Date Published: April 2, 2019
Publisher: Public Library of Science
Author(s): Yuka Okawa, Ichiro Maruko, Moeko Kawai, Taiji Hasegawa, Hisaya Arakawa, Tomohiro Iida, Pukhraj Rishi.
To examine the foveal structure and vasculature in eyes with an idiopathic epiretinal membrane (ERM).
Forty-nine eyes of 48 patients with an idiopathic ERM were studied. The superficial foveal avascular zone (FAZ) was measured by optical coherence tomography angiography (OCTA; RTVue XR Avanti, Optovue Inc., Fremont, CA), and the central foveal thickness (CFT) was measured by swept source OCT (DRI-OCT, Topcon, Japan). Twenty eyes underwent vitrectomy with internal limiting membrane (ILM) peeling, and the FAZ and CFT were evaluated pre- and postoperatively. Forty-nine eyes of 49 age-matched healthy subjects were also examined as control.
The FAZ in eyes with an ERM was significantly smaller than that of the control eyes (0.188±0.16 mm2 vs 0.328±0.14 mm2, P<0.01). The CFT in eyes with an ERM was significantly thicker than that of control eyes (315±0.14 μm vs 193±0.14 μm, P<0.01). The size of the FAZ was strongly correlated with the CFT (ERM, R = -0.753; control, R = -0.61, both P<0.01). The postoperative size of the FAZ was not significantly different from the preoperative size (0.115 mm2 vs 0.128 mm2, P = 0.17) but the CFT was significantly thinner (370 μm vs 288 μm, P<0.01) after the vitrectomy with ILM peeling in 20 eyes. The results indicate that an ERM might affect the morphology and vasculature of not only the inner but also the outer retina before and after vitrectomy with ILM peeling. The FAZ area might have been affected by the ILM peeling.
An idiopathic epiretinal membrane (ERM) can alter the foveal morphology by its traction on the retina, and the morphological changes can cause distortions of vision and reductions of the visual acuity. The results of optical coherence tomographic (OCT) studies have shown a thickening of the fovea and a disruption of the ellipsoid zone of the photoreceptors in eyes with an ERM [1–5]. The disruption of the ellipsoid zone indicates a disorder in the alignment of the photoreceptors which most likely accounts for the visual dysfunctions. Inoue et al  reported that the improvement of the visual acuity after removing an ERM was not significant after vitreous surgery. However, because there is no inner retina at the fovea, these reports only evaluated the changes of the outer retina in eyes with an idiopathic ERM.
This was a retrospective study, and the procedures used conformed to the tenets of the Declaration of Helsinki. The Institutional Review Board of the Tokyo Women’s Medical University, School of Medicine approved the procedures used. All examinations were performed after an informed consent was obtained.
The mean area of the FAZ was 0.188 ± 0.16 mm2 in the eyes with an ERM which was significantly smaller than the 0.328 ± 0.14 mm2 in the control eyes (P <0.01). The FAZ area in the eyes with an ERM was not significantly correlated with the age (R = 0.048, P = 0.74) or the BCVA (R = -0.233, P = 0.11). The area of the FAZ increased from 0.115 mm2 to 0.128 mm2 after vitrectomy in the 20 eyes with a mean follow-up period of 147 days (range 23–443 days). This increase was not significant (P = 0.17). The mean postoperative FAZ area was significantly smaller than that of the control eyes (P <0.01). The FAZ area enlarged in 14 eyes (Fig 1) and decreased in 6 eyes (Fig 2). The mean area of the FAZ with enlargement after vitrectomy was smaller than decrease in the area of the FAZ in the other eyes (0.091 mm2 vs 0.171 mm2, P = 0.06). The mean change in the ratio was not significantly correlated with the age (R = 0.421, P = 0.06) and the length of the follow-up period (R = -0.357, P = 0.12). Seven eyes were followed for more than 6 months, and the FAZ area increased in 2 eyes and decreased in 5 eyes. Although there was no significant difference between pre- and postoperative FAZ areas (0.166 mm2 vs 0.11 mm2, P = 0.30) in these eyes, the change in the ratio of the areas in the eyes with more than 6 months of follow-up was significantly smaller than that of eyes with less than 6 months of follow-up (-0.170 vs 0.750, P <0.01). The results showed that the area of the FAZ was smaller and the CFT was thicker in the eyes with an ERM than in age-matched control eyes. This difference was still present after successful removal of the ERM by vitrectomy with ILM peeling. This indicated that the tractional effects of ERM might persist even after its removal. Although the CFT became significantly thinner after vitrectomy, the decrease in the FAZ area was not significant. These results may be due to not only the centrifugal effect of ERM removal but also the centripetal movement of the retina after the ILM peeling. Source: http://doi.org/10.1371/journal.pone.0214881