Using Medicare claims data from the period of 1985 to 1989, a pooled time series design study estimated the impact of the enactment of optometry therapeutic drug prescriptive authority (TPA) laws on the level and provider share of demand for office based eye care. TPA laws expand the statutory scope of optometric services by permitting use of pharmaceutical agents to treat diseases of the eye. A fixed effect regression model tested a theory of insurance coverage expansion that predicted how TPA laws redefine the supply of eye care providers. The study found that expanding insurance coverage in the Medicare Program potentiated the impact of TPA related increases in overall demand and shifts market share from ophthalmologists to optometrists. TPA laws after the 1987 Medicare Amendment were expected to have a positive impact for all demand equations. However, the impact was not expected to be so predominant in the short run of a five year study. It appears that in the presence of insurance coverage, TPA implementation quickly changes practice styles of optometrists and ophthalmologists with resultant supplier induced demand of secondary care. Also, for TPA states consumer choice may have been affected in short order. For TPA states, greater consumer confidence in the substitutability of optometrists for ophthalmologists may stimulate higher demand and provider share for optometric eye care services.