The aim of this study was to assess the longitudinal changes in retinal nerve fibre layer (RNFL) thickness after a first attack of optic neuritis and to investigate the impact of treatment on RNFL thinning at one year after the attack. RNFL thickness of the attack and normal fellow eyes was measured by optical coherence tomography on presentation and three, six and 12 months post attack in treatment and non-treatment groups. The treatment group consisted of subjects that opted for systemic steroids to hasten recovery time, patients were not randomised into the groups. Findings showed that the baseline RNFL thickness was similar in the attack and fellow eyes. Progressive RNFL thinning was seen in the attack eye over the 12 month period. Importantly, the RNFL thickness was similar between the treatment and non-treatment groups. This has clinical significance for the treatment offered to patients following unilateral retrobulbar optic neuritis. In this study, initial treatment with systemic steroids did not alter the degree of RNFL loss at 12 months, suggesting that the treatment was ineffective. Before treatment using steroids is discarded, however, a large sample size randomised control trial is required to investigate the effectiveness of treatment in full.