Retinal thickness correlates with parietal cortical atrophy in early-onset Alzheimer's disease and controls

Reexamine the link between retinal layer thickness and cognitive function after correction of axial length: the Beijing Eye Study 2011

PURPOSE

To investigate the relationship between retinal layer thickness and cognitive function in elderly Chinese, accounting for the influence of axial length.

METHODS

The participants of the Beijing Eye Study 2011 which is a population-based cross-sectional study without any retinal or optic nerve disease underwent a series of ocular examinations including spectral-domain optical coherence tomography (OCT) of the retina. Using a multiple-surface OCT segmentation algorithm, the retina was automatically segmented into 9 layers. Cognitive function was evaluated applying the Mini Mental Statement Examination (MMSE). Cognitive impairment was defined as an MMSE score < 26.

RESULTS

The study included 2067 participants (56.7% women) (2067 eyes) with a mean age of 61.4 ± 8.4 years. After adjusting for age, gender and axial length, a lower cognitive function was related with a thinning of the ganglion cell layer (GCL) (P = 0.029, B = 0.04) and photoreceptor outer segment layer (POS) (P = 0.042, B = 0.04), while the retinal nerve fiber layer (RNFL) thickness (P = 0.144) was not significantly associated with the cognitive function score. For every unit decrease in MMSE score, the GCL and POS thickness separately decreased by 0.06 µm (95%CI: 0.01 µm, 0.12 µm), and 0.05 µm (95%CI: 0.002 µm, 0.10 µm). As compared with cognitively normal participants, those with cognitive impairment had a significantly thinner GCL (P = 0.019, OR = 1.04), and POS (P = 0.022, OR = 1.04) in multivariate logistic regression.

CONCLUSION

After adding axial length as dependence in multivariate analysis, cognitive impairment was not significantly associated with the thickness of RNFL, while the association between a lower cognitive function score and thinner GCL and POS was statistically associated in current study.

Retinal Microstructural and Microvascular Changes in Alzheimer Disease: A Review

"The eyes are a window to the brain," prompting the investigation of whether retinal biomarkers can indicate Alzheimer disease (AD) and cognitive impairment. AD is a neurodegenerative condition with a lengthy preclinical phase where pathologic changes in the central nervous system (CNS) occur before clinical symptoms. Mild cognitive impairment (MCI) often precedes AD. As part of the CNS, the retina exhibits similar pathologic changes related to AD as those seen in the brains of patients with MCI. Noninvasive imaging technologies such as optical coherence tomography (OCT) and optical coherence tomography angiography (OCTA) allow high-resolution visualization of the retina, providing an opportunity to screen and monitor AD noninvasively. In this review, we summarize the relationship between AD and retinal pathology detected by OCT and OCTA. The most common findings in patients with AD include peripapillary retinal nerve fiber layer thinning, decreased macular thickness, an enlarged foveal avascular zone, and decreased vascular densities in the superficial and deep capillary plexuses. These retinal changes correlate with magnetic resonance imaging (MRI) findings of cerebral atrophy, positron emission tomography (PET) findings of increased amyloid load, and neuropsychological testing results suggesting cognitive dysfunction. We conclude that retinal microstructural and microvascular abnormalities may serve as biomarkers for the early detection and clinical monitoring of AD and as tools for evaluating potential treatment effects. Future studies should focus on standardizing protocols for in vivo ophthalmic imaging to measure retinal pathology in AD and MCI.

Association of lamina cribrosa thickness and hippocampal volume in Alzheimer's disease patients

BACKGROUND

 Alzheimer's disease (AD) is the most common cause of dementia and affects a large portion of the elderly population worldwide.

OBJECTIVE

 To analyze the relationship between lamina cribrosa thickness (LCT) and hippocampal volume in patients with AD and mild cognitive impairment (MCI).

METHODS

 The sample in the present study consisted of 20 recently diagnosed MCI patients, 20 recently diagnosed AD patients, and 20 matched healthy volunteers. Every patient underwent magnetic resonance imaging (MRI) scans. The VolBrain software (open-access platform for MRI brain analysis) was used to calculate the hippocampal volume. Optical coherence tomography was performed to measure the LCT. Analysis of variance and Pearson chi-squared tests were employed to assess the results.

RESULTS

 The lowest total hippocampal volume (p < 0.05) was in the AD group, which was 6.14 ± 0.66 mm3, while in the control group, it was 7.7 ± 9.65 mm3, and 6.69 ± 0.46 mm3 in the MCI group. In comparison to the rest of the groups, in the AD group, the LCT was the thinnest (202.17 ± 16.35 µm). As per the results of the study population as a whole, low hippocampal volume causes low LCT, which shows an important relationship (r: 0.41; p < 0.05).

CONCLUSION

 The current findings present evidence of the relationship between hippocampal volume and LCT in patients with AD and MCI.

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.

Shared whole environmental etiology between Alzheimer's disease and age-related macular degeneration

The comorbidity of Alzheimer's disease (AD) and age-related macular degeneration (AMD) has been established in clinical and genetic studies. There is growing interest in determining the shared environmental factors associated with both conditions. Recent advancements in record linkage techniques enable us to identify the contributing factors to AD and AMD from a wide range of variables. As such, we first constructed a knowledge graph based on the literature, which included all statistically significant risk factors for AD and AMD. An environment-wide association study (EWAS) was conducted to assess the contribution of various environmental factors to the comorbidity of AD and AMD based on the UK biobank. Based on the conditional Q-Q plots and Bayesian algorithm, several shared environmental factors were identified, which could be categorized into the domains of health condition, biological sample parameters, body index, and attendance availability. Finally, we generated a shared etiology landscape for AD and AMD by combining existing knowledge with our novel findings.

Correlation between serum biomarkers, brain volume, and retinal neuronal loss in early-onset Alzheimer's disease

PURPOSE

To compare the peripapillary retinal nerve fiber layer (pRNFL), retinal nerve fiber layer (RNFL), and ganglion cell complex (GCC) thickness measurement in early-onset Alzheimer's disease (EOAD) and controls using spectral domain optical coherence tomography (SD-OCT). We also assessed the relationship between SD-OCT measurements and cognitive measures, serum biomarkers for Alzheimer's disease (AD), and cerebral microstructural volume.

METHODS

pRNFL, RNFL, and GCC thicknesses were measured in 43 EOAD and 42 controls using SD-OCT. Montreal Cognitive Assessment (MoCA) and Mini-Mental State Examination (MMSE) were used to assess cognitive status, magnetic resonance imaging (MRI) tool was used to quantify cerebral microstructural volume, and serum biomarkers were quantified from peripheral blood.

RESULTS

EOAD patients had thinner pRNFL (P < 0.001), RNFL (P = 0.008), and GCC (P = 0.018) thicknesses compared to controls after adjusting for multiple factors. pRNFL thickness correlated (P = 0.016) with serum t-tau level. Serum Aβ42 (P < 0.05) concentration correlated with RNFL thickness. Importantly, occipital lobe volume (P = 0.010) correlated with GCC thicknesses in EOAD patients.

CONCLUSION

Our findings suggest that retinal thickness may be useful markers for assessing neurodegenerative process in EOAD.

Macular vessel density in the superficial plexus is not a proxy of cerebrovascular damage in non-demented individuals: data from the NORFACE cohort

INTRODUCTION

Optical coherence tomography angiography (OCT-A) is a novel tool that allows the detection of retinal vascular changes. We investigated the association of macular vessel density (VD) in the superficial plexus assessed by OCT-A with measures of cerebrovascular pathology and atrophy quantified by brain magnetic resonance imaging (MRI) in non-demented individuals.

METHODS

Clinical, demographical, OCT-A, and brain MRI data from non-demented research participants were included. We analyzed the association of regional macular VD with brain vascular burden using the Fazekas scale assessed in a logistic regression analysis, and the volume of white matter hyperintensities (WMH) assessed in a multiple linear regression analysis. We also explored the associations of macular VD with hippocampal volume, ventricle volume and Alzheimer disease cortical signature (ADCS) thickness assessed in multiple linear regression analyses. All analyses were adjusted for age, sex, syndromic diagnosis and cardiovascular variables.

RESULTS

The study cohort comprised 188 participants: 89 with subjective cognitive decline and 99 with mild cognitive impairment. No significant association of regional macular VD with the Fazekas categories (all, p > 0.111) and WMH volume (all, p > 0.051) were detected. VD in the nasal quadrant was associated to hippocampal volume (p = 0.007), but no other associations of macular VD with brain atrophy measures were detected (all, p > 0.05).

DISCUSSION

Retinal vascular measures were not a proxy of cerebrovascular damage in non-demented individuals, while VD in the nasal quadrant was associated with hippocampal atrophy independently of the amyloid status.

A Systematic Review on Retinal Biomarkers to Diagnose Dementia from OCT/OCTA Images

Background

Traditional methods for diagnosing dementia are costly, time-consuming, and somewhat invasive. Since the retina shares significant anatomical similarities with the brain, retinal abnormalities detected via optical coherence tomography (OCT) and OCT angiography (OCTA) have been studied as a potential non-invasive diagnostic tool for neurodegenerative disorders; however, the most effective retinal changes remain a mystery to be unraveled in this review.

Objective

This study aims to explore the relationship between retinal abnormalities in OCT/OCTA images and cognitive decline as well as evaluating biomarkers' effectiveness in detecting neurodegenerative diseases.

