Change of Retinally-Induced Aniseikonia in Patients With Epiretinal Membrane After Vitrectomy

Inclusion Criteria: * Idiopathic epiretinal membrane who had impaired vision or metamorphopsia, want to undergo vitrectomy * Age more than 20 years and less than 90 years old Exclusion Criteria: * secondary epiretinal membrane due to retinal surgery, * impaired visual acuity less than 20/40 in the normal eye(Snellen chart) due to severe cataract * glaucoma patients * complication during vitrectomy (ex. Retinal tear, silicone oil injection, …) * other retinal disease except epiretinal membrane * other ocular surgery history within 3 months * intellectual problems or illiterate whom could not obtained informed consent