The pathogenesis of age-related macular degeneration

Macular Neovascularization Secondary to Subclinical Angioid Streaks in Age-Related Macular Degeneration: Treatment Response to Anti-VEGF at 2-Year Follow-up

INTRODUCTION

To characterize the response to antivascular endothelial growth factor (VEGF) treatment of macular neovascularization (MNV) secondary to age-related macular degeneration (AMD) with subclinical angioid streaks (AS) during a 2-year follow-up.

METHODS

Retrospective, longitudinal, case-control, and multicentric study. Among a cohort of neovascular AMD population, we selected patients with subclinical AS and treatment-naïve MNV treated with anti-VEGF for a 2-year follow-up. An age- and sex-matched control group with treatment-naïve MNV secondary to AMD without subclinical AS was selected. Demographics and differences in treatment response (i.e., number of injections needed, anatomical and functional outcomes) between the two groups were analyzed.

RESULTS

Among 102 eyes of 102 patients with neovascular AMD, 34 eyes of 34 patients (82 ± 6 years old) were included in the subclinical AS group, whereas 68 eyes of 68 patients (81 ± 6 years old, p = 0.342) in the control group. All eyes with subclinical AS presented RPD compared to 56% of eyes without subclinical AS (p < 0.001). During the 2-year follow-up, eyes with subclinical AS needed more injections (10.6 ± 3.2 vs 8.3 ± 3.1 injections for eyes with and without subclinical AS, respectively, p < 0.001). Visual acuity (VA) decreased during the treatment (from 0.53 ± 0.37 at the baseline to 0.69 ± 0.45 LogMAR at 2-year follow-up, p = 0.044) in eyes with subclinical AS; no VA changes were observed in the control group (p = 0.798). RPE atrophy at the end of the 2-year follow-up affected 74% of cases with subclinical AS and 29% of cases of the control group (p < 0.001).

CONCLUSIONS

MNVs secondary to AMD with subclinical AS are characterized by worse functional and anatomical outcomes after 2-year anti-VEGF treatment compared to MNV secondary to AMD without subclinical AS, supporting the different pathophysiological mechanisms involved in this recently described AMD phenotype.

Alzheimer Disease Treatment With Acetylcholinesterase Inhibitors and Incident Age-Related Macular Degeneration

Importance

Age-related macular degeneration (AMD) is a serious and common ophthalmologic disorder that is hypothesized to result, in part, from inflammatory reactions in the macula. Alzheimer disease (AD) treatment, acetylcholinesterase inhibitors (AChEIs), have anti-inflammatory effects and it remains unclear if they modify the risk of AMD.

Objective

To investigate the association between AChEI medications and the incidence of AMD.

Design, Setting, and Participants

This propensity score-matched retrospective cohort study took place at health care facilities within the US Department of Veterans Affairs (VA) health care system from January 2000 through September 2023. Participants included patients diagnosed with AD between ages 55 and 80 years with no preexisting diagnosis of AMD in the VA database.

Exposure

AChEIs prescription dispensed as pharmacologic treatments for AD.

Main Outcomes and Measure

The first diagnosis of AMD.

Results

A total of 21 823 veterans with AD (mean [SD] age, 72.3 [6.1] years; 21 313 male participants [97.7%] and 510 female participants [2.3%]) were included. Propensity score-matched Cox model reveals each additional year of AChEI treatment was associated with a 6% lower hazard of AMD (hazard ratio, 0.94; 95% CI, (0.89-0.99).

Conclusions and Relevance

This observational study reports a small reduction in the risk of AMD among veterans with AD receiving AChEIs. Randomized clinical trials would be needed to determine if there is a cause-and-effect relationship and further research is required to validate these findings across diverse populations.

Subclinical Angioid Streaks with Pseudodrusen: A New Phenotype of Age-Related Macular Degeneration

INTRODUCTION

To describe subclinical angioid streaks (AS) as a frequent, peculiar age-related macular degeneration (AMD) phenotype, comparing features of eyes with subclinical AS with those of eyes with AMD without AS.

METHODS

This was a retrospective, observational study. Among a patient cohort with AMD, we selected patients without known causes for AS whose eyes showed signs of angioid streaks (AS) on structural optical coherence tomography (OCT) but not on fundus examination. Selected OCT features of AS were Bruch's membrane (BM) breaks and large BM dehiscences.

RESULTS

Among 543 eyes of 274 patients with AMD (mean ± standard deviation: 82 ± 7 years), 73 eyes of 46 patients (81 ± 7 years; p = 0.432) showed AS features on OCT (OCT AS) that were not visible on fundus examination. Estimated prevalence of subclinical age-related AS was 13.4% (95% confidence interval 10.3-16.3%) in this AMD population. Fifty-three eyes (73%) with AS features were affected by peripapillary atrophy, often with a "petaloid-like" pattern, similar to typical features of AS disease. Almost all cases (97%) presented reticular pseudodrusen (RPD), with (41%) or without (59%) drusen showing a significant difference in RPD prevalence in OCT AS eyes in comparison to AMD eyes without subclinical AS using generalized estimating equations (P < 0.001). Among the 73 subclinical AS cases, 71 were affected by late AMD (57 with macular neovascularization, 14 with geographic atrophy), showing a more advanced AMD stage in comparison with AMD eyes without subclinical AS (P < 0.001). The following OCT features were disclosed: BM breaks in 100% of cases and BM dehiscences in 37%.

CONCLUSIONS

Subclinical AS in eyes with AMD is a peculiar phenotype of the disease, with features suggesting a primary involvement of Bruch's membrane and clinical similarities with mild, late-onset pseudoxanthoma elasticum.

