The Commission may require the complainant to sign a waiver for the Commission to obtain verification of the existence, nature, and extent of the complainant's disability from a physician or other health care provider, based on medically accepted clinical or laboratory diagnostic techniques. The determination of whether an individual has a physical or mental impairment, or is substantially limited in a major life activity, or both, shall be made on a case-by-case basis and without regard to the mitigating effects of any remedial appliance or device.