Anatomy and development of the macula: specialisation and the vulnerability to macular degeneration

The central retina vessel density and foveal avascular zone values of 792 healthy adults using optical coherence tomography angiography

BACKGROUND/OBJECTIVES

To determine normal macular vessel density (VD) and foveal avascular zone (FAZ) values using optical coherence tomography angiography (OCTA) analysis in healthy adults.

SUBJECTS/METHODS

As part of the Prospective Epidemiological Research Studies in Iran (PERSIAN) Organizational Cohort study at Mashhad University of Medical Sciences (POCM), we conducted a cross-sectional study using 3 × 3 and 6 × 6 mm OCTA scans to evaluate the VD of the macular superficial capillary plexus (SCP), deep capillary plexus (DCP), and the FAZ area in healthy adults.

RESULTS

The study included 792 participants, with a mean age of 39.8 ± 6.8 years. There were 359 males with a mean age of 39.9 ± 7.8 years and 440 females with a mean age of 39.4 ± 6 years. The mean values of various parameters were measured, including the right eye whole image SCP and DCP VDs, FAZ area, FAZ perimeter, and fovea VD in a 300 µm wide zone around FAZ (FD). These values were found to be 45.9 ± 2.6%, 50.2 ± 3%, 0.3 ± 0.1mm2, 2.1 ± 0.4 mm, and 50.4 ± 3.3%, respectively. Females and younger participants had significantly higher mean values of whole image SCP and DCP VDs. Additionally, all FAZ parameters had significantly higher values in females, while younger participants had significantly higher mean FD values. Simple linear regression analyses showed that age was negatively correlated with right eye SCP and DCP VDs.

CONCLUSION

Our study established standard SCP and DCP VD values influenced by age and gender. Age correlates negatively with both, DCP VDs correlate negatively with height and weight, and SCP VDs correlate positively with diastolic blood pressure.

Aging of the eye: Lessons from cataracts and age-related macular degeneration

Aging is the greatest risk factor for chronic human diseases, including many eye diseases. Geroscience aims to understand the effects of the aging process on these diseases, including the genetic, molecular, and cellular mechanisms that underlie the increased risk of disease over the lifetime. Understanding of the aging eye increases general knowledge of the cellular physiology impacted by aging processes at various biological extremes. Two major diseases, age-related cataract and age-related macular degeneration (AMD) are caused by dysfunction of the lens and retina, respectively. Lens transparency and light refraction are mediated by lens fiber cells lacking nuclei and other organelles, which provides a unique opportunity to study a single aging hallmark, i.e., loss of proteostasis, within an environment of limited metabolism. In AMD, local dysfunction of the photoreceptors/retinal pigmented epithelium/Bruch's membrane/choriocapillaris complex in the macula leads to the loss of photoreceptors and eventually loss of central vision, and is driven by nearly all the hallmarks of aging and shares features with Alzheimer's disease, Parkinson's disease, cardiovascular disease, and diabetes. The aging eye can function as a model for studying basic mechanisms of aging and, vice versa, well-defined hallmarks of aging can be used as tools to understand age-related eye disease.

Changes in retinal and choroidal optical coherence tomography angiography indices among young adults and children over 1 year

CLINICAL RELEVANCE

Optical coherence tomography angiography (OCT-A) indices are likely to change across time and optometrists should be aware of the variability expected during childhood development and in healthy adults.

BACKGROUND

Cross-sectional studies have shown that OCT-A indices are associated with age in adults and children. The aim of this study is to investigate longitudinal changes in retinal and choroidal OCT-A indices over 1 year among healthy children and young adults.

METHODS

This prospective longitudinal study captured macular OCT-A and OCT scans, and biometry measures at baseline and 1-year follow-up for 22 adults (18-30 years; -6.87 to +0.37 D) and 21 children (6-15 years; -5.75 to +0.25 D). Superficial and deep retinal layer, choriocapillaris and deep choroidal en face OCT-A images were analysed to extract magnification-corrected vascular indices in foveal, parafoveal and perifoveal regions. The retinal indices included foveal avascular zone metrics, perfusion, and vessel density. Flow deficit number, size, and density were extracted from choriocapillaris and perfusion density from deep choroid. Associations between annual changes in the OCT-A indices and axial length and baseline refraction were also studied.

RESULTS

Among children, significant reductions were noted only in parafoveal superficial retinal and foveal and perifoveal deep retinal layer indices over 1 year (p < 0.05). Choroidal OCT-A indices in children and both retinal and choroidal OCT-A indices in adults did not show significant changes. Myopia was associated with a larger reduction in the perifoveal retinal OCT-A indices in children, and with increases in sub-foveal and sub-parafoveal choroidal indices in adults. There were associations between OCT-A indices and axial length changes but differently in adults and children.

CONCLUSIONS

Significant changes were noted in retinal OCT-A indices over 1 year among children but not adults. In comparison, choroidal OCT-A indices in adults and children showed a stable morphology over this period of time.

Effects of post-saccadic oscillations on visual processing times

Saccadic eye movements enable us to search for the target of interest in a crowded scene or, in the case of goal-directed saccades, to simply bring the image of the peripheral target to the very centre of the fovea. This mechanism extends the use of the superior image processing performance of the fovea over a large visual field. We know that visual information is processed quickly at the end of each saccade but estimates of the times involved remain controversial. This study aims to investigate the processing of visual information during post fixation oscillations of the eyeball. A new psychophysical test measures the combined eye movement response latencies, including fixation duration and visual processing times. When the test is used in conjunction with an eye tracker, each component that makes up the 'integrated saccade latency' time, from the onset of the peripheral stimulus to the correct interpretation of the information carried by the stimulus, can be measured and the discrete components delineated. The results show that the time required to process and encode the stimulus attribute of interest at the end of a saccade is longer than the time needed to carry out the same task in the absence of an eye movement. We propose two principal hypotheses, each of which can account for this finding. 1. The known inhibition of afferent retinal signals during fast eye movements extends beyond the end point of the saccade. 2. The extended visual processing times measured when saccades are involved are caused by the transient loss of spatial resolution due to eyeball instability during post-saccadic oscillations. The latter can best be described as retinal image smear with greater loss of spatial resolution expected for stimuli of low luminance contrast.

