The Event"s lens system is a very advanced and optically correct lens. Although at first glance it looks like a flat lens, it actually changes in thickness to maintain the best optical quality possible. The power imbalance, which means how your eyes see for straight ahead, is 0.00 for both Spherical power imbalance and Astigmatism power imbalance (the value is so small it can"t be read with conventional testing equipment). What does this mean? It means what you are seeing is really where you think it is, so you can be more accurate in your shooting.