The advent of OCT imaging, especially when used postoperatively, has given the opportunity to study the healing process after macular hole surgery in a way that was previously very difficult. It is now recognized that glial bridging across the defect is one of the first steps involved in macular hole closure [14
However despite these technological advances, the role of ILM peeling on macular hole closure has not been definitively established through OCT studies. ILM peeling may work by removing existing glial cells which could exert tangential forces if left behind. Removal of these glial cells may also stimulate the additional gliosis necessary for macular hole closure by glial bridge formation.
In this study we observed an HRL on OCT imaging in the area of ILM peeling at 1 month follow up. The HRL appears to be visible after macular hole closure, and had disappeared by a mean of 164 days. As far as we are aware, this is the first time that such a sign has been reported. The HRL is currently only an OCT finding, which has been detected transiently. It is possible that our observations are affected by the presence of gas in the immediate postoperative period, as although the macular region was not covered at this stage, some gas was still present within the eye.
The aetiology and effect of this HRL on macular hole closure post-operatively is unclear. Other retinal surface changes such as epiretinal membranes (ERM) may influence surface retinal architecture and cause the formation of pseudoholes [15
]. Additionally, other authors have commented that the contracture of epiretinal membranes may be able to influence the closure of full thickness macular holes [16
]. It is therefore not inconceivable that the HRL may also exert such an effect, and possibly play a role in macular hole closure. The HRL shares some characteristics found in epiretinal membranes (ERM) such as uniform flattening of the retinal surface. In contrast to ERM however, these features are transient, and disappeared or significantly reduced in appearance over an 8 month period.
In one case, the HRL signal was observed to cross the closed macular hole (Figure 1a), suggesting that this sign could represent a transient fibrinous membrane. When the HRL is present the retinal surface appears taught and straight. This finding later disappears and is replaced by Dissociated Optic Nerve
Fibre Layer (DONFL), which appears on OCT as multiple small depressions in the contour of the retina, previously described as having a ‘moth eaten’ appearance, with multiple dark striae running in the same direction as optic nerve fibres in the region of ILM peeling [17
]. The term Concentric Macular Dark Spots (CMDS) has been proposed to refer to this appearance using the enface OCT technique. This finding has been reported to occur in 43-100% of patients postoperatively [17
]. We found that this sign was present in varying degrees in all 26 patients’ OCTs postoperatively, whether or not an HRL was present.
It may be the case that ILM peeling induces a localised pro-inflammatory effect on the retina which could in turn influence macular hole closure. It is possible that the HRL seen on OCT imaging represents such an effect and could be caused by the release of plasmin and other pro-inflammatory mediators from microscopic
cell damage resulting from the peeling process. This could explain why the HRL appearance seems to be associated with increased retinal thickness, both pre-operatively, and in the first few months postoperatively compared to the group without recorded HRL. Increased pre-operative thickening was more often associated with cystoid inflammatory changes around the FTMH which may then subsequently increase the risk of post-operative inflammatory thickening. With successive post-operative visits these thickness measurements converged between the two groups (Figure 3) suggesting that this was not just a difference in baseline anatomical characteristics between the groups. This theory would also be supported by the finding that an HRL was seen more commonly in those eyes where intravitreal triamcinolone was not used to induce a PVD. Additionally it was more common in those patients undergoing vitrectomy combined with phacoemulsification, where more inflammation might be expected. We are aware that some of our baseline differences in data such as the use of TA and combined surgery may have influenced statistical analysis with regards to CRT measurements, however with the small numbers of patients analysed, correction for these variables would not have been valid. Further larger studies on this topic may help to clarify this matter.
Transient OCT changes have been previously reported elsewhere. Clark et al. described a process, following ILM peeling, that they called swelling of the arcuate nerve fibre layer (SANFL) [19
]. They found that 31% of the cases that they reviewed postoperatively developed dark striae on infrared and auto fluorescence photographs originating from the optic nerve head, radiating in an arcuate pattern toward the macula. This was visible on OCT imaging postoperatively as swelling of the inner retinal layers and resolved after a mean period of 2 months. This SANFL is in a parafoveal anatomical region, with the documented swelling only described in the areas of striation seen on autofluorescence. Our observations are focused more on the fovea and peri- fovea. Examination of green filter infrared images of our patients with HRL did not reveal any characteristic striae of SANFL, nor did we observe the high signal change originating from the optic disc.
We have detailed statistical analysis of CRT measurements which have not been published before, and while it is possible that SANFL may also be associated with an increased CRT, we are confident that an HRL has not previously been described. It is interesting to note that both SANFL and HRL have a similar estimated incidence. It is possible that both these two series describe different aspects of the same spectrum of postoperative OCT changes which follow each other in succession, Since SANFL has been described during the first postoperative month [19
], it might be supposed that HRL follows SANFL before the appearance of DONFL/CMDS on monochromic fundus images or OCT scans.
In conclusion, HRL may represent a dynamic process during macular hole healing postoperatively. The patients found to have this sign all achieved a good anatomical and functional outcome. Analysis of our results suggests that the presence of an HRL is more apparent in patients with greater preoperative retinal thickening and cystoid macular oedema. This relationship continues to be significant in the immediate postoperative period. Patients receiving TA as an intraoperative tool are less likely to have a visible HRL postoperatively.
The clinical importance of HRL is yet to be established. In our series we compared the change in visual acuity in patients with and without an HRL, and found no statistically significant difference between the two groups. There was also no difference in macular hole size or closure rate between the two groups.
Additional larger prospective studies may be useful in defining this clinical entity in more detail, and establishing further the origins of the HRL in post-operative macular hole OCT studies.
Conflict of Interest Statement
The authors declare no conflict of interest. The data has been presented at the British and Eira Association of Vitreoretinal Surgeons annual conference in 2013.