The main findings of this study are, first, that long-term postoperatively, the median thickness of the RGC+IPL, INL, and OPL in the fovea remained slightly greater than normal while that of all other retinal layers was normal. The median foveal shape of the entire retina was slightly distorted (
Fig. 6). Second, postoperatively, central macular thickness gradually decreased (
Fig. 4A), which appears to be related to a gradual functional improvement over a period of several years (
Fig. 7).
The control individuals were of similar age distribution because slight age-related retinal thinning in normal eyes has been described.
20 Analysis of the thickness measurements derived from 51 operated eyes allows the observation of trends. Long-term after surgery, the retinal thickness of the peripheral macula returned to normal (
Fig. 4B–E) while the decrease of the thickness of the foveal area toward normal values was incomplete and delayed (
Fig. 4A). To analyze the morphology of the retina more specifically and to depict the median structure of the fovea, we used SD-OCT scans as previously described by Hood et al.
21 and previously adapted by us.
16 SD-OCT showed, in line with the results of the TD-OCT Fast Macular Thickness program, that the decrease of total retinal thickness along the horizontal meridian in the fovea remained incomplete, with slightly greater thickness of the nasal part of the fovea and parafovea compared to the temporal part (
Figs. 5G,
6G). This is in accordance with the findings of another OCT study
22 and our findings long-term after epiretinal membrane surgery.
16 Small differences in thickness measurements of individual retinal layers must be interpreted with caution because mild deviations of SD-OCT scans from the exact anatomic horizontal meridian may have introduced small errors.
Kim et al. have recently reported an elongation of foveal tissue 6 months after IMH surgery with a mean horizontal distance between the parafoveal edge of the OPL (inter-OPL distance) of 575.4 ± 94.8 μm.
15 This is in contrast to our findings, perhaps because of the longer follow-up period in our study. As shown in
Figure 6G, the median horizontal shape of the foveal pit was not elongated as compared to that in normal control eyes. We found an elongated fovea only in 4 of 51 eyes with horizontal inter-OPL distances of 572, 580, 723, and 751 μm.
In accordance with other studies,
16,23 the mild irregular shape of the retinal layers and the absence of a foveal pit (
Fig. 3) did not preclude favorable long-term postoperative visual acuity. Overall, in the present study, BCVA continuously improved postoperatively and reached good levels in most patients (
Fig. 7).
It is unclear why the decrease of central macular thickness was delayed to 28 months postoperatively, but this appears to be related to gradual functional improvement (
Figs. 4A,
7). The mean follow-up time in the present study was considerably longer than in other studies.
1–4,6–13 However, further postoperative decrease of central macular thickness after the follow-up period of this study cannot be excluded.
Preoperative macular hole size has been described as a prognostic factor for functional outcome related to a correlation of closure rate and hole size.
22 We did not find a correlation of macular hole size and final BCVA, probably because we included only macular holes successfully closed after one surgery.
There are limitations of this study. We found good long-term functional and anatomical outcome, and this is in part due to the long follow-up period (
Figs. 4,
7). However, due to the patient selection process (
Fig. 1), bias toward eyes with better outcome cannot be entirely ruled out. ICG-related phototoxicity
24 may have influenced the functional and anatomical outcome of macular hole surgery
14 in 11 eyes operated with ICG, and more “difficult” cases may have been operated with the aid of ICG between 2005 and 2007. However, we did not find a clear difference between the eyes operated without ICG between 2005 and 2007 and those operated with Brilliant Blue G between 2007 and 2009, although we did not apply statistical tests because of the limited number of eyes in each subgroup. Twenty-seven patients who refused the scheduled visit (
Fig. 1) represent a second potential source of bias. These patients may have refused the visit because of unfavorable outcome. However, this seems unlikely because the last obtained visual acuity of these patients was similar to that of the included study patients, although 5 of 27 patients had not been refracted.
In conclusion, the mean long-term functional outcome of macular hole surgery with ILM peeling is excellent, and the microstructure of the fovea recovers almost completely in most eyes. Long-term follow-up periods are warranted because the process of gradual functional and anatomical recovery after IMH surgery may continue for several years after macular hole surgery.