(a) Vending stand operators, operating stands under permits held by the Department of Aging and Disability Services pursuant to § 17a-818, shall be members of the state employees retirement system, part A, exclusive of the Social Security option and benefits in the state employees’ retirement system dependent thereon. Each such person shall annually, on or before June thirtieth, pay five per cent of his adjusted gross income, arising out of the operation of such stand, as determined under the Internal Revenue Code, during the calendar year preceding to the Department of Aging and Disability Services which shall, as the state administering agency for such persons, certify such payment and pay it over to the State Retirement Commission, provided membership of such persons in said system shall be exclusive of disability retirement upon the grounds of defects of vision.

(b) Any member of the state employees retirement system who operated vending stands under permits held by the State Board of Education and Services for the Blind pursuant to § 17a-818, prior to October 1, 1971, may obtain credit for such period or periods of service for retirement purposes, provided such member has been in the active full-time employment of the state continuously for twelve months next preceding such member’s written request to the Retirement Commission for such credit, and by making retirement contributions of five per cent of such member’s adjusted gross income arising out of the operation of such stands for each of such years with interest thereon at the rate of five per cent per year from the time of such operation to the date of payment, all as certified by the State Board of Education and Services for the Blind or, its successor agency, the Department of Rehabilitative Services. Such payments may be made in twelve equal monthly installments but such service credit shall not be granted unless payment of installments is completed.