3. Nearsighted people can undergo a medical procedure called keratotomy to produce normal (or at least more-normal) vision. In this procedure the shape of the cornea (and thus its refractive power) is changed, usually by the removal of tissue by the action of an excimer laser. If a nearsighted person has a far point 50 cm from the eye, by how much and in what direction (i. e., increase or decrease) must the refractive power of the cornea be changed in order to restore normal vision (i. e. far point at least 6 m from the eye)?