The board of trustees shall award disability benefits to eligible members who have been officially certified as having a disability by the State Medical Disability Board. The disability benefit shall be determined as follows:
(1) Upon retirement caused by disability, a member of Plan B shall be paid a disability benefit equal to the lesser of:
(a) An amount equal to two percent of the member's final compensation multiplied by his years of creditable service, but not less than thirty percent of his final compensation, or
(b) An amount equal to what the member's normal retirement benefit would be, as based on the member's current final compensation, but assuming the member remained in continuous service until his earliest normal retirement age and using those retirement benefit computation factors which would be applicable to the member's normal retirement.
(2) Upon retirement caused by disability, a member may select any of the optional modes of benefit payments provided by R.S. 11:1757. The computation of any optional benefit payment shall be based upon the option factors the system utilizes for normal retirement and the ages of the member and the option beneficiary, projected to the member's earliest normal retirement age assuming the member remained in continuous service until that time.