Methods

A systematic search was conducted on PubMed, Web of Science, and Scopus until December 2022, resulted in 64 papers using agreed search keywords, and inclusion/exclusion criteria.

Results

The superior peripapillary retinal nerve fiber layer (pRNFL) is a trustworthy biomarker to identify most Alzheimer's disease (AD) cases; however, it is inefficient when dealing with mild AD and mild cognitive impairment (MCI). The global pRNFL (pRNFL-G) is another reliable biomarker to discriminate frontotemporal dementia from mild AD and healthy controls (HCs), moderate AD and MCI from HCs, as well as identifing pathological Aβ42/tau in cognitively healthy individuals. Conversely, pRNFL-G fails to realize mild AD and the progression of AD. The average pRNFL thickness variation is considered a viable biomarker to monitor the progression of AD. Finally, the superior and average pRNFL thicknesses are considered consistent for advanced AD but not for early/mild AD.

Conclusions

Retinal changes may indicate dementia, but further research is needed to confirm the most effective biomarkers for early and mild AD.

The association between retina thinning and hippocampal atrophy in Alzheimer's disease and mild cognitive impairment: a meta-analysis and systematic review

Introduction

The retina is the "window" of the central nervous system. Previous studies discovered that retinal thickness degenerates through the pathological process of the Alzheimer's disease (AD) continuum. Hippocampal atrophy is one of the typical clinical features and diagnostic criteria of AD. Former studies have described retinal thinning in normal aging subjects and AD patients, yet the association between retinal thickness and hippocampal atrophy in AD is unclear. The optical coherence tomography (OCT) technique has access the non-invasive to retinal images and magnetic resonance imaging can outline the volume of the hippocampus. Thus, we aim to quantify the correlation between these two parameters to identify whether the retina can be a new biomarker for early AD detection.

Methods

We systematically searched the PubMed, Embase, and Web of Science databases from inception to May 2023 for studies investigating the correlation between retinal thickness and hippocampal volume. The Newcastle-Ottawa Quality Assessment Scale (NOS) was used to assess the study quality. Pooled correlation coefficient r values were combined after Fisher's Z transformation. Moderator effects were detected through subgroup analysis and the meta-regression method.

Results

Of the 1,596 citations initially identified, we excluded 1,062 studies after screening the titles and abstract (animal models, n = 99; irrelevant literature, n = 963). Twelve studies met the inclusion criteria, among which three studies were excluded due to unextractable data. Nine studies were eligible for this meta-analysis. A positive moderate correlation between the retinal thickness was discovered in all participants of with AD, mild cognitive impairment (MCI), and normal controls (NC) (r = 0.3469, 95% CI: 0.2490-0.4377, I2 = 5.0%), which was significantly higher than that of the AD group (r = 0.1209, 95% CI:0.0905-0.1510, I2 = 0.0%) (p < 0.05). Among different layers, the peripapillary retinal nerve fiber layer (pRNFL) indicated a moderate positive correlation with hippocampal volume (r = 0.1209, 95% CI:0.0905-0.1510, I2 = 0.0%). The retinal pigmented epithelium (RPE) was also positively correlated [r = 0.1421, 95% CI:(-0.0447-0.3192), I2 = 84.1%]. The retinal layers and participants were the main overall heterogeneity sources. Correlation in the bilateral hemisphere did not show a significant difference.

Conclusion

The correlation between RNFL thickness and hippocampal volume is more predominant in both NC and AD groups than other layers. Whole retinal thickness is positively correlated to hippocampal volume not only in AD continuum, especially in MCI, but also in NC.

Systematic review registration

https://www.crd.york.ac.uk/PROSPERO/, CRD42022328088.

Retinal imaging biomarkers of Alzheimer's disease: A systematic review and meta-analysis of studies using brain amyloid beta status for case definition

Introduction

We performed a systematic review and meta-analysis of the association between retinal imaging parameters and Alzheimer's disease (AD).

Methods

PubMed, EMBASE, and Scopus were systematically searched for prospective and observational studies. Included studies had AD case definition based on brain amyloid beta (Aβ) status. Study quality assessment was performed. Random-effects meta-analyses of standardized mean difference, correlation, and diagnostic accuracy were conducted.

Results

Thirty-eight studies were included. There was weak evidence of peripapillary retinal nerve fiber layer thinning on optical coherence tomography (OCT) (p = 0.14, 11 studies, n = 828), increased foveal avascular zone area on OCT-angiography (p = 0.18, four studies, n = 207), and reduced arteriole and venule vessel fractal dimension on fundus photography (p < 0.001 and p = 0.08, respectively, three studies, n = 297) among AD cases.

Discussion

Retinal imaging parameters appear to be associated with AD. Small study sizes and heterogeneity in imaging methods and reporting make it difficult to determine utility of these changes as AD biomarkers.

Highlights

We performed a systematic review on retinal imaging and Alzheimer's disease (AD).We only included studies in which cases were based on brain amyloid beta status.Several retinal biomarkers were associated with AD but clinical utility is uncertain.Studies should focus on biomarker-defined AD and use standardized imaging methods.

Retinal fingerprints of ALS in patients: Ganglion cell apoptosis and TDP-43/p62 misplacement

Introduction

Amyotrophic lateral sclerosis (ALS) is a fatal neurodegenerative disease characterized by the progressive loss of motor neuron function. Although ophthalmic deficits are not considered a classic symptom of ALS, recent studies suggest that changes in retinal cells, similar to those in the spinal cord motor neurons, have been observed in postmortem human tissues and animal models.

Methods

In this study, we examined by immunofluorescence analysis the retinal cell layers of sporadic ALS patients in post-mortem retinal slices. We evaluated the presence of cytoplasmic TDP-43 and SQSTM1/p62 aggregates, activation of the apoptotic pathway, and microglia and astrocytes reactivity.

Results

We found in the retinal ganglion cell layer of ALS patients the increase of mislocalized TDP-43, SQSTM1/p62 aggregates, activation of cleaved caspase-3, and microglia density, suggesting that retinal changes can be used as an additional diagnostic tool for ALS.

Discussion

The retina is considered part of the central nervous system, and neurodegenerative changes in the brain may be accompanied by structural and possibly functional changes in the neuroretina and ocular vasculature. Therefore, using in vivo retinal biomarkers as an additional diagnostic tool for ALS may provide an opportunity to longitudinally monitor individuals and therapies over time in a noninvasive and cost-effective manner.

Retinal Neurodegeneration Measured With Optical Coherence Tomography and Neuroimaging in Alzheimer Disease: A Systematic Review

BACKGROUND

Optical coherence tomography (OCT) has enabled several retinal alterations to be detected in patients with Alzheimer disease (AD), alterations that could be potential biomarkers. However, the relationship between the retina and other biomarkers of AD has been underresearched. We gathered and analyzed the literature about the relationship between retinal and cerebral alterations detected via neuroimaging in patients with AD, mild cognitive impairment (MCI), and preclinical AD.

METHODS

This systematic review followed the PRISMA Statement guidelines through the 27 items on its checklist. We searched in PubMed, BVS, Scopus, and the Cochrane Library, using the keywords: Alzheimer's disease, optical coherence tomography, white matter, cortex, atrophy, cortical thickness, neuroimaging, magnetic resonance imaging, and positron emission tomography. We included articles that studied the retina in relation to neuroimaging in patients with AD, MCI, and preclinical AD. We excluded studies without OCT, without neuroimaging, clinical cases, opinion articles, systematic reviews, and animal studies.

RESULTS

Of a total of 35 articles found, 23 were finally included. Although mixed results were found, most of these corroborate the relationship between retinal and brain disorders.

CONCLUSIONS

More rigorous research is needed in the field, including homogenized, longitudinal, and prolonged follow-up studies, as well as studies that include all stages of AD. This will enable better understanding of the retina and its implications in AD, leading to the discovery of retinal biomarkers that reflect brain alterations in AD patients in an accessible and noninvasive manner.

Alternative transcribed 3' isoform of long non-coding RNA Malat1 inhibits mouse retinal oxidative stress

The function of the cancer-associated lncRNA Malat1 during aging is as-of-yet uncharacterized. Here, we show that Malat1 interacts with Nucleophosmin (NPM) in young mouse brain, and with Lamin A/C, hnRNP C, and KAP1 with age. RNA-seq and RT-qPCR reveal a persistent expression of Malat1_2 (the 3'isoform of Malat1) in Malat1Δ1 (5'-1.5 kb deletion) mouse retinas and brains at 1/4th level of the full-length Malat1, while Malat1_1 (the 5'isoform) in Malat1Δ2 (deletion of 3'-conserved 5.7 kb) at a much lower level, suggesting an internal promoter driving the 3' isoform. The 1774 and 496 differentially expressed genes in Malat1Δ2 and Malat1Δ1 brains, respectively, suggest the 3' isoform regulates gene expression in trans and the 5' isoform in cis. Consistently, Malat1Δ2 mice show increased age-dependent retinal oxidative stress and corneal opacity, while Malat1Δ1 mice show no obvious phenotype. Collectively, this study reveals a physiological function of the lncRNA Malat1 3'-isoform during the aging process.

Optical coherence tomography and angiography in Alzheimer's disease and other cognitive disorders

AIMS

The aims of this study were to analyze retinal and choroidal changes on optical coherence tomography (OCT) and OCT-Angiography (OCT-A) in Alzheimer's disease (AD) patients and compare them to other forms of major dementia. We also aimed to analyze the correlation between clinical severity of global cognitive deficiency assessed by the mini-mental state exam (MMSE) score and OCT/OCT-A parameters.