The Choroidal Vascularity Index Versus Optical Coherence Tomography Angiography in the Evaluation of the Choroid with a Focus on Age-Related Macular Degeneration

The choroid is the most vascularized structure of the eye and it is fundamental for the trophism of the outer retina. Its proper functioning and homeostasis represent key points in maintaining normal retinal physiology. Choroidal alterations may be implicated in the development and progression of numerous pathologies; therefore, in-depth studies using imaging techniques can be of crucial relevance to understanding the pathophysiology of retinal-choroidal diseases. The advent of spectral-domain optical coherence tomography (SDOCT) has enabled the non-invasive study of the choroid in vivo and the most recent development, optical coherence tomography angiography (OCTA), allows for the high-resolution visualization of the choriocapillaris and the choroid in regard to vascularization. The choroidal vascularity index (CVI) is a new parameter calculated on SDOCT scans and is defined as the ratio of the luminal area to the total choroidal area. In this review, a study of the choroid using OCTA and CVI will be evaluated in depth and the pros and cons of these two methods will be analyzed, with a particular focus on age-related macular degeneration.

Age-Related Macular Degeneration With Visual Disability Is Associated With Cardiovascular Disease Risk in the Korean Nationwide Cohort

Background Age-related macular degeneration (AMD) is the leading cause of visual disability. AMD shares some risk factors with the pathogenesis of cardiovascular disease (CVD). However, previous studies examining the association between AMD and the risk of CVD provide conflicting results. Hence, we investigated the association between AMD, visual disability, and the risk of CVD. Methods and Results This is a nationwide cohort study using data from the Korean National Health Insurance System database (2009-2019) on subjects who underwent a national health screening program in 2009. A total of 3 789 963 subjects were categorized by the presence of AMD and visual disability. Visual disability was defined as a best-corrected visual acuity of ≤20/100 by validated documentation from a specialist physician. Cox regression hazard model was used to examine the hazard ratios (HRs) of CVD, including myocardial infarction and ischemic stroke, after adjusting for potential confounders. During a mean 9.77 years of follow-up, AMD was associated with a 5% higher risk of myocardial infarction (adjusted HR [aHR], 1.05 [95% CI, 1.01-1.10]) but not associated with increased risk of overall CVD (aHR, 1.02 [95% CI, 1.00-1.05]) or ischemic stroke (aHR, 1.02 [95% CI, 0.98-1.06]). However, when AMD was accompanied by visual disability, there was increased risk of CVD (aHR, 1.17 [95% CI, 1.06-1.29]), myocardial infarction (aHR, 1.18 [95% CI, 1.01-1.37]), and ischemic stroke (aHR, 1.20 [95% CI, 1.06-1.35]). These trends were more evident in women and subjects with cardiometabolic comorbidities. Conclusions AMD with visual disability, but not all AMD, was associated with an increased risk of CVD. Patients with AMD who have visual disability should be targeted for CVD prevention.

Clinicopathologic Findings in Three Siblings With Geographic Atrophy

Purpose

Age-related macular degeneration (AMD) is a leading cause of blindness among the elderly worldwide. Clinical imaging and histopathologic studies are crucial to understanding disease pathology. This study combined clinical observations of three brothers with geographic atrophy (GA), followed for 20 years, with histopathologic analysis.

Methods

For two of the three brothers, clinical images were taken in 2016, 2 years prior to death. Immunohistochemistry, on both flat-mounts and cross sections, histology, and transmission electron microscopy were used to compare the choroid and retina in GA eyes to those of age-matched controls.

Results

Ulex europaeus agglutinin (UEA) lectin staining of the choroid demonstrated a significant reduction in the percent vascular area and vessel diameter. In one donor, histopathologic analysis demonstrated two separate areas with choroidal neovascularization (CNV). Reevaluation of swept-source optical coherence tomography angiography (SS-OCTA) images revealed CNV in two of the brothers. UEA lectin also revealed a significant reduction in retinal vasculature in the atrophic area. A subretinal glial membrane, composed of processes positive for glial fibrillary acidic protein and/or vimentin, occupied areas identical to those of retinal pigment epithelium (RPE) and choroidal atrophy in all three AMD donors. SS-OCTA also demonstrated presumed calcific drusen in the two donors imaged in 2016. Immunohistochemical analysis and alizarin red S staining verified calcium within drusen, which was ensheathed by glial processes.

Conclusions

This study demonstrates the importance of clinicohistopathologic correlation studies. It emphasizes the need to better understand how the symbiotic relationship between choriocapillaris and RPE, glial response, and calcified drusen impact GA progression.

Towards a better understanding of non-exudative choroidal and macular neovascularization

Non-exudative macular and choroidal neovascularization (MNV and CNV) usually refers to the entity of treatment-naïve type 1 neovascularization in the absence of associated signs of exudation. Histopathological studies, dating back in the early 70s, identified the presence of non-exudative MNV, but the first clinical report of this finding was in the late 90s using indocyanine green angiography in eyes with age-related macular degeneration (AMD). With more advanced retinal imaging, there has been an ever increasing appreciation of non-exudative MNV associated with AMD and CNV with other macular disorders. However, consensus regarding the exact definition and the clinical management of this entity is lacking. Furthermore, there may be variation in the imaging features and clinical course suggesting that a spectrum of disease may exist. Herein, we review the large body of published work that has provided a better understanding of non-exudative MNV and CNV in the last decade. The prevalence, multimodal imaging features, clinical course, and response to treatment are discussed to elucidate further key insights about this entity. Based on these observations, this review also proposes a new theory about the origin and course of different sub-types of non-exudative MNV/CNV which can have different etiologies and pathways according to the clinical context of disease.

Choroidal Vascular Impairment in Intermediate Age-Related Macular Degeneration

Age-related macular degeneration (AMD) is a multifactorial disease, whose complete pathogenesis is still unclear. Local hemodynamics may play a crucial role in its manifestation and progression. To evaluate choroidal and retinal vascular parameters, a total of 134 eyes were analyzed, 100 with intermediate AMD and 34 age matched healthy controls. 131 eyes of 104 patients were eligible for complete image assessment and 3 eyes were excluded for insufficient image quality: Group 1: intermediate AMD (n = 97) and Group 2: healthy controls (n = 34). Spectral domain optic coherence tomography (SD-OCT) with enhanced depth imaging (EDI) and optic coherence tomography angiography (OCT-A) were acquired using Spectralis (Heidelberg Engineering). Choroid and retinal capillary plexus were evaluated and image binarization was used to obtain quantitative data. Mean age was 77.67 years old (YO) and 67.2% were women. Total subfoveal choroidal area and luminal area were significantly reduced in Group 1 compared with Group 2 (0.88 mm2 and 0.40 mm2 vs. 1.24 mm2 and 0.55 mm2, respectively) (p < 0.05). Regarding choriocapillary flow density, AMD eyes recorded reduced values (34.83%) compared with controls (36.25%) (p < 0.05). Chorioretinal vasculature is impaired in intermediate AMD patients and vascular parameters could be attractive new prognostic biomarkers. Future therapeutic approaches may target this vascular dysfunction and delay disease progression.

