Abstract
BackgroundOcular imaging receives much attention as a source of potential biomarkers for dementia. In the present study, we analyze these ocular biomarkers in cognitively impaired and healthy participants in a population aged over 90 years (= nonagenarian), and elucidate the effects of age on these biomarkers.MethodsFor this prospective cross-sectional study, we included individuals from the EMIF-AD 90+ study, consisting of a cognitively healthy (N = 67) and cognitively impaired group (N = 33), and the EMIF-AD PreclinAD study, consisting of cognitively healthy controls aged ≥60 (N = 198). Participants underwent Optical Coherence Tomography (OCT) and fundus photography of both eyes. OCT was used to asses total and individual inner retinal layer thickness in the macular region (Early Treatment Diabetic Retinopathy Study circles) as well as peripapillary retinal nerve fiber layer thickness, fundus images were analyzed with Singapore I Vessel Assessment to obtain 7 retinal vascular parameters. Values for both eyes were averaged. Differences in ocular biomarkers between the 2 nonagenarian groups were analyzed using linear regression, differences between the individual nonagenarian groups and controls were analyzed using generalized estimating equations.ResultsOcular biomarkers did not differ between the healthy and cognitively impaired nonagenarian groups. 19 out of 22 ocular biomarkers assessed in this study differed between either nonagenarian group and the younger controls.ConclusionThe ocular biomarkers assessed in this study were not associated with cognitive impairment in nonagenarians, making their use as a screening tool for dementing disorders in this group limited. However, ocular biomarkers were significantly associated with chronological age, which were very similar to those ascribed to occur in Alzheimer’s Disease.
Highlights
Ocular imaging receives much attention as a source of potential biomarkers for dementia
Both the healthy and the cognitive impairment (CI) nonagenarians differed significantly in multiple ocular biomarkers when compared to the younger control group, with most ocular parameters being lower in the nonagenarian groups. 4 out of 22 biomarkers assessed differed significantly between healthy nonagenarians and younger controls, 1 out of 22 differed between CI nonagenarians and younger controls, and 14 out of 22 differed between both CI and healthy nonagenarians compared to younger controls
A possible explanation for the lack of differences may be that other disorders that can have a profound effect on ocular biomarkers, are more prevalent in nonagenarians, and may obscure a possible neurodegenerative effect [24,25,26]. Another explanation can be that other aging related processes affect ocular biomarkers, again obscuring differences between the nonagenarian groups. We found that both nonagenarian groups showed large differences in ocular biomarkers, including total/ganglion cell layer (GCL)/inner plexiform layer (IPL) thickness in the macula, average and most individual segments pRNFL thickness and all retinal vascular parameters except tortuosity (Figs. 1 and 2, Table 3), when compared to younger healthy controls
Summary
Ocular imaging receives much attention as a source of potential biomarkers for dementia. We analyze these ocular biomarkers in cognitively impaired and healthy participants in a population aged over 90 years (= nonagenarian), and elucidate the effects of age on these biomarkers. The eye, and the retina, shares many similarities with the brain. Both are derived from the same embryological tissue and consist of a complex combination of neuronal tissue and glial cells [1, 2]. Studies have been performed on the diagnostic value of optical techniques used to examine the retina in AD, as these ocular markers may be less invasive and cheaper than most established biomarkers for brain diseases [3,4,5,6,7,8]. Studies have shown differences between individuals with and without dementia in the (micro)vascular state of their retinal vessels (such as vessel width, tortuosity and fractal dimension) through fundus photography, these results were sometimes contradicting [8,9,10,11]
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