An overview of retinal light damage models for preclinical studies on age-related macular degeneration: identifying molecular hallmarks and therapeutic targets

Age-related macular degeneration (AMD) is a complex, multifactorial disease leading to progressive and irreversible retinal degeneration, whose pathogenesis has not been fully elucidated yet. Due to the complexity and to the multiple features of the disease, many efforts have been made to develop animal models which faithfully reproduce the overall AMD hallmarks or that are able to mimic the different AMD stages. In this context, light damage (LD) rodent models of AMD represent a suitable and reliable approach to mimic the different AMD forms (dry, wet and geographic atrophy) while maintaining the time-dependent progression of the disease. In this review, we comprehensively reported how the LD paradigms reproduce the main features of human AMD. We discuss the capability of these models to broaden the knowledge in AMD research, with a focus on the mechanisms and the molecular hallmarks underlying the pathogenesis of the disease. We also critically revise the remaining challenges and future directions for the use of LD models.

Psychophysical, electrofunctional, and morphological evaluation in naïve neovascular AMD patients treated with intravitreal anti-VEGF

Objectives

The aim of this study was to investigate the retinal morpho-functional characteristics of patients with neovascular wet age-related macular degeneration (nAMD) treated with intravitreal injection (IV) of aflibercept (AFL).

Methods

The study was conducted on 35 patients previously diagnosed with type 1 nAMD who received a fixed-dosing regimen of aflibercept injections over 12 months. The goal was to assess trends in visual abilities over time by measuring visual acuity (VA), contrast sensitivity (CS), visual evoked potentials (VEPs), and spectral domain-optical coherence tomography (SD-OCT). The same psychophysical, electro-functional, and morphological tests administered at baseline (T0) were repeated 4 to 8 weeks after the last aflibercept injection (Tn), resulting in a total of six examinations.

Results

At Tn, all subjects exhibited improved VA for both far and near distances compared to values detected at T0. Similarly, VEP amplitude and latency values at Tn showed a greater P100 improvement than those observed at T0. Additionally, the CS examination at Tn demonstrated improvement, particularly at high spatial stimulation frequencies. The Tn SD-OCT results highlighted a reduction in macular thickness compared to T0 values.

Conclusions

This exploratory research indicates that intravitreal injections of AFL, following a fixed-dosing regimen, represent a valuable therapeutic approach for enhancing visual performance. This conclusion is supported by comprehensive statistical analysis of psychophysical, electro-functional, and morphological examinations within the same group of patients with nAMD, as demonstrated for the first time.

The Relationship Between Artificial Intelligence-Assisted OCT Angiography-Derived Foveal Avascular Zone Parameters and Visual-Field Defect Progression in Eyes with Open-Angle Glaucoma

Purpose

To investigate clinical factors associated with foveal avascular zone (FAZ) parameters obtained using OCT angiography (OCTA) with assistance from a previously developed artificial intelligence (AI) platform in eyes with open-angle glaucoma (OAG).

Design

Retrospective longitudinal.

Participants

This study followed up 885 eyes of 558 patients with OAG for ≥ 2 years; all eyes underwent ≥ 5 Humphrey visual-field (VF) tests and had 3.0 × 3.0 mm macular OCTA scans available.

Methods

Average total deviation (TD) in the superior, superocentral, inferocentral, and inferior sectors of the Humphrey 24-2 program was calculated. We collected 3.0 × 3.0 mm macular OCTA images from each patient and used a previously developed AI platform with these images to obtain FAZ parameters, including FAZ area, FAZ circularity index (CI), and FAZ perimeter. Multivariable linear mixed-effects models were used to analyze the relationship between FAZ parameters, TD or TD slope in each quadrant, and systemic factors, adjusting for potential confounding factors, including axial length.

Main Outcome Measures

Ophthalmic and systemic variables, FAZ parameters, and TD or TD slope in each quadrant.

Results

The multivariable model showed that FAZ parameters were correlated with both TD and TD slope in the inferocentral quadrant (β = -0.244 - 0.168, P < 0.001). Both upper-half and lower-half FAZ parameters were better associated with TD-inferocentral and TD-inferocentral slope than TD-superocentral or TD-superocentral slope in terms of β size and statistical significance, indicating that there was no evident vertical anatomical correspondence between TD in the central quadrant and FAZ parameters. Foveal avascular zone area enlargement was associated with female gender (β = 0.242, P = 0.003). Loss of FAZ circularity was associated with both aging and comorbid sleep apnea syndrome (SAS) (yes: 1, no: 0) (β = -0.188, P < 0.001; β = -0.261, P = 0.031, respectively). Foveal avascular zone perimeter elongation was associated with aging and female gender (β = 0.084, P = 0.040; β = 0.168, P = 0.042, respectively).

Conclusions

Artificial intelligence-assisted OCTA-measured FAZ enlargement and irregular shape might be good markers of ocular hypoperfusion and associated inferocentral VF defect progression in eyes with OAG. Financial Disclosure(s): The author(s) have no proprietary or commercial interest in any materials discussed in this article.

Stage-specific dynamic reorganization of genome topology shapes transcriptional neighborhoods in developing human retinal organoids

We have generated a high-resolution Hi-C map of developing human retinal organoids to elucidate spatiotemporal dynamics of genomic architecture and its relationship with gene expression patterns. We demonstrate progressive stage-specific alterations in DNA topology and correlate these changes with transcription of cell-type-restricted gene markers during retinal differentiation. Temporal Hi-C reveals a shift toward A compartment for protein-coding genes and B compartment for non-coding RNAs, displaying high and low expression, respectively. Notably, retina-enriched genes are clustered near lost boundaries of topologically associated domains (TADs), and higher-order assemblages (i.e., TAD cliques) localize in active chromatin regions with binding sites for eye-field transcription factors. These genes gain chromatin contacts at their transcription start site as organoid differentiation proceeds. Our study provides a global view of chromatin architecture dynamics associated with diversification of cell types during retinal development and serves as a foundational resource for in-depth functional investigations of retinal developmental traits.

