Hyperopia, or farsightedness, is the most common refractive eye error in Asian and non-Hispanic white (NHW) Southern California children overall, but myopia, or nearsightedness, is "relatively more prevalent" among Asian children than hyperopia or astigmatism, according to an article published online August 14 in Ophthalmology.
Ge Wen, MSc, from the Department of Preventive Medicine, University of Southern California, Los Angeles, and colleagues conducted a population-based, cross-sectional study as part of the Multi-Ethnic Pediatric Eye Disease Study (MEPEDS).
The investigators enrolled 1501 NHW and 1507 Asian children aged 6 to 72 months in Los Angeles and Riverside Counties in California. The researchers conducted in-home interviews with parents or guardians and comprehensive eye exams for the children, including cycloplegic autorefraction.
Researchers found the overall prevalence of myopia to be 1.20% (95% confidence interval [CI], 0.76% - 1.89%) among NHW children and 3.98% (95% CI, 3.11% - 5.09%) for Asian children. They found no significant differences in prevalence between sexes or ages.
They determined the prevalence of hyperopia to be 25.7% (95% CI, 23.5% - 27.9%) in NHW children and 13.5% (95% CI, 11.8% - 15.3%) in Asian children. They found no sex or age differences in prevalence for NHW children, but among Asian children, girls were more likely to have hyperopia than boys (16.2% vs 10.8%; P = .002).
The researchers found the overall prevalence of astigmatism (≥1.5 diopters) to be 6.33% (95% CI, 5.21% - 7.68%) in NHW children and 8.29% (95% CI, 7.01% - 9.80%) among Asian children. They also found the overall prevalence of astigmatism of 3.00 diopters or more to be 0.73% (95% CI, 0.41% - 1.31%) in NHW and 1.19% (95% CI, 0.76% - 1.88%) in Asian children. They found no sex differences for prevalence, but for an astigmatism of 1.5 or more diopters, prevalence was lower in each subsequent older age category in NHW children (P < .0001), but not in Asian children.
When compared with data from previous MEPEDS research, the investigators found that prevalence of myopia in NHW children (1.20%) was the lowest among 4 racial/ethnic groups, including Asian (3.98%), Hispanic (3.7%), and black (6.6%; P < .0001 for all comparisons) children. Similarly, prevalence of astigmatism (≥1.5 diopters) among NHW children was the lowest among 4 racial/ethnic groups, when compared with data from another MEPEDS paper.
Genes and Lifestyle
Genetics, as well as lifestyle and environmental factors, contribute to the differences among ethnic groups, the researchers note.
"A lot of children who have myopia have parents that have myopia, and the genetic predisposition is present to a significant extent in children of Asian descent," Rohit Varma, MD, professor and chair, Department of Ophthalmology, Illinois Eye and Ear Infirmary, University of Illinois at Chicago, and senior author of the article, told Medscape Medical News.
"In addition to that, it's thought that for children of Asian descent, their parents very early on begin to encourage activity similar to reading and doing near work," he continued. "The more time one spends doing near work early on, the higher the prevalence or rate of myopia. The eye just grows in a different manner when the child is doing a lot of near activities such as close-up computer games or reading or watching movies on iPads."
In contrast, studies have shown that NHW children who participate in a lot of outdoor activities, including viewing things at a distance, swimming, and participating in active sports, are less likely to become myopic, Dr. Varma said. That factor may also drive the difference in hyperopia, he added, with almost half as many Asian children having hyperopia. Astigmatism overlaps the 2 groups.
The new study "shows, in a way, what we already knew, that there are differences. I might say the differences are less than some people might have speculated," Michael X. Repka, MD, professor of ophthalmology and pediatrics at the Wilmer Eye Institute, Johns Hopkins University, Baltimore, Maryland, and coauthor of a similar study, commented in a telephone interview with Medscape Medical News.
Dr. Repka cautions against citing the "near theory," however, as the cause for this particular age group of 6 to 72 months. "The refractive error in this group is pretty minimal. For the hyperopia, that does not translate into 'these children need glasses.' That's the one caveat I would make here. For the farsighted patients, probably a very small portion of patients would need correction. Yes, the finding is there, but that finding of refractive error may not be pathologic in effect."
Applicable Across United States
Nevertheless, results of the latest study may be generalizable across the United States, the researchers note, because it is a population-based study. "The areas selected for doing this are similar in terms of sociodemographic and age distribution with the state of California and the United States," Dr. Varma said. "We had a participation rate of 80% to 87% who had an eye examination."
Dr. Repka agrees on the generalizability. "Population studies are not exciting because they don't tell people what to do, but they sure help ground development of practice guidelines of how to approach an individual when you have the background of this kind of number."
The authors have disclosed no relevant financial relationships.
Ophthalmology. Published online August 14, 2013. Abstract
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Cite this: Myopia May Affect Asian Kids More Than White Kids in US - Medscape - Aug 31, 2013.