We present long term site testing statistics based on DIMM and GSM data obtained at Dome C, Antarctica. These data have been collected on the bright star Canopus since the end of 2003. We give values of the integrated turbulence parameters in the visible (wavelength 500 nm). The median value we obtained for the seeing are 1.2 arcsec, 2.0 arcsec and 0.8 arcsec at respective elevations of 8m, 3m and 20m above the ground. The isoplanatic angle median value is 4.0 arcsec and the median outer scale is 7.5m. We found that both the seeing and the isoplanatic angle exhibit a strong dependence with the season (the seeing is larger in winter while the isoplanatic angle is smaller).