Development of Deep Ensembles to Screen for Autism and Symptom Severity Using Retinal Photographs

Importance

Screening for autism spectrum disorder (ASD) is constrained by limited resources, particularly trained professionals to conduct evaluations. Individuals with ASD have structural retinal changes that potentially reflect brain alterations, including visual pathway abnormalities through embryonic and anatomic connections. Whether deep learning algorithms can aid in objective screening for ASD and symptom severity using retinal photographs is unknown.

Objective

To develop deep ensemble models to differentiate between retinal photographs of individuals with ASD vs typical development (TD) and between individuals with severe ASD vs mild to moderate ASD.

Design, Setting, and Participants

This diagnostic study was conducted at a single tertiary-care hospital (Severance Hospital, Yonsei University College of Medicine) in Seoul, Republic of Korea. Retinal photographs of individuals with ASD were prospectively collected between April and October 2022, and those of age- and sex-matched individuals with TD were retrospectively collected between December 2007 and February 2023. Deep ensembles of 5 models were built with 10-fold cross-validation using the pretrained ResNeXt-50 (32×4d) network. Score-weighted visual explanations for convolutional neural networks, with a progressive erasing technique, were used for model visualization and quantitative validation. Data analysis was performed between December 2022 and October 2023.

Exposures

Autism Diagnostic Observation Schedule-Second Edition calibrated severity scores (cutoff of 8) and Social Responsiveness Scale-Second Edition T scores (cutoff of 76) were used to assess symptom severity.

Main Outcomes and Measures

The main outcomes were participant-level area under the receiver operating characteristic curve (AUROC), sensitivity, and specificity. The 95% CI was estimated through the bootstrapping method with 1000 resamples.

Results

This study included 1890 eyes of 958 participants. The ASD and TD groups each included 479 participants (945 eyes), had a mean (SD) age of 7.8 (3.2) years, and comprised mostly boys (392 [81.8%]). For ASD screening, the models had a mean AUROC, sensitivity, and specificity of 1.00 (95% CI, 1.00-1.00) on the test set. These models retained a mean AUROC of 1.00 using only 10% of the image containing the optic disc. For symptom severity screening, the models had a mean AUROC of 0.74 (95% CI, 0.67-0.80), sensitivity of 0.58 (95% CI, 0.49-0.66), and specificity of 0.74 (95% CI, 0.67-0.82) on the test set.

Conclusions and Relevance

These findings suggest that retinal photographs may be a viable objective screening tool for ASD and possibly for symptom severity. Retinal photograph use may speed the ASD screening process, which may help improve accessibility to specialized child psychiatry assessments currently strained by limited resources.

Platinum Nanozymes Counteract Photoreceptor Degeneration and Retina Inflammation in a Light-Damage Model of Age-Related Macular Degeneration

Degeneration of photoreceptors in age-related macular degeneration (AMD) is associated with oxidative stress due to the intense aerobic metabolism of rods and cones that if not properly counterbalanced by endogenous antioxidant mechanisms can precipitate photoreceptor degeneration. In spite of being a priority eye disease for its high incidence in the elderly, no effective treatments for AMD exist. While systemic administration of antioxidants has been unsuccessful in slowing down degeneration, locally administered rare-earth nanoparticles were shown to be effective in preventing retinal photo-oxidative damage. However, because of inherent problems of dispersion in biological media, limited antioxidant power, and short lifetimes, these NPs are still confined to the preclinical stage. Here we propose platinum nanoparticles (PtNPs), potent antioxidant nanozymes, as a therapeutic tool for AMD. PtNPs exhibit high catalytic activity at minimal concentrations and protect primary neurons against oxidative insults and the ensuing apoptosis. We tested the efficacy of intravitreally injected PtNPs in preventing or mitigating light damage produced in dark-reared albino Sprague-Dawley rats by in vivo electroretinography (ERG) and ex vivo retina morphology and electrophysiology. We found that both preventive and postlesional treatments with PtNPs increased the amplitude of ERG responses to light stimuli. Ex vivo recordings demonstrated the selective preservation of ON retinal ganglion cell responses to light stimulation in lesioned retinas treated with PtNPs. PtNPs administered after light damage significantly preserved the number of photoreceptors and inhibited the inflammatory response to degeneration, while the preventive treatment had a milder effect. The data indicate that PtNPs can effectively break the vicious cycle linking oxidative stress, degeneration, and inflammation by exerting antioxidant and anti-inflammatory actions. The increased photoreceptor survival and visual performances in degenerated retinas, together with their high biocompatibility, make PtNPs a potential strategy to cure AMD.

Impaired cerebrovascular reactivity correlates with reduced retinal vessel density in patients with carotid artery stenosis: Cross-sectional, single center study

BACKGROUND

The cerebral and retinal circulation systems are developmentally, anatomically, and physiologically interconnected. Thus, we hypothesized that hypoperfusion due to atherosclerotic stenosis of the internal carotid artery (ICA) can result in disturbances of both cerebral and retinal microcirculations. We aimed to characterize parameters indicating cerebrovascular reactivity (CVR) and retinal microvascular density in patients with ICA stenosis, and assess if there is correlation between them.

METHODS

In this cross-sectional study the middle cerebral artery (MCA) blood flow velocity was measured by transcranial Doppler (TCD) and, simultaneously, continuous non-invasive arterial blood pressure measurement was performed on the radial artery by applanation tonometry. CVR was assessed based on the response to the common carotid artery compression (CCC) test. The transient hyperemic response ratio (THRR) and cerebral arterial resistance transient hyperemic response ratio (CAR-THRR) were calculated. Optical coherence tomography angiography (OCTA) was used to determine vessel density (VD) on the papilla whole image for all (VDP-WIall) and for small vessels (VDP-WIsmall). The same was done in the peripapillary region: all (VDPPall), and small (VDPPsmall) vessels. The VD of superficial (VDMspf) and deep (VDMdeep) macula was also determined. Significance was accepted when p<0.05.

