Ophthalmology-Based Neuropathology Risk Factors: Diabetic Retinopathy is Associated with Deep Microinfarcts in a Community-Based Autopsy Study

Value Proposition of Retinal Imaging in Alzheimer's Disease Screening: A Review of Eight Evolving Trends

Alzheimer's disease (AD) is the leading cause of dementia worldwide. Current diagnostic modalities of AD generally focus on detecting the presence of amyloid β and tau protein in the brain (for example, positron emission tomography [PET] and cerebrospinal fluid testing), but these are limited by their high cost, invasiveness, and lack of expertise. Retinal imaging exhibits potential in AD screening and risk stratification, as the retina provides a platform for the optical visualization of the central nervous system in vivo, with vascular and neuronal changes that mirror brain pathology. Given the paradigm shift brought by advances in artificial intelligence and the emergence of disease-modifying therapies, this article aims to summarize and review the current literature to highlight 8 trends in an evolving landscape regarding the role and potential value of retinal imaging in AD screening.

Variations in Electronic Health Record-Based Definitions of Diabetic Retinopathy Cohorts: A Literature Review and Quantitative Analysis

Purpose

Use of the electronic health record (EHR) has motivated the need for data standardization. A gap in knowledge exists regarding variations in existing terminologies for defining diabetic retinopathy (DR) cohorts. This study aimed to review the literature and analyze variations regarding codified definitions of DR.

Design

Literature review and quantitative analysis.

Subjects

Published manuscripts.

Methods

Four graders reviewed PubMed and Google Scholar for peer-reviewed studies. Studies were included if they used codified definitions of DR (e.g., billing codes). Data elements such as author names, publication year, purpose, data set type, and DR definitions were manually extracted. Each study was reviewed by ≥ 2 authors to validate inclusion eligibility. Quantitative analyses of the codified definitions were then performed to characterize the variation between DR cohort definitions.

Main Outcome Measures

Number of studies included and numeric counts of billing codes used to define codified cohorts.

Results

In total, 43 studies met the inclusion criteria. Half of the included studies used datasets based on structured EHR data (i.e., data registries, institutional EHR review), and half used claims data. All but 1 of the studies used billing codes such as the International Classification of Diseases 9th or 10th edition (ICD-9 or ICD-10), either alone or in addition to another terminology for defining disease. Of the 27 included studies that used ICD-9 and the 20 studies that used ICD-10 codes, the most common codes used pertained to the full spectrum of DR severity. Diabetic retinopathy complications (e.g., vitreous hemorrhage) were also used to define some DR cohorts.

Conclusions

Substantial variations exist among codified definitions for DR cohorts within retrospective studies. Variable definitions may limit generalizability and reproducibility of retrospective studies. More work is needed to standardize disease cohorts.

Financial Disclosures

Proprietary or commercial disclosure may be found in the Footnotes and Disclosures at the end of this article.

Integrated multimodal cell atlas of Alzheimer's disease

Alzheimer's disease (AD) is the most common cause of dementia in older adults. Neuropathological and imaging studies have demonstrated a progressive and stereotyped accumulation of protein aggregates, but the underlying molecular and cellular mechanisms driving AD progression and vulnerable cell populations affected by disease remain coarsely understood. The current study harnesses single cell and spatial genomics tools and knowledge from the BRAIN Initiative Cell Census Network to understand the impact of disease progression on middle temporal gyrus cell types. We used image-based quantitative neuropathology to place 84 donors spanning the spectrum of AD pathology along a continuous disease pseudoprogression score and multiomic technologies to profile single nuclei from each donor, mapping their transcriptomes, epigenomes, and spatial coordinates to a common cell type reference with unprecedented resolution. Temporal analysis of cell-type proportions indicated an early reduction of Somatostatin-expressing neuronal subtypes and a late decrease of supragranular intratelencephalic-projecting excitatory and Parvalbumin-expressing neurons, with increases in disease-associated microglial and astrocytic states. We found complex gene expression differences, ranging from global to cell type-specific effects. These effects showed different temporal patterns indicating diverse cellular perturbations as a function of disease progression. A subset of donors showed a particularly severe cellular and molecular phenotype, which correlated with steeper cognitive decline. We have created a freely available public resource to explore these data and to accelerate progress in AD research at SEA-AD.org.

Diabetic Retinopathy and Dementia Association, Beyond Diabetes Severity

PURPOSE

To investigate whether associations between diabetic retinopathy (DR) and dementia and Alzheimer's disease (AD) remain significant after controlling for several measures of diabetes severity.

DESIGN

Retrospective cohort study.

