The PERG will be recorded from the study eye by means of hypoallergenic skin sensors Silver/Silver Chloride ink (Diopsys® proprietary Skin Sensor) on the lower eyelids. The reference sensor will be located in the contralateral eyelid and ground sensor in the central forehead area (Fz). The skin will be prepared by cleaning with eyelid cleanser (OCuSOFT®) to ensure good and stable electrical conductivity, keeping the impedances bellow 5 kohm.