Altering the NFL averaging procedure to use dB scale and VF area weighting yielded NFL WLA, which had even better correlation with VF_MD (Fig. This was improved by simply converting from µm to dB scale (Fig. The overall average NFL thickness in µm had fair correlation with VF_MD, but the relationship was highly nonlinear (Fig. The floor percentage was similar among the inferotemporal and superotemporal sectors with no clear pattern of difference. The simplifying assumption that the floor percentage is the same for all sectors was necessary as the worst sectors were always found to be inferotemporal or superotemporal. The floor value as a percentage of the reference NFL thickness was found to be 45% by pooling all sectors. Finally, the potential for more sensitive progression detection is evaluated by looking at between-visit retest variability. We then assessed whether the resulting NFL_MD has advantages over the commonly used overall NFL thickness in terms of diagnostic accuracy, staging accuracy, and correlation with VF_MD. The method converts NFL thickness to a dB scale and averages it using VF area weighting. We developed a method to estimate the VF_MD using the circumpapillary NFL thickness profile measured by OCT in the same eye. In this study, we hypothesized that reducing the differences in scaling and weighting could improve the correlation between VF and OCT measurements. In contrast, VF_MD is weighted by the VF area. For example, the NFL thickness is weighted by the length along a peripapillary circle. Differences also exist in the strategy to provide summary data for OCT and VF testing. VF maps and parameters are measured in decibel (dB) units on a logarithmic scale. OCT measures NFL and GCC in µm units, which is on a linear scale. Thus it is difficult to clinically judge whether glaucoma is progressing rapidly or not based on OCT structural measurements.Ī major reason for the frequent discordance between OCT and VF results is the way in which they are scaled. Furthermore, the speed of glaucoma progression as measured by OCT, such as NFL and macular ganglion cell complex (GCC) thinning in µm/year poorly correlates with the rate of VF changes as measured in MD trend in dB/year or Visual Field Index (VFI) trend in %/year 8, 9, 10, 11, 12. But the overall peripapillary nerve fiber layer (NFL) thickness correlates poorly with VF mean deviation (MD) 6, 7. Quantitative imaging of the optic nerve head (ONH) and retina with optical coherence tomography (OCT) 3 are widely used in diagnosis and monitoring of glaucoma 4, 5. However, VF testing is subjective, time-consuming, and poorly reproducible. Visual field (VF) test is the current standard to monitor glaucoma progression. This allows the rational use of medical, laser, and surgical treatments, all of which have significant cost, compliance, and safety issues. Glaucoma is a leading cause of blindness 1, 2, and effective glaucoma management requires early detection, followed by careful evaluation and monitoring to identify those at the highest risk for disease progression and vision loss.
It agrees well with VF_MD in early glaucoma but underestimates damage in moderate~advanced stages. It has better reproducibility than VF_MD, which may be advantageous in detecting progression. In summary, OCT-based NFL_MD has better correlation with VF_MD and greater diagnostic sensitivity than the average NFL thickness. NFL_MD had better reproducibility than VF_MD (0.35 vs 0.69 dB, p < 0.001). NFL_MD also had significantly higher sensitivity in detecting PPG (0.14 vs 0.08) and PG (0.60 vs 0.43) at the 99% specificity level. NFL_MD had significantly higher correlation (Pearson R: 0.68 vs 0.55, p < 0.001) with VF_MD than the overall NFL thickness. From the Advanced Imaging for Glaucoma study, 245 normal, 420 pre-perimetric glaucoma (PPG), and 289 perimetric glaucoma (PG) eyes were selected. The NFL_MD parameter in dB scale was calculated from the peripapillary NFL thickness profile nonlinear transformation and VF area-weighted averaging. To construct an optical coherence tomography (OCT) nerve fiber layer (NFL) parameter that has maximal correlation and agreement with visual field (VF) mean deviation (MD).