPEDS).2 Other studies have investigated the prevalence of visual impairment and ocular disease among school-aged children in the United States.3–5 These studies have highlighted ethnic disparities in eye disease, including a significantly higher prevalence of visual impairment from uncorrected refractive error among African American and Hispanic children as compared to their Asian and non-Hispanic white peers.6,7 These epidemiologic studies sampled urban populations from Los Angeles (MEPEDS1) and Baltimore (BPEDS2,4 and Preslan and Novak4), respectively. However, little is known about visual impairment and eye disease among U.S. preschoolers and school-aged children in rural areas, where access to ophthalmic care is more limited. Moreover, data on the specific epidemiology of visual impairment and eye disease among rural, low-income children of migrant farmworkers are sparse.8
An estimated 1 to 3 million migrant farmworkers currently live and work in the United States, 70% of whom are accompanied by their children. Approximately 90,000 migrant farmworker families live in the state of Georgia alone.9,10 Of the 90,000, 94.6% are Hispanic and mostly from Mexico.10 Another large plurality in Georgia are Haitian or Caribbean Islanders.11 Children of migrant farmworkers face substantial barriers to eye care, including language, lack of transportation, and financial and insurance limitations. The migrant farmworker population is also highly transient, moving from state to state in search of job opportunities. Thus, many children are unable to attend school vision screenings or pursue follow-up eye examinations.12 Given the limited access to care in this potentially high-risk population, the purpose of the current study was to estimate the prevalence of reduced visual acuity and ocular disease in children of migrant farmworkers living in Georgia.
Patients and Methods
This was a retrospective chart review of existing data from a pediatric vision screening program, Farmworker Vision Project, a collaborative effort between Emory University, the Georgia Lions Lighthouse Foundation, and the Consulate General of Mexico to improve access to eye care for migrant farmworker families in Georgia. The study was approved by the Emory University Institutional Review Board and adhered to the guidelines set forth by the Declaration of Helsinki.
The study population consisted of children of Haitian and Hispanic migrant farmworkers aged 4 to 17 years attending a migrant summer school in southern Georgia in June 2014 and June 2015. Targeting a summer school allowed assessment of young children at risk for amblyopia and older children with untreated ocular disease or uncorrected refractive error. Consent forms to take part in the screening and examination written in English, Creole, and Spanish were sent home to parents. Bilingual teachers at the migrant summer school assisted with consent and recruitment. Because some children returned the following year for screening and examination, name and date of birth were used to exclude duplicate data. Only 2014 data from these children were used.
Vision Screening and Examination Protocol
Bilingual (English and Spanish) medical students and health promoters from the Mexican consulate performed the vision screening in the migrant summer school. A pediatric ophthalmologist trained lay screeners via practice sessions in accordance with the American Association for Pediatric Ophthalmology and Strabismus vision screening recommendations.13,14 All Haitian children encountered spoke fluent English and Creole-speaking teachers at the school assisted in communication with Haitian parents.
Screening involved traditional visual acuity charts and stereopsis examination for ocular alignment. The Lea chart or HOTV chart was used for 4 and 5 year olds. For older children, the HOTV or Snellen charts were used. All visual acuity was tested at 10 feet and presenting vision was used, with children wearing spectacles if they had them. Based on the American Association for Pediatric Ophthalmology and Strabismus recommendations, a visual acuity of worse than 20/40 for age 48 to 59 months and worse than 20/30 for age 60 months or older or two or more lines of difference in visual acuity between eyes was a failing result.13–15
For any child failing the screening, a pediatric ophthalmologist performed a comprehensive ocular examination the following day in an empty schoolroom using portable equipment. This examination began with the assessment of visual acuity, fixation, and ocular alignment using the cover–uncover test. Undilated slit-lamp examination was performed. Afterwards, pupil dilation with one drop each of 1% cyclopentolate and 1% tropicamide was administered. For those patients whose pupils remained reactive to light on retinoscopy after a 30-minute waiting period, a second set of drops was administered.
