The Superficial and Deep Vascular Complexes are Damaged to Different Extents in Advanced Stages of Diabetic Retinopathy

Purpose: To identify the extent of damage to the superficial vascular complex (SVC) and deep vascular complex (DVC) as the stage of diabetic retinopathy (DR) increases. Methods: Subjects were divided into four groups: patients with type 2 diabetes without DR (Group 1), those with mild to moderate nonproliferative DR (NPDR) (Group 2), those with severe to very severe NPDR (Group 3), and those with proliferative DR (PDR) (Group 4). The vessel densities (VDs) of the SVC (SVD) and DVC (DVD) and their ratios were compared. Linear regression analyses were used to identify factors associated with the SVD/DVD ratio. Results: The SVDs were 25.5 ± 6.1, 25.1 ± 7.0, 24.5 ± 9.0, and 21.6 ± 6.9 % (P = 0.048); the DVDs 25.6 ± 5.3, 23.0 ± 7.0, 22.3 ± 8.8, and 17.5 ± 5.0 % (P < 0.001); and the SVD/DVD ratios 1.00 ± 0.16, 1.12 ± 0.20, 1.14 ± 0.33, and 1.24 ± 0.27 (P < 0.001) in Groups 1-4, respectively. In multivariate analysis, DR severity (B = 7.16, P < 0.001) and the HbA1c level (B = 1.57, P = 0.042) were significantly associated with the SVD/DVD ratio. Conclusions: Both the SVD and DVD tended to decrease in the advanced stages of DR, and the SVD/DVD ratio increased, indicating more severe damage to the DVC than the SVC. The ratio was positively associated with the HbA1c level, indicating a significant relationship between that level and DVD rather than SVD damage.