First peak fractal analysis of optical coherence tomography angiography in glaucomatous eyes

Abstract

Purpose : To evaluate fractal analysis box size resolution and self-similarity breakdown in box counting method of fractal analysis of optical coherence tomography angiography (OCTA) images in eyes with primary open angle glaucoma (POAG) or normal tension glaucoma (NTG) compared to control patients.

Methods : This retrospective study used OCTA images obtained on 40 eyes with POAG, 26 eyes with NTG, and 28 control eyes. OCTA images consisted of 4.5x4.5mm peripapillary scans obtained with the RTVue XR Avanti (Optovue Inc., Fremont, CA), standardized and binarized using ImageJ (NIH, Bethesda, MD). Fractal dimension by means of a box-counting algorithm used box sizes with increasing exponential factor of two with grid algorithm on Fractalyse (ThéMA, Besançon Cedex, France) was plotted against linear box dimension and first maximum (first peak) that represents the smallest box size resolution before breakdown of self-similarity. Statistical analysis was performed using one-way analysis of variance with post-hoc Tukey HSD.

Results : There was significant difference among control, POAG, and NTG groups (p=0.002), with POAG having larger box size (12.8±1.54) compared to control (8.0±0.0, p=0.008) and NTG groups (8.0±0.0, p<0.01). When further divided into early, moderate, and severe subgroups of POAG, there were significant differences between moderate POAG (16±5.06, p=0.03) versus control and severe POAG (16.57±3.19, p=0.001) versus control. There was also a significant difference between early POAG (9.2±1.2) versus severe POAG (p=0.006). Lastly, the NTG group showed a significant difference with moderate POAG (p=0.031) and severe POAG (p=0.001).

Conclusions : The first peak box size of fractal dimension as a function of increasing box size represents the smallest box size resolution prior to loss of uniformity of the vascular pattern’s fractal dimension. The differences in breakdown size among controls, POAG, and NTG suggest that this resolution is limited by and serves as an indicator for breakdown of self-similarity and reduced capillary density. Breakdown of self-similarity for POAG occurred at significantly higher resolution than that of controls or NTG, and more so for moderate to severe POAG subgroups, suggesting their increased loss of microvasculature and highlighting the potential of fractal analysis in establishing quantitative parameters for evaluation of glaucoma.

This is an abstract that was submitted for the 2017 ARVO Annual Meeting, held in Baltimore, MD, May 7-11, 2017.