Autorefraction and streak retinoscopy were performed. Manifest refraction in a phoropter was performed for children who were able to participate. Dilated fundus examination was performed using indirect ophthalmoscopy. For children with refractive error, spectacles were prescribed and donated free of charge through the Georgia Lions Lighthouse Foundation. Children in need of continued follow-up for an ocular abnormality were directed to a local ophthalmologist offering low-cost or Medicaid services.
Definitions of Terms
Reduced visual acuity at presentation was analyzed. It was defined as a monocular screening visual acuity of worse than 20/40 in those 48 to 59 months and worse than 20/32 in those older than 60 months, without improvement on retesting the day of examination and with an underlying ocular pathology based on examination. Reduced visual acuity was stratified into two categories: reduced visual acuity that resolved immediately with refractive correction (uncorrected refractive error) and reduced visual acuity that did not resolve immediately with refractive correction (amblyopia suspect). All visual acuities were measured prior to dilation.
Refractive error was defined as any astigmatism, hyperopia, or myopia, regardless of visual impairment status. Astigmatism (any axis) was defined as 1.50 diopters (D) or greater and high astigmatism was defined as 3.00 D or greater for all children. Myopia was defined as a spherical equivalent (SE) of 0.50 D or less, and SE hyperopia was defined as 2.00 D or greater.
Uncorrected refractive error was defined as reduced visual acuity that immediately improved refractive correction of hyperopia, myopia, and/or astigmatism as defined above. For those children wearing spectacles at presentation, uncorrected refractive error was defined as a difference between presenting and prescribed spectacles of greater than or equal to the refractive error definitions above.
The category “unilateral amblyopia-suspect” was diagnosed examination based on a two-line interocular difference in comprehensive examination worse-eye reduced visual acuity, worse than 20/32, not immediately resolving with refraction, without anterior segment or fundus abnormalities, and with at least one of the following amblyogenic risk factors: anisometropia, including anisoastigmatism of 1.50 D or greater, anisomyopia of 3.00 D or greater, or anisohyperopia of 1.00 D or greater; constant or intermittent exotropia or esotropia; clinical history of strabismus surgery; or current or historical obstruction of the visual axis. The category “bilateral amblyopia-suspect” was considered to be a reduced visual acuity of 20/40 or worse in both eyes during the comprehensive examination, not resolving with refraction, due to either bilateral obstruction of the visual axis or bilateral ametropia. Bilateral ametropia was considered to be 2.50 D or greater of astigmatism, 6.00 D SE or greater of myopia, or 4.00 D SE or greater of hyperopia.
Analysis of disease prevalence was calculated as a ratio out of the total cohort screened with available data (N = 148). Chi-square and Fisher's exact tests were used for comparison of proportions between groups. Differences in mean refractive error and mean age between ethnicities were tested using the Student's t test, given all data used in parametric testing were normally distributed. Associations of age, sex, and ethnic groups with uncorrected refractive error versus reduced visual acuity not immediately resolving with refraction were tested using multivariate logistic regression SAS software (version 9.4; SAS Institute, Inc., Cary, NC). Confidence intervals (CIs) reported are exact binomial 95% CIs. A P value of less than .05 was considered significant.
A total of 263 children's families were approached for screening and examination, and 156 children in the migrant school consented and were screened (Figure 1). Of these, 41 (26%) were found to have reduced visual acuity as defined in the Methods section and referred for comprehensive examination by a pediatric ophthalmologist on-site. Thirty-three of 41 referred children (81%) attended the comprehensive examination. The 8 children lost to follow-up were excluded from analysis. The total cohort used for analysis (N = 148) consisted of those appropriately screened and followed up for full, dilated examination if necessary.
