To demonstrate whether optical coherence tomography (OCT-3) and scanning laser ophthalmoscopy (HRT-2) can be used to measure changes of the optic disc and peripapillary retinal nerve fiber layer (RNFL) in eyes with acute retrobulbar optic neuritis that have no clinically apparent optic disc swelling. To correlate these findings with presentation magnetic resonance imaging (MRI) of the affected optic nerve. Eight consecutive patients with acute retrobulbar optic neuritis, who had no prior optic neuritis in either eye, were prospectively investigated at presentation and at between 1 and 3 months with clinical examination, OCT-3, HRT-2. At presentation, MRI of the optic nerves were performed in 7/8 patients. Compared to unaffected eyes, affected eyes without clinically seen optic disc swelling at baseline, there was a non-significant trend to increased thickness in the total RNFL, superior and nasal measurements. Baseline HRT in affected eyes showed smaller mean cup to disc ratio (p=0.003) and a smaller cup area (p=0.002) compared with the unaffected eye. The MRI-demonstrated optic nerve lesion did not correlate with OCT RNFL thickening or HRT decrease of the physiological cup. Follow-up imaging of the affected eyes showed normalization of HRT cup size parameters and OCT RNFL thickness (p<0.04). At follow-up, the temporal RNFL had thinning in 7/8 affected eyes (46.8 mum, p=0.021) compared with fellow unaffected eyes (57.8 mum), which did not change. OCT-3 and HRT demonstrate mild RNFL thickening or optic disc swelling in acute optic neuritis, even when swelling is not seen clinically. OCT-3 appears to reveal measurable RNFL thinning in the temporal quadrant after retrobulbar optic neuritis, even though vision improves. RNFL imaging may be useful in future studies of residual injury after optic neuritis.