After more than 20 years of changes in surgical methods, the closure rate of patients’ postoperative holes has been greatly improved. However, there was no unified explanation for the recovery of visual function and structure after operation. Therefore, the review provided the recovery of IMH at different stages after surgery by the changes of macular tissue structure and BCVA.
The BCVA of patients had significantly improved (Fig. 2) within 12 months after operation. Kaźmierczak23 and associates also have reported that Vision acuity improvement after MH surgery continued to improve in the first three years. The postoperative BCVA improved significantly within 12 months, and tended to be stable after 12 months which be consistent with the study of Chang et al24.
We were allowed to evaluate the concave micro-structure25 quantitatively and qualitatively, due to the birth of OCT. Postoperative micro-structural changes in the macular region involve photoreceptor defects, which were correlated with postoperative BCVA. For instance, Lee et al7 reported that the recovery time of ELM, ONL and EZ was 1.5, 2.1 and 6.1 months, respectively, and the recovery of ELM and ONL usually preceded the recovery of EZ. Similar to the finding of Lee, we concluded that change of ELM defect during 1–6 months was significant, but the repair within one month and after 6 months was not obvious (Fig. 3). We found the changes of EZ defect were significant from 1 month to more than 9 months after operation. However, the changes within 1 month were not significant (Fig. 4).
Multiple authors reported that the defects in the EZ and ELM were a major reason for unsatisfactory postoperative visual recovery16,19,24,26. Nevertheless, Ooka et al17 reported that IS/OS and ELM defect changes are not related to the changes of BCVA. Other researchers (Wakabayashi et al4, Hasebe et al27) suggested that the integrity of IS/OS is not important for predicting postoperative BCVA. However, some scholars (Yang et al28, Carpineto et al12, Goker et al21, Morawski et al29) emphasized that BCVA was significantly related to the integrity of EZ band after operative. In this review, we analyzed the correlation between BCVA and ELM defect and between BCVA and EZ defect after operation, which were proved to be significant (P ༜ 0.05) (Table 4). Kitao et al14, Houly et al15, Chang et al insisted that eyes with complete ELM layer or EZ layer have better BCVA than eyes with defects in ELM layer and EZ layer. They divided the affected eyes into three groups (ELMc/EZc: eyes with continuous ELM layer and EZ layer, ELMc/EZd: eyes with continuous ELM layer and discontinuous EZ layer, ELMd/EZd: eyes with discontinuous ELM layer and EZ layer). All of them found that the postoperative VA of ELMc/EZc group was significantly better than that of ELMc/EZd group and ELMd/EZd group, and that of ELMc/EZd group was better than that of ELMd/EZd group. Nevertheless, due to the limited research included, there may be contingency, and more articles need to do in-depth research.
The closure of MH cannot ensure the rearrangement of photoreceptors in the outer layer of the retina, which also leads to vision improvement defects. Therefore, it is very important to put forward the hypothesis of vision restoration from the perspective of pathology. The first hyperreflective zone in the outer layer of the retina was the ELM layer composed of bulges and microvilli at the end of Müller cells30. ELM layer was also the first part of retinal fovea repair after macular hole surgery31, and it was also the most important part affects the prognosis of vision12,22. However, several studies have shown that EZ was the most important structure affecting postoperative BCVA recovery. EZ band was the second hyperreflective band in the outer layer of the retina, which was a cell compartment full of mitochondria30. Contrary to our study, some studies have shown that the recovery of EZ had no significantly effect on BCVA one year after operation28. Among the studies of Kitao et al14, Houly et al15, Chang et al24, none of them showed patients with ELMd/EZc. The phenomenon showed that the recovery of EZ must be based on the recovery of ELM. As a bridge between Müller cells and photoreceptors, ELM layer played an important role in maintaining retinal structure. Because the EZ layer contains mitochondria responsible for generating cell energy, its integrity is closely related to the restoration of retinal structure. Therefore, we speculated that the recovery of EZ layer will be limited by ELM layer.
In general, the postoperative BCVA gradually improved with the repair of the outer retinal layer, and the integrity of the ELM layer and the EZ layer was an important factor affecting the postoperative BCVA.
Our study had several limitations. There were seven retrospective studies, which might have potential sources of selection bias. Several studies believed that there was a strong correlation between the recovery of the photoreceptor cone outer segment tips (COST)20, the recovery of the outer nuclear layer (ONL)22, the reduction of glial cells, as well as cone interdigitation zone (CIZ)14 with the recovery of visual function. Moreover, mean retinal sensitivity (MS)12 was also a very good outcome indicators, in addition to BCVA. However, we did not find enough relevant articles to be included in the study.