Pursuant to section 74 of the Retirement and Social Security Law, the Comptroller has the exclusive authority to determine whether a member is permanently incapacitated for the performance of gainful employment. With respect to disability retirement applications filed pursuant to section 507 of the Retirement and Social Security Law only, a determination by the Federal Social Security Administration that a member is permanently incapacitated for the performance of gainful employment shall constitute proof of permanent incapacity for retirement system purposes.