RESULTS

Twenty-four ICA stenotic patients were evaluated. Both CVR and retinal VD were characterized. There was a significant, negative correlation between CAR-THRR (median = -0.40) and VDPPsmall vessels (median = 52%), as well as between VDPPall vessels (median = 58%), and similar correlation between CAR-THRR and VDP-WIsmall (median = 49.5%) and between VDP-WIall (median = 55%).

CONCLUSION

The significant correlation between impaired cerebrovascular reactivity and retinal vessel density in patients with ICA stenosis suggests a common mechanism of action. We propose that the combined use of these diagnostic tools (TCD and OCTA) helps to better identify patients with increased ischemic or other cerebrovascular risks.

Potential roles of dietary zeaxanthin and lutein in macular health and function

Lutein, zeaxanthin, and meso-zeaxanthin are three xanthophyll carotenoid pigments that selectively concentrate in the center of the retina. Humans cannot synthesize lutein and zeaxanthin, so these compounds must be obtained from the diet or supplements, with meso-zeaxanthin being converted from lutein in the macula. Xanthophylls are major components of macular pigments that protect the retina through the provision of oxidant defense and filtering of blue light. The accumulation of these three xanthophylls in the central macula can be quantified with non-invasive methods, such as macular pigment optical density (MPOD). MPOD serves as a useful tool for assessing risk for, and progression of, age-related macular degeneration, the third leading cause of blindness worldwide. Dietary surveys suggest that the dietary intakes of lutein and zeaxanthin are decreasing. In addition to low dietary intake, pregnancy and lactation may compromise the lutein and zeaxanthin status of both the mother and infant. Lutein is found in modest amounts in some orange- and yellow-colored vegetables, yellow corn products, and in egg yolks, but rich sources of zeaxanthin are not commonly consumed. Goji berries contain the highest known levels of zeaxanthin of any food, and regular intake of these bright red berries may help protect against the development of age-related macular degeneration through an increase in MPOD. The purpose of this review is to summarize the protective function of macular xanthophylls in the eye, speculate on the compounds' role in maternal and infant health, suggest the establishment of recommended dietary values for lutein and zeaxanthin, and introduce goji berries as a rich food source of zeaxanthin.

Single-cell RNA sequencing reveals transcriptional changes of human choroidal and retinal pigment epithelium cells during fetal development, in healthy adult and intermediate age-related macular degeneration

Age-related macular degeneration (AMD) is the most prevalent cause of blindness in the developed world. Vision loss in the advanced stages of the disease is caused by atrophy of retinal photoreceptors, overlying retinal pigment epithelium (RPE) and choroidal endothelial cells. The molecular events that underline the development of these cell types from in utero to adult as well as the progression to intermediate and advanced stages AMD are not yet fully understood. We performed single-cell RNA-sequencing (RNA-Seq) of human fetal and adult RPE-choroidal tissues, profiling in detail all the cell types and elucidating cell type-specific proliferation, differentiation and immunomodulation events that occur up to midgestation. Our data demonstrate that progression from the fetal to adult state is characterized by an increase in expression of genes involved in the oxidative stress response and detoxification from heavy metals, suggesting a better defence against oxidative stress in the adult RPE-choroid tissue. Single-cell comparative transcriptional analysis between a patient with intermediate AMD and an unaffected subject revealed a reduction in the number of RPE cells and melanocytes in the macular region of the AMD patient. Together these findings may suggest a macular loss of RPE cells and melanocytes in the AMD patients, but given the complex processing of tissues required for single-cell RNA-Seq that is prone to technical artefacts, these findings need to be validated by additional techniques in a larger number of AMD patients and controls.

A Novel Transcriptome Approach to the Investigation of the Molecular Pathology of Vitreous and Retinal Detachment

Retinal detachment (RD) is one of the most common, sight-threatening ocular conditions requiring emergency intervention. Posterior vitreous detachment (PVD) occurs in the majority of an aging population whereby the vitreous body separates from the retina. It is well established that PVD is the common precursor to the most common forms of RD; however, it remains unknown why in most individuals PVD will cause no/few complications (physiological PVD) but in a small percentage will cause retinal tears and detachment (pathological PVD). Despite over 100 years of scientific research, the anatomical definitions of PVD and its pathogenesis remain controversial. Recent research has identified a novel cell population (laminocyte), present at significantly higher numbers in pathological PVD when compared to physiological PVD. We review and summarise the seven distinct clinical sub-groups of retinal breaks and focus on the role of the laminocyte in those secondary to PVD and the transcriptomic profile of this unique cell. Provisional whole transcriptome analysis using bulk RNA-Seq shows marked differentially expressed genes when comparing physiological PVD with PVD associated with RD. The limitations of bulk RNA-Seq are considered and the potential to address these using spatial transcriptomics are discussed. Understanding the pathogenesis of PVD-related retinal tears will provide a baseline for the development of novel therapeutic targets and prophylactic treatments.

Remote patient monitoring of central retinal function with MACUSTAT®: A multi-modal macular function scan

INTRODUCTION

There is significant unmet need for patient-centric remote monitoring of visual function for chronic retinal diseases, as demonstrated by the COVID-19 pandemic. The Macustat® central retinal function scan is a novel cloud-based digital health application for remote monitoring. The aim of this study is to assess the efficacy of the Macustat® compared to traditional in-office retinal evaluations.

MATERIALS AND METHODS

Patients with underlying macular pathology underwent office-based retinal and visual acuity examinations and OCT macula imaging followed by remote tele-monitoring assessment with the Macustat. Central visual function was assessed with the multi-modal Macustat test using dynamic virtual Amsler grid testing, hyperacuity perimetry and visual acuity testing. The results were compared to the findings of the in-office comprehensive retina exam and OCT evaluation.

RESULTS

The foveal acuity potential registered with the Macustat test showed high correlation with the office Snellen acuity potential 96% of eyes registered Macustat acuity within 0.2 LogMAR of office acuity measurement. In Wet AMD eyes with CNV pathology documented on OCT, the Macustat foveal function scan showed a corresponding abnormality in 89% of any CNV eyes and 100% of all visually significant CNV. In normal eyes without any visually significant edema or CNV, more than 92% showed corresponding normal retinal function scan.

