Changes of focal macular ERG following vitrectomy in eyes with idiopathic macular holes

Purpose. The visual function can be improved by vitrectomy in eyes with idiopathic macular holes (MH), however little proof has been shown by using objective visual functional tests. The purpose is to study the changes of focal macular ERG (MERG) following macular hole surgery. Methods. Twenty-three eyes with MH were evaluated by MERG before and after (2 months or longer) vitrectomy. Preoperative findings of MH showed Stage 3 (8 eyes) and Stage 2 (15 eyes). All MH were successfully closed by vitrectomy and fluid-gas exchange without using other materials such as TGF-β. MERGs were recorded using 4° and 5° stimulus spots under the fundus monitor with infrared television fundus camera (Miyake Y, 1987). The amplitude and implicit time of the b-wave were evaluated. Results. In 5° spot, data was obtained in 21 eyes. Fifteen of 21 eyes showed increased amplitude, and 9 of 18 eyes showed decreased implicit time after vitrectomy. In 4° spot, reliable data was obtained in 18 eyes. Seventeen of 18 eyes showed increased amplitude and 9 of 14 eyes showed decreased Implicit time. The implicit time of 4 eyes could not be measured preoperatively, because MERGs were non detectable. The visual acuity of 18 of 23 eyes improved two lines or more after vitrectomy. Conclusions. Successful closure of MH resulted in the improve of macular ERG. Smaller stimulus spot was more sensitive to detect the change of the foveal status following vitrectomy.