(b) In the following cases, an injured employee is presumed to be permanently and totally disabled unless the employer or carrier establishes that the employee is physically capable of engaging in at least sedentary employment within a 50-mile radius of the employee's residence:
1. Spinal cord injury involving severe paralysis of an arm, a leg, or the trunk;
2. Amputation of an arm, a hand, a foot, or a leg involving the effective loss of use of that appendage;
3. Severe brain or closed-head injury as evidenced by:
a. Severe sensory or motor disturbances;
b. Severe communication disturbances;
c. Severe complex integrated disturbances of cerebral function;
d. Severe episodic neurological disorders; or
e. Other severe brain and closed-head injury conditions at least as severe in nature as any condition provided in sub-subparagraphs a.-d.;
4. Second-degree or third-degree burns of 25 percent or more of the total body surface or third-degree burns of 5 percent or more to the face and hands; or
5. Total or industrial blindness.
In all other cases, in order to obtain permanent total disability benefits, the employee must establish that he or she is not able to engage in at least sedentary employment, within a 50-mile radius of the employee's residence, due to his or her physical limitation. Entitlement to such benefits shall cease when the employee reaches age 75, unless the employee is not eligible for social security benefits under 42 U.S.C. s. 402 or s. 423 because the employee's compensable injury has prevented the employee from working sufficient quarters to be eligible for such benefits, notwithstanding any age limits. If the accident occurred on or after the employee reaches age 70, benefits shall be payable during the continuance of permanent total disability, not to exceed 5 years following the determination of permanent total disability. Only claimants with catastrophic injuries or claimants who are incapable of engaging in employment, as described in this paragraph, are eligible for permanent total benefits. In no other case may permanent total disability be awarded.