Optical Lens: Mares offers corrective lenses for most models. In addition to negative corrective lenses (-1 to -7), positive corrective lenses (+1.5 to +3) are also available for some models. Mares mask design allows for quick and easy mounting of optical lenses. Tri-Comfort: Small horizontal ribs between the frame and the face in the area around the nose absorb and redistribute the pressure exerted by the frame on the face, increasing comfort.