Visual acuity---the ability to see objects in sharp detail---was evaluated in 1,504 children aged 30 to 71 months as part of the Baltimore Pediatric Eye Disease Study, the first large, population-based study of eye disorders in preschool children.
Ophthalmologists agree on the importance of finding and treating vision problems early in a child's life to avoid potentially life-long negative impacts. Prior to the Baltimore study, little data was available on vision disorders in very young children in the United States.
The children were evaluated in a series of vision tests, including the fixation preference test (FPT) and the Amblyopia Treatment Study test (ATS). The FPT measures an aspect of visual acuity known as fixation, the ability to focus images on the macula, the part of the eye that provides detailed vision. In the FPT, each eye is covered and then uncovered to determine how well it maintains fixation.
The specific purpose of the ATS test is to measure visual acuity in children 30 months and older. "Decreased" visual acuity in study participants was assessed by comparing the children's results to normal vision standards for their age groups. Tests were repeated for all subjects 60 days later with children wearing corrective eyewear, if needed. Subjects were classified as either non-Hispanic white or black (African-American), and results for the groups were compared. Parents of all subjects completed questionnaires regarding the mother's health during pregnancy, the child's general health and development, and any concerns about the child's ability to perform daily activities.
Overall, the prevalence of decreased visual acuity was low: 1.2 percent in white children and 1.8 percent in black. Prevalence at retesting, with corrective eyewear as needed, was 0.5 percent in whites and 1.1 percent in blacks. Differences between the two ethnic groups were not statistically significant. The most common cause of decreased acuity at initial testing was refractive error: nearsightedness, farsightedness and/or astigmatism. Only one child was found to be legally blind.
Importantly, the researchers found that FPT---considered the "clinical standard" for testing vision in preverbal children and the only test widely available to eye specialists for this age group---did not accurately identify the presence or absence of visual acuity problems in this study population. The inaccuracies became apparent when ATS and FPT results were compared for children able to perform both tests.
"These results call into question the use of FPT for clinical decision making," said lead researcher David S. Friedman, MD, PhD, Wilmer Eye Institute, Johns Hopkins School of Medicine. "Given its poor performance, the accuracy of clinical interventions based on FPT is questionable, as are studies that use FPT as an outcome measure. If the experience of this study can be generalized, the use of FPT should be reconsidered."
This research was published in the October 2008 issue of Ophthalmology, the journal of the American Academy of Ophthalmology.
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