Parafoveal vessel loss and correlation between peripapillary vessel density and cognitive performance in amnestic mild cognitive impairment and early Alzheimer's Disease on optical coherence tomography angiography

Abstract

Purpose: Patients with Alzheimer's Disease (AD) exhibit decreased retinal blood flow and vessel density (VD). However, it is not known whether these changes are also present in individuals with early AD (eAD) or amnestic type mild cognitive impairment (aMCI), an enriched pre-AD population with a higher risk for progressing to dementia. We performed a prospective case-control clinical study to investigate whether optical coherence tomography angiography (OCTA) parameters in the macula and disc are altered in those with aMCI and eAD.

Methods: This is a single center study of 32 participants. Individuals with aMCI/eAD (n = 16) were 1:1 matched to cognitively normal controls (n = 16). We evaluated OCTA images of the parafoveal superficial capillary plexus (SCP) and two vascular layers in the peripapillary region, the radial peripapillary capillary (RPC) and superficial vascular complex (SVC). Outcome vascular and structural parameters included VD, vessel length density (VLD), adjusted flow index (AFI) and structural retinal nerve fiber layer (RNFL) thickness. We compared these parameters between the two groups and examined the correlation between OCTA parameters and cognitive performance on the Montreal Cognitive Assessment (MoCA).

Results: Cognitively impaired participants demonstrated statistically significant decrease in parafoveal SCP VD and AFI as compared to controls, but no statistically significant difference in peripapillary parameters. Furthermore, we found a significant positive correlation between MoCA scores for the entire study cohort and both the parafoveal SCP VD and peripapillary RPC VLD.

Conclusion: OCTA shows significant decline in parafoveal flow and VD in individuals with early cognitive impairment related to AD, suggesting that these parameters could have potential utility as early disease biomarkers. In contrast, the presence of larger vascular channels in the peripapillary region may have obscured subtle capillary changes in that region. Overall, the correlation between vascular OCTA parameters and cognitive performance supports further OCTA studies in this population.

Conflict of interest statement

The authors have declared that no competing interests exist.

Figures

Fig 1. Optical coherence tomography angiography (OCTA) segmentation of the disc and macula.

(A) shows a 4.5 x 4.5mm2en face OCTA image of the radial peripapillary capillary (RPC) centered on the optic disc of a healthy control, and (D) shows the cross-section segmentation of the RPC. (B) shows the en face image of the superficial vascular complex (SVC) segmentation obtained from the same individual with (E) showing the cross-section of SVC. (C) shows 3.0 x 3.0mm2en face scan of the superficial capillary plexus (SCP) centered on the of the fovea of the same individual with (F) showing the cross-section segmentation of the SCP.

Fig 2. Parafoveal and peripapillary image analysis.

A healthy control’s angiograms show the superficial capillary plexus (SCP) of the macula with delineation of the parafovea between rings of 1.0mm and 3.0mm (A), after binarization of parafoveal vessels based on a background defined by the foveal avascular zone (B), and after skeletonizing all vessels to be one pixel wide (C). Bottom row shows the radial papillary capillary (RPC) layer of the same individual with the peripapillary area between rings of 2.0mm and 4.0mm centered on the optic disc and the superior quadrant of the peripapillary delineated in orange (D). Thresholding and binarization with the Phansalkar method in the peripapillary are shown (E). The large vessel masks in RPC (F) was removed from RPC images to obtain the microcapillary vessel density.