The Ozone Monitoring Instrument (OMI) is an UV-Visible imaging spectrograph using two dimensional CCD detectors to register both the spectrum and the swath perpendicular to the flight direction. This allows having a wide swath (114 degrees) combined with a small ground pixel (nominally 13 x 24 km). The instrument is planned for launch on NASA's EOS-AURA satellite in June 2003. Currently the OMI Flight Model is being build. This shortly follows the Instrument Development Model (DM) which was built to, next to engineering purposes, verify the instrument performance. The paper presents measured results from this DM for optical parameters such as distortion, optical efficiency, stray light and polarisation sensitivity. Distortion in the spatial direction is shown to be on sub-pixel level and the stray light levels are very low and almost free from ghost peaks. The polarisation sensitivity is presently demonstrated to be below 10(-3) but we aim to lower the detection limit by an order of magnitude to make sure that spectral residuals do not mix with trace gas absorption spectra. Critical detector parameters are presented such as the very high UV quantum efficiency (60% at 270 nm), dark current behavior and the sensitivity to radiation.