Vision in Alzheimer's disease: a focus on the anterior afferent pathway

Primary eyecare provision for people living with dementia: what do we need to know?

Dementia comprises a group of brain disorders characterised by loss of cognitive function. Sensory loss, predominantly vision (the focus of this review) and hearing, is a significant problem for people living with dementia. Eyecare practitioners such as optometrists therefore play an important role in identifying and addressing vision-related care needs. To support provision of high quality "dementia-friendly" eyecare, this scoping review summarises recent primary research findings and available clinical practice guidelines, to identify research gaps relating to vision and dementia, and make recommendations for future research and clinical practice. The review set a priori guidelines for the population, concept and context based on the review questions. Primary research papers (2016-2021) were included via 3-step search strategy: preliminary search to index terms, full search, search reference lists of included articles for further inclusions. Additionally, websites of eyecare professional bodies in English-speaking countries were searched to identify current clinical eyecare practice guidelines relating to dementia. Study characteristics (e.g. country, study design) were reported descriptively. Patterns within findings/recommendations from included sources were identified using thematic analysis and reported as themes. 1651 titles/abstracts and 161 full-text articles were screened for eligibility. Three clinical practice guidelines were also identified. The final review included 21 sources: 18 primary research papers and 3 clinical practice guidelines. The thematic analysis reported five key themes: Diagnosis/Screening, dementia progression, findings on clinical visual testing, tailored approach to care, improving care. This scoping review demonstrated limited information about current practices of optometrists working with people living with dementia. Recent evidence reinforces the continuing need for improved eyecare for people living with dementia, taking into account their specific needs with an individualised approach. Up-to-date practical recommendations are synthesised for eyecare providers before, during and after a consultation with a person living with dementia, to better support their care.

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.

Alzheimer's and Consciousness: How Much Subjectivity Is Objective?

Does Alzheimer Disease show a decline in cognitive functions that relate to the awareness of external reality? In this paper, we will propose a perspective that patients with increasing symptoms of AD show a change in the awareness of subjective versus objective representative axis of reality thus consequently move to a more internal like perception of reality. This paradigm shift suggests that new insights into the dynamicity of the conscious representation of reality in the AD brain may give us new clues to the very early signs of memory and self-awareness impairment that originates from, in our view the microtubules. Dialog between Adso and William, in Umberto Eco's The Name of the Rose, Third Day: Vespers. "But how does it happen," I said with admiration, "that you were able to solve the mystery of the library looking at it from the outside, and you were unable to solve it when you were inside?" "Thus, God knows the world, because He conceived it in His mind, as if it was from the outside, before it was created, and we do not know its rule, because we live inside it, having found it already made."

Subclinical retinal angiopathy associated with hereditary transthyretin amyloidosis - assessed with optical coherence tomography angiography

BACKGROUND

Retinal angiopathy is a known ocular manifestation of hereditary transthyretin amyloidosis (ATTRv). Optical coherence tomography angiography (OCT-A) is a recent noninvasive imaging technique, used in other retinal vascular diseases. Our purpose was to analyse subclinical changes in retinal vessels, with OCT-A, in patients with ATTRv amyloidosis.

METHODS

Observational cross-sectional study in Centro Hospitalar e Universitário do Porto in the cohort of patients with genetic diagnosis of ATTRv. Patients were included if they had just one eye with scalloped iris (the other eye without scalloped iris), postulating eyes were at different stages, in the same patient. Patients were excluded if they had other manifestations of ocular ATTRv amyloidosis, namely clinical retinal angiopathy and/or vitreous opacities. The group of eyes with scalloped iris were compared with eyes without scalloped iris, using paired tests. Values are shown as Δ = mean difference between groups; p = p-value, d = Cohen's d for effect size measurement.

