OCT in Alzheimer's disease: thinning of the RNFL and superior hemiretina

Retinal Microvascular and Neurodegenerative Changes in Alzheimer's Disease and Mild Cognitive Impairment Compared with Control Participants

PURPOSE

Evaluate and compare the retinal microvasculature in the superficial capillary plexus (SCP) in Alzheimer's disease (AD), mild cognitive impairment (MCI), and cognitively intact controls using OCT angiography. OCT parameters were also compared.

DESIGN

Cross-sectional study.

PARTICIPANTS

Seventy eyes from 39 AD participants, 72 eyes from 37 MCI participants, and 254 eyes from 133 control participants were enrolled.

METHODS

Participants were imaged using Zeiss Cirrus HD-5000 with AngioPlex (Carl Zeiss Meditec, Dublin, CA) and underwent cognitive evaluation with Mini-Mental State Examination.

MAIN OUTCOME MEASURES

Vessel density (VD) and perfusion density (PD) in the SCP within the Early Treatment Diabetic Retinopathy Study 6-mm circle, 3-mm circle, and 3-mm ring were compared between groups. Foveal avascular zone (FAZ) area, central subfield thickness (CST), macular ganglion cell-inner plexiform layer (GC-IPL) thickness, and peripapillary retinal nerve fiber layer (RNFL) thickness were also compared.

RESULTS

Alzheimer's participants showed significantly decreased SCP VD and PD in the 3-mm ring (P = 0.001 and P = 0.002, respectively) and 3-mm circle (P = 0.003 and P = 0.004, respectively) and decreased SCP VD in the 6-mm circle (P = 0.047) compared with MCI and significantly decreased SCP VD and PD in the 3-mm ring (P = 0.008 and P = 0.004, respectively) and 3-mm circle (P = 0.015 and P = 0.009, respectively) and SCP PD in the 6-mm circle (P = 0.033) when compared with cognitively intact controls. There was no difference in SCP VD or PD between MCI and controls (P > 0.05). FAZ area and CST did not differ significantly between groups (P > 0.05). Alzheimer's participants showed significantly decreased GC-IPL thickness over the inferior (P = 0.032) and inferonasal (P = 0.025) sectors compared with MCI and significantly decreased GC-IPL thickness over the entire (P = 0.012), superonasal (P = 0.041), inferior (P = 0.004), and inferonasal (P = 0.006) sectors compared to controls. MCI participants showed significantly decreased temporal RNFL thickness (P = 0.04) compared with controls.

CONCLUSIONS

Alzheimer's participants showed significantly reduced macular VD, PD, and GC-IPL thickness compared with MCI and controls. Changes in the retinal microvasculature may mirror small vessel cerebrovascular changes in AD.

Light-Induced Pupillary Responses in Alzheimer's Disease

The impact of Alzheimer's disease (AD) on the pupillary light response (PLR) is controversial, being dependent on the stage of the disease and on the experimental pupillometric protocols. The main hypothesis driving pupillometry research in AD is based on the concept that the AD-related neurodegeneration affects both the parasympathetic and the sympathetic arms of the PLR (cholinergic and noradrenergic theory), combined with additional alterations of the afferent limb, involving the melanopsin expressing retinal ganglion cells (mRGCs), subserving the PLR. Only a few studies have evaluated the value of pupillometry as a potential biomarker in AD, providing various results compatible with parasympathetic dysfunction, displaying increased latency of pupillary constriction to light, decreased constriction amplitude, faster redilation after light offset, decreased maximum velocity of constriction (MCV) and maximum constriction acceleration (MCA) compared to controls. Decreased MCV and MCA appeared to be the most accurate of all PLR parameters allowing differentiation between AD and healthy controls while increased post-illumination pupillary response was the most consistent feature, however, these results could not be replicated by more recent studies, focusing on early and pre-clinical stages of the disease. Whether static or dynamic pupillometry yields useful biomarkers for AD screening or diagnosis remains unclear. In this review, we synopsize the current knowledge on pupillometric features in AD and other neurodegenerative diseases, and discuss potential roles of pupillometry in AD detection, diagnosis and monitoring, alone or in combination with additional biomarkers.

