67 Pa. Code § 175.264
Right and left outside rearview mirrors shall be required with the use of a sun screening device or other material unless the sun screening device or other material is only used or applied above the AS-1 portion of the windshield as permitted in § 175.263(a) (relating to sun screening location). Each mirror shall have a minimum reflective surface of 19.5 square inches, except as otherwise provided in §§ 175.148(b) and 175.177(b) (relating to mirrors). A vehicle for which a certificate of exemption has been issued for medical reasons may be equipped with only a left outside rearview mirror, unless originally equipped with an outside rearview mirror on both sides of the vehicle.
67 Pa. Code § 175.264
This section cited in 67 Pa. Code § 175.80 (relating to inspection procedure); 67 Pa. Code § 175.110 (relating to inspection procedure); 67 Pa. Code § 175.160 (relating to inspection procedure); 67 Pa. Code § 175.190 (relating to inspection procedure); and 67 Pa. Code § 175.263 (relating to sun screening location).