U.S. Census Bureau, Revenue From Health Care Providers for Non-Patient Care (Includes Revenue From Medical Administration and Other Administrative Services, Incentive Payments, Management Fees, Medical Director Fees, Etc.) for Offices of Optometrists, All Establishments, Employer Firms [OOORFHCPFNC462132], retrieved from FRED, Federal Reserve Bank of St. Louis; https://fred.stlouisfed.org/series/OOORFHCPFNC462132, .