CONCLUSION

The Macustat demonstrates high concordance with clinical findings using traditional diagnostic devices. Home monitoring with the Macustat® may offer complementary clinical utility as a telehealth tool for the assessment of visual acuity and macular function in patients at high risk for macular disease.

Oxidative Stress Implication in Retinal Diseases-A Review

Oxidative stress (OS) refers to an imbalance between free radicals (FRs), namely highly reactive molecules normally generated in our body by several pathways, and intrinsic antioxidant capacity. When FR levels overwhelm intrinsic antioxidant defenses, OS occurs, inducing a series of downstream chemical reactions. Both reactive oxygen species (ROS) and reactive nitrogen species (RNS) are produced by numerous chemical reactions that take place in tissues and organs and are then eliminated by antioxidant molecules. In particular, the scientific literature focuses more on ROS participation in the pathogenesis of diseases than on the role played by RNS. By its very nature, the eye is highly exposed to ultraviolet radiation (UVR), which is directly responsible for increased OS. In this review, we aimed to focus on the retinal damage caused by ROS/RNS and the related retinal pathologies. A deeper understanding of the role of oxidative and nitrosative stress in retinal damage is needed in order to develop targeted therapeutic interventions to slow these pathologies.

Diabetic retinopathy with extensively large area of capillary non-perfusion: characteristics and treatment outcomes

Background

Capillary non-perfusion is an important characteristic for diabetic retinopathy (DR) indicating microvascular damage and ischemia. Data on the description and treatment outcomes of DR with large area of non-perfusion are lacking to date. We aim to describe the characteristics and treatment outcomes in a series of patients with DR who presented extensively large area of capillary non-perfusion (LACNP).

Methods

Fundus fluorescein angiograms from medical charts in patients diagnosed with DR between Jan 2017 and Dec 2019 were retrospectively reviewed. Clinical data in eyes with LACNP including imaging and laboratory findings at the first presentation were analyzed. The LACNP was defined as over 70% area of capillary non-perfusion throughout the whole image retina. The mean follow-up duration was 12.4 ± 16.7 months. Follow-up data including extensive pan-retinal photocoagulation and surgical intervention and treatment outcomes were evaluated.

Results

A total of 43 eyes in 24 patients with LACNP were included, accounting for 3.3% of DR populations in the same period. The overall percentage of non-perfusion area was 79.1 ± 8.1%. All patients received proper control of diabetes and hypertension, and extensive pan-retinal laser photocoagulation. During the follow-up periods, 20 eyes (46.5%) developed severe neovascular complications, of which 15 eyes (34.9%) underwent vitrectomy and/or anti-glaucoma surgeries. Conservative therapies including glycemic control and supplemental laser photocoagulation were conducted in 23 eyes (53.5%) without neovascular complications. In the final follow-up, best corrected visual acuity improved or maintained stable in 19 eyes (44.2%) while deteriorated in 24 eyes (55.8%).

Conclusions

The presence of LACNP is the hallmark of advanced DR and often indicates a poor visual outcome, although aggressive treatments may slow DR progression and maintain central vision for some time.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12886-022-02508-6.

Diabetic macular ischaemia- a new therapeutic target?

Diabetic macular ischaemia (DMI) is traditionally defined and graded based on the angiographic evidence of an enlarged and irregular foveal avascular zone. However, these anatomical changes are not surrogate markers for visual impairment. We postulate that there are vascular phenotypes of DMI based on the relative perfusion deficits of various retinal capillary plexuses and choriocapillaris. This review highlights several mechanistic pathways, including the role of hypoxia and the complex relation between neurons, glia, and microvasculature. The current animal models are reviewed, with shortcomings noted. Therefore, utilising the advancing technology of optical coherence tomography angiography (OCTA) to identify the reversible DMI phenotypes may be the key to successful therapeutic interventions for DMI. However, there is a need to standardise the nomenclature of OCTA perfusion status. Visual acuity is not an ideal endpoint for DMI clinical trials. New trial endpoints that represent disease progression need to be developed before irreversible vision loss in patients with DMI. Natural history studies are required to determine the course of each vascular and neuronal parameter to define the DMI phenotypes. These DMI phenotypes may also partly explain the development and recurrence of diabetic macular oedema. It is also currently unclear where and how DMI fits into the diabetic retinopathy severity scales, further highlighting the need to better define the progression of diabetic retinopathy and DMI based on both multimodal imaging and visual function. Finally, we discuss a complete set of proposed therapeutic pathways for DMI, including cell-based therapies that may provide restorative potential.

Decreased Macular Retinal Thickness in Patients With Pterygium

Purpose

To explore alterations in macular retinal thickness (RT) and analyze correlation between macular RT and pterygium area, length in pterygium patients.

Methods

Totally 13 patients with pterygium (left eye) and 13 healthy controls (left eye) were recruited. OCTA was applied to scan each eye to generate three-dimensional images. Based on the Early Treatment Diabetic Retinopathy Study (ETDRS) method, each image was divided into nine subregions for the ETDRS: central (C); inner superior (IS); outer superior (OS); inner nasal (IN); outer nasal (ON); inner inferior (II); outer inferior (OI); inner temporal (IT); and outer temporal (OT). The macular RT in each subregion was measured. Furthermore, the correlation between RT and the area, length of pterygium was analyzed.

Results

The visual acuity of pterygium patient was different from that of the control (P < 0.05). Besides, decreased intraretinal thickness of the IN and ON, increased intraretinal thickness of OT, decreased extraretinal thickness of OT, IN, ON, OS, and decreased retinal full layer thickness of medial superior, OS, IN, ON, and II subregions in pterygium group were observed. There was a negative correlation between RT of the IN and ON subregions and the length of pterygium (r = -0.5803 and r = -0.6013, P = 0.0376 and P = 0.0297). The RT of IN subregion was negatively correlated with pterygium area (r = -0.5844, P = 0.0359). According to the receiver operating characteristic analysis, in the ON subregion, the areas under the curve of the inner retinal thickness, outer retinal thickness and the whole retinal thickness were 1.0 (95% CI: 1.0), 0.882 (95% CI: 0.715 and 0.963), and 1.0 (95% CI: 1.0). The smallest area under the curve of retinal thickness in OT subregion was 0.018 (95% CI: 0-0.059).