Etiopathogenesis of non-exudative age-related macular degeneration (literature review)

The article presents an overview of modern publications on epidemiology, risk factors, and the main links of the etiology and pathogenesis of age-related macular degeneration (AMD). The nonexudative or “dry” form of age-related macular degeneration is a multifactorial progressive pathological process caused by hereditary predisposition, general and local disorders of lipid metabolism, negative changes in  the blood supply to the eye, age-related destruction of the Bruch’s membrane and retinal pigment epithelium, the appearance of signs of local and systemic inflammation, the development of oxidative stress with the impact of toxic lipoperoxidation products on the structures of the posterior segment of the eye. Recent studies have discovered new ways of retinal pigment epithelial cell death in response to oxidative stress in AMD, in particular necroptosis, which, in addition to classical apoptosis, is considered the main mechanism of this process. It is noted that the development of AMD may be associated with an age-related decrease in the level of estrogen in women. The analysis of the data on the etiopathogenesis of age-related macular degeneration presented in the modern literature indicates the need for further research and generalization of local and general pathological processes developing in the dynamics of retinal visual function disorders by specialists of various scientific disciplines. 

A histological study of atherosclerotic characteristics in age-related macular degeneration

This study investigated the pathogenesis of age-related macular degeneration (AMD) using histological methods that are commonly used for atherosclerotic vascular disease (ASVD). 1 normal, 3 early dry AMD, and 1 late dry AMD eyes were obtained from the Lions Eye Bank of Oregon and systematically dissected. They were stained with hematoxylin and eosin, Oil red O, Masson, Elastica van Gieson, Alizarin red, and Prussian blue. Additionally, the normal and late dry AMD eyes were immunostained for a-smooth muscle actin, CD45, and CD68 with Nile red and DAPI. Correlations were found between severity of AMD and lipid accumulation in the deep sclera (+), numbers of drusen between the Bruch's membrane and retinal pigment epithelium (RPE) (+), amount of collagen in the deep sclera (+), and amount of elastin in the deep sclera (-) (P < 0.1). Geographic atrophy, RPE detachment, and abnormal capillary shape and distribution in the choriocapillaris were observed in the fovea of late AMD. There were no stenosis, plaque, hemorrhage, and calcification. Additionally, late AMD tended to have higher smooth muscle thicknesses of the choroidal vascular walls, lower numbers of T lymphocytes in the choroid, and higher numbers of macrophages near the RPE and in the choroid relative to normal (P < 0.1). Macrophages-derived foam cells were detected near the Bruch's membrane in late AMD. Therefore, the present study showed many histological characteristics of ASVD in AMD, which suggests an association between them; however, there were also some histological characteristics of ASVD that were not found in AMD, which indicates that there exist pathogenic differences between them. The results generally support the vascular model of AMD, but some details still need clarification.

Choroidal Vascularity Index in Different Cohorts of Dry Age-Related Macular Degeneration

Purpose

The purpose of this study was to investigate the choroidal luminal and interstitial stromal alterations using choroidal vascularity index (CVI) among different cohorts of dry age-related macular degeneration (dAMD) compared to healthy subjects.

Methods

Four distinct cohorts were collected: three different cohorts of patients with dAMD (i.e. drusen, reticular pseudodrusen [RPD], and geographic atrophy [GA]) and an age-matched cohort of healthy subjects (controls). CVI (the ratio between the luminal choroidal area [LCA] and the total choroidal area [TCA]) was calculated in the subfoveal 1000 µm area.

Results

One hundred twenty eyes (from 120 patients) were included (30 eyes in each cohort). The mean age was 76.6 ± 7.1 years. No statistical differences were disclosed in terms of age, axial length, and central macular thickness among study groups. TCA showed a different distribution among the four cohorts (P = 0.003), mainly due to the LCA changes (P = 0.001). Interestingly, CVI showed a different distribution among the four cohorts (P < 0.001). RPD showed a lower CVI in comparison to controls (P = 0.040), whereas GA showed a lower CVI in comparison to drusen, RPD, and controls (P = 0.001, P = 0.046, and P < 0.001, respectively).

Conclusions

Different cohorts of dAMD are characterized by different impairments of the choroidal vascular and stromal components, reflecting different degrees of AMD severity.

Translational Relevance

CVI provides insights for better understanding the pathogenesis of AMD.

ASSOCIATION OF TREATMENT RESPONSE WITH QUANTITATIVE CHANGES IN CHOROIDAL NEOVASCULARIZATION AND CHOROIDAL VESSEL IN NEOVASCULAR AGE-RELATED MACULAR DEGENERATION

PURPOSE

To evaluate the association between treatment response and quantitative morphological changes in choroidal neovascularization and outer choroidal vessels using optical coherence tomography angiography (OCTA) and en face OCT in neovascular age-related macular degeneration (nAMD).

METHODS

We retrospectively analyzed 75 eyes of typical nAMD patients and 53 polypoidal choroidal vasculopathy eyes of 124 patients with OCTA performed at least 6 months after initial antivascular endothelial growth factor treatment. Quantitative parameters, including vessel area, vessel diameter, branch vessel length, fractal dimension, and lacunarity were analyzed based on en face images of the choroidal neovascularization and choroidal vessel in Haller's layer. Parameters associated with loss of logarithm of the minimum angle of resolution visual acuity with the basis of 0.3 and the treatment interval (good vs. poor responder based on 12 weeks) were analyzed. Analyses were conducted for "before OCTA" (initial visit to OCTA) and "after OCTA" (OCTA to 6 months post-OCTA).