RESULTS

Twenty-four patients (24 eyes in each group) were included. Mean age was 46.5 ± 5.0 years. Eyes with scalloped iris showed attenuated retinal vascular network: larger foveal avascular zone (FAZ) area (Δ = +0.02 mm², p = 0.002, d = 0.70); decreased foveal vascular density (Δ = -3.57%, p = 0.001, d = -0.75); superficial (Δ = -1.50%, p = 0.049, d = -0.43) and deep (Δ = -2.53%, p = 0.023, d = -0.50) plexus vascular density. Acircularity index was superior in scalloped iris eyes (Δ = 0.04, p = 0.004, d = -0.65), representing an abnormal FAZ morphology.

CONCLUSION

Scalloped iris in ATTRv eyes are associated with a more advanced subclinical retinal angiopathy, than eyes without scalloped iris. Our results identify for the first time and in vivo, early changes in retinal vessels in ATTRv amyloidosis. Henceforward, OCT-A may play a role in the evaluation of ATTRv patients oculopathy and the effectiveness of future eye targeting treatments.

Optical Coherence Tomography in Mild Cognitive Impairment: A Systematic Review and Meta-Analysis

Purpose: The use of optical coherence tomography (OCT) of the retina to detect inner retinal degeneration is being investigated as a potential biomarker for mild cognitive impairment (MCI) and Alzheimer's disease (AD), and an overwhelming body of evidence indicates that discovery of disease-modifying treatments for AD should be aimed at the pre-dementia clinical stage of AD, i.e., MCI. We aimed to perform a systematic review and meta-analysis on retinal OCT in MCI.

Methods: We performed a systematic review of the English literature in three databases (PubMed, Embase, and Latindex) for studies that measured retinal thickness using OCT in people with MCI and healthy controls, age 50 or older, between 1 January 2000 and 31 July 2019. Only cohort and case-control studies were reviewed, and independent extraction of quality data and established objective data was performed. We calculated the effect size for studies in the review that met the following criteria: (1) a statistically significant difference between MCI subjects and normal controls for several OCT variables, (2) use of spectral domain OCT, and (3) use of APOSTEL recommendations for OCT reporting. Weighted Hedges' g statistic was used to calculate the pooled effect size for four variables: ganglion cell layer-inner plexiform layer (GCL-IPL) complex thickness in micrometers (μm), circumpapillary retinal nerve fiber layer (pRNFL) thickness in μm, macular thickness in μm, and macular volume in μm³. For variables with high heterogeneity, a multivariate meta-regression was performed. We followed the PRISMA guidelines for systematic reviews.

Results: Fifteen articles met the inclusion criteria. A total of 58.9% of MCI patients had statistically significant thinning of the pRNFL compared with normal subjects, while 61.6% of all MCI patients who had macular volume measured had a statistically significant reduction in volume compared with controls, and 50.0% of the macular GCL-IPL complexes measured demonstrated significant thinning in MCI compared with normal controls. Meta-analysis demonstrated a large effect size for decreased macular thickness in MCI subjects compared with normal controls, but there was a substantial heterogeneity for macular thickness results. The other variables did not demonstrate a significant difference and also had substantial heterogeneity. Meta-regression analysis did not reveal an explanation for the heterogeneity.

Conclusions: A better understanding of the cause of retina degeneration and longitudinal, standardized studies are needed to determine if optical coherence tomography can be used as a biomarker for mild cognitive impairment due to Alzheimer's disease.

Retinal thickness as a potential biomarker in patients with amyloid-proven early- and late-onset Alzheimer's disease

Introduction

Retinal thickness measured with optical coherence tomography has been proposed as a noninvasive biomarker for Alzheimer's disease (AD). We therefore measured retinal thickness in well-characterized AD and control participants, considering ophthalmological confounders.

Methods

We included 57 amyloid-proven AD cases and 85 cognitively normal, amyloid-negative controls. All subjects underwent retinal thickness measurements with spectral domain optical coherence tomography and an ophthalmological assessment to exclude ocular disease.