METHODS

Retrospective cross-sectional evaluative study of AD, and age-and gender-matched patients with other dementias. Fundus examination, OCT and OCT-A were compared.

RESULTS

Ninety-one eyes of AD patients and 53 eyes of patients with other dementias were included. Retinal deposits were found in 6.59% of AD cases. OCT highlighted the presence of hyperreflective deposits and localized areas of outer retina and ellipsoid zone disruption, respectively in 20.87% and 15.38% of AD cases. Hyperreflective foci were noted within inner retinal layers in 4.39% of AD cases. Quantitative analysis revealed a thicker nasal retinal nerve fiber layer (p = 0.001) and ganglion cell complex in superior (p = 0.011) and temporal quadrants (p = 0.009) in eyes of AD patients, compared to other dementias. OCT-A showed a significantly higher fractal dimension of both superficial and deep capillary plexus (p = 0.005), with lower choriocapillaris density (p = 0.003) in AD patients.

CONCLUSIONS

Structural OCT could highlight the presence of hyperreflective deposits in AD, probably reflecting beta-amyloid deposits, associated to outer retinal disruptions. Quantitative OCT analysis showed structural differences between AD patients and other dementias, and combined OCT-A could identify microvascular changes in AD patients representing new potential differential diagnosis criteria.

The correlation of retinal neurodegeneration and brain degeneration in patients with Alzheimer's disease using optical coherence tomography angiography and MRI

Introduction

Pathological changes in Alzheimer's disease can cause retina and optic nerve degeneration. The retinal changes are correlated with cognitive function. This study aimed to explore the relationship of retinal differences with neuroimaging in patients with Alzheimer's disease, analyze the association of cognitive function with retinal structure and vascular density, and identify potential additional biomarkers for early diagnosis of Alzheimer's disease.

Method

We performed magnetic resonance imaging (MRI) scans and neuropsychological assessments in 28 patients with mild Alzheimer's disease and 28 healthy controls. Retinal structure and vascular density were evaluated by optical coherence tomography angiography (OCTA). Furthermore, we analyzed the correlation between neuroimaging and OCTA parameters in patients with mild Alzheimer's disease with adjustment for age, gender, years of education, and hypertension.

Results

In patients with mild Alzheimer's disease, OCTA-detected retinal parameters were not significantly correlated with MRI-detected neuroimaging parameters after Bonferroni correction for multiple testing. Under multivariable analysis controlled for age, gender, years of education, and hypertension, the S-Hemi (0-3) sector of macular thickness was significantly associated with Mini-cog (β = 0.583, P = 0.002) with Bonferroni-corrected threshold at P < 0.003.

Conclusion

Our findings suggested decreased macular thickness might be associated with cognitive function in mild AD patients. However, the differences in retinal parameters didn't correspond to MRI-detected parameters in this study. Whether OCTA can be used as a new detection method mirroring MRI for evaluating the effect of neuronal degeneration in patients with mild Alzheimer's disease still needs to be investigated by more rigorous and larger studies in the future.

Correlation between retinal structure and brain multimodal magnetic resonance imaging in patients with Alzheimer's disease

Background

The retina imaging and brain magnetic resonance imaging (MRI) can both reflect early changes in Alzheimer's disease (AD) and may serve as potential biomarker for early diagnosis, but their correlation and the internal mechanism of retinal structural changes remain unclear. This study aimed to explore the possible correlation between retinal structure and visual pathway, brain structure, intrinsic activity changes in AD patients, as well as to build a classification model to identify AD patients.

Methods

In the study, 49 AD patients and 48 healthy controls (HCs) were enrolled. Retinal images were obtained by optical coherence tomography (OCT). Multimodal MRI sequences of all subjects were collected. Spearman correlation analysis and multiple linear regression models were used to assess the correlation between OCT parameters and multimodal MRI findings. The diagnostic value of combination of retinal imaging and brain multimodal MRI was assessed by performing a receiver operating characteristic (ROC) curve.

Results

Compared with HCs, retinal thickness and multimodal MRI findings of AD patients were significantly altered (p < 0.05). Significant correlations were presented between the fractional anisotropy (FA) value of optic tract and mean retinal thickness, macular volume, macular ganglion cell layer (GCL) thickness, inner plexiform layer (IPL) thickness in AD patients (p < 0.01). The fractional amplitude of low frequency fluctuations (fALFF) value of primary visual cortex (V1) was correlated with temporal quadrant peripapillary retinal nerve fiber layer (pRNFL) thickness (p < 0.05). The model combining thickness of GCL and temporal quadrant pRNFL, volume of hippocampus and lateral geniculate nucleus, and age showed the best performance to identify AD patients [area under the curve (AUC) = 0.936, sensitivity = 89.1%, specificity = 87.0%].

Conclusion

Our study demonstrated that retinal structure change was related to the loss of integrity of white matter fiber tracts in the visual pathway and the decreased LGN volume and functional metabolism of V1 in AD patients. Trans-synaptic axonal retrograde lesions may be the underlying mechanism. Combining retinal imaging and multimodal MRI may provide new insight into the mechanism of retinal structural changes in AD and may serve as new target for early auxiliary diagnosis of AD.

A multi-regression framework to improve diagnostic ability of optical coherence tomography retinal biomarkers to discriminate mild cognitive impairment and Alzheimer’s disease

Background

Diagnostic performance of optical coherence tomography (OCT) to detect Alzheimer’s disease (AD) and mild cognitive impairment (MCI) remains limited. We assessed whether compensating the circumpapillary retinal nerve fiber layer (cpRNFL) thickness for multiple demographic and anatomical factors as well as the combination of macular layers improves the detection of MCI and AD.

Methods

This cross-sectional study of 62 AD (n = 92 eyes), 108 MCI (n = 158 eyes), and 55 cognitively normal control (n = 86 eyes) participants. Macular ganglion cell complex (mGCC) thickness was extracted. Circumpapillary retinal nerve fiber layer (cpRNFL) measurement was compensated for several ocular factors. Thickness measurements and their corresponding areas under the receiver operating characteristic curves (AUCs) were compared between the groups. The main outcome measure was OCT thickness measurements.

Results

Participants with MCI/AD showed significantly thinner measured and compensated cpRNFL, mGCC, and altered retinal vessel density (p < 0.05). Compensated RNFL outperformed measured RNFL for discrimination of MCI/AD (AUC = 0.74 vs 0.69; p = 0.026). Combining macular and compensated cpRNFL parameters provided the best detection of MCI/AD (AUC = 0.80 vs 0.69; p < 0.001).

Conclusions and relevance

Accounting for interindividual variations of ocular anatomical features in cpRNFL measurements and incorporating macular information may improve the identification of high-risk individuals with early cognitive impairment.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13195-022-00982-0.

A systematic survey of advances in retinal imaging modalities for Alzheimer's disease diagnosis

Recent advances in retinal imaging pathophysiology have shown a new function for biomarkers in Alzheimer's disease diagnosis and prognosis. The significant improvements in Optical coherence tomography (OCT) retinal imaging have led to significant clinical translation, particularly in Alzheimer's disease detection. This systematic review will provide a comprehensive overview of retinal imaging in clinical applications, with a special focus on biomarker analysis for use in Alzheimer's disease detection. Articles on OCT retinal imaging in Alzheimer's disease diagnosis were identified in PubMed, Google Scholar, IEEE Xplore, and Research Gate databases until March 2021. Those studies using simultaneous retinal imaging acquisition were chosen, while those using sequential techniques were rejected. "Alzheimer's disease" and "Dementia" were searched alone and in combination with "OCT" and "retinal imaging". Approximately 1000 publications were searched, and after deleting duplicate articles, 145 relevant studies focused on the diagnosis of Alzheimer's disease utilizing retinal imaging were chosen for study. OCT has recently been demonstrated to be a valuable technique in clinical practice as according to this survey, 57% of the researchers employed optical coherence tomography, 19% used ocular fundus imaging, 13% used scanning laser ophthalmoscopy, and 11% have used multimodal imaging to diagnose Alzheimer disease. Retinal imaging has become an important diagnostic technique for Alzheimer's disease. Given the scarcity of available literature, it is clear that future prospective trials involving larger and more homogeneous groups are necessary, and the work can be expanded by evaluating its significance utilizing a machine-learning platform rather than simply using statistical methodologies.

Machine learning based on Optical Coherence Tomography images as a diagnostic tool for Alzheimer's disease

AIMS

We mainly evaluate retinal alterations in Alzheimer's disease (AD) patients, investigate the associations between retinal changes with AD biomarkers, and explore an optimal machine learning (ML) model for AD diagnosis based on retinal thickness.

METHODS

A total of 159 AD patients and 299 healthy controls were enrolled. The retinal parameters of each participant were measured using optical coherence tomography (OCT). Additionally, cognitive impairment severity, brain atrophy, and cerebrospinal fluid (CSF) biomarkers were measured in AD patients.

RESULTS

AD patients demonstrated a significant decrease in the average, superior, and inferior quadrant peripapillary retinal nerve fiber layer, macular retinal nerve fiber layer, ganglion cell layer (GCL), inner plexiform layer (IPL) thicknesses, as well as total macular volume (TMV) (all p < 0.05). Moreover, TMV was positively associated with Mini-Mental State Examination and Montreal Cognitive Assessment scores, IPL thickness was correlated negatively with the medial temporal lobe atrophy score, and the GCL thickness was positively correlated with CSF Aβ₄₂ /Aβ₄₀ and negatively associated with p-tau level. Based on the significantly decreased OCT variables between both groups, the XGBoost algorithm exhibited the best diagnostic performance for AD, whose four references, including accuracy, area under the curve, f1 score, and recall, ranged from 0.69 to 0.74. Moreover, the macular retinal thickness exhibited an absolute superiority for AD diagnosis compared with other enrolled variables in all ML models.