Families of children approached for screening or examination. RVA = reduced visual acuity
Demographic characteristics of the children are presented in Table 1. There was a significant difference in mean age among those wearing (11.7 ± 2.8 years) and not wearing (9.6 ± 3.0 years) spectacles (P = .03). There was no other significant difference in any demographic factor by ethnicity, age group, or gender using chi-square analysis and in age using the Student's t test.
Demographic Distribution and Basic Clinical Characteristics of Migrant Farmworker Children by Ethnicity
Overall, 33 of 148 (22%) patients had worse-eye reduced visual acuity. Of those children found to have reduced visual acuity, 3 of 33 (9%) patients had normal visual acuity on retesting. The remaining 30 of 148 (20%) (95% CI: 14 to 28) patients had worse-eye reduced visual acuity. The prevalence of reduced visual acuity was stratified by ethnicity and type, immediately resolving with refractive correction or not, in the better and worse eye among migrant farmworker children (Table 2). Controlling for gender, no significant associations were found between age group, ethnicity, and reduced visual acuity by multivariate logistic regression. Uncorrected refractive error that improved with immediate refraction accounted for 25 of 30 (83%) patients with worse-eye reduced visual acuity. No significant association was found between uncorrected refractive error and ethnicity, age, age group, or gender (Fisher's exact test and multivariate logistic regression). All reduced visual acuity that did not immediately resolve was attributed to suspected amblyopia; no other ocular pathology was found among this group of migrant farmworker children.
Prevalence of Presenting Visual Impairment Stratified by Ethnicity and Type (Resolving vs Non-resolving)
The mean refractive error of astigmatism was significantly higher among Hispanics (2.4 ± 1.4) with any worse-eye related visual acuity than among Haitians (1.0 ± 0.7) (P = .01, Student's t test). The prevalence of worse-eye reduced visual acuity from high astigmatism was significantly different between ethnicities (0% of Haitians and 10% of Hispanics had high astigmatism) (P = .02, Fisher's exact test). Using multivariate logistic regression, worse-eye reduced visual acuity from astigmatism was found to be significantly associated with age (weakly decreasing with age as a continuous variable) when controlled for ethnicity and sex (P = .02; adjusted odds ratio: 0.8 [95% CI: 0.77 to 0.97]). Multivariate logistic regression showed no further associations between types of refractive error, age, gender, and ethnicity.
The prevalence of amblyopia suspects was 5 of 148 (3% [95% CI: 1 to 8]) children. One child was a suspect for bilateral ametropic amblyopia and there were four unilateral amblyopia suspects. Amblyopia suspects had anisometropia as set forth in the definitions in 4 of 5 (80% [95% CI: 30 to 100]) of all cases, 3 of 4 (75% [95% CI: 20 to 100]) of unilateral cases, and 4 of 148 (3% [95% CI: 1 to 7]) of all migrant children. Thus, 4 of 5 (80%) cases of suspected amblyopia were secondary, at least in part, to uncorrected refractive error. One amblyopia suspect had a constant exotropia. Overall, strabismus was found in 9 of 148 (6% [95% CI: 3 to 11]) children.
Our study is one of the first to examine reduced visual acuity and eye disease in the children of migrant farmworkers in the United States. The current study also reveals not only that migrant farmworker children have a high prevalence of reduced visual acuity, but also that much of this reduced acuity is a result of uncorrected refractive error. The prevalence of reduced visual acuity among migrant farmworker children was 20% (95% CI: 14 to 28) in the worse eye and 14% (95% CI: 9 to 20) in the better eye. In 83% (20 of 30) of patients, worse-eye related visual acuity was secondary to uncorrected refractive error. If amblyopia suspects with anisometropic and bilateral ametropia are included (29 of 30 [97%] patients), worse-eye prevalence of visual impairment was secondary to uncorrected refractive error.
