Young Hispanic children may be more likely to have the vision defect astigmatism than their African-American peers, a new study finds.

Astigmatism refers to a distortion in the curvature of the cornea that can blur near and distance vision. Fairly little has been known about how widespread the problem is among preschool children, and how their susceptibility may vary by ethnicity.

In the new study, researchers found that among 3,000 Hispanic children between the ages of 6 months and 6 years, 17 percent had at least mild astigmatism and 3 percent had a significant degree of astigmatism that would generally require corrective lenses.

Those figures compared with rates of 13 percent and 1 percent, respectively, among 3,000 African-American children in the same age group.

The study, published in the journal Ophthalmology, cannot reveal why the ethnic difference exists. However, it’s likely that genetic influences are involved, according to senior researcher Dr. Rohit Varma, of the Doheny Eye Institute in Los Angeles.

Previous studies have found astigmatism to be very common among Native Americans, Varma noted in an interview, and many Hispanic people have significant Native American ancestry in their backgrounds.

Varma’s team also found that astigmatism was most common in the first year of life, but then declined. This pattern is seen among children of all races, he said, and it reflects a maturation of the eye, as infants begin using their eyes more and simply spending an increasing amount of time with their eyes open.

The findings are based on data from a larger study of pediatric eye diseases among infants and young children living in Los Angeles County. All the participants underwent a comprehensive eye exam; astigmatism was detected using an instrument that measures how light is changed as it enters the eye.

Overall, Varma’s team found, astigmatism was most common among infants - seen in about 40 percent of Hispanic and 25 percent of black 6-month-olds. Those rates dropped steeply in children older than one year, and the divergence between Hispanic and African-American children also narrowed in older kids.

When it came to significant astigmatism - a degree that Varma said would “absolutely” require corrective lenses - rates were also initially relatively high in infancy, then dropped before gradually increasing again. Among 6-year-olds, about 5 percent of Hispanic children had significant astigmatism, as did roughly 2 percent of African-American children.

Varma said the findings suggest that it may be particularly important to be on the lookout for astigmatism in young Hispanic children. But they also indicate, he said, that astigmatism detected in a child’s first year often normalizes on its own - regardless of ethnicity.

The U.S. Preventive Services Task Force recommends that all children younger than 5 be screened for vision problems, strabismus (a misalignment of the eyes) and amblyopia (poor vision in an eye that is physically normal).

Similarly, the American Academy of Pediatrics recommends that eye evaluations be part of infants’ and preschoolers’ routine well-child visits. Early vision assessments can be done by testing a child’s ability to fix on and follow objects; children younger than 3 or 4 typically are not mature enough for standard visual acuity tests, like reading an eye chart.

It is difficult, Varma noted, for parents to know whether a young child has vision problems. Preschoolers are typically unable to verbalize such difficulties, and may not even know their vision is not as sharp as it should be, as they would have no other experience to compare it with.

SOURCE:  Ophthalmology, online September 30, 2010.