An ellipse of the dark area is always seen whenever the light is allowed to pass through bifocal glasses [[Figure 1]a- white arrow]. Differential refraction, causing differential prismatic deflection, at the junction of 2 optically dissimilar surfaces forms a scotoma between the 2 zones as shown. The roving ring scotoma with its jack-in-the-box phenomenon of strong-plus (aphakic) spectacle lenses.