Choroidal structural changes correlate with severity of diabetic retinopathy in diabetes mellitus

This study aims to investigate the choroidal thickness and choroidal vascular density parameters and their correlation with severity of diabetic retinopathy (DR) in diabetes mellitus (DM) patients.

An observational cross-sectional study was conducted of 104 eyes, which were divided into 4 groups: Healthy controls (n = 38), DM with no DR eyes (n = 22), panretinal photocoagulation-untreated non-proliferative DR eyes (PRP-untreated NPDR eyes) (n = 24), PRP-untreated proliferative DR eyes (PRP-untreated PDR eyes) (n = 20). Optical coherence tomography (OCT) was performed. The total choroidal area (TCA), stromal area (SA), the luminal areas (LA) and the ratio of the luminal to choroidal area (L/C ratio) were compared. The choroidal parameters were also compared between PRP untreated and PRP-treated DR eyes.

The L/C ratio values were 0.68 ± 0.06 in controls and 0.63 ± 0.04 in DM eyes (P < 0.001). But there were no statistically significant differences in retinal nerve fiber layer (RNFL) thickness, retinal thickness and subfoveal choroidal thickness (SCT) measurements between the two groups (P = 0.407, P = 0.654 and P = 0.849; respectively). The vessel density values were significantly different in DM with no DR eyes, PRP-untreated NPDR eyes and PRP-untreated PDR eyes (P < 0.001 for SCT, TCA and SA). The L/C ratio values in the three groups were significant different (P = 0.019). There was no significant difference in SCT, TCA, LA, SA and the L/C ratio between PRP-untreated and PRP-treated DR eyes.

Eyes of patients with DM showed the L/C ratio decreased compared with normal controls. The SCT increased, but L/C ratio significantly decreased with severity of DR eyes compared with DM and normal eyes. Changes in the L/C ratio may predict DR development before they are otherwise evident clinically. Choroidal blood flow deficit can be an early pathologic change in DR.