May 31, 2019 Conference
Dr. Kyle Kovacs
Dr. Ron Adelman, Yale University Eye Center
Purpose: While the retinal vasculature has had its fractal dimension well studied, similar analysis of the choroidal vasculature has never been evaluated. This observational study evaluates the fractal dimension of choroidal vasculature using wide field ICG angiography. While retinal vasculature follows the model of diffusion limited aggregation, we hypothesize that choroidal vasculature more closely follows the percolation model.
Methods: Both wide-field indocyanine green (ICG) angiography and fluorescein angiography (FA) were retrospectively reviewed in 27 eyes. Both types of images were binarized using the NIH’s ImageJ software, then evaluated for fractal dimension using the box counting method in an automated fashion, centered at the optic disc, from the temporal edge of the macula to an equivalent distance nasally, using the FracLac application for ImageJ. These values were then compared using a Student’s T test.
Results: The average fractal dimension of choroidal vasculature by ICG was 1.847. The fractal dimension of retinal vasculature by FA with these techniques was on average 1.703, in close agreement with previous literature, and statistically significantly different from the fractal dimension of ICG (p < 0.05).
Conclusions: While the fractal dimension of the retinal vasculature observed here closely agrees with the model for diffusion limited aggregation, which theoretically approaches 1.7, the high fractal dimension of the choroidal vasculature more closely agrees with the percolation model, with or without trapping, with predicted values of 1.82 and 1.89, respectively. Regardless, this analysis fits with the previously understood model that embryologic choroidal development follows the spreading pigmentation of in the retinal pigment epithelium, which may fit with a percolation model, in contrast to retinal vascular development that may be induced by local metabolic needs, fitting with the aggregation model.