MODEL RELEASED. Electroretinogram. Hands attaching a gold-foil electrode to a woman's lower eyelid for a multifocal electroretinogram (MFERG) eye test. MFERG allows eye diseases to be detected at an early stage. The woman will look at the pattern of flickering hexagons behind her. Light-sensitive cells in the retina at the back of her eyes conv- ert the light from the hexagons into electrical signals. These are picked up by the electrodes on her eyelids and face, and converted into a map of visual response. The health of the different areas of the eye can be assessed, as each hexagon is seen by a separate bit of the retina. This test is being developed at Glasgow University, Scotland.