Results

Retinal thickness did not discriminate cases from controls, including stratified analyses for early- versus late-onset AD. We found significant associations between macular thickness and global cortical atrophy [β -0.358; P = .01] and parietal cortical atrophy on magnetic resonance imaging [β -0.371; P < .01] in AD cases.

Discussion

In this study, representing the largest optical coherence tomography cohort with amyloid-proven AD cases, we show that retinal thickness does not discriminate AD from controls, despite evident changes on clinical, neuroimaging, and CSF measures, querying the use of retinal thickness measurements as an AD biomarker.

Retinal thickness as potential biomarker in posterior cortical atrophy and typical Alzheimer's disease

BACKGROUND

Retinal thickness can be measured non-invasively with optical coherence tomography (OCT) and may offer compelling potential as a biomarker for Alzheimer's disease (AD). Retinal thinning is hypothesized to be a result of retrograde atrophy and/or parallel neurodegenerative processes. Changes in the visual pathway are of particular interest in posterior cortical atrophy (PCA), the most common atypical AD phenotype predominantly affecting the parietal-occipital cortices. We therefore evaluated retinal thickness as non-invasive biomarker of neurodegeneration in well-characterized participants with posterior cortical atrophy (PCA) and typical Alzheimer's disease (tAD).

METHODS

Retinal thickness measures were acquired from 48 patient participants (N = 25 PCA; N = 23 tAD) fulfilling consensus diagnostic criteria and 70 age-matched controls. Participants were recruited between 2014 and 2016. All participants underwent optical coherence tomography (OCT) imaging, including measurement of peripapillary retinal nerve fiber layer (pRNFL) thickness and total macular thickness (mRT). Participants did not show evidence of any significant ophthalmological conditions. Subgroup analyses were performed in participants with available MRI and CSF measures, providing evidence of neurodegeneration and underlying AD pathology respectively.

RESULTS

There was no evidence of overall between-group differences in pRNFL thickness (mean PCA 98.7 ± 12.2; tAD 99.9 ± 8.7; controls 99.6 ± 10.0 μm, one-way analysis of variance (ANOVA) p = 0.92) or total mRT (mean PCA 266.9 ± 16.3; tAD 267.8 ± 13.6; controls 269.3 ± 13.6 μm, one-way ANOVA p = 0.75). Similarly, subgroup analysis with MRI biomarkers (PCA = 18, tAD = 17, controls = 31) showing neurodegeneration, and CSF biomarkers (PCA = 18, tAD = 14, controls = 13) supporting underlying AD pathology did not provide evidence of overall between-group differences in pRNFL or mRT measures (all p > 0.3).

CONCLUSIONS

Retinal thickness did not discriminate tAD and PCA from controls or from one another despite unequivocal differences on standard clinical, neuro-imaging and CSF measures. Findings from this well-characterized sample, including cases with PCA, do not support the hypothesis that retinal neurodegeneration, measured using conventional OCT, is a useful biomarker for AD or PCA.

Introducing volume 8 of Neurodegenerative Disease Management

Welcome to the eighth volume of Neurodegenerative Disease Management. At the start of a new volume, it is interesting to look back at which content proved most popular in 2017, and also to take a look forward to the content of this issue and beyond.