RESULTS

In typical nAMD, visual acuity loss before OCTA was associated with a higher SD of choroidal neovascularization diameter and lower choroidal fractal dimension. Visual acuity loss after OCTA in typical nAMD was associated with higher lacunarity of the choroid. Poor responders before OCTA were not associated with any factor. Poor responders after OCTA were associated with a lower SD of outer choroidal vessel diameter in typical nAMD. In polypoidal choroidal vasculopathy, no factor was associated with clinical outcomes in either period.

CONCLUSION

Quantitative analyses of choroidal neovascularization on OCTA and choroidal vessels on en face OCT provide information about treatment response, including changes in visual acuity and treatment interval, in nAMD.

Retinal Vessel Functionality Is Linked With ARMS2 A69S and CFH Y402H Polymorphisms and Choroidal Status in AMD Patients

Purpose

We aimed to investigate the reactivity of retinal vessels to a flickering stimulus in patients with age-related macular degeneration (AMD) and healthy participants. We also assessed whether the parameters of retinal vessels are dependent on genetic predisposition.

Methods

A total of 354 patients with AMD and 121 controls were recruited for the study. All participants underwent thorough ophthalmologic examination and static and dynamic retinal vessel analysis. AMD risk polymorphisms were genotyped in the CFH and ARMS2 genes.

Results

We found no differences between the AMD group and controls in central retinal arteriolar equivalent (CRAE), central retinal venular equivalent (CRVE), arteriovenous ratio (AVR), dynamic analysis of arteries (DAAs), or dynamic analysis of veins (DAVs). Eyes with early AMD presented with significantly higher AVR values than eyes with late AMD. In the AMD group, DAA correlated positively with both choroidal thickness (Rs = 0.14, P = 0.00096) and choroidal volume (Rs = 0.23, P < 0.0001), and no such associations were observed in the controls. We found significantly lower DAA (1.47 ± 1.50) in TT homozygotes for the ARMS2 A69S polymorphism in comparison with GG homozygotes (2.38 ± 1.79) and patients with GG + GT genotypes (2.28 ± 1.84). We also observed less prominent DAV (3.24 ± 1.71) in patients with TC + CC genotypes in the CFH Y402H polymorphism compared with TT homozygotes (3.83 ± 1.68).

Conclusions

Our findings suggest that retinal microcirculation appears to be associated with the genetic background, choroidal parameters, and clinical features of the patients with AMD.

Bruch's Membrane and the Choroid in Age-Related Macular Degeneration

A healthy choroidal vasculature is necessary to support the retinal pigment epithelium (RPE) and photoreceptors, because there is a mutualistic symbiotic relationship between the components of the photoreceptor/retinal pigment epithelium (RPE)/Bruch's membrane (BrMb)/choriocapillaris (CC) complex. This relationship is compromised in age-related macular degeneration (AMD) by the dysfunction or death of the choroidal vasculature. This chapter will provide a basic description of the human Bruch's membrane and choroidal anatomy and physiology and how they change in AMD.The choriocapillaris is the lobular, fenestrated capillary system of choroid. It lies immediately posterior to the pentalaminar Bruch's membrane (BrMb). The blood supply for this system is the intermediate blood vessels of Sattler's layer and the large blood vessels in Haller's layer.In geographic atrophy (GA), an advanced form of dry AMD, large confluent drusen form on BrMb, and hyperpigmentation (presumably dysfunction in RPE) appears to be the initial insult. The resorption of these drusen and loss of RPE (hypopigmentation) can be predictive for progression of GA. The death and dysfunction of CC and photoreceptors appear to be secondary events to loss in RPE. The loss of choroidal vasculature may be the initial insult in neovascular AMD (nAMD). We have observed a loss of CC with an intact RPE monolayer in nAMD, by making RPE hypoxic. These hypoxic cells then produce angiogenic substances like vascular endothelial growth factor (VEGF), which stimulate growth of new vessels from CC, resulting in choroidal neovascularization (CNV). Reduction in blood supply to the CC, often stenosis of intermediate and large blood vessels, is associated with CC loss.The polymorphisms in the complement system components are associated with AMD. In addition, the environment of the CC, basement membrane and intercapillary septa, is a proinflammatory milieu with accumulation of proinflammatory molecules like CRP and complement components during AMD. In this toxic milieu, CC die or become dysfunctional even early in AMD. The loss of CC might be a stimulus for drusen formation since the disposal system for retinal debris and exocytosed material from RPE would be limited. Ultimately, the photoreceptors die of lack of nutrients, leakage of serum components from the neovascularization, and scar formation.Therefore, the mutualistic symbiotic relationship of the photoreceptor/RPE/BrMb/CC complex is lost in both forms of AMD. Loss of this functionally integrated relationship results in death and dysfunction of all of the components in the complex.

MicroRNAs in Vascular Eye Diseases

Since the discovery of the first microRNA (miRNA) decades ago, studies of miRNA biology have expanded in many biomedical research fields, including eye research. The critical roles of miRNAs in normal development and diseases have made miRNAs useful biomarkers or molecular targets for potential therapeutics. In the eye, ocular neovascularization (NV) is a leading cause of blindness in multiple vascular eye diseases. Current anti-angiogenic therapies, such as anti-vascular endothelial growth factor (VEGF) treatment, have their limitations, indicating the need for investigating new targets. Recent studies established the roles of various miRNAs in the regulation of pathological ocular NV, suggesting miRNAs as both biomarkers and therapeutic targets in vascular eye diseases. This review summarizes the biogenesis of miRNAs, and their functions in the normal development and diseases of the eye, with a focus on clinical and experimental retinopathies in both human and animal models. Discovery of novel targets involving miRNAs in vascular eye diseases will provide insights for developing new treatments to counter ocular NV.

