Epiretinal membrane is common disease, affecting 5~10 % incidence over 60 years old population. It reduce visual acuity, cause metamorphopsia. In the past, vitrectomy and epiretinal membranectomy was indicated in patients with visual acuity less than 20/40, but nowadays with technical improvement and surgical instrument renovation, it seems to have been changed the surgical indication. Therefore, we plan to evaluate the changes of binocular visual acuity, aniseikonia in patients with epiretinal membrane.

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

patients with epiretinal membrane who had metamorphopsia or had imparied vision, therefore planned to undergo vitrectomy