((a)) ** .—**
((1)) In making a determination of disability of a member of the armed forces for purposes of this chapter, the Secretary concerned—
((A)) shall, to the extent feasible, utilize the schedule for rating disabilities in use by the Department of Veterans Affairs, including any applicable interpretation of the schedule by the United States Court of Appeals for Veterans Claims; and
((B)) except as provided in paragraph (2), may not deviate from the schedule or any such interpretation of the schedule.
((2)) In making a determination described in paragraph (1), the Secretary concerned may utilize in lieu of the schedule described in that paragraph such criteria as the Secretary of Defense and the Secretary of Veterans Affairs may jointly prescribe for purposes of this subsection if the utilization of such criteria will result in a determination of a greater percentage of disability than would be otherwise determined through the utilization of the schedule.
((b)) ** .—** In making a determination of the rating of disability of a member of the armed forces for purposes of this chapter, the Secretary concerned shall take into account all medical conditions, whether individually or collectively, that render the member unfit to perform the duties of the member’s office, grade, rank, or rating.