The Associations among Metamorphopsia, Orientation Discrimination Threshold, and Retinal Layer Thickness in Patients with Idiopathic Epiretinal Membrane

PURPOSE: To explore the association among the metamorphopsia identified by Amsler grid test, orientation discrimination threshold (ODT), and retinal layer thickness in patients with idiopathic epiretinal membrane (ERM).

METHODS: A total of 48 ERM patients were divided into a fovea-spared (FS) group (n = 12) and a fovea-involved (FI) group (n = 36). A total of 23 visually normal people served as controls. Metamorphopsia was first assessed with an Amsler grid. The ODT was quantified with groups of briefly displayed short line segments. Inner and outer retinal layer thickness (IRLT and ORLT) was measured with spectral domain optical coherence tomography.

RESULTS: A total of 12 patients with ERM (1 in FS and 11 in FI) reported abnormalities in the Amsler grid test. The ODT values were significantly elevated in patients in both FS (7.48 ± 1.94°, p < 0.001) and FI groups (10.14 ± 2.28°, p < 0.001) when compared to normal (4.22 ± 0.80). Receiver operating characteristic (ROC) analyses of ODT to distinguish Amsler positive and negative patients yielded an area under the curve (AUC) of 0.829. The IRLT was significantly thicker (386.6 ± 95.1 µm vs. 127.5 ± 17.6 in normal) and ORLT were significantly thinner (88.11 ± 8.24 vs. 94.39 ± 5.66 in normal) in the FI group. ROC analyses to distinguish Amsler positive and negative patients yield an AUC of 0.917 using IRLT and 0.719 using ORLT. ODT correlated tightly with the thicker IRLT in both the FS and FI groups, and with the thinner ORLT in the FI group.

CONCLUSIONS: In patients with ERM, ODT reflects functional changes that are not detected by the Amsler grid test and correlates with changes in inner retina layer thickness well.