CONCLUSION

We identified the retinal alterations in AD patients and found that macular thickness and volume were associated with AD severity and biomarkers. Furthermore, we confirmed that OCT combined with ML could serve as a potential diagnostic tool for AD.

Posterior pole analysis and ganglion cell layer measurements in Alzheimer's disease

AIM

To compare posterior pole analysis and ganglion cell layer (GCL) of patients with Alzheimer's disease (AD) and controls.

METHOD

Patients diagnosed with mild and moderate AD included in the study. Posterior pole analysis and GCL measurements were investigated by dividing the macula into superior and inferior hemifields and 5 corresponding zones.

RESULTS

There were no significant differences between groups for retinal thickness measurements in any retinal zone. GCL measurements showed lower measurements in moderate AD group for GCL thickness in the superior zone 2 (p:0.025) and inferior zone 2 (p = 0.048) compared to mild AD and controls. A moderate AD status was found to cause a decrease of 5.349 µm in the GCL-SZ2 value [p:0.037].

CONCLUSION

GCL measurements in the moderate AD group show significant thinning in superior and inferior Zone 2, which may be a biomarker for AD.

Association of Optical Coherence Tomography and Optical Coherence Tomography Angiography Retinal Features With Visual Function in Older Adults

Importance

Although there is abundant evidence relating neuronal and vascular optical coherence tomography (OCT) and OCT angiography (OCTA) measures to retinal disease, data on the normative distribution of retinal features and their associations with visual function in a healthy, older, community-based population are sparse.

Objectives

To characterize the normative OCT and OCTA measures in older adults and describe their associations with visual function.

Design, Setting, and Participants

This was a cross-sectional, observational study conducted from May 17, 2017, to May 31, 2019. The study included a community-based sample. Participants in the Atherosclerosis Risk in Communities study from Jackson, Mississippi (all self-reported Black participants), and Washington County, Maryland (all self-reported White participants), were recruited in the Eye Determinants of Cognition study (EyeDOC). Data analyses were conducted from June 14, 2020, to May 31, 2021.

Main Outcomes and Measures

Retinal measurements, including retinal nerve fiber layer (RNFL) thickness, macular ganglion cell complex (GCC) thickness, macular vessel density (VD) in the superficial capillary plexus (SCP) and deep capillary plexus (DCP), and foveal avascular zone (FAZ) area, were captured with spectral-domain OCT and OCTA. Visual function, including presenting distance vision, corrected distance vision, near visual acuity (VA), and contrast sensitivity (CS), was assessed.

Results

A total of 759 participants (mean [SD] age, 80 [4.2] years; 480 female participants [63%]; 352 Black participants [46%]) were included in the study. Mean (SD) GCC thickness (89.2 [9.3] μm vs 92.3 [8.5] μm) and mean (SD) FAZ (0.36 [0.16] mm2 vs 0.26 [0.12] mm2) differed between Jackson and Washington County participants, respectively. Mean (SD) RNFL thickness and mean (SD) VD in SCP and DCP were greater for participants 80 years or younger than for participants older than 80 years (RNFL: ≤80 years, 93.2 [10.5] μm; >80 years, 91.1 [11.6] μm; VD SCP, ≤80 years, 44.3% [3.5%]; >80 years, 43.5% [3.8%]; VD DCP, ≤80 years, 44.7% [4.9%]; >80 years, 43.7% [4.8%]). Linear regression showed each 10-μm increment in RNFL thickness and GCC thickness was positively associated with 0.016 higher logCS among all participants (RNFL: 95% CI, 0.005-0.027; P = .004; GCC: 95% CI, 0.003-0.029; P = .02), with stronger associations among Jackson participants. The associations of VA and structural measures were found only in Jackson participants, with coefficients per 10-μm increment of 0.012 logMAR VA (RNFL: 95% CI, 0.000-0.023; P = .049) and 0.020 logMAR VA (GCC: 95% CI, 0.004-0.034; P = .04).

Conclusions and Relevance

In this cross-sectional study, better CS was associated with greater RNFL thickness and GCC thickness, but no visual measures were associated with angiographic features overall. These findings suggest that clinical application of normative references for OCT- and OCTA-based measures should consider demographic and community features.

The retina: A window in which to view the pathogenesis of Alzheimer's disease

Alzheimer's disease (AD) is the most familiar type of dementia affecting elderly populations worldwide. Studies of AD patients and AD transgenic mice have revealed alterations in the retina similar to alterations which occur in the AD brain. Moreover, AD retinal pathology occurs even earlier than AD brain pathology. Importantly, non-invasive imaging techniques can be utilized for retinal observation due to the unique optical transparency of the eye, which acts as a convenient window in which preclinical pathology in the AD brain can be monitored. In this review, we overview the existing literature covering different forms of AD retinal pathology and propose a basis for the clinical application of using the retina as a window to view AD during preclinical and clinical stages.

Rational design and synthesis of a novel BODIPY-based probe for selective imaging of tau tangles in human iPSC-derived cortical neurons

Numerous studies have shown a strong correlation between the number of neurofibrillary tangles of the tau protein and Alzheimer's disease progression, making the quantitative detection of tau very promising from a clinical point of view. However, the lack of highly reliable fluorescent probes for selective imaging of tau neurofibrillary tangles is a major challenge due to sharing similar β–sheet motifs with homologous Amyloid-β fibrils. In the current work, we describe the rational design and the in silico evaluation of a small-size focused library of fluorescent probes, consisting of a BODIPY core (electron acceptor) featuring highly conjugated systems (electron donor) with a length in the range 13–19 Å at C3. Among the most promising probes in terms of binding mode, theoretical affinity and polarity, BT1 has been synthesized and tested in vitro onto human induced pluripotent stem cells derived neuronal cell cultures. The probe showed excellent photophysical properties and high selectivity allowing in vitro imaging of hyperphosphorylated tau protein filaments with minimal background noise. Our findings offer new insight into the structure-activity relationship of this class of tau selective fluorophores, paving the way for boosting tau tangle detection in patients possibly through retinal spectral scans.

Alzheimer's Disease Seen through the Eye: Ocular Alterations and Neurodegeneration

Alzheimer’s Disease (AD) is one of the main neurodegenerative diseases worldwide. Unfortunately, AD shares many similarities with other dementias at early stages, which impedes an accurate premortem diagnosis. Therefore, it is urgent to find biomarkers to allow for early diagnosis of the disease. There is increasing scientific evidence highlighting the similarities between the eye and other structures of the CNS, suggesting that knowledge acquired in eye research could be useful for research and diagnosis of AD. For example, the retina and optic nerve are considered part of the central nervous system, and their damage can result in retrograde and anterograde axon degeneration, as well as abnormal protein aggregation. In the anterior eye segment, the aqueous humor and tear film may be comparable to the cerebrospinal fluid. Both fluids are enriched with molecules that can be potential neurodegenerative biomarkers. Indeed, the pathophysiology of AD, characterized by cerebral deposits of amyloid-beta (Aβ) and tau protein, is also present in the eyes of AD patients, besides numerous structural and functional changes observed in the structure of the eyes. Therefore, all this evidence suggests that ocular changes have the potential to be used as either predictive values for AD assessment or as diagnostic tools.

Neuro-Retina Might Reflect Alzheimer's Disease Stage

BACKGROUND

Alzheimer's disease (AD) pathological hallmarks were found in retinas of AD patients. Several studies showed a significant reduction of neuro-retina thickness measured through optical coherence tomography (OCT) in AD patients, but possible correlations between retina morphology, cognition, and cerebrospinal fluid (CSF) AD biomarkers (Aβ42, t-tau, and p-tau) have been poorly investigated so far.

OBJECTIVE

In the present cross-sectional study, we measured the thickness of neuro-retinal layers through OCT searching for possible correlations with patients' cognitive performances and CSF AD biomarkers.

METHODS

137 consecutive subjects [43 with AD, 37 with mild cognitive impairment (MCI), and 57 healthy controls (HC)], received an OCT scan acquisition to measure the peripapillary retinal nerve fiber layer (RNFL) thickness. In a subsample of 21 AD, 18 MCI, and 18 HC, the macular volume of ganglion cell layer (GCL), inner plexiform layer (IPL), and inner nuclear layer was computed. A comprehensive neuropsychological assessment and CSF AD biomarkers' concentrations were available in AD and MCI patients.

RESULTS

Peripapillary RNFL, global, and in superior quadrant was significantly thinner in AD and MCI patients when compared to HC, while macular GCL volume was significantly reduced only in AD. RNFL thickness in nasal and inferior quadrants was correlated with single CSF AD biomarker concentrations, but no differences were found in retina morphology depending on the presence of a CSF profile typical for AD. Memory performances were positively associated with GCL and IPL volume.

CONCLUSION

Our findings might propose OCT as a reliable and easy to handle tool able to detect neuro-retinal atrophy in AD in relation with cognitive performances.

