Natural course of LMH in myopic eyes
Currently, studies on the natural history of LMH in high myopia are limited(15, 16, 20-23). In contrast to myopic eyes, LMH has a stable clinical course in normal eyes.(7, 23, 24) Thoedossiadis and associates(23) examined the natural course of LMH in non-myopic eyes. Visual acuity was stable in 78% of cases over a mean follow-up of 37.1 months. Experts in the field generally agree that LMH in non-myopic eyes is a stable condition without much progression over time.(25) However, LMH in highly myopic eyes often coexists with MTM, which complicates patient outcomes due to the presence of complex tractional forces around the macular region.(26) Hence, LMH in myopic eyes likely represents a distinct entity, with different morphological features compared to the degenerative or tractional types described by Govetto et al.(6)
The available studies on LMH in highly myopic eyes had varying conclusions. Rino et al. showed in their series that myopic LMH with posterior staphyloma progresses during the lifetime of a patient.(16) On the other hand, Tanaka et al(15) concluded in their long-term study that LMH in high myopia is a stable condition which seldom progresses into FTMH. Similarly, LMH was found to be stable in visual and anatomic outcomes over a long-term period in pathological myopia cases.(7) In the current study, LMH in the myopic eye was found to be an unstable condition. The majority of cases, with or without foveoschisis, showed evidence of visual declines and progressive EZ disruptions over time. This study also identified the presence of foveoschisis and vitreomacular traction as risk factors for the development of FD and FTMH.
Pathogenesis of FS in causing FTMH
Myopic retinoschisis (MRS) is considered one of the most frequent complications of MTM.(8, 9, 14, 27) Clinical studies on MRS revealed that 4.8-29.2% of myopic eyes had both LMH and MRS.(8, 9, 15). LMH, on the other hand, was considered a potential intermediate phase before the development of FTMH in highly myopic eyes.(11) In concordance with previous studies,(11, 15, 16) this study revealed the presence of foveoschisis as a risk factor for the development of FTMH or foveal detachment in the long term. This echoes our understanding of the pathogenesis of FTMH in highly myopic eyes. The presence of FS indicates the presence of a prominent anteroposterior vitreomacular traction force. In addition, macular retinoschisis itself promotes a tangential or multidirectional traction force, which increases the risk of foveal detachment or FTMH. (10) In the LMH without foveoschisis group, the structural parameters of LMH remained stable, but the visual function and EZ integrity did decline over time. However, surgical intervention was seldom required in this LMH group, as the risk of developing foveoschisis or impending macular holes was smaller compared to the group with co-existing FS.
Surgical decision on operating on FS eyes with lamellar holes
Both the timing and techniques for the surgical treatment of LMH remain controversial. Witkin et al. believe that there is no evidence showing the benefit of surgical intervention in non-myopic eyes.(28) In contrast, vitrectomy with removal of the ERM-ILM complex has been shown in other studies to be beneficial in terms of functional and anatomical improvements.(4, 29-32) Macular surgeries in highly myopic eyes, however, remain a challenge for many surgeons. In these pathological myopic eyes, the ILM appears thin, sticky, and strongly adheres to the retina. In addition, chorioretinal atrophy limits the contrast for the membrane peeling procedure. These factors increased the chances of an iatrogenic retinal break and macular injuries. Hence, it is a well-accepted consensus that observation and conservative approaches for LMH related to high myopia are necessary, given its static visual acuity. However, the timing of ILM peeling in the presence of myopic FS or worsening FS is a difficult decision. The thin residual central foveal tissue is likely to be damaged during the operative procedure and may lead to iatrogenic FTMH. The reported rates of FTMH development ranged from 16.7% to 20.8% after ILM peeling in FS eyes.(33) Foveal-sparing ILM peeling procedures were therefore introduced to avoid FTMH development.(33-35) However, this technique remains surgically challenging, and there is no consensus on the size of the residual ILM area. From the results of our study, the authors suggest considering earlier surgical interventions for LMH in myopic eyes when there is co-existence of FS.
ERM associated with LMH
The pathogenesis and role of ERM in the development of FTMH in highly myopic eyes are not fully understood. In conjunction with many reported series,(2, 4, 23, 29) ERM was identified in most cases in the current study.
Regarding the formation of ERM, the abnormal vitreous-retinal interface and the presence of posterior vitreous adherence in myopic eyes play important roles in the pathogenesis of ERM.
This hypothesis was further supported by a histological study; reports on the histological composition of ERM in idiopathic LMH showed a component of glial cells from vitreous collagen.(3, 36, 37) Tanaka et al. reported that 17 of 24 myopic eyes affected by LMH (70.83%) were associated with ERM. Similarly, Rino et al. reported that ERMs, especially atypical contractile ERMs, were commonly associated with LMH in eyes with pathological myopia. Different types of ERMs, including convention and atypical ones, have been reported to be highly prevalent in myopic lamellar holes.(3, 5, 38) Witkin and associates(2) reported that the contraction of the perifoveal complex of ERM and the existing anteroposterior vitreous traction can lead to the formation and progression of LMH. Theodossiadis et al. reported that ERM contributed to the enlargement of the LMH. (23) However, the role of ERM in causing LMH progression is not well understood. Our study reported that nearly all cases (94%) were associated with ERM, but this study did not find any association between the morphology of ERM and changes in the residual foveal thickness or visual acuity. In our study, ERM did not add to the risk of visual decline, RFT thinning, or FTMH development. Further studies investigating both the microscopic composition of ERM in myopic eyes and the long-term macroscopic morphology changes are advised.
Study strengths and weaknesses
Our study provides a good documentation of the natural progression of LMHs in highly myopic eyes due to its regular monitoring and long-term follow up period. It provided a glimpse into the course of disease by being one of the longest follow-up studies compared to the concurrent literature. Due to the surgical complexity and slow progression of the disease status, many patients with high myopia and LMH in our study adopted a non-surgical conservative approach, which allowed us to monitor the respective changes over time. Serial monitoring using OCT scans was performed, and comparisons can be made since the scans were applied with reference to patients’ previous scans. In contrast to previous studies,(4, 15, 16, 23) our study showed that LMHs in myopic eyes are potentially progressive in nature, and the risk of deterioration to FD or FTMH increases with the coexistence of foveoschisis and VMT. However, this study has a relatively small sample size. Prospective studies with larger sample sizes are recommended to investigate the natural course of this disorder and to identify other potential risk factors related to the progression of LMH.