METHODS

Adult Changes in Thought (ACT) is a prospective cohort study of adults aged ≥65 years, randomly selected and recruited from the membership rolls of Kaiser Permanente Washington, who are dementia free at enrollment and followed biennially until incident dementia. The ACT participants were included in this study if they had type 2 diabetes mellitus at enrollment or developed it during follow-up, and data were collected through September, 2018 (3516 person-years of follow-up). Diabetes was defined by ≥ 2 diabetes medication fills in 1 year. Diagnosis of DR was based on International Classification of Diseases Ninth and Tenth Revision codes. Estimates of microalbuminuria, long-term glycemia, and renal function from longitudinal laboratory records were used as indicators of diabetes severity. Alzheimer's disease and dementia were diagnosed using research criteria at expert consensus meetings.

RESULTS

A total of 536 participants (median baseline age 75 [interquartile range 71-80], 54% women) met inclusion criteria. Significant associations between DR >5 years duration with dementia (hazard ratio 1.81 [95% CI 1.23, 2.65]) and AD (1.80 [1.15, 2.82]) were not altered by adjustment for estimates of microalbuminuria, long-term glycemia, and renal function (dementia: 1.69 [1.14, 2.50]; AD: 1.73 [1.10, 2.74]).

CONCLUSIONS

Among people with type 2 diabetes, DR itself appears to be an important biomarker of dementia risk in addition to glycemia and renal complications.

Diabetic rats with high levels of endogenous dopamine do not show retinal vascular pathology

Purpose

Limited research exists on the time course of long-term retinal and cerebral deficits in diabetic rodents. Previously, we examined short term (4-8 weeks) deficits in the Goto-Kakizaki (GK) rat model of Type II diabetes. Here, we investigated the long-term (1-8 months) temporal appearance of functional deficits (retinal, cognitive, and motor), retinal vascular pathology, and retinal dopamine levels in the GK rat.

Methods

In GK rats and Wistar controls, retinal neuronal function (electroretinogram), cognitive function (Y-maze), and motor function (rotarod) were measured at 1, 2, 4, 6, and 8 months of age. In addition, we evaluated retinal vascular function (functional hyperemia) and glucose and insulin tolerance. Retinas from rats euthanized at ≥8 months were assessed for vascular pathology. Dopamine and DOPAC levels were measured via HPLC in retinas from rats euthanized at 1, 2, 8, and 12 months.

Results

Goto-Kakizaki rats exhibited significant glucose intolerance beginning at 4 weeks and worsening over time (p < 0.001). GK rats also showed significant delays in flicker and oscillatory potential implicit times (p < 0.05 to p < 0.001) beginning at 1 month. Cognitive deficits were observed beginning at 6 months (p < 0.05), but no motor deficits. GK rats showed no deficits in functional hyperemia and no increase in acellular retinal capillaries. Dopamine levels were twice as high in GK vs. Wistar retinas at 1, 2, 8, and 12 months (p < 0.001).

Conclusion

As shown previously, retinal deficits were detectable prior to cognitive deficits in GK rats. While retinal neuronal function was compromised, retinal vascular pathology was not observed, even at 12+ months. High endogenous levels of dopamine in the GK rat may be acting as an anti-angiogenic and providing protection against vascular pathology.

Association Between Diabetic Retinopathy, Brain Structural Abnormalities, and Cognitive Impairment for Accumulated Evidence in Observational Studies

PURPOSE

To evaluate the association between diabetic retinopathy (DR) and cerebral disease or cognitive impairment.

DESIGN

Systematic review and meta-analysis.

METHOD

The hypothesis was formulated prior to data collection. Cross-sectional studies and cohort studies that assessed the association between any measure of DR and cerebral small vessel disease or any type of cognitive impairment in diabetic participants were included. The data were independently extracted by two investigators. This systematic review and meta-analysis adhered to the Preferred Reporting Items for Systematic Reviews and Meta-analyses and Meta-analysis of Observational Studies in Epidemiology guidelines RESULTS: A total of 27 studies were included. The combined odds ratio of 5 cross-sectional/cohort studies that reported that the associations between DR and cerebral structural changes was 1.75 (95% confidence interval [CI]: 1.36-2.25). The combined hazard ratio of 4 cohort studies that examined the association between DR and cognitive impairment events was 1.47 (95% CI: 1.22-1.78). The combined odds ratio of 14 cross-sectional/cohort studies that examined the association between DR and different cognitive impairment events was 1.43 (95% CI: 1.06-1.93). The overall coefficient (β) of 4 studies that examined the relationship between DR and specific cognitive performance was 0.09 (95% CI: 0.00-0.18). Considering the quality of the data, we have performed subgroup analysis in studies scored >7 and studies scored ≤7, respectively, according to the Newcastle-Ottawa scale.