Is age-related macular degeneration a local manifestation of systemic disorder? Changes in nailfold capillaries at age-related macular degeneration

AIMS

Determining whether nailfold capillary involvement is present in patients with Age-related macular degeneration (AMD) and whether there are different nailfold capillaroscopy findings between wet and dry types.

METHODS

From January 2016 to December 2017, with an initial diagnosis of AMD, 53 consecutive adult patients (AMD group) and 91 age- and sex-matched healthy individuals were studied prospectively. There was no history of any other ocular disease and other disease affecting nailfold capillaries. All subjects underwent a complete ophthalmic examination. The classified and advanced stages of wet and dry types were not included. All nailfold capillaroscopy examinations were performed by the same rheumatologist.

RESULTS

It was found that the frequency of major capillaroscopic findings such as capillary ectasia, micro-hemorrhage, tortuosity, neo-formation, bizarre capillary, and bushy capillaries increased in the AMD group according to the normal group, but no significant relationship was found for capillary aneurysm. In dry or wet type of AMD in terms of ectasia, micro-hemorrhage, tortuosity, neo-formation, bizarre structure, bushy structure, or aneurism of nailfold capillaries, no significant correlation was found.

CONCLUSIONS

Nailfold capillaroscopy can detect microvascular changes in the nailfold capillary, in early and late stages of AMD. There were morphological changes in the nailfold capillaries of AMD patients, suggesting that there are systemic superficial microvascular changes that may be due to the systemic nature of the disease.

Superior cervical gangliectomy induces non-exudative age-related macular degeneration in mice

Non-exudative age-related macular degeneration, a prevalent cause of blindness, is a progressive and degenerative disease characterized by alterations in Bruch's membrane, retinal pigment epithelium, and photoreceptors exclusively localized in the macula. Although experimental murine models exist, the vast majority take a long time to develop retinal alterations and, in general, these alterations are ubiquitous, with many resulting from non-eye-specific genetic manipulations; additionally, most do not always reproduce the hallmarks of human age-related macular degeneration. Choroid vessels receive sympathetic innervation from the superior cervical ganglion, which, together with the parasympathetic system, regulates blood flow into the choroid. Choroid blood flow changes have been involved in age-related macular degeneration development and progression. At present, no experimental models take this factor into account. The aim of this work was to analyze the effect of superior cervical gangliectomy (also known as ganglionectomy) on the choroid, Bruch's membrane, retinal pigment epithelium and retina. Adult male C57BL/6J mice underwent unilateral superior cervical gangliectomy and a contralateral sham procedure. Although superior cervical gangliectomy induced ubiquitous choroid and choriocapillaris changes, it induced Bruch's membrane thickening, loss of retinal pigment epithelium melanin content and retinoid isomerohydrolase, the appearance of drusen-like deposits, and retinal pigment epithelium and photoreceptor atrophy, exclusively localized in the temporal side. Moreover, superior cervical gangliectomy provoked a localized increase in retinal pigment epithelium and photoreceptor apoptosis, and a decline in photoreceptor electroretinographic function. Therefore, superior cervical gangliectomy recapitulated the main features of human non-exudative age-related macular degeneration, and could become a new experimental model of dry age-related macular degeneration, and a useful platform for developing new therapies.

Summary: Ubiquitous alteration of choroid circulation causes localized retinal alterations in mice that are similar to human non-exudative age-related macular degeneration, thus providing a new potential experimental model of the disease.

Negative Regulators of Angiogenesis, Ocular Vascular Homeostasis, and Pathogenesis and Treatment of Exudative AMD

Angiogenesis, the formation of new blood vessels from pre-existing capillaries, is very tightly regulated and normally does not occur except during developmental and reparative processes. This tight regulation is maintained by a balanced production of positive and negative regulators, and alterations under pathological conditions such as retinopathy of prematurity, diabetic retinopathy, and age-related macular degeneration can lead to growth of new and abnormal blood vessels. Although the role of proangiogenic factors such as vascular endothelial growth factor has been extensively studied, little is known about the roles of negative regulators of angiogenesis in the pathogenesis of these diseases. Here, we will discuss the role of thrombospondin-1 (TSP1), one of the first known endogenous inhibitors of angiogenesis, in ocular vascular homeostasis, and how its alterations may contribute to the pathogenesis of age-related macular degeneration and choroidal neovascularization. We will also discuss its potential utility as a therapeutic target for treatment of ocular diseases with a neovascular component.

Epidemiology of age-related macular degeneration (AMD): associations with cardiovascular disease phenotypes and lipid factors

Age-related macular degeneration (AMD) is the leading cause of irreversible blindness in adults over 50 years old. Genetic, epidemiological, and molecular studies are beginning to unravel the intricate mechanisms underlying this complex disease, which implicate the lipid-cholesterol pathway in the pathophysiology of disease development and progression. Many of the genetic and environmental risk factors associated with AMD are also associated with other complex degenerative diseases of advanced age, including cardiovascular disease (CVD). In this review, we present epidemiological findings associating AMD with a variety of lipid pathway genes, cardiovascular phenotypes, and relevant environmental exposures. Despite a number of studies showing significant associations between AMD and these lipid/cardiovascular factors, results have been mixed and as such the relationships among these factors and AMD remain controversial. It is imperative that researchers not only tease out the various contributions of such factors to AMD development but also the connections between AMD and CVD to develop optimal precision medical care for aging adults.

Tunicamycin-induced Endoplasmic Reticulum Stress Upregulates the Expression of Pentraxin 3 in Human Retinal Pigment Epithelial Cells

PURPOSE

To investigate the production of long pentraxin 3 (PTX3) in response to tunicamycin-induced endoplasmic reticulum (ER) stress and its role in ER stress-associated cell death, PTX3 expression was evaluated in the human retinal pigment epithelial cell line, ARPE-19.

METHODS

PTX3 production in ARPE-19 cells was analyzed in the absence or presence of tunicamycin treatment by enzyme-linked immunosorbent assay. PTX3 protein and mRNA levels were estimated using western blot analysis and real-time reverse transcription-polymerase chain reaction, respectively. Protein and mRNA levels of CCAAT-enhancer-binding protein homologous protein (CHOP) and ARPE-19 cell viability were measured in the presence of tunicamycin-induced ER stress in control or PTX3 small hairpin RNA (shRNA)-transfected ARPE-19 cells.