Feasibility study for detection of retinal amyloid in clinical trials: The Anti-Amyloid Treatment in Asymptomatic Alzheimer's Disease (A4) trial

INTRODUCTION

The retina and brain exhibit similar pathologies in patients diagnosed with neurodegenerative diseases. The ability to access the retina through imaging techniques opens the possibility for non-invasive evaluation of Alzheimer's disease (AD) pathology. While retinal amyloid deposits are detected in individuals clinically diagnosed with AD, studies including preclinical individuals are lacking, limiting assessment of the feasibility of retinal imaging as a biomarker for early-stage AD risk detection.

METHODS

In this small cross-sectional study we compare retinal and cerebral amyloid in clinically normal individuals who screened positive for high amyloid levels through positron emission tomography (PET) from the Anti-Amyloid Treatment in Asymptomatic Alzheimer's Disease (A4) trial as well as a companion cohort of individuals who exhibited low levels of amyloid PET in the Longitudinal Evaluation of Amyloid Risk and Neurodegeneration (LEARN) study. We quantified the number of curcumin-positive fluorescent retinal spots from a small subset of participants from both studies to determine retinal amyloid deposition at baseline.

RESULTS

The four participants from the A4 trial showed a greater number of retinal spots compared to the four participants from the LEARN study. We observed a positive correlation between retinal spots and brain amyloid, as measured by the standardized uptake value ratio (SUVr).

DISCUSSION

The results of this small pilot study support the use of retinal fundus imaging for detecting amyloid deposition that is correlated with brain amyloid PET SUVr. A larger sample size will be necessary to fully ascertain the relationship between amyloid PET and retinal amyloid both cross-sectionally and longitudinally.

Neural and Retinal Characteristics in Relation to Working Memory in Older Adults with Mild Cognitive Impairment

OBJECTIVE

This study investigated the relationship between neural activities and retinal structures associated with working memory (WM) in older adults with mild cognitive impairment (MCI).

METHODS

Eleven older adults with MCI and 29 healthy controls (60 to 73 years old) were tested. All participants underwent an event-related potential (ERP) recording while performing the two-back memory task. The Optical coherence tomography angiography (OCT-A) was administered to examine the perfusion and vessel density in the retina.

RESULTS

Results showed that WM performance in the MCI group was negatively associated with ERP latencies in central parietal regions (CP6 and CP8) (ps< 0.05). The left nasal vessel and perfusion densities were negatively correlated with the latencies in these two central parietal regions and positively related to WM performance only in the MCI group (ps< 0.05).

CONCLUSION

The findings on WM, central parietal brain activity, and left nasal vessel and perfusion densities in the retina help us gain a better understanding of the neural and retinal underpinnings of WM in relation to MCI.

Vision loss and hallucinations: perspectives from neurology and ophthalmology

PURPOSE OF REVIEW

The aim of this article is to summarize the evidence for visual impairment as a risk factor for visual hallucinations in neurologic disease and recent advances in our understanding of the central visual pathways that mediate this association.

RECENT FINDINGS

Recent studies have described the prevalence Charles Bonnet syndrome and questioned its lack of association with cognitive impairment, used advanced neuroimaging to show that disinhibition of the occipital lobe is involved in the pathogenesis of visual hallucinations in Parkinson's disease, and demonstrated that visual impairment because of eye disease is a consistent risk factor for visual hallucinations across a number of different neurodegenerative disease populations.

SUMMARY

Through connections between the primary visual cortex and other brain structures, visual function is closely tied to visual hallucinations. Given that the vast majority of vision loss is caused by ophthalmic disease, much of which is preventable or treatable, the detection and treatment of vision loss in at-risk populations may reduce the burden and consequences of visual hallucinations in older adults.

Neurocognitive Assessment and Retinal Thickness Alterations in Alzheimer Disease: Is There a Correlation?

BACKGROUND

The relation of retinal thickness to neuropsychological indexes of cognitive impairment in patients with Alzheimer disease (AD) remains an area of investigation. The scope of this investigation was to compare volume and thickness changes of neuronal retinal layers in subjects with AD with those of age-matched healthy controls and to estimate the relation between cognitive functioning evaluated by neuropsychological assessment and thickness changes of the retina.

METHODS

This was a prospective single-site study where we evaluated 25 subjects with probable AD matched for age, sex, and education to 17 healthy control subjects (HC). All participants underwent a full medical evaluation, neuropsychological assessment, and optical coherence tomography (OCT) to evaluate the peripapillary retinal nerve fiber layer (pRNFL) thickness, ganglion cell complex (GCC) thickness, and macular volume.

RESULTS

The pRNFL thickness of AD patients showed a significant overall reduction compared with healthy controls (P = <0.0001). Furthermore, pRNFL was reduced in each retinal quadrant, particularly the inferior, nasal, and superior quadrants. GCC thickness and macular volume were reduced in AD patients in comparison with HC (P = 0.004; P = 0.001). Of particular interest was the correlation between OCT findings and neuropsychological assessment; we did not find a significant association of retinal thinning with worse MMSE score, but reduction of macular volume was associated with worse constructional praxis performance. Impairment of semantic-lexical and processing speed was associated with attenuation of macular GCC thickness.

CONCLUSIONS

OCT can show early thickness changes in AD patients with subtle memory disturbances. These results suggest that correlations between retinal thinning and cognitive performance warrant further investigation.

Past, present and future role of retinal imaging in neurodegenerative disease

Retinal imaging technology is rapidly advancing and can provide ever-increasing amounts of information about the structure, function and molecular composition of retinal tissue in humans in vivo. Most importantly, this information can be obtained rapidly, non-invasively and in many cases using Food and Drug Administration-approved devices that are commercially available. Technologies such as optical coherence tomography have dramatically changed our understanding of retinal disease and in many cases have significantly improved their clinical management. Since the retina is an extension of the brain and shares a common embryological origin with the central nervous system, there has also been intense interest in leveraging the expanding armamentarium of retinal imaging technology to understand, diagnose and monitor neurological diseases. This is particularly appealing because of the high spatial resolution, relatively low-cost and wide availability of retinal imaging modalities such as fundus photography or OCT compared to brain imaging modalities such as magnetic resonance imaging or positron emission tomography. The purpose of this article is to review and synthesize current research about retinal imaging in neurodegenerative disease by providing examples from the literature and elaborating on limitations, challenges and future directions. We begin by providing a general background of the most relevant retinal imaging modalities to ensure that the reader has a foundation on which to understand the clinical studies that are subsequently discussed. We then review the application and results of retinal imaging methodologies to several prevalent neurodegenerative diseases where extensive work has been done including sporadic late onset Alzheimer's Disease, Parkinson's Disease and Huntington's Disease. We also discuss Autosomal Dominant Alzheimer's Disease and cerebrovascular small vessel disease, where the application of retinal imaging holds promise but data is currently scarce. Although cerebrovascular disease is not generally considered a neurodegenerative process, it is both a confounder and contributor to neurodegenerative disease processes that requires more attention. Finally, we discuss ongoing efforts to overcome the limitations in the field and unmet clinical and scientific needs.

Assessing the Retinal Microvasculature in Individuals With Early and Late-Onset Alzheimer's Disease

BACKGROUND AND OBJECTIVE

To evaluate retinal microvascular changes in early and late-onset Alzheimer's disease (AD).

PATIENTS AND METHODS

Eighty-six eyes of 50 late-onset AD participants, 27 eyes of 15 early onset AD participants, and 111 eyes of 57 cognitively normal controls were included. Optical coherence tomography angiography (OCTA) vessel density (VD) and perfusion density (PD) in Early Treatment Diabetic Retinopathy Study 3-mm and 6-mm circles and rings were assessed.

RESULTS

There was decreased PD in early onset AD 3-mm circle (P = .026) and ring (P = .026) versus controls as well as in late-onset AD 3-mm circle (P = .023) and ring (P = .023) versus controls. There was decreased VD in late-onset AD 3-mm circle (P = .012) and ring (P = .006). No parameters differed between early and late-onset AD (P > .05).

CONCLUSIONS

AD eyes exhibited decreased retinal microvascular density compared to controls. Retinal parameters may not differ between early onset AD and late-onset AD after adjusting for age. [Ophthalmic Surg Lasers Imaging Retina. 2021;52:336-344.].

Retinal Microvascular Alterations as the Biomarkers for Alzheimer Disease: Are We There Yet?

BACKGROUND

Alzheimer disease (AD) is a heterogeneous and multifactorial disorder with an insidious onset and slowly progressive disease course. To date, there are no effective treatments, but biomarkers for early diagnosis and monitoring of disease progression offer a promising first step in developing and testing potential interventions. Cerebral vascular imaging biomarkers to assess the contributions of vascular dysfunction to AD are strongly recommended to be integrated into the current amyloid-β (Aβ) [A], tau [T], and neurodegeneration [(N)]-the "AT(N)" biomarker system for clinical research. However, the methodology is expensive and often requires invasive procedures to document cerebral vascular dysfunction. The retina has been used as a surrogate to study cerebral vascular changes. There is growing interest in the identification of retinal microvascular changes as a safe, easily accessible, low cost, and time-efficient approach to enhancing our understanding of the vascular pathogenesis associated with AD.

EVIDENCE ACQUISITION

A systemic review of the literature was performed regarding retinal vascular changes in AD and its prodromal stages, focusing on functional and structural changes of large retinal vessels (vessels visible on fundus photographs) and microvasculature (precapillary arterioles, capillary, and postcapillary venules) that are invisible on fundus photographs.