The prevalence of worse-eye reduced visual acuity from suspected amblyopia (3%) was slightly higher than amblyopia in the MEPEDS: African American = 1.5% (95% CI: 0.9 to 2.1), Hispanic = 2.6% (95% CI: 1.8 to 3.4), and white and Asian = 1.8% (95% CI: 1.1 to 2.9); and BPEDS: non-Hispanic white children = 1.8% (95% CI: 0.9 to 3.1) and African American = 0.8% (95% CI: 0.3 to 1.7).16–18 Although the small sample size limits comparison, Hispanic farmworker children, comprising 64% of the sample group, may be disproportionately affected by amblyopia, accounting for all 5 cases, reflecting similar trends among Hispanic children in the Refractive Error Study in Children, MEPEDS, and BPEDS studies. Our study is limited by its cross-sectional nature and lack of follow-up because the children were not examined after optical treatment to see if their vision improved with spectacle wear; it was not possible to determine if true amblyopia was present at the time of vision screening. Children with reduced visual acuity at presentation could only be classified as “amblyopia suspects” based on presence of reduced visual acuity in one or both eyes combined with presence of an amblyogenic risk factor.
Nevertheless, an important finding in the current study is that, similar to the MEPEDS, a majority of unilateral suspected amblyopia is in part secondary to refractive error.16,17 This finding confirms the need for early screening of migrant farmworker children for amblyogenic refractive error.
Our study likely shows a higher prevalence of reduced visual acuity compared to the MEPEDS and the BPEDS because of the higher rates of uncorrected refractive error. Our study showed that 15% (7% to 27%) of Haitian children and 16% (9% to 25%) of Hispanic children had worse-eye uncorrected refractive error. This is a much higher prevalence than found in African Americans (4.3%) and Hispanics (5.3%) in the MEPEDS.7 Our study does include school-aged children who would presumably have more myopic error.19 However, our study finds similar prevalence in reduced acuity and myopia between those aged 4 through 6 years and older. Thus, the high prevalence of reduced acuity may not simply be an artifact of age and may be related to a truly higher rate of all types of uncorrected refractive error.
The prevalence of uncorrected refractive error in our study is also higher than previously published rates in school children. There have been few studies of visual impairment and refractive error in school-aged children in the United States. The Baltimore Vision Screening Project, examining U.S. inner-city school children, reported a rate of uncorrected refractive error of 6.1%, which is higher than the MEPEDS and the BPEDS. In addition to the older age of the children, which may have increased refractive error, the authors cite access to care as a predominant issue preventing spectacle correction.5 The Refractive Error Study in Children also reported varying levels of uncorrected refractive error causing worse-eye prevalence of visual impairment.20–23 Uncorrected refractive error ranged in prevalence from 1.2% in South Africa21 to as high as 29.1% in south urban China.22 In the one Latin American country studied (Chile), the prevalence of visual impairment from uncorrected refractive error was 9.8%.23 Thus, the children of migrant farmworkers have a prevalence of uncorrected refractive error more aligned to Asian and Latin American countries than to school children in the United States. It is possible that this high prevalence represents high rates of refractive error in this population and poor access to vision screening and eye care.
The prevalence of uncorrected astigmatism is significantly higher among Hispanics (16%) compared to Haitians (6%) (P = .05). This higher prevalence among Hispanics supports the current literature in both preschool and school-aged children.7,24 Visually impaired Hispanic farmworker children also required a significantly higher cylinder correction (2.4 ± 1.4 D) than Haitian children (1.0 ± 0.7 D) (P = .01) and had significantly higher rates of high astigmatism (10% vs 0%). The only association of refractive error with age found was that worse-eye reduced visual acuity from astigmatism weakly decreases with age when controlled for ethnicity and sex (P = .02; adjusted odds ratio: 0.8 [95% CI: 0.77 to 0.97]). A similar association showing a decrease in astigmatism with age has been found previously among preschool children.25
The children of migrant farmworkers are a highly transient population with socioeconomic barriers that can inhibit both research and eye care.12 Our study is a glimpse into the eye health of a profoundly marginalized population of children. The greatest limitation of our study is its small sample size and non-random sampling method. It is also subject to selection bias, particularly given the percentage of families from each year who refused to participate. Over both years, 66% of families agreed to participate in the study. If the children whose parents refused consent had lower prevalence of reduced acuity and eye disease, this would tend to overestimate of reduced acuity and eye disease among our sample population. Alternatively, if the families who did not consent refused because their children already had eye care providers for known pathology, this might underestimate the prevalence of refractive error and eye disease. Furthermore, because this was a sample from a single school it is possible that there was familial clustering, which would tend to overestimate reduced acuity and eye disease.
