Association of cognitive function with Neurofilament light chain in the aqueous humor of human eye

Applications of Digital Enzyme-Linked Immunosorbent Assays in Ophthalmology

Digital enzyme-linked immunosorbent assays (dELISAs) very sensitively detect biomarkers that cannot be measured using traditional methods. The molecules are confined within a small volume, their counts accurately computed, and the results rapidly delivered. Digital ELISAs find many applications. In recent years, such ELISAs have become increasingly used to aid ophthalmological diagnoses and treatments, and have revolutionized the field. This article reviews the applications of dELISAs in clinical practice, especially in the sphere of ophthalmology.

Neurodegenerative biomarkers in different chambers of the eye relative to plasma: an agreement validation study

BACKGROUND

Protein biomarkers have been broadly investigated in cerebrospinal fluid and blood for the detection of neurodegenerative diseases, yet a clinically useful diagnostic test to detect early, pre-symptomatic Alzheimer's disease (AD) remains elusive. We conducted this study to quantify Aβ40, Aβ42, total Tau (t-Tau), hyperphosphorylated Tau (ptau181), glial fibrillary acidic protein (GFAP) and neurofilament light chain (NfL) in eye fluids relative to blood.

METHODS

In this cross-sectional study we collected vitreous humor, aqueous humor, tear fluid and plasma in patients undergoing surgery for eye disease. All six biomarkers were quantitatively measured by digital immunoassay. Spearman and Bland-Altman correlation analyses were performed to assess the agreement of levels between ocular fluids and plasma.

RESULTS

Seventy-nine adults underwent pars-plana vitrectomy in at least one eye. Of the 79, there were 77 vitreous, 67 blood, 56 tear fluid, and 51 aqueous samples. All six biomarkers were quantified in each bio-sample, except GFAP and NfL in tear fluid due to low sample volume. All six biomarkers were elevated in vitreous humor compared to plasma samples. T-Tau, ptau181, GFAP and NfL were higher in aqueous than in plasma, and t-Tau and ptau181 concentrations were higher in tear fluid than in plasma. Significant correlations were found between Aβ40 in plasma and tears (r = 0.5; p = 0.019), t-Tau in plasma and vitreous (r = 0.4; p = 0.004), NfL in plasma and vitreous (r = 0.3; p = 0.006) and plasma and aqueous (r = 0.5; p = 0.004). No significant associations were found for Aβ42, ptau181 and GFAP among ocular fluids relative to plasma. Bland-Altman analysis showed aqueous humor had the closest agreement to plasma across all biomarkers. Biomarker levels in ocular fluids revealed statistically significant associations between vitreous and aqueous for t-Tau (r = 0.5; p = 0.001), GFAP (r = 0.6; p < 0.001) and NfL (r = 0.7; p < 0.001).

CONCLUSION

AD biomarkers are detectable in greater quantities in eye fluids than in plasma and show correlations with levels in plasma. Future studies are needed to assess the utility of ocular fluid biomarkers as diagnostic and prognostic markers for AD, especially in those at risk with eye disease.

The risk of dementia or cognitive impairment in patients with cataracts: a systematic review and meta-analysis

OBJECTIVES

The aim of this study was to investigate whether cataract disease is associated with the risk of developing dementia or cognitive impairment.

METHODS

A systematic search of the literature in PubMed, the Extracts Database (Embase), the Cochrane Library and the Web of Science databases was performed from the inception data of each database until 1 September 2022. Sensitivity analyses were performed to assess the robustness and reliability of the overall findings. All extracted data were statistically analyzed using Stata software v.16.0. Publication bias was assessed using funnel plots and the Egger test.

RESULTS

There were 11 publications included in this study, which consisted of 489,211participants, spanning 10 countries from 2012 to 2022. Aggregation suggested that cataracts were associated with cognitive impairment (odds ratio [OR] = 1.32; 95% CI: 1.21-1.43; I 2 = 45.4.%; p = 0.000). The presence of cataracts is significantly associated with an increased risk of developing all-cause dementia (relative risk [RR] = 1.17; 95% CI: 1.08-1.26; I2 = 0.0%; p = 0.000). In subgroup analyses, having cataracts may increase the risk of Alzheimer's disease (hazard ratio [HR] = 1.28; 95% CI: 1.13-1.45; I2 = 0.0%; p = 0.000) and vascular dementia (HR = 1.35; 95% CI = 1.06-1.73; I2 = 0.0%, p = 0.015). The data from the Egger's test showed no significant evidence of publication bias.

CONCLUSIONS

Cataracts are associated with the risk of cognitive impairment and dementia, including Alzheimer's disease, and vascular dementia.

Aqueous and Plasma Levels of Phosphorylated Tau 181 in Individuals with Normal Cognition

Background

Plasma and cerebrospinal fluid (CSF) levels of p-tau181 have been associated with Alzheimer's disease (AD). The retina and vitreous have shown measurable quantities of phosphorylated tau 181 (p-tau181). The aqueous humor, which can be collected during cataract surgery, may have measurable concentrations of p-tau181.

Objective

To determine whether p-tau181 is detectable in the aqueous humor and if so, whether it is associated with other measures that might be consistent with AD such as higher plasma p-tau181 concentration and lower Montreal Cognitive Assessment (MoCA-BLIND version 7.1) score.

Methods

Aqueous humor samples, blood samples, and MoCA-BLIND scores were collected from patients who did not carry a clinical diagnosis of cognitive impairment at the time of cataract surgery. Aqueous p-tau181 concentrations and plasma p-tau181 concentrations were then measured using ultra-sensitive single-molecule assay ELISA technology. A rank-transformed mixed-effects multivariate regression model was used to determine associations between aqueous concentrations, plasma concentrations, and MoCA-BLIND scores.

Results

16 eyes of 16 participants were enrolled with an average age of 71.6. Average MoCA-BLIND score was 20.6/22, average aqueous p-tau181 concentration was 6.4 pg/mL, and average plasma p-tau181 concentration was 3.1 pg/mL. Higher plasma p-tau181 was significantly associated with higher aqueous p-tau181 (p = 0.02). Aqueous p-tau181 and plasma p-tau181 were negatively associated with MoCA-BLIND scores (p = 0.005 and p = 0.001 respectively) in these patients.

Conclusions

Aqueous p-tau181 is positively correlated with plasma p-tau181 and is negatively correlated with MoCA-BLIND scores. Further study in individuals with mild cognitive impairment or AD characterized by cerebrospinal fluid and volumetric MRI metrics may yield further insights.