⭕ Diopsys VEP ERG in like new cosmetic condition and working order. Under 2 years old. Comes with a 30 day right of return. VEP measures the electrical activity in the vision system. When light from an image enters your eye, it is converted into electrical energy at the retina and travels through the optic nerve to the visual cortex of the brain which processes vision. The Diopsys VEP test measures the strength of the signal reaching your visual cortex and how fast it gets there. Pattern ERG measures the function of your retina - the light-sensitive layer at the back of your eye. When light from an image enters the eye, it is converted into electrical energy by specialized cells in the retina. These cells send electrical impulses through the optic nerve to the brain where the image is processed. The Diopsys ERG test records how well the cells of the retina are conveying electrical. Delivery available.