Due to the retrospective nature of this analysis, the eye charts used in each age group were not standardized. As such, visual acuity may have been underestimated in 4 to 5 year olds and overestimated in the older children using HOTV charts. As a screening effort, there was no additional follow-up to determine the best-corrected visual acuity of patients once they had been wearing their new correction for a few weeks. Furthermore, although the prevalence of uncorrected refractive error was high, this prevalence only accounts for presenting vision; it may not account for children who had but did not bring their spectacles. Finally, because this was a screening measure, amblyopia suspects were referred to follow-up if needed. However, given the transient nature of the population, we were unable to track follow-up visual acuity or response to penalization therapy. Future studies examining long-term visual outcomes in such patients, while logistically difficult, would be worthwhile.
The children of migrant farmworkers have a significantly higher rate of reduced visual acuity, largely from uncorrected refractive error, than Hispanic and African American preschool and school-aged children in the United States. The rate of amblyopia detected in our study is similar to that reported in the general population; however, in our population, amblyopia would have gone undetected without this screening effort. Furthermore, a substantial amount of children at risk for amblyopia detected in our study have uncorrected anisometropia. Although further research must be done to clarify the epidemiology of visual impairment and eye disease among migrant farmworker children, our study reveals a large unmet spectacle need and a need for screening to prevent amblyopia. Because of the substantial socioeconomic barriers that the children of migrant farmworkers face, a concentrated effort is needed to improve screening and access to eye care for this population.
- Varma R, Deneen J, Cotter S, et al. The Multi-Ethnic Pediatric Eye Disease Study: design and methods. Ophthalmic Epidemiol. 2006;13:253–262. doi:10.1080/09286580600719055 [CrossRef]
- Friedman DS, Repka MX, Katz J, et al. Prevalence of decreased visual acuity among preschool-aged children in an American urban population: the Baltimore Pediatric Eye Disease Study, methods, and results. Ophthalmology. 2008;115:1786–1795. doi:10.1016/j.ophtha.2008.04.006 [CrossRef]
- Zadnik K, Satariano WA, Mutti DO, Sholtz RI, Adams AJ. The effect of parental history of myopia on children's eye size. JAMA. 1994;271:1323–1327. doi:10.1001/jama.1994.03510410035029 [CrossRef]
- Preslan MW, Novak A. Baltimore vision screening project. Phase 2. Ophthalmology. 1998;105:150–153. doi:10.1016/S0161-6420(98)91813-9 [CrossRef]
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- Tarczy-Hornoch K, Cotter SA, Borchert M, et al. Prevalence and causes of visual impairment in Asian and non-Hispanic white pre-school children: Multi-Ethnic Pediatric Eye Disease Study. Ophthalmology. 2013;120:1220–1226. doi:10.1016/j.ophtha.2012.12.029 [CrossRef]
- Multi-Ethnic Pediatric Eye Disease Study Group. Prevalence and causes of visual impairment in African-American and Hispanic preschool children: the Multi-Ethnic Pediatric Eye Disease Study. Ophthalmology. 2009;116:1990–2000. doi:10.1016/j.ophtha.2009.03.027 [CrossRef]
- Miller PG. Vision screening for migrant children. Child Today. 1976;5:6–7.
- Larson AC. Migrant and Seasonal Farmworker Enumeration Profiles Study Georgia. Cordele, GA: Georgia State Office of Rural Health; 2008.
