Background/aims Chiasmal compression affects the crossed nerve fibres originating from the nasal hemiretina, as opposed to the uncrossed fibres from the temporal hemiretina. The objectives were to evaluate circumpapillary retinal nerve fibre layer (cpRNFL) thickness by spectral-domain optical coherence tomography in eyes with band atrophy (BA) accompanying temporal hemianopia due to chiasmal damage and to estimate the distribution pattern of cpRNFL from the nasal hemiretina.

Methods This cross-sectional study included 53 eyes with optic neuropathy due to chiasmal lesions and 72 normal eyes. Visual field sensitivity (VFS) was evaluated by standard automated perimetry. Eyes with abnormalities in the nasal visual hemifield were excluded. The structure-function relationships (cpRNFL thickness and VFS in the temporal hemifield) were evaluated in eyes with BA. The base levels composed of only non-neuronal elements and cpRNFL from the temporal hemiretina were estimated in the average and 12 sector-cpRNFL thicknesses using regression analysis.

Results The base level in the average cpRNFL thickness was 71.2 µm in eyes with BA, which corresponded to 70% of average thickness of normal controls. However, the estimated base level of 12 sector-cpRNFL thicknesses represented the unique distribution pattern, in which base level-thickness localised at the 1 o'clock and 5 o'clock sectors was extensively reduced, with an even distribution of base levels at other sectors.

Conclusions The RNFL originating from the nasal hemiretina is estimated to enter into the optic disc predominantly at the 1 o'clock and 5 o'clock angles.