(a) The employer shall only be liable for the percentage of permanent disability directly caused by the injury arising out of and occurring in the course of employment.
(b) If the applicant has received a prior award of permanent disability, it shall be conclusively presumed that the prior permanent disability exists at the time of any subsequent industrial injury. This presumption is a presumption affecting the burden of proof.
(c) (1) The accumulation of all permanent disability awards issued with respect to any one region of the body in favor of one individual employee shall not exceed 100 percent over the employee’s lifetime unless the employee’s injury or illness is conclusively presumed to be total in character pursuant to Section 4662. As used in this section, the regions of the body are the following:
(A) Hearing.
(B) Vision.
(C) Mental and behavioral disorders.
(D) The spine.
(E) The upper extremities, including the shoulders.
(F) The lower extremities, including the hip joints.
(G) The head, face, cardiovascular system, respiratory system, and all other systems or regions of the body not listed in subparagraphs (A) to (F), inclusive.
(2) Nothing in this section shall be construed to permit the permanent disability rating for each individual injury sustained by an employee arising from the same industrial accident, when added together, from exceeding 100 percent.