A 3D model to evaluate retinal nerve fiber layer thickness deviations caused by the displacement of optical coherence tomography circular scans in cynomolgus monkeys (Macaca fascicularis)

The main objective of the study was to analyze deviations in retinal nerve fiber layer (RNFL) thickness measurements caused by the displacement of circular optic disc optical coherence tomography scans. High-density radial scans of the optic nerve heads of cynomolgus monkeys were acquired. The retinal nerve fiber layer was manually segmented, and a surface plot of the discrete coordinates was generated. From this plot, the RNFL thicknesses were calculated and compared between accurately centered and intentionally displaced circle scans. Circle scan displacement caused circumpapillary retinal nerve fiber layer thickness deviations of increasing magnitude with increasing center offset. As opposed to the human eye, horizontal displacement resulted in larger RNFL thickness deviations than vertical displacement in cynomolgus monkeys. Acquisition of high-density radial scans allowed for the mathematical reconstruction and modelling of the nerve fiber layer and extrapolation of its thickness. Accurate and strictly repeatable circle scan placement is critical to obtain reproducible values, which is essential for longitudinal studies.