CONCLUSION

The present meta-analysis suggests that DR is associated with an increased risk of structural abnormalities in the brain and cognitive impairment. This association remained significant after adjusting for blood glucose, and the presence of hypertension, indicating that DR is an important danger signal for cerebral abnormalities.

Ophthalmic conditions associated with dementia risk: The Cardiovascular Health Study

INTRODUCTION

Ophthalmic conditions and dementia appear to overlap and may share common pathways, but research has not differentiated dementia subtypes.

METHODS

Diagnoses of cataracts, age-related macular degeneration (AMD), diabetic retinopathy (DR), and glaucoma were based on medical histories and International Classification of Diseases, Ninth Revision (ICD-9) codes for 3375 participants from the Cardiovascular Health Study. Dementia, including Alzheimer's disease (AD) and vascular dementia (VaD), was classified using standardized research criteria.

RESULTS

Cataracts were associated with AD (hazard ratio [HR] = 1.34; 95% confidence interval [CI] = 1.01-1.80) and VaD/mixed dementia (HR = 1.41; 95% CI = 1.02-1.95). AMD was associated with AD only (HR = 1.87; 95% CI = 1.13-3.09), whereas DR was associated with VaD/mixed dementia only (HR = 2.63; 95% CI = 1.10-6.27).

DISCUSSION

Differential associations between specific ophthalmic conditions and dementia subtypes may elucidate pathophysiologic pathways. Lack of association between glaucoma and dementia was most surprising from these analyses.

Protein and Imaging Biomarkers in the Eye for Early Detection of Alzheimer's Disease

Alzheimer's disease (AD) is one of the most common causes of dementia worldwide. Although no formal curative therapy exists for the treatment of AD, considerable research has been performed to identify biomarkers for early detection of this disease, and thus improved subsequent management. Given that the eye can be examined and imaged non-invasively with relative ease, it has emerged as an exciting area of research for evidence of biomarkers and to aid in the early diagnosis of AD. This review explores the current understanding of both protein and retinal imaging biomarkers in the eye. Herein, primary findings in the literature regarding AD biomarkers associated with the lens, retina, and other ocular structures are reviewed.

Altered spontaneous brain activity in patients with diabetic optic neuropathy: A resting-state functional magnetic resonance imaging study using regional homogeneity

BACKGROUND

Diabetes is a common chronic disease. Given the increasing incidence of diabetes, more individuals are affected by diabetic optic neuropathy (DON), which results in decreased vision. Whether DON leads to abnormalities of other visual systems, including the eye, the visual cortex, and other brain regions, remains unknown.

AIM

To investigate the local characteristics of spontaneous brain activity using regional homogeneity (ReHo) in patients with DON.

METHODS

We matched 22 patients with DON with 22 healthy controls (HCs). All subjects underwent resting-state functional magnetic resonance imaging. The ReHo technique was used to record spontaneous changes in brain activity. Receiver operating characteristic (ROC) curves were applied to differentiate between ReHo values for patients with DON and HCs. We also assessed the correlation between Hospital Anxiety and Depression Scale scores and ReHo values in DON patients using Pearson correlation analysis.

RESULTS

ReHo values of the right middle frontal gyrus (RMFG), left anterior cingulate (LAC), and superior frontal gyrus (SFG)/left frontal superior orbital gyrus (LFSO) were significantly lower in DON patients compared to HCs. Among these, the greatest difference was observed in the RMFG. The result of the ROC curves suggest that ReHo values in altered brain regions may help diagnose DON, and the RMFG and LAC ReHo values are more clinically relevant than SFG/LFSO. We also found that anxiety and depression scores of the DON group were extremely negatively correlated with the LAC ReHo values (r = -0.9336, P < 0.0001 and r = -0.8453,P < 0.0001, respectively).

CONCLUSION

Three different brain regions show ReHo changes in DON patients, and these changes could serve as diagnostic and/or prognostic biomarkers to further guide the prevention and treatment of DON patients.

Does Retinal Ganglion Cell Loss Precede Visual Field Loss in Glaucoma?

It is often said that substantial retinal ganglion cells are lost before glaucomatous damage is detected by standard automated perimetry. There are 4 key articles referenced to support this belief. To test the hypothesis that the 4 key articles are incorrectly cited, the publications in the first 6 months of 2019 that reference 1 or more of these 4 articles were examined. In particular, the degree to which the quotes from these 2019 publications accurately reflected the evidence in the 4 key articles was assessed. These quotes are inadequately supported by the data, and in some cases even by the conclusions found in the abstracts of the key articles. This is despite several review articles that have questioned the evidence in these key articles. Further, a case can be made that the evidence in the key articles better supports the opposite conclusion. That is, the data suggest that sensitivity loss can be seen on standard automated perimetry before retinal ganglion cells are missing.