RESULTS

The protein and mRNA levels of PTX3 were found to be significantly increased by tunicamycin treatment. PTX3 production was significantly decreased in inositol-requiring enzyme 1α shRNA-transfected ARPE-19 cells compared to control shRNA-transfected cells. Furthermore, pretreatment with the NF-κB inhibitor abolished tunicamycin-induced PTX3 production. Decreased cell viability and prolonged protein and mRNA expression of CHOP were observed under tunicamycin-induced ER stress in PTX3 shRNA transfected ARPE-19 cells.

CONCLUSIONS

These results suggest that PTX3 production increased in the presence of tunicamycin-induced ER stress. Therefore, PTX3 could be an important protector of ER stress-induced cell death in human retinal pigment epithelial cells. Inositol-requiring enzyme 1α and the NF-κB signaling pathway may serve as potential targets for regulation of PTX3 expression in the retina. Therefore, their role in PTX3 expression needs to be further investigated.

A Revised Hemodynamic Theory of Age-Related Macular Degeneration

Age-related macular degeneration (AMD) afflicts one out of every 40 individuals worldwide, causing irreversible central blindness in millions. The transformation of various tissue layers within the macula in the retina has led to competing conceptual models of the molecular pathways, cell types, and tissues responsible for the onset and progression of AMD. A model that has persisted for over 6 decades is the hemodynamic, or vascular theory of AMD progression, which states that vascular dysfunction of the choroid underlies AMD pathogenesis. Here, we re-evaluate this hypothesis in light of recent advances on molecular, anatomic, and hemodynamic changes underlying choroidal dysfunction in AMD. We propose an updated, detailed model of hemodynamic dysfunction as a mechanism of AMD development and progression.

Color vision deficits in intermediate age-related macular degeneration

PURPOSE

To assess the effect of intermediate age-related macular degeneration (AMD) on foveal cone-contrast thresholds.

METHODS

We measured L-M and S-cone-contrast thresholds in subjects with intermediate AMD (n = 10) and age-matched control subjects (n = 10). Monocular, foveal 3-degree Gaussian blobs (600-millisecond raised cosine) were presented at 16 cone ratios throughout L-, M-, and S-cone space, and threshold contours were modeled with probability summation between two independent detection mechanisms. The role that preretinal absorption plays in aging was also evaluated by simulation with FG15 and neutral-density filters.

RESULTS

Aging results in loss of neural sensitivity, not explained by lens changes. On average, intermediate AMD was associated with reduced sensitivity in both color and luminance channels (p < 0.05) that appeared to indicate greater involvement of S-cones. When data were normalized to age-expected values, the changes to cone sensitivity were shown to be consistent (∼200% loss) across L-M, M-L, and S-cone mechanisms. In comparison, the luminance (L + M) mechanism showed relative sparing (155% loss, p < 0.05).

CONCLUSIONS

Eyes with the same phenotype of intermediate AMD can have varying degrees of color threshold loss. Functional markers enhance the clinical definition of disease expression in AMD.

Delayed patchy choroidal filling in the Comparison of Age-Related Macular Degeneration Treatments Trials (CATT)

PURPOSE

To determine the relationship between delayed patchy choroidal filling and morphologic and functional outcomes among eyes treated with ranibizumab or bevacizumab.

DESIGN

Cohort study.

METHODS

Comparison of Age-related Macular Degeneration Treatment Trials participants were assigned randomly to ranibizumab or bevacizumab on a monthly or as-needed schedule. Presence of delayed patchy choroidal filling and morphologic and functional outcomes were evaluated among eyes with gradable fluorescein angiography at baseline (n = 973) and at 1 year (n = 860) eyes.

RESULTS

Delayed filling was present in 75 (7.7%) of 973 eyes at baseline. Eyes with incident delayed filling at 1 year (23 [2.9%] of 798) showed a mean decrease of 1.7 letters in visual acuity, whereas eyes without incident delayed filling had a mean improvement of 8.1 letters (difference [Δ], -9.8; 95% confidence interval [CI] , -15.8 to -3.9; P < .01). Eyes with incident delayed filling had a larger increase in mean total lesion area of choroidal neovascularization (3.00 mm(2)) than eyes without incident delayed filling (0.56 mm(2); Δ , 2.4; 95% CI, 0.4 to 4.4; P = .02). The proportion with incident delayed filling at 1 year was similar among eyes treated with ranibizumab (10 [2.4%] of 413) or bevacizumab (13 [3.3%] of 385; P = .53) and among eyes treated monthly (12 [3.1%] of 388) or as needed (11 [2.7%] of 410; P = .83).

CONCLUSIONS

Delayed patchy choroidal filling was uncommon at baseline. Although only a small percentage of eyes demonstrated delayed filling during the first year of anti-vascular endothelial growth factor treatment, these eyes had worse visual acuity and a larger increase in total lesion area of choroidal neovascularization.

Neutral sphingomyelinase inhibition decreases ER stress-mediated apoptosis and inducible nitric oxide synthase in retinal pigment epithelial cells

Endoplasmic reticulum (ER) stress and excessive nitric oxide production via the induction of inducible nitric oxide synthase (NOS2) have been implicated in the pathogenesis of ocular diseases characterized by retinal degeneration. Previous studies have revealed the sphingomyelinase/ceramide pathway in the regulation of NOS2 induction. Thus, the objective of this study was to determine the activity of the sphingomyelinase/ceramide pathway, assess nitric oxide production, and examine apoptosis in human retinal pigment epithelial (RPE) cells undergoing ER stress. Sphingomyelinase (SMase) activity; nuclear factor κB (NF-κB) activation; NOS2, nitrite/nitrate, and nitrotyrosine levels; and apoptosis were determined in cultured human RPE cell lines subjected to ER stress via exposure to tunicamycin. Induction of ER stress was confirmed by increased intracellular levels of ER stress markers including phosphorylated PKR-like ER kinase, C/EBP-homologous protein, and 78-kDa glucose-regulated protein. ER stress increased nuclear translocation of NF-κB, NOS2 expression, nitrite/nitrate levels, and nitrotyrosine formation and caused apoptosis in RPE cell lines. Inhibition of neutral SMase (N-SMase) activity via GW 4869 treatment caused a significant reduction in nuclear translocation of NF-κB, NOS2 expression, nitrite/nitrate levels, nitrotyrosine formation, and apoptosis in ER-stressed RPE cells. In conclusion, N-SMase inhibition reduced nitrative stress and apoptosis in RPE cells undergoing ER stress. Obtained data suggest that NOS2 can be regulated by N-SMase in RPE cells experiencing ER stress.

