In total, 322 eyes of 248 patients from Sankara Nethralaya and 22 eyes of 18 patients from LVPEI met the quality criteria and were included in the final analysis. Out of these 344 eyes, 116 (33.7%) eyes had PPL and 228 (66.3%) eyes had PCL which is similar to the distribution in the overall cohort reported previously(14). 175 (50.9%) eyes were left eyes, and 169 (49.1%) were right eyes. Among eyes with PPL, 19 (16.4%) had mild NPDR, 42 (36.2%) had moderate NPDR, 34 (29.3%) eyes had severe NPDR, and 21 (18.1%) had PDR. In the group with PCL, 32 (14.8%) had mild NPDR, 84 (38.9%) had moderate NPDR, 53 (24.5%) eyes had severe NPDR, and 47 (21.8%) eyes had PDR (Table 2).
Among the 12 eyes with a DRSS score of 0 (i.e. no DR withing the 7SF), by definition all eyes with any DR lesions in the extended fields were PPL (100%). Among eyes with mild NPDR (51 eyes), 19 (37.3%) had PPL and 32 (62.8%) had PCL. In the group with moderate NPDR (126 eyes), 42 (33.3%) eyes had PPL and 84 (66.7%) eyes had PCL. In eyes with severe NPDR (87 eyes), 34 (39.1%) eyes had PPL, and 53 (60.9%) eyes had PCL. Among eyes with PDR (68 eyes), 21 (30.9%) eyes had PPL and 47 (69.1%) eyes had PCL (Table 2).
Scp Layer
Comparison of eyes with PCL and PPL without considering the DR severity level showed that in the SCP layer, the inner zone of PCL cases had numerically higher PD% and VLD values, while in the outer zone, PPL cases had higher values for these parameters (Table 1). None of the differences, however, were significantly different between two groups.
In the SCP layer, assessment of the PD% in the inner ring showed a numerically higher values in the PCL group among eyes with mild or moderate NPDR and higher values in the PPL group among eyes with severe NPDR and PDR (Table 2). However, none of these differences were statistically significant. For the inner ring, with the exception of eyes with mild NPDR, for all other DR severity levels with PPL had numerically higher PD% values in the outer ring. The differences, however, were not statistically significant.
Assessment of VLD in the inner and outer ring showed numerically higher VLD values in eyes with mild NPDR and PCL, whereas for all other DR severity levels, there was a numerically higher VLD in eyes with PPL. Again, these differences were not statistically significant. There was no difference in fractal dimensions (FD) between the group with PPL (1.54 ± 0.03) and PCL (1.54 ± 0.04)( P-value = 0.149).
Dcp Layer
In the DCP layer, cases with PCL had numerically higher values for VLD and PD% in both the inner and outer parafoveal rings. None of the differences, however, were statistically significantly (Table 1).
In the DCP layer, assessment of PD% in the inner ring showed that the cases with PPLs in the groups with mild NPDR and PDR have numerically higher PD% values, while PCL with moderate and severe NPDR have numerically higher PD% values than cases with PPL. The difference was statistically significantly different in the group with moderate NPDR, while the rest of the differences were not statistically significantly different. In the outer ring, except for the PCL cases in the moderate NPDR group, PD% was numerically higher in the PPL cases across all DR severity levels. The differences were not significantly different.
Assessment of VLD in the inner ring showed that in the mild NPDR and PDR groups, cases with PPL had numerically higher VLD values than eyes with PCL, whereas for moderate and severe NPDR eyes, cases with PPL had numerically higher VLD values. Again, none of the differences were statistically significantly different. In the outer ring, cases with PCL had numerically higher VLD values for all DR severity levels, but the differences were not significantly different. There was no difference in FD between groups with a mean FD of 1.62 ± 0.01 in both groups (p = 0.362)
Foveal Avascular Zone (Faz) Characteristics
FAZ characteristics of both groups is summarized in Table 3. The FAZ area and perimeter were not statistically significantly different between the two groups. However, the PCL group had a larger maximum diameter (Lmajor) and smaller minimum diameter (Lminor) suggesting a more oval shape compared to the PPL group. This is corroborated by the higher roundness (p = 0.037) and circularity (p = 0.061), and lower axial ratio (p = 0.208) in the PPL cases. The inter-grader reliability for segmentation of the FAZ border revealed a good inter-grader reliability of 86% (ICC 3,2 = 0.855).
Table 3
Comparison of the foveal avascular zone (FAZ) characteristics between the two groups. Values are presented as mean ± standard deviation. PPL = predominantly peripheral lesion; PCL = predominantly central lesions.
| PPL | PCL | P value |
Area (mm2) | 0.490 ± 0.166 | 0.511 ± 0.466 | 0.363 |
Maximum diameter (Lmajor)(mm) | 0.951 ± 0.196 | 0.968 ± 0.358 | 0.360 |
Minimum diameter (Lminor)(mm) | 0.714 ± 0.119 | 0.709 ± 0.180 | 0.418 |
Perimeter (mm) | 2.756 ± 0.564 | 2.797 ± 0.975 | 0.378 |
Circularity | 0.812 ± 0.130 | 0.781 ± 0.130 | 0.061 |
Roundness | 0.690 ± 0.104 | 0.662 ± 0.101 | 0.037 |
Axial ratio | 1.335 ± 0.191 | 1.358 ± 0.178 | 0.208 |