According to our cases, vitreous opacities floating around the optic disc could affect RNFL thickness measurement with Cirrus high-definition OCT. The opacities could influence the RNFL thickness values (1) when the peripapillary vitreous opacities crossed the scan circle, (2) when they were presented as red color codes in the RNFL deviation map, and (3) when they were demonstrated as black spots in the RNFL thickness map. Although the peripapillary vitreous opacities crossed the scan circle, the RNFL thickness values did not change remarkably when they were not presented as red color codes in the RNFL deviation map and were not visible in the RNFL thickness map. In addition, vitreous opacity could cause an error in the determination of the optic nerve head margin, resulting in a disc center displacement. A decentered OCT scan, described previously,4 could change RNFL thickness characteristics.