Amblyopia refers to unilateral or bilateral reduction in best corrected visual acuity, not directly attributed to structural abnormality of the eye or posterior visual pathways. Early detection of amblyopia is crucial to obtaining the best response to treatment. Amblyopia responds best to treatment in the first few years of life. In the past several years a series of studies undertaken by the Pediatric Eye Disease Investigator Group (PEDIG) have been designed to evaluate traditional methods for treating amblyopia and provide evidence on which to base treatment decisions. This article summarizes and discusses the findings of the PEDIG studies to date.
Key points
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Amblyopia is the most common cause of vision loss in children.
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Early detection and treatment of amblyopia are critical to restoring vision in amblyopic eyes.
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Regular vision screening and appropriate referral to a pediatric ophthalmologist are important steps in the detection of children at risk for amblyopia.
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The Pediatric Eye Disease Investigator Group (PEDIG) has published several studies in recent years providing evidence on which to base treatment decisions. Newer treatments including atropine drops and oral levodopa have been evaluated.
With an estimated prevalence of 2% to 4% in North America, amblyopia accounts for more cases of unilateral reduced vision in children than all other causes combined. By definition, amblyopia refers to unilateral or, less commonly, bilateral reduction in best corrected visual acuity, not directly attributed to a structural abnormality of the eye or posterior visual pathways. Its primary causes are strabismus, anisometropia (significant difference in refractive error between the 2 eyes) or bilateral high refractive errors, and stimulus deprivation. Early detection of amblyopia is crucial in obtaining the best response to treatment. If amblyopia goes unrecognized or untreated past the early years of life, it often cannot be successfully treated and vision cannot be fully restored in the amblyopic eye. Although there are exceptions to the rule, most ophthalmologists regard the age of visual maturity to be approximately 8 to 9 years of age. Beyond visual maturity, most cases of amblyopia respond poorly to any form of treatment. It is also generally accepted that amblyopia responds best to treatment in the first few years of life.
The earliest clinical description of human amblyopia is generally credited to Le Cat in 1713. Although amblyopia as a disease has been relatively well understood for many years and the treatment modalities have remained fairly standard, in the past several years much has been published regarding this disease, owing mostly to a series of Amblyopia Treatment Studies (ATS) undertaken by the Pediatric Eye Disease Investigator Group (PEDIG). These studies were designed to evaluate the traditional methods for treating amblyopia and provide evidence on which to base treatment decisions. Before the PEDIG studies, most published studies on amblyopia treatment were large retrospective reviews.
Formed in 1997, and funded by the National Eye Institute, PEDIG is a collaborative network facilitating multicenter clinical research in strabismus, amblyopia, and other eye disorders that affect children. There are more than 100 participating sites with more than 200 pediatric ophthalmologists and optometrists in the United States, Canada, and the United Kingdom. PEDIG has completed more than 15 ATS to date, many with multiple phases. The published findings of the PEDIG ATS to date are summarized in Table 1 .
