Applicants for license and pilots applying for increase or renewal of license shall be examined for visual acuity and color perception by a physician or an optometrist designated by the commissioners or, with the permission of the commissioners, by a personal physician or optometrist. Examinations by persons designated by the board will be at the board's expense. Examinations by personal physicians or optometrists will be at the expense of the individual being examined. If the physician or optometrist reports that a pilot or an applicant for license is deficient in either visual acuity or color perception, the commissioners may, at their discretion, refuse to grant a license, increase, or renewal.