Novel endogenous glycan therapy for retinal diseases: safety, in vitro stability, ocular pharmacokinetic modeling, and biodistribution

Asialo, tri-antennary oligosaccharide (NA3 glycan) is an endogenous compound, which supports proper folding of outer segment membranes, promotes normal ultrastructure, and maintains protein expression patterns of photoreceptors and Müller cells in the absence of retinal pigment epithelium support. It is a potential new therapeutic for atrophic age-related macular degeneration (AMD) and other retinal degenerative disorders. Herein, we evaluate the safety, in vitro stability, ocular pharmacokinetics and biodistribution of NA3. NA3 was injected into the vitreous of New Zealand white rabbits at two concentrations viz. 1 nM (minimum effective concentration (MEC)) and 100 nM (100XMEC) at three time points. Safety was evaluated using routine clinical and laboratory tests. Ocular pharmacokinetics and biodistribution of [(3)H]NA3 were estimated using scintillation counting in various parts of the eye, multiple peripheral organs, and plasma. Pharmacokinetic parameters were estimated by non-compartmental modeling. A 2-aminobenzamide labeling and hydrophilic interaction liquid interaction chromatography were used to assess plasma and vitreous stability. NA3 was well tolerated by the eye. The concentration of NA3 in eye tissues was in the order: vitreous > retina > sclera/choroid > aqueous humor > cornea > lens. Area under the curve (0 to infinity) (AUC∞) was the highest in the vitreous thereby providing a positive concentration gradient for NA3 to reach the retina. Half-lives in critical eye tissues ranged between 40 and 60 h. NA3 concentrations were negligible in peripheral organs. Radioactivity from [(3)H]NA3 was excreted via urine and feces. NA3 was stable at 37°C in vitreous over a minimum of 6 days, while it degraded rapidly in plasma. Collectively, these results document that NA3 shows a good safety profile and favorable ocular pharmacokinetics.

Age-related macular degeneration revisited--piecing the puzzle: the LXIX Edward Jackson memorial lecture

PURPOSE

To present the current understanding of age-related macular degeneration (AMD) pathogenesis, based on clinical evidence, epidemiologic data, histopathologic examination, and genetic data; to provide an update on current and emerging therapies; and to propose an integrated model of the pathogenesis of AMD.

DESIGN

Review of published clinical and experimental studies.

METHODS

Analysis and synthesis of clinical and experimental data.

RESULTS

We are closer to a complete understanding of the pathogenesis of AMD, having progressed from clinical observations to epidemiologic observations and clinical pathologic correlation. More recently, modern genetic and genomic studies have facilitated the exploration of molecular pathways. It seems that AMD is a complex disease that results from the interaction of genetic susceptibility with aging and environmental factors. Disease progression also seems to be driven by a combination of genetic and environmental factors.

CONCLUSIONS

Therapies based on pathophysiologic features have changed the paradigm for treating neovascular AMD. With improved understanding of the underlying genetic susceptibility, we can identify targets to halt early disease and to prevent progression and vision loss.

Cellular and physiological mechanisms underlying blood flow regulation in the retina and choroid in health and disease

We review the cellular and physiological mechanisms responsible for the regulation of blood flow in the retina and choroid in health and disease. Due to the intrinsic light sensitivity of the retina and the direct visual accessibility of fundus blood vessels, the eye offers unique opportunities for the non-invasive investigation of mechanisms of blood flow regulation. The ability of the retinal vasculature to regulate its blood flow is contrasted with the far more restricted ability of the choroidal circulation to regulate its blood flow by virtue of the absence of glial cells, the markedly reduced pericyte ensheathment of the choroidal vasculature, and the lack of intermediate filaments in choroidal pericytes. We review the cellular and molecular components of the neurovascular unit in the retina and choroid, techniques for monitoring retinal and choroidal blood flow, responses of the retinal and choroidal circulation to light stimulation, the role of capillaries, astrocytes and pericytes in regulating blood flow, putative signaling mechanisms mediating neurovascular coupling in the retina, and changes that occur in the retinal and choroidal circulation during diabetic retinopathy, age-related macular degeneration, glaucoma, and Alzheimer's disease. We close by discussing issues that remain to be explored.

Understanding age-related macular degeneration (AMD): relationships between the photoreceptor/retinal pigment epithelium/Bruch's membrane/choriocapillaris complex

There is a mutualistic symbiotic relationship between the components of the photoreceptor/retinal pigment epithelium (RPE)/Bruch's membrane (BrMb)/choriocapillaris (CC) complex that is lost in AMD. Which component in the photoreceptor/RPE/BrMb/CC complex is affected first appears to depend on the type of AMD. In atrophic AMD (~85-90% of cases), it appears that large confluent drusen formation and hyperpigmentation (presumably dysfunction in RPE) are the initial insult and the resorption of these drusen and loss of RPE (hypopigmentation) can be predictive for progression of geographic atrophy (GA). The death and dysfunction of photoreceptors and CC appear to be secondary events to loss in RPE. In neovascular AMD (~10-15% of cases), the loss of choroidal vasculature may be the initial insult to the complex. Loss of CC with an intact RPE monolayer in wet AMD has been observed. This may be due to reduction in blood supply because of large vessel stenosis. Furthermore, the environment of the CC, basement membrane and intercapillary septa, is a proinflammatory milieu with accumulation of complement components as well as proinflammatory molecules like CRP during AMD. In this toxic milieu, CC die or become dysfunction making adjacent RPE hypoxic. These hypoxic cells then produce angiogenic substances like VEGF that stimulate growth of new vessels from CC, resulting in choroidal neovascularization (CNV). The loss of CC might also be a stimulus for drusen formation since the disposal system for retinal debris and exocytosed material from RPE would be limited. Ultimately, the photoreceptors die of lack of nutrients, leakage of serum components from the neovascularization, and scar formation. Therefore, the mutualistic symbiotic relationship within the photoreceptor/RPE/BrMb/CC complex is lost in both forms of AMD. Loss of this functionally integrated relationship results in death and dysfunction of all of the components in the complex.

