Except as provided in subsection (b) of this section, a permanent total disability shall be determined in accordance with the facts in each case. Absent conclusive proof to the contrary, the loss or loss of use of any of the following constitutes a permanent total disability: both arms; both eyes; both feet; both hands; both legs; or a combination of any 2 of the following: an arm; an eye; a foot; a hand; and a leg.