Eye test can help detect early Alzheimer’s
Parafoveal flow and vessel density (VD) are significantly reduced in individuals with early cognitive impairment and may serve as early biomarkers for Alzheimer’s disease (AD), according to a recent study.
“Taken together, our results show parafoveal hypoperfusion in subjects with early cognitive impairment as well as a correlation between cognitive performance and vascular density in the macula and disc. These relationships support the potential for retinal capillary imaging to serve as a biomarker for early cognitive impairment,” said researchers.
Of the 32 study participants, 13 had amnestic type mild cognitive impairment (aMCI), three had early AD (eAD) and 16 were cognitively healthy and were designated as controls. Cognitive performance, as measured by the Montreal Cognitive Assessment (MoCA), was worse in the aMCI/eAD group. All participants had best-corrected visual acuity ≥20/40 and intraocular pressure ≤21 mmHg. [PLoS One 2019;14:e0214695]
Parafoveal vessel density in the superficial capillary plexus (SCP) layer was significantly lower in the aMCI/eAD participants relative to the controls (40.67±5.23 percent vs 44.50±4.11 percent; p=0.028). A similar finding was reported for the adjusted flow index at the same layer (0.376±0.041 vs 0.407±0.037; p=0.047).
No such effect was observed for the parafoveal vessel length density (VLD) at the SCP (16.41±3.60 percent vs 16.73±2.64 percent; p=0.722).
Similarly, between-group differences were null in other layers of the disc. For instance, both VD (43.16±4.88 percent vs 45.00±3.58 percent; p=0.251) and VLD (16.72±20.0 percent vs 17.30±141 percent; p=0.486) at the superficial vascular plexus were statistically comparable between the aMCI/eAD and control groups.
The same was true for global (p=0.187), superior (p=0.624) and capillary (p=0.056) VD and VLD (p=0.156) at the radical peripapillary capillary (RPC).
However, Pearson and Spearman correlation analysis revealed a significant link between MoCA scores and VD at the parafoveal SCP (R, 0.361; p=0.043) and VLD at the RPC (R, 0.463; p=0.010). This suggests that capillary density in the macula and optic nerve may be correlated with cognitive performance, researchers explained.
“Our data indicate that vessel dropout in the inner retina may occur as early as in the eAD and aMCI stage,” they added. “We postulate that the lack of significant findings in the disc compared to findings in the macula could be related to our small sample size or anatomical differences between the two areas.”
In the present study, optical coherence tomography angiography was used for the acquisition and analysis of images of the macula and the whole retina. Photos were automatically segmented to delineate the layers, such as the RPC and SCP.
“Future studies with larger samples and longitudinal design will be important to elucidate whether these angiographic biomarkers have sufficient sensitivity and specificity to screen for cognitive impairment, monitor disease progression, or predict future cognitive decline,” said researchers, noting that such an approach would have great clinical impact due to the invasiveness of current methods of prediction.
“There is also currently a largely unmet need for validated, noninvasive tools that identify subjects with early impairment and classify them according to their risk of progression. These tools would significantly facilitate clinical trials and research studies, allowing early therapeutic interventions to be targeted to the subjects who are most at-risk,” they added.