(a) An employee is entitled to supplemental income benefits if on the expiration of the impairment income benefit period computed under Section 408.121(a)(1) the employee:
(1) has an impairment rating of 15 percent or more as determined by this subtitle from the compensable injury;
(2) has not returned to work or has returned to work earning less than 80 percent of the employee's average weekly wage as a direct result of the employee's impairment;
(3) has not elected to commute a portion of the impairment income benefit under Section 408.128; and
(4) has complied with the requirements adopted under Section 408.1415.
(b) If an employee is not entitled to supplemental income benefits at the time of payment of the final impairment income benefit because the employee is earning at least 80 percent of the employee's average weekly wage, the employee may become entitled to supplemental income benefits at any time within one year after the date the impairment income benefit period ends if:
(1) the employee earns wages for at least 90 days that are less than 80 percent of the employee's average weekly wage;
(2) the employee meets the requirements of Subsections (a)(1), (3), and (4); and
(3) the decrease in earnings is a direct result of the employee's impairment from the compensable injury.