- Kandel W. Profile of Hired Farmworkers, A 2008 Update. Economic Research Service, U.S. Dept of Agriculture; 2008.
- U.S. Department of Housing and Urban Development. Common Questions about Migrant/Farmworkers. Washington, DC: Author; 2016.
- Gwyther ME, Jenkins M. Migrant farmworker children: health status, barriers to care, and nursing innovations in health care delivery. J Pediatr Health Care. 1998;12:60–66. doi:10.1016/S0891-5245(98)90223-1 [CrossRef]
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- American Association for Pediatric Ophthalmology and Strabismus. Techniques for Pediatric Vision Screening. http://www.aapos.org/terms/conditions/131. Published 2014.
- Committee on Practice and Ambulatory Medicine Section on OphthalmologyAmerican Association of Certified OrthoptistsAmerican Association for Pediatric Ophthalmology and StrabismusAmerican Academy of Ophthalmology. Eye examination in infants, children, and young adults by pediatricians: organizational principles to guide and define the child health care system and/or improve the health of all children. Ophthalmology. 2003;110:860–865. doi:10.1016/S0161-6420(03)00414-7 [CrossRef]
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- Tarczy-Hornoch K, Varma R, Cotter S, et al. Multi-Ethnic Pediatric Eye Disease Study Group. Prevalence of amblyopia and strabismus in African American and Hispanic children ages 6 to 72 months the Multi-Ethnic Pediatric Eye Disease Study. Ophthalmology. 2008;115:1229–1236. doi:10.1016/j.ophtha.2007.08.001 [CrossRef]
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- Rudnicka AR, Kapetanakis VV, Wathern AK, et al. Global variations and time trends in the prevalence of childhood myopia, a systematic review and quantitative meta-analysis: implications for aetiology and early prevention. Br J Ophthalmol. 2016;100:882–890. doi:10.1136/bjophthalmol-2015-307724 [CrossRef]
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Demographic Distribution and Basic Clinical Characteristics of Migrant Farmworker Children by Ethnicity
|Characteristic||Total Population (N = 148)||Haitian (n = 54)||Hispanic (n = 94)|
|Age (mean ± SD)||9.8 ± 3.0||11 ± 3.1||9.5 ± 3.0|
|Age group (n [%])|
| 4 to 7 years||41 (28%)||12 (22%)||29 (31%)|
| 8 to 17 years||107 (72%)||42 (78%)||65 (69%)|
|Male (n [%])||76 (51%)||23 (43%)||53 (56%)|
|Wearing spectacles at presentation (n [%])||11 (7%)||2 (4%)||9 (10%)|
|Reported blurry vision (n [%])||12 (8%)||6 (11%)||6 (6%)|
Prevalence of Presenting Visual Impairment Stratified by Ethnicity and Type (Resolving vs Non-resolving)a
|Type||Worse Eye||Better Eye||Type||Worse Eye||Better Eye||Type||Worse Eye||Better Eye|
|Non-resolving (amblyopia)||5 (3%) (1 to 8)||2 (1%) (0 to 5)||Non-resolving (amblyopia)||0 (0%) (0)||0 (0%) (0)||Non-resolving (amblyopia)||5 (5%) (2 to 12)||2 (2%) (0 to 7)|
|Resolving (with refractive correction)||25 (16%) (11 to 24)||18 (12%) (7 to 19)||Resolving (with refractive correction)||9 (16%) (8 to 29)||6 (11%) (4 to 23)||Resolving (with refractive correction)||16 (17%) (10 to 26)||12 (13%) (7 to 21)|
|Total (N =148)||30 (20%) (14 to 28)||20 (14%) (9 to 20)||Total (n = 54)||9 (17%) (8 to 29)||6 (11%) (4 to 23)||Total (n = 94)||21 (22%) (14 to 32)||14 (15%) (8 to 24)|