Screenings for amblyopia should be standardized

"In the absence of universally accepted guidelines for preschool vision screening and comprehensive eye examinations, local and state mandates and recommendations vary considerably," said France, a certified orthopist at the department of ophthalmology, University of Wisconsin School of Medicine, Madison. "To promote and protect the visual development of young children and encourage uniform testing and reporting criteria, the vision screening committee of the American Association for Pediatric Ophthalmology and Strabismus (AAPOS) developed evidence-based guidelines for the detection of amblyogenic risk factors," France explained.

Known risk factors

"Amblyogenic risk factors were identified through analysis of large-scale, population-based, clinical data and treatment outcome studies of amblyopia in screened and controlled populations," France explained. "Validation studies of photoscreening equipment and screening programs were analyzed and clinical experience was considered."

She described typical children who may present to a screening clinic and may be more challenging for the clinicians to identify as amblyopic. One child, for example, has bilateral hyperopia; his brother has an astigmatic correction. France considered the question of whether either child is at risk of developing amblyopia or already has developed amblyopia.

"Each of these children's amblyopia could easily go undetected, untreated, and unnoticed," she emphasized.

To set standards and establish criteria for failure, normal refractive errors at different ages had to be considered, because age clearly makes a difference in the development of refractive errors, France explained.

"High degrees of hypermetropia in newborns and considerable astigmatism up to the age of 6 months have been reported to decrease considerably by the age of 1 year," she said. "There is a controversy about whether children under the age of 1 year should be screened for amblyogenic risk factors."

In one study, more than 31,000 infants under age 1 were screened, and fewer than 40% had any findings on complete eye examinations. The mild symmetric refractive errors that were observed in these study patients were not considered amblyogenic and were not treated.

"With the current guidelines, there is no specification for patient age; however, the AAPOS committee recommends that the findings in children 42 months of age and older be separated from those under 42 months of age in order to understand better the vision factors in the two age groups," according to France.

"The topic of age and the optimal time to treat amblyogenic risk factors is important and deserves further attention," she stated.

Increased risk

Regarding risk factors, anisometropia and substantial refractive errors of any type increase the risk of amblyopia, she said. Anisometropia is considered the leading cause of amblyopia. One study reported that 98% of patients with spherical hyperopic anisometropia > 2 D had amblyopia and 42% with spherical hyperopic anisometropia > 1 D and < 2 D had amblyopia, but less than 2.6% had amblyopia when 1 D was considered. Another trial found no patient with anisometropia < 1.5 D unless strabismus was associated. Based on these findings, "the current guidelines state that 1.5 D or greater is a risk factor for the development of amblyopia," she said.

A study of children with hyperopia found that more than 5% to 6% had a refractive error > 3 D. Children who exceeded that had 13 times the risk of developing strabismus and six times the risk of developing amblyopia. The current guidelines, she noted, therefore recommend 3.5 D.