Clinical assessment of accommodative facility, accommodative rock, positive/negative relative accommodation and convergence and fusion convergence reserves. All lenses are chemically hardened glass making them more durable than plastic lenses. The flipper handle and body is printed with the power and the – + sign is clearly printed and embossed on the flipper body for better viewing in a dark room. Our stock prisms are right handed but we can custom make any flipper. All powers come with optional colored handles.