Abstract
PurposeTo quantify vessel tortuosity and fractal dimension of the superficial capillary plexus (SCP) of the macula in different stages of diabetic retinopathy (DR), and following panretinal photocoagulation (PRP) using optical coherence tomography angiography (OCTA).Methods75 eyes of 75 subjects were divided into five groups; healthy controls, diabetes with no clinical DR, non-proliferative diabetic retinopathy (NPDR), proliferative diabetic retinopathy (PDR) and patients who received PRP for PDR (PDR+PRP).For vessel tortuosity, SCP slabs from 3x3 mm macular OCTA scans were processed using imageJ (NIH, USA), where large perifoveal vessels were traced and their length was measured with tortuosity calculated as the ratio between the actual length and the straight Euclidean length. For fractal dimension, SCP slabs were processed and imported to Fractalyse (ThéMA, France), where box-counting analyses produced fractal dimension values.ResultsWe found a significant difference in vessel tortuosity and fractal dimension between the five groups (one-way ANOVA, p < 0.001both). NPDR and PDR had significantly more tortuous vessels and lower fractal dimension compared to healthy controls (Tukey HSD: p = 0.02, 0.015,0.015 and <0.001, respectively). Fractal dimension was also significantly lower in NPDR and PDR compared to eyes with no clinical DR (p <0.001 both), and in PDR compared to NPDR (p = 0.014). Following PRP, vessel tortuosity was significantly lower and fractal dimension was higher in PDR+PRP compared to PDR (p = 0.001 and 0.031, respectively).ConclusionsWe used macular OCTA scans to demonstrate significantly higher perifoveal large vessel tortuosity, and lower fractal dimension in NPDR and PDR compared to healthy controls. Vessel tortuosity shows more dramatic normalization than fractal dimension and could be explored as a sensitive marker for successful PRP.
Highlights
Retinal vessel tortuosity and retinal vascular fractal dimension are global measures of retinal vascular geometry that have been studied intensely.[1,2,3] Increased vessel tortuosity is thought to reflect an increase in the hydrostatic pressure as a response to autoregulatory arteriolar dilatation caused by tissue hypoxia.[4]
We found a significant difference in vessel tortuosity and fractal dimension between the five groups
non-proliferative diabetic retinopathy (NPDR) and proliferative diabetic retinopathy (PDR) had significantly more tortuous vessels and lower fractal dimension compared to healthy controls (Tukey Honest Significant Difference (HSD): p = 0.02, 0.015,0.015 and
Summary
Retinal vessel tortuosity and retinal vascular fractal dimension are global measures of retinal vascular geometry that have been studied intensely.[1,2,3] Increased vessel tortuosity is thought to reflect an increase in the hydrostatic pressure as a response to autoregulatory arteriolar dilatation caused by tissue hypoxia.[4]. The impact of diabetes on retinal vessel tortuosity has been studied extensively in literature. [1, 7,8,9] Higher HbA1c has been associated with increased arteriolar tortuosity in type 1 diabetic patients with non-proliferative diabetic retinopathy.[1] greater arteriolar tortuosity has been associated with a higher incidence of diabetic retinopathy (DR), as well as grade 1 nephropathy.[9,10,11,12] Large retinal vessels were more tortuous in diabetic eyes compared to healthy controls.[7, 13] One study went as far as to suggest that increased vessel tortuosity and elongation may predict the development of diabetic macular edema (DME).[5]
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