['Loss of retinal ganglion cell-inner plexiform layer (GCIPL) thickness has been shown in different optic neuropathies. In this study, we evaluated the capability of GCIPL analysis by optical coherence tomography (OCT) to detect early neuronal loss during the time course of nonarteritic anterior ischemic optic neuropathy (NAION).', 'Twenty-four patients with unilateral NAION participated in this prospective, comparative study. Affected and unaffected eyes underwent spectral domain OCT measurement of the retinal nerve fiber layer (RNFL), total macula, and GCIPL thicknesses. These measurements were recorded in the acute phase (within 7 days) and at 1, 3, and 6 months.', 'At the initial presentation and 1, 3, and 6 months, the mean RNFL thickness in the NAION eyes was 236.5 μm ± 74.2, 157.1 μm ± 45.7, 61.4 μm ± 6.1, and 55.0 μm ± 19.5, respectively. Similar to RNFL, thinning of the mean total macular thickness in inner and outer rings started after 3 months and thicknesses decreased to 307.7 μm ± 15.3 and 273.1 μm ± 21.2 after 3 months and to 309.1 μm ± 15.0 and 273.4 μm ± 13.8 after 6 months, compared with unaffected contralateral eyes, respectively (all P < 0.0001). Thinning of the GCIPL was first evident in the affected NAION eyes at 1 month, and the mean inner and outer GCIPL thicknesses were 62.8 μm ± 14.6 and 53.9 μm ± 7.2 at 1 month in the NAION eyes compared with unaffected eyes (P < 0.001). After 3 and 6 months, the inner and outer GCIPL thicknesses were 51.1 μm ± 8.1 and 47.4 μm ± 5.31, and 50.6 μm ± 11.5 and 47.9 μm ± 5.6, respectively.'] Does retinal Ganglion Cell Loss precede Retinal Nerve Fiber Thinning in Nonarteritic Anterior Ischemic Optic Neuropathy?