| Study | No. of Patients (Age at Enrollment) | Follow-Up Period | Result |
|---|---|---|---|
| Randomized trial comparing occlusion vs pharmacologic for moderate amblyopia (ATS 1) | 419 (3 to <7 y) | 6 mo | VA improved in both groups: 3.16 lines in occlusion group; 2.84 lines in atropine group Mean difference = 0.34 lines (95% CI, 0.05–0.6) VA ≥20/30 and/or improved by ≥3 lines in 79% of occlusion group and 74% of atropine group |
| Randomized trial comparing occlusion vs pharmacologic therapy for moderate amblyopia (ATS 1) | 419 (3 to <7 y) | 2 y | VA improved in both groups: 3.7 lines in occlusion group; 3.6 lines in atropine group Mean difference = 0.01 lines (95% CI, −0.02 to 0.04) Atropine or patching for an initial 6-mo period produced a similar improvement in amblyopia 2 y after treatment |
| Randomized trial comparing part-time vs full-time patching for severe amblyopia (ATS 2A) | 175 (3 to <7 y) | 4 mo | VA improved in both groups: 4.8 lines in the 6-h patching group; 4.7 lines in the full-time patching (all hours or all but 1 h per day) group Mean difference = 0.02 lines (95% CI, −0.04 to 0.07) |
| Randomized trial comparing part-time vs minimal-time patching for moderate amblyopia (ATS 2B) | 189 (3 to <7 y) | 4 mo | VA improvement in both groups was 2.40 lines Mean difference = −0.007 lines (95% CI, −0.050 to 0.036) VA ≥20/32 and/or ≥3 lines in 62% of patients in both groups VA improvement similar for 2 h of daily patching and 6 h of daily patching |
| Evaluation of treatment of amblyopia (ATS 3) | 507 (7–17 y) | 6 mo | For moderate amblyopia in children 7 to <13 y old, 36% achieved 20/25 or better with optical correction/occlusion/atropine use compared with 14% with optical correction alone ( P <.001) For severe amblyopia in children 7 to <13 y old, 23% achieved 20/40 or better with optical correction/patching compared with 5% with optical correction alone ( P <.004) For moderate amblyopia in teenagers 13–17 y old, 14% achieved 20/25 or better with optical correction/occlusion compared with 11% with optical correction alone ( P = .52) For severe amblyopia in teenagers 13–17 y old, 14% achieved 20/25 or better with optical correction/occlusion compared with 0% with optical correction alone ( P = .13) |
| Randomized trial comparing daily atropine vs weekend atropine for moderate amblyopia (ATS 4) | 168 (3 to <7 y) | 4 mo | VA improvement in both groups was 2.3 lines Mean difference = 0.00 (95% CI, −0.04 to 0.04) 47% of daily group and 53% of the weekend group had either VA ≥20/25 or greater than or equal to that of the nonamblyopic eye |
| Prospective noncomparative trial to evaluate 2 h of daily patching for amblyopia (ATS 5, eyeglasses-only phase) | 84 (3 to <7 y) | Up to 30 wk | Amblyopia improved with optical correction by ≥2 lines in 77% Amblyopia resolved with optical correction in 27% (95% CI, 18%–38%) |
| Randomized trial to evaluate 2 h daily patching for amblyopia (ATS 5, randomization phase) | 180 (3 to <7 y) | 5 wk | After a period of treatment with eyeglasses until vision stopped improving, patients treated with 2 h of daily patching combined with 1 h of near visual tasks had an improvement in VA of 1.1 lines compared with 0.5 lines in the control group Mean difference (adjusted) = 0.07 lines (95% CI, 0.02–0.12; P = .006) |
| Randomized trial to compare near vs distance activities while occluded (ATS 6) | 425 (3 to <7 y) | 17 wk | At 8 wk, improvement in amblyopic eye VA averaged 2.6 lines in the distance activities group and 2.5 lines in the near activities group (95% CI for difference, −0.3 to 0.3 line) Groups appeared statistically similar at the 2-wk, 5-wk, and 17-wk visits At 17 wk, children with severe amblyopia improved a mean of 3.7 lines with 2 h patching |
| Treatments of bilateral refractive amblyopia (ATS 7) | 113 (3 to <10 y) | 1 y | Binocular VA improved on average 3.9 lines (95% CI, 3.5–4.2) At 1 y, 74% had binocular VA of 20/25 or better |
| Randomized trial comparing atropine vs atropine plus a plano lens for the fellow eye in children 3–6 y (ATS 8) | 180 (3 to <7 y) | 18 wk | Ambloypic eye VA was 20/25 or better in 29% of the atropine-only group and in 40% of the atropine plus plano lens group ( P = .03) More patients in the atropine plus plano lens group had reduced fellow eye acuity at 18 wk; however, there were no cases of persistent reverse amblyopia |
| Randomized trial comparing occlusion vs atropine for amblyopia (ATS 9) | 193 (7 to <13 y) | 17 wk | Similar improvement in VA in both groups Amblyopic eye VA of 20/25 or better in 17% of atropine group and 24% of the patching group (95% CI, −3% to 17%) |