Spectral-Domain OCT Measurements in Alzheimer's Disease: A Systematic Review and Meta-analysis

TOPIC

OCT is a noninvasive tool to measure specific retinal layers in the eye. The relationship of retinal spectral-domain (SD) OCT measurements with Alzheimer's disease (AD) and mild cognitive impairment (MCI) remains unclear. Hence, we conducted a systematic review and meta-analysis to examine the SD OCT measurements in AD and MCI.

CLINICAL RELEVANCE

Current methods of diagnosing early AD are expensive and invasive. Retinal measurements of SD OCT, which are noninvasive, technically simple, and inexpensive, are potential biomarkers of AD.

METHODS

We conducted a literature search in PubMed and Excerpta Medica Database to identify studies published before December 31, 2017, that assessed the associations between AD, MCI, and measurements of SD OCT: ganglion cell-inner plexiform layer (GC-IPL), ganglion cell complex (GCC), macular volume, and choroidal thickness, in addition to retinal nerve fiber layer (RNFL) and macular thickness. We used a random-effects model to examine these relationships. We also conducted meta-regression and assessed heterogeneity, publication bias, and study quality.

RESULTS

We identified 30 eligible studies, involving 1257 AD patients, 305 MCI patients, and 1460 controls, all of which were cross-sectional studies. In terms of the macular structure, AD patients showed significant differences in GC-IPL thickness (standardized mean difference [SMD], -0.46; 95% confidence interval [CI], -0.80 to -0.11; I2 = 71%), GCC thickness (SMD, -0.84; 95% CI, -1.10 to -0.57; I2 = 0%), macular volume (SMD, -0.58; 95% CI, -1.03 to -0.14; I2 = 80%), and macular thickness of all inner and outer sectors (SMD range, -0.52 to -0.74; all P < 0.001) when compared with controls. Peripapillary RNFL thickness (SMD, -0.67; 95% CI, -0.95 to -0.38; I2 = 89%) and choroidal thickness (SMD range, -0.88 to -1.03; all P < 0.001) also were thinner in AD patients.

CONCLUSIONS

Our results confirmed the associations between retinal measurements of SD OCT and AD, highlighting the potential usefulness of SD OCT measurements as biomarkers of AD.

The Retina as a Window or Mirror of the Brain Changes Detected in Alzheimer's Disease: Critical Aspects to Unravel

Alzheimer's disease is the most frequent cause of dementia worldwide, representing a global health challenge, with a massive impact on the quality of life of Alzheimer's disease patients and their relatives. The diagnosis of Alzheimer's disease constitutes a real challenge, because the symptoms manifest years after the first degenerative changes occurring in the brain and the diagnosis is based on invasive and/or expensive techniques. Therefore, there is an urgent need to identify new reliable biomarkers to detect Alzheimer's disease at an early stage. Taking into account the evidence for visual deficits in Alzheimer's disease patients, sometimes even before the appearance of the first disease symptoms, and that the retina is an extension of the brain, the concept of the retina as a window to look into the brain or a mirror of the brain has received increasing interest in recent years. However, only a few studies have assessed the changes occurring in the retina and the brain at the same time points. Unlike previous reviews on this subject, which are mainly focused on brain changes, we organized this review by comprehensively summarizing findings related with structural, functional, cellular, and molecular parameters in the retina reported in both Alzheimer's disease patients and animal models. Moreover, we separated the studies that assessed only the retina, and those that assessed both the retina and brain, which are few but allow establishing correlations between the retina and brain. This review also highlights some inconsistent results in the literature as well as relevant missing gaps in this field.

The role of ophthalmic imaging in central nervous system degeneration in systemic lupus erythematosus

Systemic lupus erythematosus (SLE) is an autoimmune connective tissue disorder that can involve any organ system. Central nervous system involvement can be a severe life threatening complication, ultimately resulting in severe neurodegenerative changes. Magnetic resonance imaging suggests that neurodegeneration, which may have deleterious effects on brain function, may occur early in SLE and experimental models suggest that neuroprotection may be feasible and beneficial. The retina is an extension of the brain. Recent ophthalmic imaging technologies are capable of identifying early changes in retinal and choroidal morphology and circulation that may reflect CNS degeneration. However, their utility in monitoring CNS involvement in SLE has been poorly studied as these have only been performed in small cohorts, in a cross-sectional design, non-quantitatively and without correlation to disease activity. The authors aim to review the current understanding of neurodegeneration associated with SLE, with particular focus on the visual pathway. We describe the neuropathology of the visual system in SLE and the evidence for retinal and choroidal neurodegenerative and microvascular changes using optical coherence tomography technology. We aim to describe the potential role of optical imaging modalities in NPSLE diagnosis and their likely impact on the study of neuronal function.