RESULTS

Static and dynamic retinal microvascular alterations such as retinal arterial wall motion, blood flow rate, and microvascular network density were reported in AD, mild cognitive impairment, and even in the preclinical stages of the disease. The data are somewhat controversial and inconsistent among the articles reviewed and were obtained based on cross-sectional studies that used different patient cohorts, equipment, techniques, and analysis methods.

CONCLUSIONS

Retinal microvascular alterations exist across the AD spectrum. Further large scale, within-subject longitudinal studies using standardized imaging and analytical methods may advance our knowledge concerning vascular contributions to the pathogenesis of AD.

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.

Relation of retinal and hippocampal thickness in patients with amnestic mild cognitive impairment and healthy controls

OBJECTIVE

Investigating retinal thickness may complement existing biological markers for dementia and other neurodegenerative diseases. Although retinal thinning is predictive for cognitive decline, it remains to be investigated if and how this feature aligns with neurodegeneration elsewhere in the brain, specifically in early disease stages.

METHODS

Using optical coherence tomography and magnetic resonance imaging, we examined retinal thickness as well as hippocampal structure in patients with amnestic mild cognitive impairment and healthy controls.

RESULTS

The groups did not differ in hippocampal and retinal thickness measures. However, we detected a correlation of peripapillary retinal nerve fiber layer thickness and hippocampal thickness in healthy people but not in cognitively impaired patients. The ratio of hippocampus to retina thickness was significantly smaller in patients with mild cognitive impairment and correlated positively with cognitive performance.

CONCLUSIONS

Different temporal trajectories of neurodegeneration may disrupt transregional brain structure associations in patients with amnestic mild cognitive impairment.

The application of optical coherence tomography angiography in Alzheimer's disease: A systematic review

INTRODUCTION

Discovering non-invasive and easily acquired biomarkers that are conducive to the accurate diagnosis of dementia is an urgent area of ongoing clinical research. One promising approach is retinal imaging, as there is homology between retinal and cerebral vasculature. Recently, optical coherence tomography angiography (OCT-A) has emerged as a promising new technology for imaging the microvasculature of the retina.

METHODS

A systematic review and meta-analysis was conducted to examine the application of OCT-A in dementia.

RESULTS

Fourteen studies assessing OCT-A in preclinical Alzheimer's disease (AD), mild cognitive impairment, or AD were included. Exploratory meta-analyses revealed a significant increase in the foveal avascular zone area and a significant decrease in superficial parafoveal and whole vessel density in AD, although there was significant heterogeneity between studies.

DISCUSSION

Although certain OCT-A metrics may have the potential to serve as biomarkers for AD, the field requires further standardization to allow conclusions to be reached regarding their clinical utility.

The Contribution of Ocular Biomarkers in the Differential Diagnosis of Alzheimer's Disease versus Other Types of Dementia and Future Prospects

With dementia becoming increasingly prevalent, there is a pressing need to become better equipped with accurate diagnostic tools that will favorably influence its course via prompt and specific intervention. The overlap in clinical manifestation, imaging, and even pathological findings between different dementia syndromes is one of the most prominent challenges today even for expert physicians. Since cerebral microvasculature and the retina share common characteristics, the idea of identifying potential ocular biomarkers to facilitate diagnosis is not a novel one. Initial efforts included studying less quantifiable parameters such as aspects of visual function, extraocular movements, and funduscopic findings. However, the really exciting prospect of a non-invasive, safe, fast, reproducible, and quantifiable method of pinpointing novel biomarkers has emerged with the advent of optical coherence tomography (OCT) and, more recently, OCT angiography (OCTA). The possibility of analyzing multiple parameters of retinal as well as retinal microvasculature variables in vivo represents a promising opportunity to investigate whether specific findings can be linked to certain subtypes of dementia and aid in their earlier diagnosis. The existing literature on the contribution of the eye in characterizing dementia, with a special interest in OCT and OCTA parameters will be reviewed and compared, and we will explicitly focus our effort in advancing our understanding and knowledge of relevant biomarkers to facilitate future research in the differential diagnosis between Alzheimer's disease and common forms of cognitive impairment, including vascular dementia, frontotemporal dementia, and dementia with Lewy bodies.

Visual Abnormalities Associate With Hippocampus in Mild Cognitive Impairment and Early Alzheimer's Disease

Background and Objective: Alzheimer's disease (AD) has been shown to affect vision in human patients and animal models. This study was conducted to explore ocular abnormalities in the primary visual pathway and their relationship with hippocampal atrophy in patients with AD and mild cognitive impairment (MCI). The aim of this study was to investigate the potential value of ocular examinations as a biomarker during the AD progression. Methods: Patients with MCI (n = 23) or AD (n = 17) and age-matched cognitively normal controls (NC; n = 19) were enrolled. Pattern visual-evoked potentials (PVEP), flash electroretinogram (FERG) recordings and optical coherence tomography (OCT) were performed for all participants. Hippocampal volumes were measured by 3T magnetic resonance imaging. Cognitive function was assessed by Mini Mental State Examination (MMSE), Montreal Cognitive Assessment (MoCA) and Alzheimer's Disease Assessment Scale-cognitive subscale (ADAS-cog). Pearson correlation was employed to analyze the potential associations between ocular abnormalities and hippocampal volumes. Hierarchical regression models were conducted to determine associations between cognitive performances and ocular abnormalities as well as hippocampal volumes after adjusting for confounding factors including age, sex, cognitive reserve, and APOE4 status. Results: PVEP amplitude of P100 waveform was significantly decreased in AD patients compared to MCI and normal individuals. In FERG test, delayed latencies of rod response, rod cone response and 3.0 flicker time were found in cognitively impaired groups, indicating dysfunctions of both the rod and cone systems in the disease progression. OCT test revealed reduced macular retinal nerve fiber layer (m-RNFL) thickness in MCI and AD patients, which significantly correlated with brain structure of hippocampus particularly vulnerable during the progression of AD. Interestingly, P100 amplitude showed a significant association with hippocampal volumes even after adjusting confounding factors including age, sex, and cognitive reserve. Hierarchical regression analysis further demonstrated that m-RNFL thickness, as well as hippocampal volumes, significantly associated with ADAS-cog scores. Conclusion: P100 amplitude and m-RNFL thickness showed significant correlations with brain structure involved in AD-related neurodegeneration, and therefore proved to be potential indicators of brain imaging pathologies.

Changes in retinal microvasculature and retinal layer thickness in association with apolipoprotein E genotype in Alzheimer's disease

Biomarker tests of Alzheimer’s disease (AD) are invasive and expensive. Recent developments in optical coherence tomography (OCT) and OCT angiography (OCTA) have enabled noninvasive, cost-effective characterization of retinal layer vasculature and thickness. Using OCTA and OCT, we characterized retinal microvascular changes in the mild cognitive impairment (MCI) stage of AD and assessed their correlation with structural changes in each retinal neuronal layer. We also evaluated the effect of the APOE-ε4 genotype on retinal microvasculature and layer thickness. Retinal layer thickness did not differ between MCI patients (40 eyes) and controls (37 eyes, all p > 0.05). MCI patients had lower vessel density (VD) (p = 0.003) of the superficial capillary plexus (SCP) and larger foveal avascular zone area (p = 0.01) of the deep capillary plexus (DCP) than those of controls. VD of the SCP correlated with the ganglion cell layer (r = 0.358, p = 0.03) and inner plexiform layer thickness (r = 0.437, p = 0.007) in MCI patients. APOE-ε4-carrying MCI patients had a lower VD of the DCP than non-carriers (p = 0.03). In conclusion, retinal microvasculature was reduced in patients with AD-associated MCI, but retinal thickness was not changed; these changes might be affected by the APOE genotype. OCTA of the retinal microvasculature may be useful to detect vascular changes in AD.

Optical Coherence Tomography in Patients with Alzheimer's Disease: What Can It Tell Us?

PURPOSE

Although Alzheimer's disease (AD) is a leading cause of dementia worldwide, its clinical diagnosis remains a challenge. Optical coherence tomography (OCT) and OCT with angiography (OCTA) are non-invasive ophthalmic imaging tools with the potential to detect retinal structural and microvascular changes in patients with AD, which may serve as biomarkers for the disease. In this systematic review, we evaluate whether certain OCT and OCTA parameters are significantly associated with AD and mild cognitive impairment (MCI).

METHODS

PubMed database was searched using a combination of MeSH terms to identify studies for review. Studies were organized by participant diagnostic groups, type of imaging modality, and OCT/OCTA parameters of interest. Participant demographic data was also collected and baseline descriptive statistics were calculated for the included studies.

RESULTS

Seventy-one studies were included for review, representing a total of 6757 patients (2350 AD, 793 MCI, 2902 healthy controls (HC), and 841 others with a range of other neurodegenerative diagnoses). The mean baseline ages were 72.78±3.69, 71.52±2.88, 70.55±3.85 years for AD, MCI and HC groups, respectively. The majority of studies noted significant structural and functional decline in AD patients when compared to HC. Although analysis of MCI groups yielded more mixed results, a similar pattern of decline was often noted amongst patients with MCI relative to HC. OCT and OCTA measurements were also shown to correlate with established measures of AD such as neuropsychological testing or neuroimaging.

CONCLUSION

OCT and OCTA show great potential as non-invasive technologies for the diagnosis of AD. However, further research is needed to determine whether there are AD-specific patterns of structural or microvascular change in the retina and optic nerve that distinguish AD from other neurodegenerative diseases. Development of sensitive and specific OCT/OCTA parameters will be necessary before they can be used to detect AD in clinical settings.

