This review suggests that two hours patching and six hours patching have similar effectiveness for moderate amblyopia irrespective of its cause.15, 38 However, Singh et al., 2008 favored 6 hours patching over two hours patching for the mixed type of amblyopia (MD 1.3;95% CI,-2.05to-0.54)15. Since significant heterogeneity (I2 = 88%) was evident, the studies were not pooled. The evidence concerning the event of reverse amblyopia and adherence is limited. Only a study reported that both two hours and six hours patching are equally tolerated and comparable adherence.38
This study also found that the pooled mean visual acuity difference in the amblyopic eye between six hours and full-time patching is nil (MD, 0.00; 95% CI, -0.54 to 0.55). This finding is supported by a meta-analysis study which concluded that part-time occlusion and full- time occlusion are equally effective.28 Independently, three authors agreed that both six hours patching and full time patching are equally effective.38, 42, 44 PEDIG 2003b also showed that the success rate of six hours (93%) and full-time patching are also comparable (84.5%). However, significant reverse amblyopia in the full-time group (11%) was also noted as compared to part-time groups (4%).42 Regardless of the cause of amblyopia, Singh et al 2008 found that six hours and full-time patching can produce a similar visual outcome for mild to moderate amblyopia and severe amblyopia.15
Regarding atropine versus patching, majority of the trials concluded that both treatment modalities are equally effective. Similarly, previous review reported that both conventional occlusion and atropine produce comparable visual acuity improvement in the amblyopic eye and atropine penalization was implicated as first line treatment for amblyopia.27 However, in this review patching is favorable over atropine (pooled MD, 0.25 lines; 95% CI, 0.01 to 0.48). In addition, the weighted probability of achieving a visual acuity of greater or equal 2 LogMAR line is slightly higher for patching as compared to atropine but it was not significant (RR, 1.08; 95% CI, 0.98 to 1.18). However, the pooled risk of developing reverse amblyopia was lower by 19% for patching groups as compared to atropine (RR, 0.19; 95% CI: 0.06, 0.57). On the other hand, the pooled RR estimate suggests that the adherence rate for patching is lower by 10% from atropine even if there was disagreement between the individual studies. As a subgroup analysis, it was found that effectiveness difference between patching and atropine was not explained by the variation of the patching dose and age participants at the time enrollment.
Several strengths can be recognized in the review, in which both primary and secondary outcomes are considered to choose the most effective and safe modality. Moreover, serious caution was taken while selecting the studies, particularly those conducted on residual amblyopia and visual acuity stabilization with optical correction. Though publication bias and risk of bias are an unavoidable issue in a review article, it was not too foreboding for this review. The majority of the studies were RCT trial, which is free of allocation concealment bias, random sequence generation, attrition bias and reporting bias. So the validity of the studies is fair.
Even if the majority of included trials free from the risk of bias, the blinding of the participants was not clearly disclosed. This review did not incorporate cost-effectiveness data which is important to choose economically efficient treatment modality. In addition, studies with variable length of follow up were synthesized. This review also did not include active amblyopia treatments which require the interaction patients with the treatment like a video game, vision therapy, and near activities. Since the number of studies that could be included is relatively small and heterogeneity was evident, meta-analysis was carried out for some of research questions. Moreover, this review did not aim to answer which intervention resolve faster.
Overall, this systematic review implicated that the choice of amblyopia treatment should rely on both primary and secondary outcomes. Regardless of the cause of amblyopia, selection of the modality depends on the severity of amblyopia. This review also indicates that atropine and full-time patching should be given under close follow up to prevent reverse amblyopia. Treatment adherence is compromised as the number of patching hours increase. Hence, strong physician-parents integration might be crucial for maximizing the adherence rate. Further research concerning the cost-effectiveness of the modalities, active amblyopia treatments and the optimal time (when maximum visual acuity is achieved) should be conducted.