To study retinal nerve fiber layer (RNFL) thickness by optical coherence tomog raphy (OCT) in unaffected carriers with Leber’s hereditary optic neuropathy (LH ON) mutations. Crosssectional study. Sixty-six unaffected carriers (44 females and 22 males) were analyzed and compared with an age-matched control group of 7 0 patients (40 females and 30 males). The statistical analysis was performed aft er grouping both the patients and the control group on the basis of gender and, for unaffected carriers only, mitochondrial DNA mutation. The Fast RNFL Thicknes s (3.4) scan acquisition protocol was used. Retinal nerve fiber layer thickness as measured by OCT. With respect to the control group, unaffected male carriers showed a thicker RNFL in the temporal and inferior quadrants and in the 360°ave rage measurement (P=0.025, P=0.03, and P=0.018, respectively). These differences reached statistical significance in subjects carrying the 11 778 mutation, wher eas only a trend was detected in those with the 3 460 mutation. Unaffected femal e carriers had an increased thickness in the temporal quadrant when compared wit h the control group (P=0.003) and no differences in the other measurements. The increase in temporal sectors was statistically significant in females with the 1 1 778 mutation, whereas a trend was detected in those with the 3 460 mutation. A thickening of the temporal fibers was detected in all subgroups of unaffected c arriers. This is the first evidence indicating the preferential involvement of t he papillomacular bundle in subclinical LHON. This notion previously was based o n the early loss of fibers from the temporal quadrant in acute LHON and the sele ctive loss of small-caliber fibers at histopathology. Our study also revealed t hat males have a more diffuse involvement than females. To study retinal nerve fiber layer (RNFL) thickness by optical coherence tomog raphy (OCT) in unaffected carriers with Leber’s hereditary optic neuropathy (LH ON) mutations. Crosssectional study. Sixty-six unaffected carriers (44 females and 22 males) were analyzed and compared with an age-matched control group of 7 0 patients (40 females and 30 males). The statistical analysis was performed a group of both the patients and the control group on the basis of gender and, for unaffected carriers only, mitochondrial DNA mutation . The Fast RNFL Thicknes s (3.4) scan acquisition protocol was used. Retinal nerve fiber layer thickness as measured by OCT. With respect to the control group, unaffected male carriers showed a thicker RNFL in the temporal and inferior quadrants and in the 360 ​​° a differential rage measurement (P = 0.025, P = 0.03, and P = 0.018, respectively). These differences reached statistical significance in subjects carrying the 11 778 mutation, wher eas only a trend was detected in tho se with the 3 460 mutation. Unaffected femal e carriers had an increased thickness in the temporal quadrant when compared wit h the control group (P = 0.003) and no differences in the other measurements. The increase in temporal segments was substantially significant in females with the 1 1 778 mutation, while a trend was detected in those with the 3 460 mutation. A thickening of the temporal fibers was detected in all subgroups of unaffected c arriers. This is the first evidence indicating the preferential involvement of t he papillomacular bundle in This notion was based on the early loss of fibers from the temporal quadrant in acute LHON and the sele ctive loss of small-caliber fibers at histopathology. Our study also revealed t hat males have a more diffuse involvement than females.