## 4 Discussion  
The aim of this study was to evaluate the long-term functional and anatomical outcomes after PPV with ERM and ILM peeling in patients with alterations of the CB. A significant overall mean gain in BCVA of 2.5 lines (0.22 LogMAR units) was achieved, and ERM was completely removed in the central macular region in 98.5% of eyes. After a mean follow-up of 20 months, the mean CB stage improved significantly (\(p\) = 0.002) from 0.55 to 0.27 and the mean ERM stage was reduced significantly from 2.45 to 0.01. Confirming the results of our short-term follow-up study [29], the preoperative stage of ERM did not have a statistically significant impact on the mean BCVA change following surgery (\(p\) = 0.528). Looking at the presented long-term results, CB stage at baseline did not prove to be a significant predictor of BCVA change after surgery (\(p\) = 0.939). This is contrary to the findings of our earlier results, where we found that the presence of alterations of the CB appeared to be an indicator for poorer functional outcomes in short-term follow-up [29]. According to the results of the present study, the observed short-term effect of CB alterations on BCVA diminishes in the long-term. Furthermore, BCVA at baseline was a significant predictor of BCVA improvement after surgery (\(p\) < 0.001). As expected, patients with higher BCVA at baseline reached better BCVA results in the long-term follow-up. Confirming the results of the short-term follow-up, when comparing the procedures that included cataract removal to those without, no significant difference could be observed in the in the visual and morphological outcome (\(p\) = 0.196). Other studies have already described modifications of the outer retinal morphology [27; 28]. Additionally, these changes were categorized into progressive stages beginning with the cotton ball sign, followed by foveolar detachment and resulting in an acquired vitelliform lesion as the final stage [7]. While a progression in the stage of CB alteration has already been linked to a decrease in BCVA [7], the influences of surgical removal of ERM on specific changes in the CB and the associated functional outcome have, to our knowledge, only been evaluated for short-term follow-up [29]. Comparing the composition of our cohort to that of [PERSON] et al., CB alterations were more frequent (34% vs. 22%); \begin{table}
\begin{tabular}{c c c} \hline
**BCVA Difference before vs. after Surgery** & **Mean** & \(p\)**-Value \({}^{\star}\)** \\ \hline ERM before surgery & & 0.528 \\ Stage 1 & \(-\)0.258 & \\ Stage 2 & \(-\)0.251 & \\ Stage 3 & \(-\)0.183 & \\ Stage 4 & \(-\)0.197 & \\ CB before surgery & & 0.841 \\ Stage 0 & \(-\)0.254 & \\ Stage 1 & \(-\)0.175 & \\ Stage 2 & \(-\)0.080 & \\ Stage 3 & \(-\)0.168 & \\ \hline \end{tabular} \({}^{\star}\)ANOVA analysis (Tukey HSD).  
\end{table} 
Table 3: Influence of surgery on best corrected visual acuity (BCVA) difference stratified by baseline parameters. however, the distribution of the different stages of CB alterations was comparable to their group (stage 1: 55% vs. 62.1%; stage 2: 23% vs. 17.2%; and stage 3: 23% vs. 20.7%). In the present study, we did not detect a significant correlation between BCVA and the stage of ERM at baseline. This is contrary to the findings of other groups, which reported that higher ERM stages at baseline correlated with lower BCVA at baseline and after surgery respectively [4; 30; 31]. As expected, most of the ERMs could be removed completely in the central foveal region (98.5%, \(p<0.001\)), leading to a significant gain in vision of almost 2.5 lines (\(p<0.001\)). These findings are coherent with those of other groups which have evaluated the influence of ERM removal on visual acuity outcome [25; 26]. [PERSON] et al. and [PERSON] et al. similarly described improvements in BCVA of more than two lines in 77% and 70% of their patients respectively [29; 30].