Metabolic physiology in age related macular degeneration

Ischemia and hypoxia have been implicated in the pathophysiology of age related macular degeneration (AMD). This has mostly been based on studies on choroidal perfusion, which is not the only contributor to retinal hypoxia found in AMD eyes. Other features of AMD may also interfere with retinal oxygen metabolism including confluent drusen, serous or hemorrhagic retinal detachment, retinal edema and vitreoretinal adhesion. Each of these features contributes to retinal hypoxia: the drusen and retinal elevation by increasing the distance between the choriocapillaris and retina; vitreoretinal adhesion by reducing diffusion and convection of oxygen towards and vascular endothelial growth factor (VEGF) away from hypoxic retinal areas. Hypoxia-inducible-factor is known to exist in subretinal neovascularization and hypoxia is the main stimulus for the production of VEGF. Each feature may not by itself create enough hypoxia and VEGF accumulation to stimulate wet AMD, but they may combine to do so. Choroidal ischemia in AMD has been demonstrated by many researchers, using different technologies. Choroidal ischemia obviously decreases oxygen delivery to the outer retina. Confluent drusen, thickening of Bruch's membrane and any detachment of retina or retinal pigment epithelium, increases the distance between the choriocapillaris and the retina and thereby reduces the oxygen flux from the choroid to the outer retina according to Fick's law of diffusion. Retinal elevation and choroidal ischemia may combine forces to reduce choroidal oxygen delivery to the outer retina, produce retinal hypoxia. Hypoxia leads to production of VEGF leading to neovascularization and tissue edema. A vicious cycle may develop, where VEGF production increases effusion, retinal detachment and edema, further increasing hypoxia and VEGF production. Adhesion of the viscous posterior vitreous cortex to the retina maintains a barrier to diffusion and convection currents in the vitreous cavity according to the laws of Fick's, Stokes-Einstein and Hagen-Poiseuille. If the vitreous is detached from the surface of the retina, the low viscosity fluid transports oxygen and nutrients towards an ischemic area of the retina, and cytokines away from the retina, at a faster rate than through attached vitreous gel. Vitreoretinal adhesion can exacerbate retinal hypoxia and accumulation of cytokines, such as VEGF. Vitreoretinal traction can also cause hypoxia by retinal elevation. Conceivably, the basic features of AMD, drusen, choroidal ischemia, and vitreoretinal adhesion are independently determined by genetics and environment and may combine in variable proportions. If the resulting hypoxia and consequent VEGF accumulation crosses a threshold, this will trigger effusion and neovascularization.

Relationship between RPE and choriocapillaris in age-related macular degeneration

PURPOSE

The purpose of this study was to examine the relationships between choriocapillaris (CC) and retinal pigment epithelial changes in age-related macular degeneration (AMD). Morphologic changes in the retinal pigment epithelium (RPE)/choriocapillaris complex were quantified in dry and wet forms of AMD, and the results were compared with those in aged control eyes without maculopathy.

METHODS

Postmortem choroids from three aged control subjects, five subjects with geographic atrophy (GA), and three subjects with wet AMD were analyzed using a semiquantitative computer-assisted morphometric technique developed to measure the percentages of retinal pigment epithelial and CC areas in choroidal wholemounts incubated for alkaline phosphatase activity. The tissues were subsequently embedded in methacrylate and were sectioned so that structural changes could be examined.

RESULTS

There was a linear relationship between the loss of RPE and CC in GA. A 50% reduction in vascular area was found in regions of complete retinal pigment epithelial atrophy. Extreme constriction of remaining viable capillaries was found in areas devoid of RPE. Adjacent to active choroidal neovascularization (CNV) in wet AMD, CC dropout was evident in the absence of retinal pigment epithelial atrophy, resulting in a 50% decrease in vascular area. Lumenal diameters of the remaining capillaries in wet AMD eyes were similar to those in control eyes.

CONCLUSIONS

The primary insult in GA appears to be at the level of the RPE, and there is an intimate relationship between retinal pigment epithelial atrophy and secondary CC degeneration. CC degeneration occurs in the presence of viable RPE in wet AMD. The RPE in regions of vascular dropout are presumably hypoxic, which may result in an increase in VEGF production by the RPE and stimulation of CNV.

Erythropoietin as a novel therapeutic agent for atrophic age-related macular degeneration

The purpose of this article is to propose a novel therapeutic approach to the treatment of age-related macular degeneration (ARMD), the leading cause of blindness in the elderly population (over 60 years of age) in developed countries. Although recent advances have been made in the treatment of the neovascular form of ARMD, there is still no effective treatment for the most prevalent atrophic form of ARMD. Although the exact etiology and molecular pathogenesis of the atrophic ARMD are not fully understood, it is believed that oxidative stress and local inflammation play a major role in the pathologic processes and that the disease is triggered by dysfunction in the retinal pigment epithelia, leading to the degeneration of macular photoreceptor cells, followed by irreversible loss of vision. Considering that erythropoietin (EPO) has antioxidant, anti-inflammatory, and neuroprotective properties, we hypothesize that it can be developed as a novel therapeutic agent for the treatment of the atrophic form of ARMD. Future studies are needed to confirm or rule out this hypothesis. If successful, such studies may also help shield the lights on molecular mechanisms of atrophic ARMD.