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To the Editor.
The Quinn et al commentary1 comparing the efficacy of various patching protocols for the treatment of amblyopia confirms a previous compilation of multiple reports2 that found no relationship between duration or type of therapy used and visual outcome.
Performance improvement on vision tests normally occurs in children with increasing age, literacy, and experience.3 Improved acuity also was demonstrated in clinical trials in which acuity of the patched eyes improved at the same rate as the unpatched eyes.4 The conclusions concerning the efficacy of treatment in the commentary, reached without the benefit of a control group or correcting for placebo effects, might therefore be too optimistic. For example, a previous Pediatric Eye Disease Investigator Group (PEDIG) study reported that baseline visual acuity in the amblyopic eyes at age of enrollment showed a steady improvement with increasing age before treatment. The percentage of children with 20/100 at 3 years old was 40%, and this percentage decreased to 19% at age 6 years. Only 7% of children had acuities of 20/50 at age 3 years in the poorer eye, and this percentage increased to 27% at age 6 years before treatment was instituted.5
Patient selection in the PEDIG studies presents another cause for concern. From 47 clinical sites, 209 children were recruited.6 These sites were all active pediatric practices that each certainly contained >5 children with amblyopia. The winnowing that occurred "allows bias to enter in and constitutes a subtle manipulation of trial results."7
Success in amblyopia treatment is usually defined in terms of relative improvement rather than achievement of a specified functional status. For the majority of patients, successful treatment (by this criterion) will still not result in normal vision or even vision levels adequate for driving or reading. Therefore, positive comments about outcome may raise expectations that will not be fulfilled.
Amblyopia is a diagnosis of exclusion made only after organic causes for decreased acuity have been eliminated. Diagnostic modalities have improved8,9 since the original definitions of amblyopia were developed >2 centuries ago,10 but there still is an almost total reliance on subjective ophthalmoscopic observations and patient responses. Readily available methods such as biometry, retinal photography, and magnification-corrected optic-disk imaging that permit documentation of optic-nerve hypoplasia12 and/or dysplasia12 are rarely used, even by research groups.
The practice of medicine requires constant reevaluation of traditional concepts and methods as new modalities for diagnosis and prevention become available. The acceptance of occlusion as the unquestioned mainstay of treatment for unilateral poor vision in children risks imposing unnecessary treatment and distracts researchers from investigating measures to prevent impaired vision in childhood.
REFERENCES
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