Amyloid-beta and phosphorylated tau in post-mortem Alzheimer's disease retinas

In-vivo labeling of retinal amyloid-beta(Aβ) and tau has potential as non-invasive biomarker for Alzheimer's disease (AD). However, literature on the presence of Aβ and phosphorylated tau (pTau) in AD retinas is inconclusive. We therefore assessed the presence of Aβ and pTau in post-mortem retinas in 6 AD and 6 control cases who donated brains and eyes to the Netherlands Brain Bank. Neuropathological diagnosis of AD was made according to NIA-AA criteria. Formalin fixed retinas were dissected in quadrants and cross-sections of medial and superior retinas were made. Immuno-histochemical stainings were performed for Aβ, amyloid precursor protein (APP) and pTau. To assess translation to an in-vivo set up using curcumin as labelling fluorophore, co-stainings with curcumin were performed. No typical Aβ-plaques and neurofibrillary tangles, like in the cerebral cortex, were observed in AD retinas. A diffuse immunoreactive signal for pTau was increased in the inner and outer plexiform layers of the retina in AD cases compared to control cases with absence of cerebral amyloid pathology. Immunostaining with anti-Aβ and anti-APP antibodies yielded signal in ganglion cells, amacrine cells, horizontal cells and Müller cells in both control and AD cases. We observed small extracellular deposits positive for anti-Aβ antibodies 12F4 and 6E10 and negative for 4G8 and curcumin. A subset of these deposits could be characterized as corpora amylacea. In conclusion we found that retinal manifestations of AD pathology appear to be different compared to cerebral AD pathology. Using a qualitative cross-sectional approach, we did not find Aβ/APP related differences in the retina between AD and control subjects. In contrast, tau related changes were found to be present in cases with cerebral AD pathology, suggesting retinal tau as a potential biomarker for AD.

Principles of OCTA and Applications in Clinical Neurology

PURPOSE OF REVIEW

The article reviews the recent findings on the use of optical coherence tomography angiography (OCTA) in neurology.

RECENT FINDINGS

OCTA is a new addition to the powerful and complementary technology of the OCT. Due to its noninvasiveness, and reproducibility, it is possible to obtain high-resolution 3D images of the vessels of the human eye. As the vessels of the retina with the presence of endothelial cell's tight junctions resemble the brain vessels, it was hypothesized that the imaging of the retinal vessels might bring insight into brain vessels. OCTA has been effectively used to predict retinal vessel abnormalities in dementia, demyelization, optic disc neuropathies, and inherited degenerative diseases. Most common findings were decrease of vascular density and flow and an increase of avascular zones. Although OCTA is a relative new technology, recent studies show that it can be successfully applied in neurology.

Visual Features in Alzheimer's Disease: From Basic Mechanisms to Clinical Overview

Alzheimer's disease (AD) is the leading cause of dementia worldwide. It compromises patients' daily activities owing to progressive cognitive deterioration, which has elevated direct and indirect costs. Although AD has several risk factors, aging is considered the most important. Unfortunately, clinical diagnosis is usually performed at an advanced disease stage when dementia is established, making implementation of successful therapeutic interventions difficult. Current biomarkers tend to be expensive, insufficient, or invasive, raising the need for novel, improved tools aimed at early disease detection. AD is characterized by brain atrophy due to neuronal and synaptic loss, extracellular amyloid plaques composed of amyloid-beta peptide (Aβ), and neurofibrillary tangles of hyperphosphorylated tau protein. The visual system and central nervous system share many functional components. Thus, it is plausible that damage induced by Aβ, tau, and neuroinflammation may be observed in visual components such as the retina, even at an early disease stage. This underscores the importance of implementing ophthalmological examinations, less invasive and expensive than other biomarkers, as useful measures to assess disease progression and severity in individuals with or at risk of AD. Here, we review functional and morphological changes of the retina and visual pathway in AD from pathophysiological and clinical perspectives.

The role of optical coherence tomography and infrared oculography in assessing the visual pathway and CNS in multiple sclerosis

In this review, a current overview is provided of how optical coherence tomography and infrared oculography can aid in assessing the visual system and CNS in multiple sclerosis (MS). Both afferent and efferent visual disorders are common in MS and visual complaints can have a tremendous impact on daily functioning. Optical coherence tomography and infrared oculography can detect and quantify visual disorders with high accuracy, but could also serve as quantitative markers for inflammation, neurodegeneration and network changes including cognitive decline in MS patients. The assessment of the efferent and afferent visual pathways is relevant for monitoring and predicting the disease course, but is also potentially valuable as an outcome measure in therapeutic trials.