Minimal internal limiting membrane peeling with ILM flap technique for idiopathic macular holes: a preliminary study

Internal limiting membrane (ILM) peeling has been accepted as one of the standardized procedures in idiopathic macular hole (IMH) surgery. Although ILM peeling is favorable for macular hole closure [1], especially for those with large hole sizes, it may also cause side-effects on retinal microstructure and function. The reported retinal microstructure abnormities after ILM peeling include inner retinal dimplings [2], dissociated retinal nerve fiber layer (RNFL) [3], and reduced parafoveal retinal thickness [4].

With the application of en face optical coherence tomography (OCT), inner retinal dimplings has been appreciated, corresponding to ganglion cell RNFL thinning [2, 5, 6]. Though the development of inner retinal dimplings is poorly understood, it has been indicated that it may be due to injury of the Müller cell footplates [2, 7, 8]. The visual recovery after IMH surgery is associated with the integrity of retinal microstructure such as inner retinal dimplings, external limiting membrane (ELM), ellipsoid zone (EZ), and retinal pigment epithelium status [9‐11]. Using the focal macular electroretinogram, Terasaki et al [12] found that there was delayed and limited B-wave recovery in the first 6 months after ILM peeling for patients with IMH.

To avoid or minimize the damage of retinal microstructure by ILM peeling, some surgeons introduced new techniques aiming to preserve the ILM for IMH [13, 14]. Of note, new techniques can only be induced in clinical practice and on condition of not compromising the IMH closure rate. On the other hand, the inverted ILM flap technique, first reported by Michalewska et al [15], has been demonstrated to improve the closure rate for those large or chronic IMHs. It is hypothesized that the inverted ILM flap may provide a scaffold for tissue proliferation.

Here, in consideration of adverse effects of routine ILM peeling, the authors describe a minimal ILM peeling method with ILM flap technique for IMH eyes in order to preserve the ILM and ensure the IMH closure rate.

To date, we have performed the technique on 12 eyes with IMH in 12 consecutive patients. The preoperative baseline characteristics of all cases are shown in Table 1. The patient population consisted of 8 women (75%) of and 4 men, with a mean age of 62.83 ± 8.64 years (48–77 years). The main macular hole size was 564.67 ± 262.28 μm.

Successful MH closure was obtained in all cases. No intraoperative or postoperative complications occurred with the new technique. All cases achieved quick macular hole closure on SD-OCT within 1 week and no reopenning during follow-ups after surgery. Inner retinal dimplings were observed in local ILM-free retinas with en face mode in 7 eyes (58.3%) at the end of follow-up (Fig. 2). The postoperative OCT scanning also clearly showed a thin layer structure over the fovea in 8 eyes, indicating the inverted ILM was not dislocated (Fig. 2). The mean BCVA (logMAR) remarkably improved from 0.83 ± 0.33 at baseline to 0.39 ± 0.28 (p <  0.001) after surgery. Significant improvement of the mERG response density was also found after surgery in the central (R1), para-central (R2), R1/R2, R1/R3, R1/R4, and R1/R5 ring ratios. From baseline to last follow-up, mERG response increased with statistical significance in R1 (p = 0.001), R2 (p = 0.033), and R1/R2 (p = 0.018) (Table 2).

Peeling or not peeling the ILM has been frequently discussed over the past decades [1, 4]. Recently, more and more evidence has indicated inner retinal damage after ILM peeling on en face SD-OCT [2, 3, 6, 18]. Furthermore, histological findings further have confirmed that ILM specimens contain neuron elements [8]. All these suggest the importance of the ILM integrity. Herein, we developed here a novel method of minimal ILM peeling with inverted ILM flap technique.

