Detecting Preschoolers at Risk for Vision Loss
Simple office test identifies "lazy eye" early, when it's most treatable
April 10, 2006
A simple 3-second office screening test may enable pediatricians to identify amblyopia, or vision loss in one eye, in children as young as two, report ophthalmologists at Children's Hospital Boston in the April Archives of Ophthalmology. Amblyopia, also known as "lazy eye," affects 3 to 5 percent of all children and is the leading cause of vision loss in childhood. Because preschoolers cannot reliably communicate or read eye charts, amblyopia often goes undetected at the time when it is most correctable.
"The eyes of a child with amblyopia can look perfectly fine, but one eye is slowly going blind," says senior author David Hunter, MD, chief of ophthalmology at Children's Hospital Boston, who sees patients at the hospital's Boston and Waltham centers and developed the screening instrument while at Johns Hopkins. "Once a child reaches school age, treatment is less likely to restore useful vision. We'd really like to begin treating them when they're three years old - or younger."
Amblyopia is caused by under use of one eye, usually due to a misalignment (known as strabismus) or weaker focusing power compared with the other eye (anisometropia). In both situations, the child's stronger eye becomes dominant, while vision in the weaker eye deteriorates as the brain loses its ability to interpret visual information from that eye. If the problem is detected early, ideally before age four or five, irreversible vision loss can be prevented by patching the stronger eye or blurring it with eyedrops, forcing the child to use the weaker eye.
The new screening instrument, known as the Pediatric Vision Scanner, is designed to be easy for pediatricians and pediatric nurses to use. It looks like a hand-held camera and displays a visual target: a blinking light inside a bull's eye. As the child looks at this target, the device scans the eyes' retinas with a low-power laser to take a series of five readings of the eyes' alignment and ability of both eyes to focus on the target simultaneously. An overall score below 60 percent (fewer than three successes in five attempts) indicates that the child should be referred to a pediatric ophthalmologist for further examination.
In their study, Hunter and colleagues evaluated 77 children, aged two to 18, who were patients at Children's ophthalmology clinic or their siblings. All subjects underwent a complete "gold standard" examination by an orthoptist or pediatric ophthalmologist to identify risk factors for amblyopia: 37 children were diagnosed with strabismus, three with anisometropia and 37 had neither condition and served as controls. Each child was also tested with the Pediatric Vision Screener by an investigator who was unaware of the "gold standard" findings.
The device reliably identified all 37 children with strabismus and could detect very fine degrees of eye misalignment. It also identified all three children with anisometropia. One quarter of the children with strabismus and all three children with anisometropia were between the ages of two and four. All 37 children in the control group passed the exam.
Hunter's group has since tested 50 more children, with similar results. He hopes to increase pediatricians' awareness of amblyopia and persuade health insurers and government agencies to support routine amblyopia screening for preschool-age children. While a number of states have mandated a full eye exam by eye specialists before entry to school, this is too late to treat amblyopia successfully, Hunter says, adding that an early screening eye exam in the pediatrician's office would be less expensive and likely to reach more children than a full eye exam. He is now refining his device, with plans to begin field-testing it in pediatricians' offices within one to two years.
This study excluded children under age two from analysis because they weren't interested enough in the target to consistently look at it. The new prototype under development is hoped to extend amblyopia screening to as early as 12 months of age, by using a more appealing target that combines a flashing white light and a beeping tone.
Funding for the study was provided by the Research to Prevent Blindness, the Massachusetts Lion's Eye Research Foundation, the National Institutes of Health and the Helena Rubenstein Foundation.
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Children's Hospital Boston is the nation's premier pediatric medical center. Founded in 1869 as a 20-bed hospital for children, today it is a 347-bed comprehensive center for pediatric and adolescent health care grounded in the values of excellence in patient care and sensitivity to the complex needs and diversity of children and families. More than 100 outpatient specialty clinics are located at Children's. Children's Hospital Boston is the primary pediatric teaching affiliate of Harvard Medical School, home to the world's leading pediatric research enterprise, and the largest provider of health care to the children of Massachusetts. For more information about the hospital visit: www.childrenshospital.org.
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