The current meta-analysis summarized the anatomical and functional outcomes and the postoperative complications of ICG-stained ILM peeling with a total of 858 case eyes and 727 control eyes. The results indicated that the rate of VA and the risk of postoperative visual field defects were worse in the ICG group than in the non-ICG group. However, the anatomical outcomes and other postoperative complications were similar (P>0.05). The additional analyses showed that VA improvement over varied follow-up durations and that the VA of the ICG group was worse only within the first postoperative year; no difference existed at later follow-up dates. No differences were observed between the ICG group and the unstained group. However, the postoperative VA in the ICG group was worse compared with that in the other stains group. Although the anatomical and functional outcomes were not significantly different between the low ICG concentration group and the non-ICG group, the high ICG concentration group showed a better secondary closure rate but a worse VA outcome.
Since Kim first proposed the use of ICG to stain the ILM for better visualization and to assistant with ILM removal in 1999 
, ILM peeling and ICG staining have been regarded as potential methods for improving anatomical and functional outcomes 
. However, the use of ICG in MH surgery was followed by reports of postoperative adverse effects 
, and no concordant conclusion about the value of ICG was achieved. In 2008, Rodrigues and collaborators 
conducted a meta-analysis to evaluate ICG in the management of MHs and reached the conclusion that ICG-assisted ILM peeling was related to no differences in the closure rate, a worse VA and an increased risk of RPE changes. However, because the included studies had a cut-off date of June 2004 and the studies included were not directly comparative studies, our updated meta-analysis was of certain importance.
The anatomical outcomes of the ICG group and non-ICG group were not significantly different, regardless of the use of other stains in the control group. In a retrospective multicenter study including 1627 eyes, patients in whom ICG was used to stain the ILM had a lower percentage of anatomical success 
. However, the study was limited because its aim was to compare MH surgery with and without ILM peeling and the use of ICG was not standardized. Meanwhile, there were also reports indicating no innocuous or helpful effects of ICG use for MH surgery 
. In this meta-analysis, no differences were identified following the use of ICG in MH surgery. However, relatively high concentrations (over 0.1%) were found to correlate with a better secondary closure rate. Kwok and colleagues 
reported that 0.125% ICG resulted in significantly better ILM staining than concentrations of 0.025% to 0.05% ICG, but no difference in peeling time was observed. It is possible that a higher concentration of ICG increased the visibility of the ILM and improved the rate of complete ILM peeling, avoiding secondary adjunct use of ICG.
Similar to the previous meta-analysis 
, worse functional outcomes were also detected in this study. Since ICG was first used in MH surgery, significantly worse visual outcomes have been reported by several case series and clinical trials 
. The increased postoperative complication rate may have resulted in a lower VA improvement 
. Another hypothesis was that a deeper cleavage plane moved to the innermost layers after the application of ICG 
. In additional analyses, a significant difference in VA improvement was found between ICG use and the use of other stains, while in our study, no significant differences were found between ICG use and no ICG. The use of ICG did not decrease VA improvement, perhaps because of the advanced technique of the surgeons and increased experience with the application of ICG 
. Compared with the other stains group, worse functional outcomes were found in the ICG group. Meanwhile, ICG use did not result in better anatomical outcomes when compared to the use of other stains, and it was a great challenge to the importance of ICG in ILM peeling. In the present study, a higher ICG concentration was correlated with less VA improvement, and this was in agreement with reports demonstrating that a lower ICG concentration provided a better VA outcome 
. However, even though worse functional outcomes were observed over a short-term follow up in the ICG group, the long-term follow up demonstrated no difference between the ICG group and the non-ICG group. Similar long-term VA outcome following ILM peeling with and without ICG were previously reported by several studies 
The results failed to demonstrate a relationship between ICG application and RPE changes. The causes of RPE changes were described as follows: 1) ICG was the result of direct toxicity to the RPE; 2) ICG enhanced phototoxicity to the RPE 
. Burk and associates 
applied 0.5% ICG during autopsies and observed no effects on the RPE. RPE changes were observed after a 3-day exposure period in a rabbit model 
. The application of ICG in cultured human RPE cells resulted in decreased mitochondrial enzyme activity, while no cellular morphological or ultrastructural changes were observed 
. Another in vitro experiment showed that ICG was toxic to cultured RPE cells following exposure to concentrations between 0.5% and 0.05% for 3 minutes; no toxicity was observed with trypan blue. 
. Several reports have demonstrated that lower ICG concentrations, shorter exposure times and appropriate light use were possible methods of decreasing the toxicity of ICG 
. In this meta-analysis, after excluding the studies demonstrating no RPE changes in both the ICG and non-ICG groups, the earliest included studies were published in 2006 
. The resulting increased experience with ICG application is a possible explanation for the different results obtained in the present study when compared with a previous meta-analysis 
With the exception of RPE changes, several postoperative complications are thought to be associated with ICG use, including visual field defects, a reduced rate of MH closure, ICG persistence in the retina and optic nerve, optic atrophy, macular edema and retinal tears 
. In this meta-analysis, only visual defects were observed to be significantly different. Although visual field defects have been considered common in MH surgery with and without the use of ICG 
, several authors have reported an increased rate of visual field defects in ICG-stained eyes 
. The application of fluid-air 
was regarded as a common explanation for the visual field defects, and potential toxicity of ICG to the optic nerve was also reported 
. However, as the techniques of the surgeons and their experience with ICG application increased, this adverse effect was possible to avoid.
In the included studies, 4 studies 
reported the osmolarity values (242 to 295 mOsm), while the most common osmolarity was 270 mOsm. A total of 14 studies reported the solvent used. Stalmans et al 
reported that hypo-osmolar solutions resulted in higher cell death, while the iso-osmolar solutions was not related with RPE cell survival and it was the hypo-osmolarity rather than ICG itself related to the toxicity. However, another study 
reported that hypo-osmolarity alone didn't produce toxicity, while it produced cell damage when low osmolarity was combined with ICG. There was no accordant opinion in the relationship between osmolarity and ICG toxicity and more studies are required. Glucose 5% and BSS are solvent usually used and both of them might result in damaging effect 
. Compared with ICG diluted with BSS, ICG diluted with glucose 5% produced a shift of the absorption band toward longer wavelengths 
and there was a hypothesis that the light-absorbing proprieties of dye altered by glucose 5% would reduce the photosensitivity; however, no definitive evidences to prove this existed by now.
The strengths of current meta-analysis were as follows. First, the relatively high number of the included studies and cases provided a better power for the analysis. Second, the consonance of the previous results and the sensitivity analysis demonstrate that the conclusions from this analysis were robust. Despite these advantages, some limitations of the current study should not be ignored. First, this study was limited by the low quality of the retrospective studies included and the lack of RCT-based evidence. It's hard to conduct a meta-analysis in surgical practice and the main challenges of observational studies included selection bias, confounding bias known or unknown, and reporting bias. Second, the symptom duration and MH stage in each trial were not perfectly matched, which may also influence the outcomes of interest. Third, some parameters of interest demonstrated a large degree of heterogeneity. Some were explained, but the heterogeneity of the increased LogMAR was not explained. This may be the result of different surgical techniques or different methods of measuring the LogMAR VA in different trials.
Leaving the limitations aside, we believe that the results of the current meta-analysis are credible. Because the anatomical and functional outcomes of the ICG-stained group were not better, there is no evidence of clinical superiority of ICG use in MH surgery. Because ICG resulted in less VA improvement than other stains group, such as trypan blue, the toxicity of ICG should be considered when choosing the various staining methods.