Among the hypotheses concerning the pathogenesis of IMH, the most extensively accepted one is that the abnormal longitudinal (or anterior-posterior) traction by the posterior vitreous cortex on the macular fovea causes the hole while the tangential traction by the ILM enlarges the hole afterwards. The macular hole then usually has an “hourglass” shape, with the edge of the hole curled-up on OCT images. In this new technique of minimally peeling the ILM with the aid of gas or silicon oil, the macular traction force is relieved and the detached edge of the macular hole is reattached. In the conventional ILM peeling method, in which a large area of ILM is peeled off, the tangential traction in this technique is not fully relieved. Therefore, we used the ILM flap technique to provide a scaffold to further facilitate the macular hole closure. To date, we have successfully performed this technique in 12 eyes. Retinal dimplings were only observed in local areas of ILM-free retina with en face OCT scanning, suggesting that ILM peeling is the main cause of retinal dimplings. In this study, the incidence of retinal dimplings is 58.3% (7/12), similar to the previously reported, 43 to 86% after ILM peeling [18]. Similarly, Tian et al [14] reported the peeled ILM reposition technique, which preserve the integrity of retina, also yielded better microstructural outcomes of inner retina.

In our new technique, attention should be paid during the air-fluid exchange. We suggested that the flute needle should be placed inferior to the MH to avoid the dislocation of ILM flap. For IMHs smaller than 650 μm, the cavity is filled with air while silicon oil should be used for larger IMHs. Patients were instructed to keep a facedown posture in order to maintain the inverted ILM covering the MH. The postoperative OCT scanning clearly showed a thin layer structure over the fovea in 8 eyes, indicating the inverted ILM was not dislocated. For the other four cases, which the thin layer over the fovea could not be identified, we speculate that the inverted ILM might be attached tightly to the macular and OCT cannot show this structure.

We did not perform the vitreous base shaving. Scleral-depressed shaving of the vitreous base is mostly recommended as part of pars plana vitrectomy (PPV) for primary rhegmatogenous retinal detachment [19, 20]. It has been postulated that the vitreous base may form a scaffold for the development of future anterior proliferative vitreoretinopathy (PVR), and that vitreous base contraction may cause new retinal tears and subsequent retinal detachment [21]. However, complications such as PVR or retinal tears are rarely reported and barely occur in clinical practice. In addition, in the ear of microincisional vitrectomy durgery, small gauges with the trocar/cannula system theoretically create less traction on the vitreous base during instrument entry and exit vitrectomy. Therefore, we think shaving of the vitreous base is not necessary for “simple” macular surgery. Finally, scleral-depressed shaving of vitreous base may be associated with iatrogenic retinal breaks, cataract formation, zonular dehiscence and increased risk of intraoperative choroidal hemorrhage [22]. Of note, shaving of vitreous base is recommended for experienced surgeons and for those large macular holes because this procedure allows injection of more gas mixture into the eye and subsequently prolongs the effect of the gas tamponade. It shows that iatrogenic retinal breaks with vitrectomy under air is less than that with the standard vitrectomy under fluid for macular diseases [23]. In our case series, scleral-depressed peripheral examinations were performed at the end of each surgery and no retinal break was identified in each case at the end of the procedure. As reported, the incidence of retinal breaks of macular diseases such as epiretinal membrane (ERM) and MH was low, ranging from 0 to 15.8% [23‐29], but with an average of less than 2.0% [23‐27]. The 0% rate of complications in our technique may be owing to the non-scleral-depressed shaving of the vitreous base, vitrectomy by only one experienced surgeon (P.X), and the relatively small sample size.

This study has several limitations. Firstly, this was a preliminary study with no comparison, a further prospective and comparative study with more cases, long-term follow-ups, more outcomes (such as microperimetry) will be needed to verify the efficiency of retinal protection between our technique and routine ILM peeling technique. Secondly, the number of the cases included were relatively small. Thirdly, the macular holes we reported ranged widely in size, ranging from 188 to 918 μm. Finally, this technique actually required more manipulations on macular and longer study curve for younger surgeons.

In conclusion, the new surgical technique is safe and efficient in treating IMHs. By minimally peeling the ILM, most of the ILM around the MH is preserved, which may be favorable for better inner retinal microstructure after surgery. With the inverted ILM technique, the MH can be more easily closed, especially for those with larger hole size. However, more cases with various hole size and longer follow-up are needed to further confirm the safety and efficiency of this new technique.