Optic neuritis (ON) causes axonal loss as reflected by thinning of retinal nerve fiber layer (RNFL) and can be tracked by optical coherence tomography (OCT) about 6 months after ON onset, when swelling of optic nerve head (ONH) has vanished. Changes of macular ganglion cell layer (GCL) thickness provide another window to track the disease process in ON. GCL thinning over time in relation to RNFL change after ON remains elusive. Using OCT, we followed 4 patients with acute unilateral isolated ON for more than 9 months. A diagnosis of multiple sclerosis (MS) was established in all 4 patients. First follow-up was 2-3 weeks after ON onset, and thereafter every 2-3 months. RNFL swelling peaked during first month after acute ON, followed by rapidly reduced swelling (pseudoatrophy) during following 2 months, and thereafter successively vanished 6 months after ON onset. GCL thinning was observed 1-3 months after ON onset, i.e. already during optic disk swelling and before real RNFL thinning. The results imply that quantifying GCL thickness provides opportunities to monitor early axonal loss and ON-to-MS progression, and facilitates distinguishing real atrophy from pseudoatrophy of RNFL after acute ON.