<qa>  What is the electrode taped to the forehead?- Electroretinogram ERG to examine what happens to the eyes after a flash of bright light. For this test, the patient sits in a dark room for 30 minutes with his or her eyes patched. Then, a small silver disk electrode is taped to the forehead, the eye patches are removed, the surface of the eye is numbed with eye drops and contact lenses are placed on the eyes. The patient looks inside a large empty bowl and then a light flashes, first in the dark and then with a light turned on inside the bowl. The contact lenses sense small electrical signals generated by the retina when the light flashes. 