| Randomized trial comparing Bangerter filters vs occlusion for the treatment of moderate amblyopia in children (ATS 10) | 186 (3 to <10 y) | 24 wk | Similar improvement in VA in both groups Amblyopic eye VA of 20/25 or better in 36% of Bangerter group and 31% of patching group ( P = .86) Patching was not superior (95% CI difference between groups, −0.06 to 0.83 line) |
| Randomized trial to evaluate combined patching and atropine for residual amblyopia (ATS 11) | 55 (3 to <10 y) | 10 wk | Before enrollment, eligible subjects had no improvement with 6 h daily patching or daily atropine Intensive treatment group had 6 h of prescribed daily patching combined with daily atropine; weaning group had 4 wk of reduced treatment, then stopped Amblyopic eye VA improved similarly in both groups, an average of 0.56 lines in the intensive group (95% CI, 0.18–0.93) and 0.53 lines in the weaning group (95% CI, −0.04 to 1.10) |
| Nonrandomized prospective trial of eyeglasses alone for strabismic and strabismic-anisometropic combined amblyopia in children (ATS 13) | 146 (3 to <7 y) | 28 wk | Mean 2.6 lines improvement (95% CI, 2.3–3.0) 75% improved ≥2 lines and 54% improved ≥3 lines Resolution in 32% (95% CI, 24%–41%) Treatment effect was greater for combined-mechanism amblyopia (3.2 vs 2.3 lines; adjusted P = .003) |
As presented as part of a 2006 Symposium at the Joint Meeting of the American Orthoptic Council, the American Association of Certified Orthoptists, and the American Academy of Ophthalmology, and subsequently reported in the American Orthoptic Journal in 2007, David K. Wallace has summarized several questions regarding amblyopia and its treatment that have been addressed by the PEDIG studies, including the following:
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How well do glasses alone treat amblyopia?
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Do we really know that patching works?
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How many daily hours of prescribed patching are necessary?
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What happens when patching is stopped?
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Does patching work in older children?
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Does atropine work as well as patching?
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How often does atropine need to be used?
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If improvement plateaus with patching, is it beneficial to increase patching time?
The following discussion summarizes the findings of the various PEDIG studies as they relate to these questions.
How well do glasses alone treat amblyopia?
This question was the subject of the spectacle phase of ATS 5. Eighty-four patients participated, ranging in age from 3 to 7 years. Follow-up was up to 30 weeks. The results of this study demonstrated that 77% of amblyopic eyes improved by 2 or more lines of vision by using optical correction alone. Resolution of amblyopia using optical correction alone occurred in 27% of patients.
Do we really know that patching works?
This question was the subject of the ATS 5 randomized clinical trial phase. A total of 180 patients, ranging in age from 3 to 7 years, were followed for 5 weeks. After no further vision improvement with glasses alone, these patients were treated with 2 hours per day of patching combined with 1 hour of near visual tasks. In this group of patients, vision improved 1.1 lines compared with 0.5 lines in a control group.
How many daily hours of prescribed patching are necessary?
ATS 2A compared full-time with 6 hours of daily patching for those with visual acuity 20/100 to 20/400. A total of 175 patients between the ages of 3 and 7 years participated, with a follow-up of 4 months. In these patients, the vision improved 4.8 lines in the group patching 6 hours per day and 4.7 lines in the group patching full time. ATS 2B compared 6 hours of daily patching with 2 hours of patching per day for those with visual acuities ranging from 20/40 to 20/80. A total of 189 patients ranging in age from 3 to 7 years were studied, with a follow-up of 4 months. The improvement of visual acuity was 2.4 lines in both groups, indicating that 2 hours of daily patching can be equally as effective as 6 hours per day.
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