Retinal Vascular Fractal Dimension Measurement and Its Influence from Imaging Variation: Results of Two Segmentation Methods

Abstract

Aim: To assess the influences of imaging variation (different photographic angle) on the measurement of retinal vascular fractal dimension (D_f), using two segmentation methods.

Materials and methods: Nonlinear orthogonal projection segmentation (International Retinal Imaging Software-Fractal, termed IRIS-Fractal) and curvature-based segmentation (Singapore Institute Vessel Assessment-Fractal, termed SIVA-Fractal) methods were used to measure D_f and were assessed for their reproducibility in detecting retinal vessels of 30 stereoscopic pairs of optic disc color images. Each pair was taken from the same eye with slightly different angles of incidence. Each photograph of the pairs had subtle variations in brightness between areas temporal and nasal to the optic disc.

Results: Intragrader reproducibility of D_f measurement was similar (intraclass correlation 0.81 and 0.96, respectively) for IRIS-Fractal and SIVA-Fractal. Within-image pair Pearson’s correlation coefficients (r) of D_f measurements were moderate for both methods (0.57 and 0.48, respectively).

Conclusions: Both nonlinear orthogonal projection and curvature-based retinal vessel segmentation methods were found to be sensitive to variations in image brightness, resulting from iris shadowing associated with different angle of photographic incidence.

KEYWORDS::

• Blue Mountains Eye Study
• Fractal dimension
• Methodology
• Photographic angle of incidence
• Retinal vasculature

ACKNOWLEDGMENTS

This work was supported by grants from the Australian National Health & Medical Research Council, Canberra Australia (Grant Nos. 153948, 211069, and 302068); Pfizer Australia (Cardiovascular Lipid Grant No. 2007); and Diabetes Australia Research Trust (Grant No. 2007). Preliminary findings of this study were presented in part at the 2008 Annual Meeting of the Association for Research in Vision and Ophthalmology, Fort Lauderdale, Florida, USA.

Declaration of interest: The authors report no conflicts of interest. The authors alone are responsible for the content and writing of the article.