Retinal Optical Coherence Tomography Metrics Are Unchanged in Verubecestat Alzheimer's Disease Clinical Trial but Correlate with Baseline Regional Brain Atrophy

BACKGROUND

We performed exploratory analyses of retinal thickness data from a clinical trial of the AβPP cleaving enzyme (BACE) inhibitor verubecestat in patients with Alzheimer's disease (AD).

OBJECTIVE

To evaluate: 1) possible retinal thickness changes following BACE inhibition; and 2) possible association between retinal thickness and brain atrophy.

METHODS

Retinal thickness was measured using spectral-domain optical coherence tomography in a 78-week randomized placebo-controlled trial of verubecestat in 1,785 patients with mild-to-moderate AD. Changes from baseline in retinal pigment epithelium, macular grid retinal nerve fiber layer, central subfield retinal thickness, and macular grid volume were evaluated for verubecestat versus placebo. Correlation analyses were performed to investigate the potential association between macular grid retinal nerve fiber layer and central subfield retinal thickness with brain volumetric magnetic resonance imaging (vMRI) data at baseline, as well as correlations for changes from baseline at Week 78 in patients receiving placebo.

RESULTS

Verubecestat did not significantly alter retinal thickness during the trial compared with placebo. At baseline, mean macular grid retinal nerve fiber layer and central subfield retinal thickness were weakly but significantly correlated (Pearson's r values≤0.23, p-values < 0.01) with vMRI of several brain regions including whole brain, hippocampus, and thalamus. At Week 78, correlations between retinal thickness and brain vMRI changes from baseline in the placebo group were small and mostly not statistically significant.

CONCLUSION

BACE inhibition by verubecestat was not associated with adverse effects on retinal thickness in patients with mild-to-moderate AD. Correlations between retinal thickness and brain volume were observed at baseline.

TRIAL REGISTRATION

Clinicaltrials.gov NCT01739348 (registered December 3, 2012; https://clinicaltrials.gov/ct2/show/NCT01739348).

Correlations between retinal nerve fiber layer thickness and cognitive progression in Parkinson's disease: A longitudinal study

BACKGROUND

Retinal abnormalities measured by optical coherence tomography (OCT) have been detected in both Parkinson's disease (PD) and Alzheimer's disease (AD). Cognitive impairment is not only found in AD, but 75-90% of PD patients will also develop dementia in the late stage of disease. We assessed whether baseline retinal nerve fiber layer (RNFL) thickness predicted worsening of cognitive status over time and the correlation between RNFL thickness and the detailed impaired cognitive domains in PD.

METHODS

RNFL thickness was measured using high-definition OCT in 78 non-dementia PD patients. Clinical and cognitive assessments were performed at baseline and at 3.61 ± 0.65 years follow-up. Linear mixed-effects models were used to examine associations between RNFL thickness and the changes in cognitive test scores, after adjusting for age, sex, disease duration and education.

RESULTS

Analysis of outcomes according to baseline RNFL tertiles showed worse performance in global cognitive tests, delayed memory, and executive functions in patients with a thin RNFL. During follow-up, greater cognitive deterioration was found in thin RNFL tertile patients. Lower baseline average RNFL thickness was associated with greater annualized decline in Mini-Mental State Examination and Montreal Cognitive Assessment.

CONCLUSION

The correlation between RNFL thickness and cognitive dysfunction suggests that OCT may be useful for predicting cognitive dysfunction in PD patients.

The Retinal Inner Plexiform Synaptic Layer Mirrors Grey Matter Thickness of Primary Visual Cortex with Increased Amyloid β Load in Early Alzheimer's Disease

The retina may serve as putative window into neuropathology of synaptic loss in Alzheimer's disease (AD). Here, we investigated synapse-rich layers versus layers composed by nuclei/cell bodies in an early stage of AD. In addition, we examined the associations between retinal changes and molecular and structural markers of cortical damage. We recruited 20 AD patients and 17 healthy controls (HC). Combining optical coherence tomography (OCT), magnetic resonance (MR), and positron emission tomography (PET) imaging, we measured retinal and primary visual cortex (V1) thicknesses, along with V1 amyloid β (Aβ) retention ([11C]-PiB PET tracer) and neuroinflammation ([11C]-PK11195 PET tracer). We found that V1 showed increased amyloid-binding potential, in the absence of neuroinflammation. Although thickness changes were still absent, we identified a positive association between the synapse-rich inner plexiform layer (IPL) and V1 in AD. This retinocortical interplay might reflect changes in synaptic function resulting from Aβ deposition, contributing to early visual loss.

Neurofilament light chain in the vitreous humor of the eye

BACKGROUND

Neurofilament light chain (NfL) is a promising biomarker of neurodegeneration in the cerebrospinal fluid and blood. This study investigated the presence of NfL in the vitreous humor and its associations with amyloid beta, tau, inflammatory cytokines and vascular proteins, apolipoprotein E (APOE) genotypes, Mini-Mental State Examination (MMSE) scores, systemic disease, and ophthalmic diseases.

METHODS

This is a single-site, prospective, cross-sectional cohort study. Undiluted vitreous fluid (0.5-1.0 mL) was aspirated during vitrectomy, and whole blood was drawn for APOE genotyping. NfL, amyloid beta (Aβ), total Tau (t-Tau), phosphorylated Tau (p-Tau181), inflammatory cytokines, chemokines, and vascular proteins in the vitreous were quantitatively measured by immunoassay. The main outcome measures were the detection of NfL levels in the vitreous humor and its associations with the aforementioned proteins. Linear regression was used to test the associations of NfL with other proteins, APOE genotypes, MMSE scores, and ophthalmic and systemic diseases after adjustment for age, sex, education level, and other eye diseases.

RESULTS

NfL was detected in all 77 vitreous samples. NfL was not found to be associated with ophthalmic conditions, APOE genotypes, MMSE scores, or systemic disease (p > 0.05). NfL levels were positively associated with increased vitreous levels of Aβ40 (p = 7.7 × 10-5), Aβ42 (p = 2.8 × 10-4), and t-tau (p = 5.5 × 10-7), but not with p-tau181 (p = 0.53). NfL also had significant associations with inflammatory cytokines such as interleukin-15 (IL-15, p = 5.3 × 10-4), IL-16 (p = 2.2 × 10-4), monocyte chemoattractant protein-1 (MCP1, p = 4.1 × 10-4), and vascular proteins such as vascular endothelial growth factor receptor-1 (VEGFR1, p = 2.9 × 10-6), Vegf-C (p = 8.6 × 10-6), vascular cell adhesion molecule-1 (VCAM-1, p = 5.0 × 10-4), Tie-2 (p = 6.3 × 10-4), and intracellular adhesion molecular-1 (ICAM-1, p = 1.6 × 10-4).

CONCLUSION

NfL is detectable in the vitreous humor of the eye and significantly associated with amyloid beta, t-tau, and select inflammatory and vascular proteins in the vitreous. Additionally, NfL was not associated with patients' clinical eye condition. Our results serve as a foundation for further investigation of NfL in the ocular fluids to inform us about the potential utility of its presence in the eye.

Correlation between brain volume and retinal photoreceptor outer segment volume in normal aging and neurodegenerative diseases

PURPOSE

To investigate the association between outer retinal layer metrics, including photoreceptor outer segment volume, on spectral-domain optical coherence tomography (OCT) and brain volume on MRI in normal aging, Alzheimer's disease and Parkinson's disease.

METHODS

This was an exploratory analysis of a cross-sectional cohort study that was approved by the Cleveland Clinic Institutional Review Board to evaluate neurodegenerative disorders. Subjects aged ≥ 50 were recruited. A comprehensive neurological exam, brain MRI with volumetric evaluation, and OCT were performed for each subject. Outer retinal layer parameters, including ellipsoid zone (EZ) to retinal pigment epithelium (RPE) volume (i.e., surrogate for panmacular photoreceptor outer segment volume), were evaluated with a novel OCT analysis platform.

RESULTS

Of 85 subjects, 64 eyes of 64 subjects met MRI and OCT quality control criteria. Total brain volume (%ICV) significantly correlated with EZ-RPE volume in the normal cognition control group (n = 31, Pearson correlation coefficient 0.514, P < .01), the Parkinson's disease group (n = 19, Pearson correlation coefficient 0.482, P = .04), and the Alzheimer's dementia group (n = 14, Pearson correlation coefficient 0.526, P = .05). Multiple linear regression analysis revealed that photoreceptor outer segment (i.e., EZ-RPE) volume was an independent, influential factor on total brain volume in all study subjects (Coefficient 15.2, 95% confidence interval 7.8-22.6, P < .001).

CONCLUSION

Outer retinal parameters on OCT may serve as a novel biomarker related to brain volume. This correlation was noted in control subjects suggesting a possible developmental link between retina and brain volume. This relationship was also maintained with atrophic neurodegenerative disorders. Further research is needed to explore possible threshold differences for underlying neurodegenerative disorders.