Change in retinal structural anatomy during the preclinical stage of Alzheimer's disease

INTRODUCTION

We conducted a 27-month longitudinal study of mid-life adults with preclinical Alzheimer's disease (AD), using spectral domain optical coherence tomography to compare changes in volume and thickness in all retinal neuronal layers to those of age-matched healthy control subjects.

METHODS

Fifty-six older adults (mean age = 65.36 years) with multiple risk factors for AD completed spectral domain optical coherence tomography retinal imaging and cognitive testing at baseline. Twenty-seven months later, they completed the same examinations and an 18F-florbetapir positron emission tomography imaging study.

RESULTS

Compared to healthy control subjects, those in the preclinical stage of AD showed a significant decrease in macular retinal nerve fiber layer (mRNFL) volume, over a 27-month follow-up interval period, as well as a decrease in outer nuclear layer and inner plexiform layer volumes and thickness in the inferior quadrant. However, only the mRNFL volume was linearly related to neocortical positron emission tomography amyloid standardized uptake value ratio after controlling for any main effects of age (R2 = 0.103; ρ = 0.017). Furthermore, the magnitude of mRNFL volume reduction was significantly correlated with performance on a task of participants' abilities to efficiently integrate visual and auditory speech information (McGurk effect).

DISCUSSION

We observed a decrease in mRNFL, outer nuclear layer, and inner plexiform layer volumes, in preclinical AD relative to controls. Moreover, the largely myelinated axonal loss in the RNFL is related to increased neocortical amyloid-β accumulation after controlling for age. Volume loss in the RNFL, during the preclinical stage, is not related to performance on measures of episodic memory or problem solving. However, this retinal change does appear to be modestly related to relative decrements in performance on a measure of audiovisual integration efficiency that has been recently advanced as a possible early cognitive marker of mild cognitive impairment.

Optical Coherence Tomography in Alzheimer's Disease and Other Neurodegenerative Diseases

Over the past decade, a surge of evidence has documented various pathological processes in the retina of patients suffering from mild cognitive impairment, Alzheimer's disease (AD), Parkinson's disease (PD), and other neurodegenerative diseases. Numerous studies have shown that the retina, a central nervous system tissue formed as a developmental outgrowth of the brain, is profoundly affected by AD. Harboring the earliest detectable disease-specific signs, amyloid β-protein (Aβ) plaques, the retina of AD patients undergoes substantial ganglion cell degeneration, thinning of the retinal nerve fiber layer, and loss of axonal projections in the optic nerve, among other abnormalities. More recent investigations described Aβ plaques in the retina located within sites of neuronal degeneration and occurring in clusters in the mid- and far-periphery of the superior and inferior quadrants, regions that had been previously overlooked. Diverse structural and/or disease-specific changes were also identified in the retina of PD, Huntington's disease, and multiple sclerosis patients. The pathological relationship between the retina and brain prompted the development of imaging tools designed to noninvasively detect and monitor these signs in living patients. One such tool is optical coherence tomography (OCT), uniquely providing high-resolution two-dimensional cross-sectional imaging and three-dimensional volumetric measurements. As such, OCT emerged as a prominent approach for assessing retinal abnormalities in vivo, and indeed provided multiple parameters that allowed for the distinction between normal aged individuals and patients with neurodegenerative diseases. Beyond the use of retinal optical fundus imaging, which recently allowed for the detection and quantification of amyloid plaques in living AD patients via a wide-field view of the peripheral retina, a major advantage of OCT has been the ability to measure the volumetric changes in specified retinal layers. OCT has proven to be particularly useful in analyzing retinal structural abnormalities consistent with disease pathogenesis. In this review, we provide a summary of OCT findings in the retina of patients with AD and other neurodegenerative diseases. Future studies should explore the combination of imaging early hallmark signs together with structural-functional biomarkers in the accessible retina as a practical means of assessing risk, disease progression, and therapeutic efficacy in these patients.