This study had several limitations of note. First, although we only used good-quality images for study inclusion, the impact of poor-quality or artifacts on OCT/OCTA images in real-world clinical settings should not be overlooked.
36 Moreover, the high variability in VF examinations observed in advanced glaucoma may have influenced the S-F and V-F relationships.
37 However, although these limitations may be pronounced in cross-sectional studies, they can be mitigated in longitudinal studies.
36 Hence, longitudinal research conducted over extended periods, such as in the present study, remains crucial for accurate interpretation. Second, the definition of advanced glaucoma (MD < −15 dB) that we here used was somewhat arbitrary. While we carefully selected this criterion by considering the measurement floor of SD-OCT thickness parameters and the same threshold value used by previous reports,
9,20,21 the definition of advanced glaucoma may be considered differently in relation to the location of VF defects or the application of different VF grading system. Third, while OCTA provides the automatic calculation of average VD values in the six sectors of circumpapillary region through built-in software, Cirrus SD-OCT, on the other hand, does not offer direct automatic calculation of six sectoral cpRNFLT based on the Garway-Heath map. Therefore sectoral cpRNFLT estimated manually using Cirrus SD-OCT clock-hour map may be less accurate compared to OCTA-based sectoral cpVD value. Fourth, six OCT/OCTA sectors based on the Garway-Heath map may not exhibit a complete topographical correspondence with VFMS sectors due to individual variations in macular anatomy, including variations in the foveal and cpRNFL distribution. For instance, the displacement of fovea-to-optic disc center in myopic eyes owing to optic disc tilt/rotation or axial elongation may render structure- and vasculature-function correlation maps imprecise due to deviations from the Garway-Heath map.
22,38 Nonetheless, it is important to note that these limitations are consistently applied to the evaluation of both S-F and V-F relationships within each individual in the current study. Fifth, we did not assess the potential impact of systemic hypotensive medications or topical anti-glaucomatous eye treatments on VD measurements.
39 Furthermore, modifications to these medications during follow-up periods were not taken into account. Sixth, trend analysis of global indices such as VF MD to define VF progression may underestimate the rate of progression in advanced glaucoma because of the influence of test points without detectable sensitivity (blind locations) and a floor effect.
40 Our current findings should therefore be interpreted with caution in light of these confounding factors. Finally, as our study subjects were enrolled from a single tertiary academic center and were solely of Korean ethnicity, our findings may not be fully applicable more generally.