Conclusion

RT of pterygium patients was significantly decreased, and the main alterations occurred in the temporal side suggesting there might exist retinal structural alterations in pterygium.

Unsuspected Central Vision Decrease from Macular Ganglion Cell Loss after Posterior Segment Surgery

PURPOSE

To describe a novel post-surgical complication of circumscribed macula ganglion cell loss as an apparent cause of unsuspected vision loss following posterior segment surgery.

METHODS

Patients were seen in referral and were evaluated with comprehensive examination to include optical coherence tomography (OCT) and microperimetry.

RESULTS

All 8 patients had a sudden central vision loss following vitrectomy and many patients suspected the central loss was present even before the eye patch was removed on the first postoperative day. Of the 8, 1 had a vitrectomy with no membrane peeling while the remaining 7 had membrane peeling. The mean post-operative visual acuity was 20/200. The mean ganglion cell layer (GCL) volume was 0.69 µm3 in the involved eye and 1.035 µm3 in the fellow eye (P<.001). The global retinal nerve fiber layer (RNFL) thicknesses in the involved and fellow eyes were 81.3 and 90 µm respectively (P = .08). The outer retinal architecture was unremarkable in the involved eyes and did not appear to explain the poor acuity. The GCL volume loss was not necessarily associated with RNFL thicknesses that were in the abnormal range or in optic nerve pallor. Microperimetry showed severe depression of the threshold sensitivities.

CONCLUSION

Severe loss of the macular ganglion cells may occur after vitrectomy and is associated with central vision loss. The diagnosis is made by having a high index of suspicion when examining OCT B-scan images and by evaluating GCL volumes. The frequency of this occurrence is currently unknown.

The relationship between perifoveal capillary ring alterations and visual acuity in diabetic retinopathy

Background/Aim. The relationship between the foveal avascular zone (FAV) and visual acuity (VA) in retinal dis-eases remains a matter of discussion. The aim of this study was to determine the impact of diabetic macular ischemia (DMI) on VA through the analysis of the perifoveal capillary network in various stages of diabetic retinopathy - DR (non-proliferative diabetic retinopathy ? NPDR and proliferative diabetic retinopathy ? PDR). Methods. Qualitative and quantitative analysis of 143 angiograms of patients with different stages of DR was performed. The degree of macular ischemia was assessed by the analysis of 2 parameters: perifoveal capillary ring, ie, the FAZ outline irregularity, and capillary loss. Finally, a comparison was made between the degree of macular ischemia with the best-corrected VA, depending on macular thickness. Results. In the eyes with mild and moderate NPDR, without significant macular thickening, no statistically significant decrease in VA caused by macular ischemia was noticed (p = 0.81). Opposite, in a subgroup with severe NPDR and PDR, without significant macular thickening, a statistically significant difference was presented among eyes with moderate and severe macular ischemia compared to eyes with lower grades of macular ischemia (p = 0.021 and p = 0.018, respectively). In the eyes with moderate NPDR and mild macular ischemia, the increase in macular thickness resulted in a statistically insignificant decrease in VA compared to eyes with a normal macular thickness (p = 0.088). However, in the eyes with severe NPDR, every pathological increase in macular thickness caused a statistically significant decrease in VA, regardless of the degree of macular ischemia (p = 0.018?0.040). A similar relationship was also found in the eyes with PDR (p = 0.017?0.042). In the eyes with a statistically significant decrease in VA, most of the examined eyes (98%) had the FAZ outline irregularity in the nasal perifoveal subfield. Conclusion. In the absence of significant macular thickening, the destruction of one-half of the perifoveal capillary network, or greater, is associated with reduced VA. The location of macular ischemic changes in the nasal parts of the perifoveal capillary ring plays a crucial role in its effects on visual function.

Decreased retinal microvasculature densities in pterygium

AIM

To investigate the retinal vascular network alterations in eyes of patients with pterygium.

METHODS

Totally 18 left eyes from 18 female pterygium patients and 18 left eyes from 18 female healthy control subjects were enrolled. Optical coherence tomography angiography (OCTA) images were generated of the superficial retinal layer and deeper retinal layer of the macular retina for each eye. The microvascular (MIR) and macrovascular (MAR) densities were calculated and MIR, MAR, and total microvascular (TMI) density was compared in the healthy control and pterygium groups.

RESULTS

In pterygium group, in the superficial retinal layer, the vascular density in superficial MIR, superior right (SR), inferior right (IR), right (R), superficial central annuli (SC)1, SC2, and SC3 decreased significantly in the macular area (P<0.05). Furthermore, the vascular density in all those decreased regions except R, was significantly and negatively correlated with the disease course (r=-0.6038 to -0.7762, P=0.0008), and the area size of pterygium (r=-0.6043 to -0.9508, P<0.05). For the deeper retinal layer, the density of deep total microvessel (DTMI), deeper MIR, SR, IR, R, DC2, and DC3 decreased significantly in macular area of pterygium patients (P<0.05). Furthermore, the vascular density in all those decreased regions was significantly and negatively correlated with the disease course (r=-0.6901 to -0.7795, P=0.0015), and the area size of pterygium (r=-0.6043 to -0.9563, P<0.05). No statistically significant differences and correlation was found in other region density (|r|<0.47, P>0.05).

CONCLUSION

OCTA findings suggest that pterygium patients present with decreased retinal MIR density, and the major vascular alterations occurr mainly on the bitamporal side. The vascular density of the superficial SC1, SC2, SC3 adjacent to the foveal and deep layer of DC2, DC2 regions, significantly decreased.

Light-Induced Smooth Endoplasmic Reticulum Rearrangement in a Unique Interlaced Compartmental Pattern in Macaca mulatta RPE

Purpose

To investigate light-induced modifications of the smooth endoplasmic reticulum of the RPE in primates.

Methods

Eyes of three terminally anesthetized Rhesus monkeys were exposed to 5000 lux for 10 minutes or kept in the dark. Transmission electron microscopy and electron tomography were conducted on small fragments of retina sampled from different regions of the retina.

