Retinal nerve fibre layer thickness change in the parapapillary region

Purpose To assess radial changes in the retinal nerve fibre layer thickness (RNFLT) in the temporal parapapillary region. Methods Using radial optical coherence tomographic images of the optic nerve head, we measured in a sample of participants of the population-based Beijing Eye Study the RNFLT in the temporal horizontal parapapillary region at locations ‘A’ (intact inner (INL) and outer (ONL) nuclear layer), ‘B’ (INL/ONL end), ‘C’ (just beyond the INL/ONL end) in the parapapillary gamma zone centre and at the disc border. Exclusion criterion was any optic nerve damage including glaucoma. Results The study included 47 eyes (47 participants). RNFLT increased (p<0.001) from 86±24 µm at ‘A’ (optic disc centre distance (ODCD): 1523±477 µm) to 128±42 µm at ‘B’ (ODCD: 1192±394 µm) and to 190±64 µm at ‘C’ (ODCD: 1023±312 µm). The increasing RNFLT measurements from location ‘A’ to ‘B’ by 49% and from ‘B’ to ‘C’ by 49% were double as high as geometrically expected (‘A’ to ‘B’: 1523 µm/1192 µm (28%); ‘B’ to ‘C’: 1192 µm/1023 µm (17%)). In the temporal parapapillary gamma zone (detected in 23 eyes), RNFLT changed from the mid of gamma zone (ODCD: 1069±291 µm) to the disc border (ODCD: 618±228 µm) from 210±76 µm to 238±81 µm (or +13%), while the ODCD decreased by 42%. Conclusions RNFLT in the temporal horizontal parapapillary region markedly increased just beyond (in direction to the disc border) of the INL/ONL end while within gamma zone RNFLT changed only marginally. Absence of underlying INL/ONL was associated with pronounced RNFL thickening, without major further radial RNFLT changes in gamma zone. These findings may be of importance for RNFLT measurements in highly myopic eyes.