Early Glasses Do the Trick for Bilateral Amblyopia

TAMPA, Fla., Oct. 2 -- Early prescription of glasses for children with bilateral refractive amblyopia may prevent a lifetime of visual disability, a team of pediatric ophthalmologists has found.

Young children with bilateral amblyopia given glasses early had a mean improvement in binocular visual acuity of four Snellen lines, and three-fourths saw 20/25 or better at one year, reported David K. Wallace, M.D., M.P.H. of Duke, and colleagues in the Pediatric Eye Disease Investigators Group, based here, in the October issue of the American Journal of Ophthalmology.

"This study shows that glasses are a powerful treatment for bilateral amblyopia in children," said Paul A. Sieving, M.D., Ph.D., director of the National Eye Institute, which funded the study. "When we detect and treat this problem early in life, most children are able to achieve normal vision."

Bilateral refractive amblyopia can result when children have large degrees of uncorrected hypermetropia, astigmatism or both, the authors noted. It occurs in only four of 830 children in one study, compared with a two to three per 100 estimated prevalence for standard "lazy eye" amblyopia, but the condition can cause significant visual disability if not treated during childhood.

"The presumed mechanism of bilateral refractive amblyopia is pattern vision deprivation," the authors wrote. "Abnormal binocular interaction with suppression also may contribute in those cases with concomitant strabismus."

The authors conducted a prospective study in 27 community- and university-based sites, with the goal of determining the time course and the amount of binocular visual acuity improvement with standard therapy.

They enrolled 113 children, mean age 5.1 + 1.3 years, all of whom had untreated bilateral refractive amblyopia. The authors defined the conditions as 20/40 to 20/400 best-corrected binocular visual acuity in the presence of 4.00 diopters (D) or more of hypermetropia by spherical equivalent, 2.00 D or more of astigmatism, or both in each eye.

The children were prescribed glasses that fully corrected for anisometropia, astigmatism, and myopia, or, in the case of hypermetropia fully corrected or undercorrected symmetrically by no more than 1.50 D in both eyes. There were no untreated controls.

The authors measured best-corrected binocular and monocular visual acuities at baseline and at five, 13, 26, and 52 weeks. The main outcome measure was binocular acuity at one year.

They found "mean binocular visual acuity improved from 0.50 logarithm of the minimum angle of resolution (logMAR) units (20/63) at baseline to 0.11 logMAR units (20/25) at one year." This translated into a mean improvement of 3.9 lines (95% confidence interval 3.5 to 4.2) on the Snellen chart.

The degree of improvement was significantly greater among those children with worse baseline acuity. For 84 children with baseline binocular acuity of 20/40 to 20/80, the mean improvement at one year was 3.4 Snellen lines (95% CI, 3.2 to 3.7). For 16 children with baseline binocular acuity of 20/100 to 20/320, the mean improvement at one year was 6.3 lines (95% CI, 5.1 to 7.5, P<0.001).

Only 12% of the children required additional treatment for amblyopia, with either patching of the stronger eye or visual blocking with atropine.

The cumulative probability that the children would have binocular visual acuity of 20/25 or better was 21% at five weeks, 46% at 13 weeks, 59% at 26 weeks, and 74% at 52 weeks.

"Although there was no untreated control group, the observed improvement substantially exceeded any expected learning or age effect," the authors wrote. "Visual acuity improvement was accompanied by a corresponding improvement in stereopsis, with 60% of children improving by at least two levels on the Randot Preschool Stereoacuity Test."