We evaluated the usefulness of neuroretinal rim (NRR) thicknesses, measured in clock-hour sectors with Cirrus HD- optical coherence tomography (OCT), for diagnosing preperimetric glaucoma (PPG).This prospective study included 39 eyes of 39 patients with PPG and 39 eyes of 39 controls that were matched to patients for age and refractive error. We measured the circumpapillary retinal nerve fiber layer (cpRNFL) thickness, macular ganglion cell-inner plexiform layer (GCIPL) thickness, and optic nerve head (ONH) parameters with OCT. The clock-hour NRR thicknesses were derived from a 360° circumferential rim thickness curve. We analyzed the area under the receiver operating characteristics curve (AUROC), cutoff values, and sensitivities at specificities of 90% and 95%.The largest AUROCs were observed for the NRR thickness at 6 o'clock (0.823), the inferior RNFL thickness (0.821), the average RNFL thickness (0.819), and the NRR thickness at 7 o'clock (0.818). The performance of the NRR thickness at 6 o'clock was comparable to the best performances of the cpRNFL, GCIPL, and ONH parameters (all p >0.05).The ability of the clock-hour NRR thickness assessment to diagnose PPG was comparable to the diagnostic abilities of cpRNFL, GCIPL, and ONH parameters. The best indicator of PPG was the NRR thickness parameter that was at 6 o'clock. This finding could play a role in detecting early structural changes in PPG.