By analysis of the microvessel, macrovascular ring, and microvessel density in superficial layer (Figure 4) and deep layer (Figure 5) between the two groups , we found that the vascular density of SMIR in the pterygium group was decreased significantly when compared to the healthy control group (P < 0.05, Figure 4A). Similarly, the vascular density of DTMI and DMIR in deep layer pterygium patients also decreased significantly (P < 0.05, Figure 5A) . However, MAR density was not significantly altered in either layer. Using the hemispheric partition and Early Treatment Diabetic Retinopathy Study (ETDRS) method for comparison, we found that the vascular density of SR, IR, and R in superficial layer was decreased significantly (P < 0.05, Figure 4B and 4C) , and the vascular density in SR, IR, and R in the deep layer decreased significantly (P < 0.05, Figure 5B and 5C) as well. Using the central annuli method for comparison, we found that the vascular density in region of SC1, SC2, and SC3 in the superficial layer was decreased significantly (P < 0.05, Figure 4D). For the deep retinal layers, the vascular density in the regions of DC2 and DC3 also decreased significantly (P < 0.05, Figure 5D). No statistically significant differences were observed in other regions (P> 05).
The retinal vessel density measured by OCTA showed the best sensitivity and specificity to differentiate pterygium from healthy control. In the superficial layer, the SC2 density had the highest positive likelihood ratios in the pterygium group, while SC1 showed the lowest negative likelihood ratio (Figure 6A). ROC analysis revealed that SC2 had the highest sensitivity and specificity with the ROC curve 0.85 (95% confidence interval [CI] = 0.72-0.98), and SC1 had the lowest sensitivity and specificity with the ROC curve 0.63 (95% CI of 0.44-0.82) (Figure 6A). Similarly, in the deep retinal layer, the DC2 density had the highest positive likelihood ratios in the pterygium group, while the IR showed the lowest negative likelihood ratio (Figure 6B). ROC analysis revealed that DC2 had the highest sensitivity and specificity with the ROC curve 0.85 (95% confidence interval [CI] = 0.72-0.98), and IR had the lowest sensitivity and specificity with the ROC curve 0.72 (95% CI of 0.54-0.89) (Figure 6B).
We next investigated the correlation among SMIR, SR, IR, SC1, SC2, and SC3 in the superficial retinal layer with disease course in pterygium group. In the pterygium group, the correlation coefficient of SMIR density and disease course was –0.7662 , and the correlation coefficient of the SR density with disease course was –0.6038. And the correlation coefficient of IR density with disease course was –0.6234, and the correlation coefficient of the SC1 density and disease course was –0.7762. Besides, the correlation coefficient of SC2 density with disease course was –0.7123, and the correlation coefficient of the SC3 density with disease course was –0.6615. No correlation in other region density with disease course was found (|r|<0.47, P>0.05). These results indicated that decreased macular density in superficial layer of SMIR, SR, IR, SCI, SC2 and SC3 might be negatively correlated with the disease course, suggesting that the longer the disease course, the lower vascular density in those regions.
Besides, we also analyzed the correlation between the vascular density of superficial retinal and the area size of pterygium. Our analyzed data showed that in the pterygium group, the correlation coefficient of SMIR density with the area size of pterygium was -0.9508, and the correlation coefficient of the SR density with the area size of pterygium was –0.8935. And the correlation coefficient of IR density with pterygium area size was –0.9359, and the correlation coefficient of the R density with the area size of pterygium was –0.6043. Besides, the correlation coefficient of SC1, SC2 and SC3 densities with the area size of pterygium was –0.8217, -0.8976 and -0.7757, respectively (Figure 8). No correlation in other region density with area size of pterygium was found (|r|<0.47, P>0.05). These results indicated that decreased macular density in superficial layer of SMIR, SR, IR, R, SCI, SC2 and SC3 might be negatively correlated with the area size of pterygium, suggesting that the bigger the area size of pterygium, the lower vascular density in those regions.
Furthermore, in deep retinal layer, we also analyzed the vascular densities of deep retinal (deep microvessels), and showed that in the pterygium group, the correlation coefficient of DTMI density with disease course was –0.7003, and the correlation coefficient of the DMIR density with disease course was –0.6901. And the correlation coefficient of SR density with disease course was –0.7795, and the correlation coefficient of the IR density with disease course was –0.7198. Besides, the correlation coefficient of R, DC2, and DC3 density with disease course was –0.7608, -7504 and -0.7195, respectively (Figure 9). No correlation in other region density with disease course was found (|r|<0.47, P>0.05). These results indicated that decreased macular density in deep layer of DTMI, DMIR, SR, IR, R, DC2, and DC3 might be negatively correlated to the disease course, suggesting that the longer the disease course, the lower vascular density in those regions.
Besides, we also analyzed the correlation between the vascular density of deep retinal and the area size of pterygium, and showed that in the pterygium group, the correlation coefficient of DTMI density with the area size of pterygium was -0.9563, and the correlation coefficient of the DMIR density with the area size of pterygium was –0.9508. And the correlation coefficient of SR density with pterygium area size was –0.8935, and the correlation coefficient of the IR density with the area size of pterygium was –0.9359. Besides, the correlation coefficient of R, DC2 and DC3 densities with the area size of pterygium was – 0.6043, -0.8976 and -0.7757, respectively (Figure 10). No correlation in other region density with area size of pterygium was found (|r|<0.47, P>0.05). These results indicated that decreased macular density in deep layer of DTMI, DMIR, SR, IR, R, DC2 and DC3 might be negatively correlated to the area size of pterygium, suggesting that the bigger the area size of pterygium, the lower vascular density in those regions.