Contact lenses incorporating asymmetric radial power profiles that increase the radial dioptric power from the center to the margin of the optical zone of the lenses may be utilized to prevent andor slow myopia progression. They are respectively mounted on opposite sides of a split shaft connected by a torsion bar. The first end 11a is attached to an air bag main body. An adjustment screw has a first threaded surface threadingly engaged with the stud threaded surface of the mounting stud, and a second threaded surface threadingly engaged with the bushing threaded surface of the bushing.