I went to Federoptics at Cervantes 12 in Tortosa.  That's the same street as the Santander Bank is in, on the corner of the square.  The chap there speaks excellent English and a prescription cost me 30 euros.  It is free if you buy new glasses there, but when my wife bought new glasses at a different opticians the cost rose from the basic frames at 125e to 400e.  So I just took the prescription and then ordered new specs over the internet from 'glasses frames and lenses' - excellent service and my new bifocals with trendy frames and polychromatic lenses just cost £127
including delivery to Spain.