Retinal Nerve Fiber Layer Thickness Modifications After ILM Peeling Antonio Ciardella

Advantages:

To identify retinal nerve fiber layer (RNFL) thickness modifications after internal limiting membrane (ILM) peeling for idiopathic macular hole (MH) and epiretinal membrane (ERM) and to correlate it to visual field (VF) changes and to the postoperative appearance of early transient edematous swelling of the arcuate RNFL (SANFL) and of later dissociated optic nerve fiber layer (DONFL).

Methods:

Interventional, prospective, non-randomized case series. 30 eyes of 30 patients (73.5 ±6.6 years), who underwent ILM peeling after staining with brilliant blue G for idiopathic MH and ERM at Santa Orsola-Malpighi Hospital, Bologna, Italy between December 2010 and May 2011, were included. Best corrected visual acuity (BCVA), intraocular pressure (IOP), biomicroscopy, stereoscopic fundus examination, color (Topcon fundus camera, Topcon Medical System, Oakland, NJ), autofluorescence (AF), blue light images, spectral domain OCT (SD-OCT) of the macular region and of the peripapillary RNFL, using a device with an incorporated eye-tracking feature to obtain reliable follow-up measurements (Spectralis HRA+OCT, Heidelberg Engineering, Heidelberg, Germany), were performed in both eyes before and 1, 3 and 6 months after surgery. AF imagines were used in the first postoperative visit to better seen SANFL appearance, as 1 to 7 hypofluorescent striae originating from the optic nerve head and running between the macula and the vascular arcades; instead color, blue light and SD-OCT of the macular region imagines were evaluated to better visualize DONFL appearance at 3 and 6 postoperative months. Six peripapillary sectors (superotemporal, temporal, inferotemporal, inferonasal, nasal, superonasal) and global RNFL thickness, were evaluated. VF (Humphrey central 30-2) was performed preoperatively and 6 months postoperatively. Data were analyzed using Friedman, Mann-Whitney, Wilcoxon, Spearman and Fisher tests.

Effectiveness / Safety:

BCVA, expressed in LogMAR, significantly improved after surgery (0.51 ±0.29 vs. 0.14 ±0.16, p<0.001). Friedman test showed significant modifications of RNFL thickness in all the sectors (for all variables p<0.0001). Specifically, 1 month after surgery SD-OCT images showed a significant increase of RNFL thickness in all the sectors but the temporal one and a progressive return to basal values at the 3th postoperative month. At the 6-th postoperative month, RNFL thickness was significantly lower than basal values in the superotemporal, inferotemporal and temporal sectors (114.6 ±19 µm vs. 130.2 ±24.7 µm, p<0.001; 125.5 ±23.8 µm vs. 136.2 ±17.5 µm, p<0.05 and 70.2 ±17.4 µm vs. 98.5 ±27.7 µm, p<0.001). Significant correlation was found between preoperative and postoperative RNFL thickness in each sector evaluated (p<0.001) and an average increase of the RNFL thickness of 10.2 ±4.9 µm was noted 1 month after surgery. Subsequently, an average reduction of the superotemporal, inferotemporal and temporal RNFL thickness of 18.2 ±9.8 µm was seen 6 months after surgery. No IOP and VF difference was found in the study eye during the follow up period and when compared to the fellow eye. SANFL appearance was found in 17 patients (56%), while DONFL appearance in 15 (50%). No correlation was found between RNFL thickness and neither VF nor SANFL or DONFL appearance.

Take home message:

Our study suggests that macular surgery leads to significant peripapillary RNFL thickness modifications. Specifically, the global postoperative 1st-month increase of RNFL thickness could be due to a diffuse inflammatory process related to pars plana vitrectomy, independently to SANFL appearance. The 6th-month reduction of the temporal, superotemporal and inferotemporal RNFL thickness, without VF defects, could indicate an early damage to the arcuate RNFL, independently to DONFL appearance. This selective reduction could be due to a possible damage of the inner retinal layer after ILM peeling. The average thickness reduction of these sectors should be taken into account when surgery is performed in glaucomatous or myopic eyes.