Any coordinated member who retires prior to the time the member becomes eligible for Social Security old age retirement benefits shall be entitled to elect to receive a Social Security leveling adjustment optional annuity from the teachers retirement fund association. The Social Security leveling adjustment optional annuity shall be established by the board of the teachers retirement fund association. It shall take the form of an annuity payable for the period prior to the member’s becoming eligible for Social Security old age retirement benefits in an amount greater than the amount of the member’s annuity calculated pursuant to section 354A.31 on the basis of the age of the member at retirement but equal insofar as possible to the Social Security old age retirement benefit and the adjusted retirement annuity amounts payable immediately subsequent to becoming eligible for Social Security old age retirement benefits in an amount less than the amount of the member’s annuity calculated pursuant to section 354A.31 on the basis of the age of the member at retirement. The optional form shall be the actuarial equivalent to the normal forms provided in section 354A.31. In establishing the optional form, the board shall obtain the written recommendation of the actuary retained under section 356.214 and the recommendation shall be a part of the permanent records of the board.