Background: We aimed to investigate the deformation of the outer nuclear layer using optical coherence tomography in patients with epiretinal membrane (ERM) and its relationship with metamorphopsia.
Methods: Thirty-nine eyes from 39 patients with ERM were included in the study. Patients with the subtypes of pseudo macula hole and lamellar hole were excluded. Twenty-one fellow eyes without macular disease were included as normal controls. Forty-nine B-scan images were obtained in the range of 20 degrees around the macula using SD-OCT. The outer nuclear layer (ONL) was evaluated as a three-dimensional image (3D-ONL) reconstructed using the distance between the ONL and retinal pigment epithelium (RPE) line. The deformation of the ONL was figured at the reference plane and evaluation plane (ONL-B). The characteristic parameters of the ONL-B were defined as circularity, area ratio, and axis ratio. The correlations between these parameters and visual acuity and MCHART score ratio (MH/MV) were then evaluated.
Results: ONL height was significantly higher in ERM patients than in normal controls (54.1 ± 5.3 μm and 84.1 ± 12.9 μm, respectively; P < 0.001). In ERM patients, the MV score was 0.53 ± 0.50, the MH score was 0.71 ± 0.61, and the distance from the RPE line to the ONL-B was 153.5 ± 13.5 μm. The axis of the ONL-B in normal controls and ERM patients was - 6.25 ± 21.8 and - 1.28 ± 29.1, respectively, which indicates that the ONL is horizontally long in both normal individuals and ERM patients. The circularity and area ratio were significantly smaller in ERM patients than in normal controls. In all ERM patients, MH/MV had a significant correlation with axis (r = - 0.29, p = 0.034), circularity (r = - 0.28, p = 0.044), and area ratio (r = - 0.47, p = 0.001). Moreover, we found that the correlation was more significant if the subjects had an axis of the ONL within ±10 degrees (n = 16); the correlations of MH/MV with axis (r = - 0.29, p = 0.034), circularity (r = - 0.53, p = 0.021), and area ratio were more significant (r = - 0.78, P < 0.0001).
Conclusion: The ONL is horizontally long in normal individuals and ERM patients. The direction of metamorphopsia is correlated with the direction of ONL deformation.
Keywords: Epi retinal membrane; M chart; Metamorphopsia; Outer nuclear layer.