Retinal changes in Alzheimer's disease- integrated prospects of imaging, functional and molecular advances

Alzheimer's Disease (AD) is a devastating neurodegenerative disorder of the brain, clinically characterised by cognitive deficits that gradually worsen over time. There is, at present, no established cure, or disease-modifying treatments for AD. As life expectancy increases globally, the number of individuals suffering from the disease is projected to increase substantially. Cumulative evidence indicates that AD neuropathological process is initiated several years, if not decades, before clinical signs are evident in patients, and diagnosis made. While several imaging, cognitive, CSF and blood-based biomarkers have been proposed for the early detection of AD; their sensitivity and specificity in the symptomatic stages is highly variable and it is difficult to justify their use in even earlier, pre-clinical stages of the disease. Research has identified potentially measurable functional, structural, metabolic and vascular changes in the retina during early stages of AD. Retina offers a distinctively accessible insight into brain pathology and current and developing ophthalmic technologies have provided us with the possibility of detecting and characterising subtle, disease-related changes. Recent human and animal model studies have further provided mechanistic insights into the biochemical pathways that are altered in the retina in disease, including amyloid and tau deposition. This information coupled with advances in molecular imaging has allowed attempts to monitor biochemical changes and protein aggregation pathology in the retina in AD. This review summarises the existing knowledge that informs our understanding of the impact of AD on the retina and highlights some of the gaps that need to be addressed. Future research will integrate molecular imaging innovation with functional and structural changes to enhance our knowledge of the AD pathophysiological mechanisms and establish the utility of monitoring retinal changes as a potential biomarker for AD.

Association of Cognitive Function with Amyloid-β and Tau Proteins in the Vitreous Humor

BACKGROUND

The eye may serve as source for diagnostic testing for early detection of Alzheimer's disease (AD). Examination of amyloid-β (Aβ) and tau protein content in human vitreous and its correlation to neuro-cognition may improve ocular-based AD detection methods.

OBJECTIVE

To evaluate levels of Aβ and tau protein in human vitreous humor and investigate the clinical predictive role of these proteins as early diagnostic markers of AD.

METHODS

A prospective, single-center, multi-surgeon cohort study. Vitreous humor samples from 80 eyes were measured quantitatively for Aβ40-42, pTau, and tTau. Linear regression was used to test associations between AD biomarker levels, Mini-Mental State Exam (MMSE), and serum apolipoprotein E (APOE) allele status, with adjustment for age, sex, and education level of patients.

RESULTS

Lower MMSE scores were significantly associated with lower levels of vitreous Aβ40 (p = 0.015), Aβ42 (p = 0.0066), and tTau (p = 0.0085), and these biomarkers were not associated with any pre-existing eye conditions. Presence of the ɛ4 allele and the ɛ2 allele approached significance with reduced Aβ40 level (p = 0.053) and increased p-Tau level (p = 0.056), respectively.

CONCLUSION

Patients with poor cognitive function have significantly lower vitreous humor levels of AD-related biomarkers Aβ40, Aβ42, and tTau. These biomarkers do not correlate with underlying eye conditions, suggesting their specificity in association with cognitive change. This is the first study to our knowledge to correlate cognition with AD-related proteins in the vitreous humor. Results suggest ocular proteins may have a role for early dementia detection in individuals at risk for AD.

Structure and function of the perivascular fluid compartment and vertebral venous plexus: Illumining a novel theory on mechanisms underlying the pathogenesis of Alzheimer's, cerebral small vessel, and neurodegenerative diseases

Blood dynamically and richly supplies the cerebral tissue via microvessels invested in pia matter perforating the cerebral substance. Arteries penetrating the cerebral substance derive an investment from one or two successive layers of pia mater, luminally apposed to the pial-glial basal lamina of the microvasculature and abluminally apposed to a series of aquaporin IV-studded astrocytic end feet constituting the soi-disant glia limitans. The full investment of successive layers forms the variably continuous walls of the periarteriolar, pericapillary, and perivenular divisions of the perivascular fluid compartment. The pia matter disappears at the distal periarteriolar division of the perivascular fluid compartment. Plasma from arteriolar blood sequentially transudates into the periarteriolar division of the perivascular fluid compartment and subarachnoid cisterns in precession to trickling into the neural interstitium. Fluid from the neural interstitium successively propagates into the venules through the subarachnoid cisterns and perivenular division of the perivascular fluid compartment. Fluid fluent within the perivascular fluid compartment flows gegen the net direction of arteriovenular flow. Microvessel oscillations at the central tendency of the cerebral vasomotion generate corresponding oscillations of within the surrounding perivascular fluid compartment, interposed betwixt the abluminal surface of the vessels and internal surface of the pia mater. The precise microanatomy of this most fascinating among designable spaces has eluded the efforts of various investigators to interrogate its structure, though most authors non-consensusly concur the investing layers effectively and functionally segregate the perivascular and subarachnoid fluid compartments. Enlargement of the perivascular fluid compartment in a variety of neurological disorders, including senile dementia of the Alzheimer's type and cerebral small vessel disease, may alternately or coordinately constitute a correlative marker of disease severity and a possible cause implicated in the mechanistic pathogenesis of these conditions. Venular pressures modulating oscillatory dynamic flow within the perivascular fluid compartment may similarly contribute to the development of a variety among neurological disorders. An intimate understanding of subtle features typifying microanatomy and microphysiology of the investing structures and spaces of the cerebral microvasculature may powerfully inform mechanistic pathophysiology mediating a variety of neurovascular ischemic, neuroinfectious, neuroautoimmune, and neurodegenerative diseases.

Optical Coherence Tomography Angiography in Neurodegenerative Diseases: A Review

Background

Optical coherence tomography angiography (OCT-A) has emerged as a novel, fast, safe and non-invasive imaging technique of analyzing the retinal and choroidal microvasculature in vivo. OCT-A captures multiple sequential B-scans performed repeatedly over a specific retinal area at high speed, thus enabling the composition of a vascular map with areas of contrast change (high flow zones) and areas of steady contrast (slow or no flow zones). It therefore provides unique insight into the exact retinal or choroidal layer and location at which abnormal blood flow develops. OCTA has evolved into a useful tool for understanding a number of retinal pathologies such as diabetic retinopathy, age-related macular degeneration, central serous chorioretinopathy, vascular occlusions, macular telangiectasia and choroidal neovascular membranes of other causes. OCT-A technology is also increasingly being used in the evaluation of optic disc perfusion and has been suggested as a valuable tool in the early detection of glaucomatous damage and monitoring progression.

Objective

To review the existing literature on the applications of optical coherence tomography angiography in neurodegenerative diseases.

Summary

A meticulous literature was performed until the present day. Google Scholar, PubMed, Mendeley search engines were used for this purpose. We used 123 published manuscripts as our references. OCT-A has been utilized so far to describe abnormalities in multiple sclerosis (MS), Alzheimer’s disease, arteritic and non-arteritic optic neuropathy (AION and NAION), Leber’s hereditary optic neuropathy (LHON) papilloedema, Parkinson’s disease, Huntington’s disease, amyotrophic lateral sclerosis (ALS), Wolfram syndrome, migraines, lesions of the visual pathway and cerebral autosomal dominant arteriopathy with subcortical infarcts and leukoencephalopathy (CADASIL). It appears that OCT-A findings correlate quite well with the severity of the aforementioned diseases. However, OCT-A has its own limitations, namely its lack of wide-field view of the peripheral retina and the inaccurate interpretation due to motion artifacts in uncooperative groups of patients (e.g. children). Larger prospective longitudinal studies will need to be conducted in order to eliminate the aforementioned limitations.

Optical coherence tomography angiography as a potential screening tool for cerebral small vessel diseases

Background

The retina and the brain share anatomic, embryologic, and physiologic characteristics. Therefore, retinal imaging in patients with brain disorders has been of significant interest. Using optical coherence tomography angiography (OCTA), a novel quantitative method of measuring retinal vasculature, we aimed to evaluate radial peripapillary capillary (RPC) network density and retinal nerve fiber layer (RNFL) thickness in cognitively impaired patients and determine their association with brain imaging markers.

Methods

In this prospective cross-sectional study, a total of 69 patients (138 eyes) including 29 patients with amyloid-positive Alzheimer’s disease-related cognitive impairment (ADCI), 25 patients with subcortical vascular cognitive impairment (SVCI), and 15 amyloid-negative cognitively normal (CN) subjects were enrolled. After excluding eyes with an ophthalmologic disease or poor image quality, 117 eyes of 60 subjects were included in the final analyses. Retinal vascular [capillary density (CD) of the radial peripapillary capillary (RPC) network] and neurodegeneration markers [retinal nerve fiber layer (RNFL) thickness at four quadrants] were measured using OCTA and OCT imaging. Brain vascular (CSVD score) and neurodegeneration markers (cortical thickness) were assessed using 3D brain magnetic resonance imaging. The CD and RNFL thickness and their correlation with brain imaging markers were investigated.

Results

The SVCI group showed lower CD in the temporal quadrant of the RPC network compared to the CN group (mean (SD), 42.34 (6.29) vs 48.45 (7.08); p = 0.001). When compared to the ADCI group, the SVCI showed lower CD in the superior quadrant (mean (SD), 60.14 (6.42) vs 64.15 (6.39); p = 0. 033) as well as in the temporal quadrant (ADCI 45.76, SVCI 42.34; p = 0.048) of the RPC network. The CD was negatively correlated with CSVD score in the superior (B (95%CI), − 0.059 (− 0.097 to − 0.021); p = 0.003) and temporal (B (95%CI), − 0.048 (− 0.080 to − 0.017); p = 0.003) quadrants of the RPC network. RNFL thickness did not differ among the groups nor did it correlate with cortical thickness.

Conclusions and relevance

The microvasculature of the RPC network was related to the CSVD burden. However, the RNFL thickness did not reflect cerebral neurodegeneration. Noninvasive and rapid acquisition of the OCTA image might have the potential to be used as a screening tool to detect CSVD.