PurposeTo evaluate the differences in structural parameters in patients with open-angle glaucoma (OAG), high myopia (M), and both diseases (OAG-M) concurrently.Methods42 subjects with OAG (n = 14), M (n = 14) and OAG-M (n = 14) were included in a prospective pilot study. Mean peripapillary retinal nerve fiber layer (RNFL) thickness, RNFL in superior, temporal, inferior, nasal quadrants, macular ganglion cell complex (GCC) and its’ layers, vessel density (VD) of optic nerve head (ONH) and macula were evaluated.ResultsThe OAG-M group showed significantly lowest thickness of mean peripapillary RNFL 89 (49–103) μm (p = 0.021), temporal quadrant 64.5 (51–109) μm (p = 0.001) and inferior quadrant 107 (64–124) μm (p = 0.025). The macular RNFL was thinnest in the OAG-M group (p <0.001). Macular VD in inferior quadrant was lowest in OAG-M group at superficial capillary plexus 45.92 (40.39–51.72) % (p = 0.014) and choriocapillaris 51.62 (49.87–56.63) % (p = 0.035). The lowest ONH VD of temporal quadrant was found in the OAG-M group 52.15 (35.73–59.53) % (p = 0.001) in the superficial capillary plexus. Similarly, the lowest VD of inferior quadrant was found in OAG-M group in the choriocapillaris 54.42 (46.31–64.64) % (p<0.001).ConclusionsThe M group showed the least thinning in the peripapillary RNFL thickness in the temporal quadrant and macular RNFL compared to other two groups. The highest macular VD in the inferior quadrant was in the M group in the superficial capillary plexus, deep capillary plexus and choriocapillaris. The M group showed highest VD in the temporal quadrant and in total VD of ONH at the superficial capillary plexus and in total VD of ONH at the deep capillary plexus.Practical recommendationsThe observed decrease in peripapillary RNFL thickness of the temporal quadrant, macular RNFL thickness, the decrease of macular VD at the inferior quadrant and decrease in VD of the ONH temporal quadrant in deep capillary plexus could be beneficial for diagnosing glaucoma in high myopia.