Optical Coherence Tomography Angiography Fractal Dimension in Alzheimer’s Disease, Mild Cognitive Impairment and Cognitively Healthy Controls

Abstract

Purpose : Fractal dimension (FD), a metric ranging between 1 and 2 with higher values reflecting increased complexity of a vascular network, can be calculated from optical coherence tomography angiography (OCT-A) scans to distinguish eyes with retinal vascular changes from those without. We compared FD of 6x6 mm macular superficial capillary plexus OCT-A scans in subjects with Alzheimer’s disease (AD), mild cognitive impairment (MCI), and cognitively healthy controls. We also investigated how age and sex may correlate with FD among controls.

Methods : Zeiss Cirrus HD-5000 Angioplex OCT-A (software v11.0) was used to prospectively image nondiabetic adults with no ocular comorbidities aged ≥50 years with symptomatic AD or MCI, as well as age-matched cognitively healthy controls. 6x6 mm OCT-A scans with signal strength <7/10 or significant artifact were excluded. One eye per patient was randomly selected for analysis. FD was calculated using multifractal analysis after automated vessel segmentation. The Wilcoxon rank-sum test was used to compare FD across cohorts and compare FD between sexes among controls. Spearman’s correlation coefficient was used to explore association between FD and age among controls. P<0.05 was considered statistically significant.

Results : Demographic features and mean FD for each cohort are summarized in Table 1. Among controls, FD was significantly inversely correlated with age (Spearman’s correlation coefficient = -0.205; P =0.018) and trended toward being lower in males (P = 0.057). Across cohorts, FD was significantly lower in AD than controls (P = 0.046) and in AD than MCI (P = 0.018), but there was no difference between MCI and controls (P = 0.409). In subgroup analysis by sex, FD remained significantly lower in AD than MCI among females (P = 0.031). In subgroup analysis by age grouped by <70 years vs. ≥70 years, there was no difference in FD between cohorts.

Conclusions : AD may be associated with reduced superficial capillary plexus vascular complexity, as quantified by FD. Our analysis of one of the largest existing cohorts of older adult cognitively healthy subjects suggests that FD may decrease with age and be in lower in males, which should be accounted for when analyzing FD.

This is a 2020 ARVO Annual Meeting abstract.

 

Table 1. Demographics and fractal dimensions