Amblyopia is a condition that occurs when a child’s visual system does not develop properly, resulting in abnormal sight in one or both eyes. The condition is sometimes called “lazy eye.” The condition affects as many as three percent of children in the United States. It is the most common cause of monocular visual impairment in both children and young and middle-aged adults.
The disorder is caused by any condition that sends the brain abnormal or unequal visual input during infancy or childhood. These conditions can include an imbalance in the positioning of the eyes, such as strabismus, in which the eyes are crossed inward (esotropia) or turned outward (exotropia). Amblyopia also can result from a major difference in refractive error between the two eyes, such as nearsightedness, farsightedness, or astigmatism. Less common causes of amblyopia are cornea and lens diseases and injury to the eye of a young child. The results reported in this study do not include amblyopia from these less common causes.
It has been commonly thought that the best time to try to correct amblyopia was during infancy or early childhood before the eyes and the entire visual system, including the brain, have fully matured. Although most eye care professionals agreed that amblyopia could be treated effectively in young children, many have thought that treatment beyond a certain age is ineffective. Some clinicians thought that a treatment response was unlikely after the age of six or seven years, while others considered age nine or ten years to be the upper age limit for successful treatment.
There had been limited data available to eye researchers on treatment of children older than seven. However, some clinicians reported that treatment did benefit older children. To prepare for a possible randomized clinical trial on treating amblyopia in older children, the National Eye Institute (NEI) funded a pilot study that was completed in 2003. The pilot study showed that after treatment, 27 percent of 66 children with amblyopia, ages ten through 17 years, improved their vision in the affected eye. They gained the ability to read two or more lines of a standard eye chart. The results justified the NEI-funded, Randomized Trial of Treatment of Amblyopia in Children 7 to < 18 Years Old. The trial was coordinated by the Pediatric Eye Disease Investigator Group (PEDIG), a network of eye care professionals at universities and community offices in North America.
The purpose of this trial was to treat two age sets of “older” children, seven through 12 years old and 13 through 17 years old, with conventional amblyopia treatments, both patching and atropine eye drops. At 49 clinical sites nationwide, 507 children with amblyopic eye vision ranging from 20/40 to 20/400 were recruited into the trial from October 2002 to March 2004. Eye care professionals then prescribed new eye glasses for all the study children, to obtain the “optimal optical correction.” Both sets of children were then randomly divided into either a “treatment group” or an “optical-correction-only group,” children who received only glasses.
In the treatment group, seven- through 12-year-old children received two to six hours daily patching of the unaffected eye with near activities, plus daily atropine drops in that eye to temporarily blur their near vision. The 13 through 17-year-old children in the treatment group received the patching and near activities but not the eye drops. The near activities included hand-held computer games, homework, reading, computer work, and the use of workbooks designed for the study with mazes, and word finds. Vision improvement in the eye with amblyopia occurred over a period of six to 24 weeks.
The results confirm the pilot study results that conventional treatment of amblyopia can be effective in children even after age seven. As is the case with patients younger than seven, however, most of the older patients are also left with some remaining visual impairment despite treatment. The investigators are continuing to study the children for a year after stopping their treatment to determine whether the benefit reported in this paper will be sustained.
The study authors also reported that patients participating in the clinical trial may differ from patients in usual clinical practice. The children in the study, with the guidance of their parents, may have a different level of compliance than may be achieved in clinical practice.
For decades, patching the unaffected eye had been the standard treatment for amblyopia. In March 2002, NEI-supported researchers reported the effectiveness of drug therapy with an eye drop (atropine) that dilates the pupil and blurs the image seen by the unaffected eye during near viewing. In May 2003, results of another NEI-funded study, also conducted by the PEDIG at 35 clinical sites, indicated that patching the unaffected eye of children with moderate amblyopia for two hours daily works as well as patching the eye for six hours.