Fractal analysis of retinal vessels suggests that a distinct vasculopathy causes lacunar stroke

Abstract

Objectives: Lacunar strokes account for 25% of all ischemic strokes and may represent the cerebral manifestation of a systemic small vessel vasculopathy of unknown etiology. Altered retinal vessel fractal dimensions may act as a surrogate marker for diseased cerebral vessels. We used a cross-sectional study to investigate fractal properties of retinal vessels in lacunar stroke.

Methods: We recruited patients presenting with lacunar stroke and patients with minor cortical stroke as controls. All patients were examined by a stroke expert and had MRI at presentation. Digital retinal photographs were taken of both eyes. Monofractal and multifractal analyses were performed with custom-written semiautomated software.

Results: We recruited 183 patients. Seventeen were excluded owing to poor photographic quality, leaving 166 patients (86 with lacunar and 80 with cortical stroke). The mean age was 67.3 years (SD 11.5 years). The patients with lacunar stroke were younger but the prevalence of diabetes, hypertension, and white matter hyperintensities did not differ between the groups. The mean Dbox (monofractal dimension) was 1.42 (SD 0.02), the mean D0 (multifractal dimension) 1.67 (SD 0.03). With multivariate analysis, decreased Dbox and D0 (both representing decreased branching complexity) were associated with increasing age and lacunar stroke subtype after correcting for hypertension, diabetes, stroke severity, and white matter hyperintensity scores.

Conclusions: Lacunar stroke subtype and increasing age are associated with decreased fractal dimensions, suggesting a loss of branching complexity. Further studies should concentrate on longitudinal associations with other manifestations of cerebral small vessel disease.

Figure 1 Retinal images showing the processing, segmentation, and skeletonization steps Top left image (A) is the original color image which is processed to grayscale (top right B) which is then segmented to produce the bottom left image (C). Finally, this image is skeletonized to produce the bottom right image (D) upon which fractal analyses are based.

Figure 2 Segmented vessel maps of 2 retinal vascular trees The image on the left (A) was the highest fractal dimension in this study (multifractal D0 1.736) and the image on the right (B) the lowest fractal dimension (multifractal D0 1.622). Note these images are segmented vessel maps for illustration purposes. We used the skeletonized images to actually perform the fractal analysis.