Structure-function relationship among three types of spectral-domain optical coherent tomography instruments in measuring parapapillary retinal nerve fibre layer thickness.

Objective: To compare the relationships of parapapillary retinal nerve fibre layer (RNFL) thickness among three spectral-domain optical coherence tomography (SD-OCT) instruments with visual field sensitivity (VFS).

Methods: One hundred and thirteen eyes of 113 Japanese subjects with glaucoma (mean deviation in standard automated perimetry = -8.9 ± 6.7 dB) were imaged by Cirrus, RTVue and 3D OCT. The average hemi-superior and hemi-inferior RNFL thicknesses were obtained. In addition, the structure-function relationship using two retinotopic maps that consisted of six or nine sectors was also evaluated. Decibel (dB) scale and 1/Lamert (1/L) were used to express VFS. RNFL thickness correlation with corresponding VFS in visual field sectors was compared among the three instruments. Background RNFL thickness (non-neuronal tissue) for each instrument was estimated using a linear regression model at 1/L = 0.

Results: The correlation between the average hemi-superior and hemi-inferior RNFL thickness in the three SD-OCT instruments with corresponding VFS was similar. In the analysis of retinotopic maps, 3D OCT showed a higher correlation in superotemporal sectors than RTVue, whereas RTVue had a stronger relationship in the nasal sector than Cirrus. The background RNFL thickness extrapolated was approximately 60% that of normal eyes in all the instruments.

Conclusions: The three SD-OCT showed similar overall correspondence with VFS with a partially discordant retinotopic relationship. RNFL measured with any SD-OCT devices likely contains non-neuronal tissue, comprising 60% of its thickness.