Results

RPE cells smooth endoplasmic reticulum shows a previously unknown arrangement characterized by an interlaced compartmental pattern (ICP). Electron tomograms and 3D-modelling demonstrated that the smooth endoplasmic reticulum with an ICP (ICPSER) consisted of four parallel, independent and interwoven networks of tubules arranged as interconnected coiled coils. Its architecture realized a compact labyrinthine structure of tightly packed tubules stabilized by intertubular filamentous tethers. On average, the ICPSER is present in about 14.6% of RPE cells. Although ICPSER was preferentially found in cells located in the peripheral and in the para/perifoveal retina, ICPSER cells significantly increased in number upon light exposure in the para/perifovea and in the fovea.

Conclusions

An ICPSER is apparently a unique feature to primate RPE. Its rapid appearance in the area centralis of the retina upon light exposure suggests a function related to the foveate structure of primate retina or to the diurnal habits of animals that may require additional protection from photo-oxidation or enhanced requests of visual pigments regeneration.

Complement Factor H Loss in RPE Cells Causes Retinal Degeneration in a Human RPE-Porcine Retinal Explant Co-Culture Model

Age-related Macular degeneration (AMD) is a degenerative disease of the macula affecting the elderly population. Treatment options are limited, partly due to the lack of understanding of AMD pathology and the lack of suitable research models that replicate the complexity of the human macula and the intricate interplay of the genetic, aging and lifestyle risk factors contributing to AMD. One of the main genetic risks associated with AMD is located on the Complement Factor H (CFH) gene, leading to an amino acid substitution in the Factor H (FH) protein (Y402H). However, the mechanism of how this FH variant promotes the onset of AMD remains unclear. Previously, we have shown that FH deprivation in RPE cells, via CFH silencing, leads to increased inflammation, metabolic impairment and vulnerability toward oxidative stress. In this study, we established a novel co-culture model comprising CFH silenced RPE cells and porcine retinal explants derived from the visual streak of porcine eyes, which closely resemble the human macula. We show that retinae exposed to FH-deprived RPE cells show signs of retinal degeneration, with rod cells being the first cells to undergo degeneration. Moreover, via Raman analyses, we observed changes involving the mitochondria and lipid composition of the co-cultured retinae upon FH loss. Interestingly, the detrimental effects of FH loss in RPE cells on the neuroretina were independent of glial cell activation and external complement sources. Moreover, we show that the co-culture model is also suitable for human retinal explants, and we observed a similar trend when RPE cells deprived of FH were co-cultured with human retinal explants from a single donor eye. Our findings highlight the importance of RPE-derived FH for retinal homeostasis and provide a valuable model for AMD research.

Distributions of Radial Peripapillary Capillary Density and Correlations with Retinal Nerve Fiber Layer Thickness in Normal Subjects

BACKGROUND The aim of this study was to investigate distribution rules of radial peripapillary capillaries (RPCs) density and correlations with retinal nerve fiber layers (RNFL) thickness in normal subjects. MATERIAL AND METHODS We included 78 eyes of 78 healthy subjects examined by optical coherence tomography angiography (OCTA). RPCs density and RNFL thickness were measured automatically. Distributions of RPCs density and RNFL thickness were analyzed at different locations. Correlations of these 2 parameters and relationship with large vessels were evaluated by Spearman test. RESULTS Average density for overall, peripapillary, and inside disc RCPs was 56.12±2.51%, 58.56±2.84%, and 60.16±4.01%, respectively. Overall and peripapillary RCPs density were positively correlated with RNFL thickness (r=0.595, P.

Depth-Resolved Visualization of Perifoveal Retinal Vasculature in Preterm Infants Using Handheld Optical Coherence Tomography Angiography

Purpose

To establish methods to visualize depth-resolved perifoveal retinal vasculature in preterm infants using handheld optical coherence tomography angiography (OCT-A).

Methods

In this exploratory study, eyes of preterm infants were imaged using an investigational noncontact, handheld swept-source OCT-A device as part of the prospective BabySTEPS infant retinal imaging study. We selected high-quality OCT-A volumes at two developmental stages for analysis. Customized MATLAB scripts were used to segment retinal layers, test offset parameters, and generate depth-resolved OCT-A slabs. The superficial (SCP), intermediate (ICP), and deep (DCP) capillary plexuses were visualized and qualitatively assessed by three image graders.

Results

Six eyes from six preterm infants were included in this analysis. A three-layered perifoveal retinal vasculature was successfully visualized in all three eyes (three infants) in the 40 weeks postmenstrual age (PMA) group (one of three eyes with treated type 1 retinopathy of prematurity [ROP]). No obvious ICP or DCP was found in good-quality scans of the three eyes (three infants) in the 35 weeks PMA group (three of three eyes developed type 1 ROP).

Conclusions

Custom segmentation parameters are useful to visualize perifoveal retinal vasculature in preterm infants. At term age, a three-layered capillary structure is visible in most eyes, while prior to detectable flow within the ICP and DCP, the perifoveal vasculature may be better visualized in two layers.

Translational Relevance

Development of segmentation parameters for depth-resolved OCT-A of perifoveal retinal vasculature in preterm infants facilitates the study of human retinal vascular development and vascular pathologies of ROP.

The electroretinogram in the genomics era: outer retinal disorders

The inherited retinal diseases (IRDs) have traditionally been described phenotypically with the description evolving to incorporate more sophisticated structural and functional assessments. In the last 25 years there has been considerable advances in the understanding of underlying genetic aetiologies. The role of the ophthalmologist is now to work in a multi-disciplinary team to identify the disease-causing genotype, which might be amenable to gene-directed intervention. Visual electrophysiology is an important tool to assist the ophthalmologist in guiding the clinical geneticist to reach a final molecular diagnosis. This review outlines the physiological basis for the ISCEV standard electrophysiology tests, the role of electrophysiology in localising the functional deficit, correlation with structural findings to guide diagnosis and finally management of IRDs in the era of genomics with emphasis on the outer retina.

