Australian kids found to have low rate of visual impairment

October 1, 2005

Fort Lauderdale, FL—Australian children have a relatively low prevalence of visual impairment. The primary causes of visual problems are uncorrected astigmatism and amblyopia, according to Dana Robaei, MBBS, MPH, who spoke at the annual meeting of the Association for Research in Vision and Ophthalmology.

Fort Lauderdale, FL-Australian children have a relatively low prevalence of visual impairment. The primary causes of visual problems are uncorrected astigmatism and amblyopia, according to Dana Robaei, MBBS, MPH, who spoke at the annual meeting of the Association for Research in Vision and Ophthalmology.

Dr. Robaei and colleagues conducted a population-based study, the Sydney Myopia Study, of 6-year-old children during 2003 and 2004. The cross-sectional study was based on a random sample of 1,740 schoolchildren who attended public, private, and religious schools in Sydney. The sample was ethnically diverse and representative of the population of the city; 37% of the participants were non-European, 20% were East Asian, and other large groups included Indian and Middle Eastern.

Each child underwent measurement of the distance visual acuity (logarithm of the minimum angle of resolution [logMAR]). The anterior segment was examined by slit-lamp examination. Cycloplegia was induced with cyclopentolate and the fundus was examined and photographed. Autorefraction was performed 20 to 25 minutes after instillation of the cycloplegic agent, Dr. Robaei explained.

Dr. Robaei explained that for the purposes of this study if the child's cycloplegic spherical equivalent refraction was between –0.5 and 2 D, he or she was considered not to have a significant refractive error. In this study, amblyopia was defined as corrected visual acuity of less than 20/40 and a two-line differential between the two eyes in association with strabismus, high ametropic anisometropia, or form deprivation. Visual impairment was defined as mild if the visual acuity was better than 20/40 to 20/60, moderate 20/80 to 20/160, and severe 20/200 or worse.

"The mean uncorrected visual acuity (UCVA) for the entire study population was approximately equal to 20/32. There was no difference in the visual acuity levels between the right and left eyes," said Dr. Robaei, a research officer at the Center for Vision Research, University of Sydney, Sydney, Australia. "There was a difference in visual acuity based on gender, with boys having a slightly better visual acuity level than the girls; this only reached significance in the right eye. The difference was equivalent to less than one logMAR letter, but it agrees with the findings of other population-based studies in adults, such as the Beaver Dam Eye Study and the Blue Mountain Eye Study."

In children without any significant eye conditions, the presence of a spherical equivalent refraction between –0.5 and 2.50 D was not associated with visual impairment. Although a few children had reduced visual acuity in this refractive range, this was probably due to lack of cooperation during the examination.

"The prevalence of visual impairment in our sample was very low. Only 4.1% of children had any visual impairment in at least one eye. We found that girls had significantly more visual impairment compared with boys," Dr. Robaei said. "The overall prevalence of visual impairment was not associated with age or the level of parental education, but we did find a significant association of visual impairment with socioeconomic indicators such as parental employment status. Children with a low socioeconomic background had significantly more visual impairment."

When the investigators divided the children based on mild, moderate, or severe visual impairment, there were no children with severe bilateral impairment, but 0.2% had severe impairment in one eye (two with amblyopia, one Coats' disease, one myopia). Moderate impairment in the better eye was found in 0.3% of the population, all of which resulted from myopia. Mild impairment was found in 1% of the population, most of which resulted from refractive error, according to Dr. Robaei.

Prevalence of impairment

"Overall, uncorrected refractive error was responsible for 69% of the impairment. Amblyopia was the second most common cause of the impairment. Only 2.8% of the children had a retinal disorder," she said.

When the investigators looked at refractive error, astigmatism was the single largest cause of visual impairment. Interestingly, the astigmatism was also unlikely to have been corrected, in contrast to myopia, which was very often corrected in these children.