Quantification of retinal non-perfusion in eyes with diabetic retinopathy to study the association with retinal neovascularisation: INSPIRED study report 3.

BACKGROUND/AIMS: To characterise the distribution of retinal non-perfusion and its relationship with neovascularisation elsewhere (NVE) and visual acuity (VA) in referable diabetic retinopathy (DR) using ultra-widefield fluorescein angiography (UWFA).

METHODS

Eyes with treatment-naïve moderately severe non-proliferative DR (NPDR) to proliferative diabetic retinopathy (PDR) (Diabetic Retinopathy Severity Scale (DRSS) level 43-60) with available UWFA were included in this study. Total and zonal non-perfusion and NVE area were manually delineated across concentric zones (central 1-10 mm, extended posterior >10-20 mm and mid-peripheral >20-30 mm diameter). The Non-Perfusion Index (NPI) was calculated as the ratio of non-perfused area to total area per zone. Associations between NPI, NVE, DR severity and best-recorded VA (BRVA) were assessed.

RESULTS

A total of 133 eyes (60.9% NPDR, 39.1% PDR) were analysed. The highest NPI occurred in the mid-periphery (20-30 mm) and posterior pole (15-20 mm) zones, with nasal preponderance. NVE was most frequently observed in the posterior pole (66%) and nasal quadrants. Central and mid-peripheral NPI correlated with NVE area in corresponding zones, showing quadrant-specific associations. Receiver operating characteristic analysis identified a total NPI threshold of 0.23 to differentiate PDR from NPDR (area under the curve=0.798), with the lowest threshold in the superior quadrant. Neither NPI nor NVE area correlated with BRVA.

CONCLUSION

NVE represents a localised response to adjacent ischaemia predominantly affecting the nasal and extended posterior retina. NPI threshold of 0.23 distinguishes proliferative from non-proliferative stages, with the superior quadrant showing greater susceptibility to NVE at lower ischaemic levels. No significant correlation found between NPI, NVE area and visual acuity.