The effect of myopic optic disc tilt on measurement of spectral-domain optical coherence tomography parameters

Background To compare the spectral-domain optical coherence tomography (SD-OCT) parameters, including ganglion cell-inner plexiform layer (GCIPL) thickness, retinal nerve fibre layer (RNFL) thickness and optic nerve head (ONH) parameters between glaucomatous eyes with myopic tilted optic disc and non-tilted optic disc, and to investigate the effect of optic disc tilt on the diagnostic performance of these parameters. Methods The study included 82 patients with glaucoma and 41 refraction-matched normal subjects. The OCT parameters and their diagnostic abilities were compared between the non-tilted disc group (N=41) and tilted disc group (N=41). Results The ONH parameters in the tilted disc group, except the rim area, were significantly smaller than in the non-tilted disc group. The temporal RNFL was significantly thicker in the tilted disc group compared with the non-tilted group. In addition, the diagnostic capabilities of the vertical cup-to-disc area (CDR) and temporal RNFL thickness in the tilted disc group were inferior to those in the non-tilted disc group. However, there were no significant differences in GCIPL thickness between the two glaucoma groups. Furthermore, the diagnostic capability of GCIPL thickness in the tilted disc group was comparable to that in the non-tilted disc group. The ovality index was significantly associated with temporal RNFL thickness in both regression analyses. Conclusions The diagnostic capacities of temporal RNFL thickness and vertical CDR should be interpreted with caution in glaucomatous eyes with tilted optic discs. Macular GCIPL measurement provides reliable diagnostic parameters, regardless of the degree of optic disc tilt.