Retinal dopamine loss in Parkinson disease (PD) is reflected by visual neurophysiological dysfunction. We measured the thickness of the circumpapillary retinal nerve fiber layer (RNFL) in PD patients using optical coherence tomography. The thickness in the inferior quadrant of PD patients (147 +/- 20 microns) was significantly thinner than that of controls (173 +/- 12 microns; p=0.002), while the inferotemporal area was the thinnest (146 +/- 24 vs. 191 +/- 21 microns; p=0.0003). The results show significant loss of RNFL thickness in PD at specific sites.