Perceived metamorphopsia and orientation discrimination threshold before and after the surgical removal of epiretinal membrane

Purpose: To quantify the changes in perceived metamorphopsia and orientation discrimination threshold (ODT) before and after surgical removal of idiopathic epiretinal membrane (ERM), and to investigate the association to pre and post-surgical changes in the thickness of retinal layers. Method: A prospective study, a total of 17 subjects with idiopathic ERM were recruited. Best-corrected visual acuity (BCVA) was evaluated with EDTRS chart. Metamorphopsia was measured with Amsler grid. The ODT was quantified with groups of briefly displayed short line segments in 3-donw-1-up staircase algorithm. Inner and outer retinal layer thickness (IRLT and ORLT) was measured with spectral domain optical coherence tomography. All measured were done before and after surgical removal of the ERM. Results: With surgical removal of the ERM, the BCVA significantly improved (0.468±0.304logMAR vs 0.202±0.190logMAR, before and after respectively, p=0.002). In five subjects who reported subjective distortion with Amsler grid before the surgery, three stayed positive and two turned negative after the surgery. However, two subjects who were Amsler grid negative pre-surgery became positive post-surgery. In 14 subjects, ODT values reduced after the removal of ERM, with the mean ODT was significantly went from 10.6±2.8 degree from surgery to 8.0±2.7 degree after surgery (p < 0.01). Inner retina layer thickness greatly decreased after the surgery (390.4±126.9 um vs. 254.4±64.7 um, before and after respectively, p < 0.01), while out retina layer thickness did not show significant change (87.8±6.9 um vs. 87.8±7.6 um, before and after respectively, p=0.972). The improvement in ODT significantly correlated with the thinning of the IRLT (p < 0.05). Conclusion: In patients who received surgical removal of ERM, changes in ODT reflects the functional changes better than Amsler grid and correlates with changes in inner retina layer thickness well.