Abstract
PurposeTo evaluate tangential morphological changes in the outer retina and assess their correlation with the degree of metamorphopsia in patients with idiopathic epiretinal membrane (ERM).MethodsThis retrospective study included patients with idiopathic ERM who underwent vitrectomy between January 2018 and December 2019. We evaluated the preoperative examination results. Using cross-sectional spectral-domain optical coherence tomography (OCT) images along the horizontal/vertical meridian through the fovea, we defined a new parameter, tangential displacement (TD), as the tangential component of the position vector of the distorted outer nuclear layer caused by ERM. Visual function measurements included M-CHARTS results (vertical/horizontal metamorphopsia score [MV/MH]) and best-corrected visual acuity (BCVA). The correlations among the OCT parameters including TD and central foveal thickness (CFT) with visual function measurements were determined.ResultsOverall, 78 eyes of 76 patients (49 females; mean age, 67.9 [± standard deviation, 7.5 years]) were included. The mean horizontal TD was 24.0 ± 73.9 μm, which was significantly different from 0 (p = 0.005). The mean vertical TD was 6.0 ± 76.2 μm, which was not significantly different from 0. The absolute value of horizontal TD was significantly correlated with MV (r = 0.513, p < 0.01) and MH (r = 0.423, p < 0.01). The absolute value of vertical TD was also significantly correlated with MV (r = 0.274, p = 0.02) and MH (r = 0.413, p < 0.01). However, neither value was significantly correlated with BCVA. Multiple regression analysis showed that the horizontal absolute TD was an independent factor associated with both MV (β = 0.635, p < 0.001) and MH (β = 0.259, p = 0.048).ConclusionWe found that ERM tended to distort the outer retinal layer toward the temporal side of the fovea. The tangential distortion of this layer was associated with the degree of metamorphopsia, suggesting that misalignment of parafoveal photoreceptors causes metamorphopsia in patients with ERM.
Highlights
Idiopathic epiretinal membrane (ERM) is a relatively common retinal condition characterized by the formation of translucent membrane tissue on the surface of the neurosensory retina
The current study presents evidence about tangential morphological changes in the outer retina due to ERM and their correlation with metamorphopsia
We designed “tangential displacement (TD)” as a new parameter to quantify the tangential component of morphological changes in the outer retina
Summary
Idiopathic epiretinal membrane (ERM) is a relatively common retinal condition characterized by the formation of translucent membrane tissue on the surface of the neurosensory retina. Several studies have been performed to assess the correlation between changes in retinal microstructure and metamorphopsia using SD-OCT. The thickness of the inner nuclear layer (INL) [3,4,5,6,7], inner retinal layer (vitreous surface to the outer border of the INL) [8], outer nuclear layer (ONL) plus outer plexiform layer (OPL) [6], and central foveal thickness (CFT) [4, 6] have been reported to be associated with metamorphopsia. Ichikawa et al reported that ERM contraction leads to displacement of Müller cells, which are found in the INL, from their original locations. The authors suggested that irregular photoreceptor stimulation through distorted Müller cells may cause metamorphopsia [7]. Photoreceptor misalignment itself has been considered the main cause of metamorphopsia [9]
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