The contact lens, a thin plastic lens worn between the eye and eyelid, usually serves the same general corrective purpose as conventional glasses, but may be worn for cosmetic or therapeutic purposes as well. Leonardo da Vinci is frequently credited with having introduced the general principle of contact lenses, but it was A.E. Fick, a Swiss physician, who made the first, albeit uncomfortable, contact lens in 1887. According to estimates, how many people use contact lenses worldwide? Discuss