Visual Field Test With Gaze Check Tasks: Application in a Homonymous Hemianopic Patient Unaware of the Visual Defects

Gaze control is required for applying visual stimuli to a particular area of the visual field. We developed a visual field test with gaze check tasks to investigate hemianopia. In this test, participants must report the presence or absence of visual stimuli when a small object at the fixation point vibrates. Trials in the absence of visual stimuli were used as gaze check tasks, since the vibration could be observed only when the gaze was directed at the fixation point. We evaluated the efficacy of our test in four control participants and one patient with homonymous hemianopia who was unaware of the defects in the left visual field. This patient presented hemianopia in the test with gaze check tasks, but not when the gaze check tasks were omitted. The patient showed spontaneous gaze movements from the fixation point to the upper left direction, as well as scanning of the left visual field during the test without gaze check tasks. Thus, we concluded that the visual defects in this patient were compensated in daily life by spontaneous eye movements coordinated with visual information processing. The present results show the usefulness of the visual field test with gaze check tasks.

PHOTORECEPTOR DAMAGE IN DIABETIC CHOROIDOPATHY

PURPOSE

To investigate the relationship between choriocapillaris (CC) hypoperfusion and photoreceptor alterations in eyes with nonproliferative diabetic retinopathy (NPDR).

METHODS

In this prospective, observational, case-control study, 30 eyes (30 patients) with NPDR and 30 healthy eyes from 30 controls were enrolled at the University G. d'Annunzio, Chieti-Pescara, Italy. This study cohort underwent an ophthalmologic examination, including optical coherence tomography and optical coherence tomography angiography. The main outcome measures were as follows: 1) "normalized" reflectivity of en face image segmented at the ellipsoid zone level, which was calculated to quantify the photoreceptor damage, and 2) CC perfusion density. Secondary outcome measures were as follows: 1) superficial retinal capillary plexus (SCP), intermediate retinal capillary plexus (ICP), and deep retinal capillary plexus (DCP) perfusion density (based on the area of vessels); 2) SCP, ICP, and DCP vessel length density (based on a map with vessels of 1-pixel width); and 3) SCP, ICP, and DCP vessel diameter.

RESULTS

Mean ± SD age was 58.9 ± 11.1 years (range 38-79 years) in the NPDR group and 61.7 ± 11.3 years (range 39-87 years) in the control group (P > 0.05 for all the comparisons). Compared with controls, NPDR eyes displayed a lower "normalized" reflectivity (0.96 ± 0.25 in controls and 0.73 ± 0.19 in the NPDR group, P < 0.0001). Moreover, the NPDR group was characterized by an impaired perfusion in both the retinal and choroidal vasculature. In multiple regression analysis, ellipsoid zone "normalized" reflectivity displayed a significant direct association with CC perfusion density in patients with NPDR (P = 0.025 and P = 0.476, in NPDR and controls, respectively).

CONCLUSION

Eyes with NPDR are affected by macular hypoperfusion and photoreceptor damage, the latter investigated as ellipsoid zone "normalized" reflectivity. The diabetic choroidopathy seems to be strongly associated with photoreceptor damage.

Association of macular and choroidal perfusion with long-term visual outcomes after macula-off rhegmatogenous retinal detachment

BACKGROUND/AIMS

To examine the relationship between macular perfusion, as assessed using optical coherence tomography angiography (OCTA), and long-term visual outcome after surgical repair of macula-off rhegmatogenous retinal detachment (RRD).

METHODS

A prospective study of 29 patients who had undergone successful surgical repair of macula-off RRD. OCTA imaging was performed at month 3 and repeated at months 6 and 12 after surgery. Associations between OCTA parameters including, foveal avascular zone (FAZ) area, vessel density (VD) in the superficial capillary plexus (SCP) and deep capillary plexus (DCP), choriocapillaris flow deficit features and logMAR best-corrected visual acuity (VA) were assessed using a random intercept hybrid linear mixed model.

RESULTS

Over the 1-year follow-up, VA improved (0.025 logMAR/ month, 95% CI 0.015 to 0.035) and FAZ area decreased (-0.020 mm²/month, 95% CI -0.032 to -0.007). Better VA after surgery was significantly associated with denser superficial VD (β=0.079, 95% CI 0.026 to 0.131), lower number of choriocapillaris flow deficits (β=-0.087, 95% CI -0.154 to -0.021) and larger average size of choriocapillaris flow deficits (β=0.085, 95% CI 0.022 to 0.147), after adjusting for baseline VA, types of surgery and other factors.

CONCLUSIONS

OCTA measures of vascular perfusion in the macula may provide new pathophysiological insights and prognostic information related to macula-off RRD.

Foveal changes in aquaporin-4 antibody seropositive neuromyelitis optica spectrum disorder are independent of optic neuritis and not overtly progressive

BACKGROUND AND PURPOSE

Foveal changes were reported in aquaporin-4 antibody (AQP4-Ab) seropositive neuromyelitis optica spectrum disorder (NMOSD) patients; however, it is unclear whether they are independent of optic neuritis (ON), stem from subclinical ON or crossover from ON in fellow eyes. Fovea morphometry and a statistical classification approach were used to investigate if foveal changes in NMOSD are independent of ON and progressive.

METHODS

This was a retrospective longitudinal study of 27 AQP4-IgG + NMOSD patients (49 eyes; 15 ON eyes and 34 eyes without a history of ON [NON eyes]), follow-up median (first and third quartile) 2.32 (1.33-3.28), and 38 healthy controls (HCs) (76 eyes), follow-up median (first and third quartile) 1.95 (1.83-2.54). The peripapillary retinal nerve fibre layer thickness and the volume of combined ganglion cell and inner plexiform layer as measures of neuroaxonal damage from ON were determined by optical coherence tomography. Nineteen foveal morphometry parameters were extracted from macular optical coherence tomography volume scans. Data were analysed using orthogonal partial least squares discriminant analysis and linear mixed effects models.

RESULTS

At baseline, foveal shape was significantly altered in ON eyes and NON eyes compared to HCs. Discriminatory analysis showed 81% accuracy distinguishing ON vs. HCs and 68% accuracy in NON vs. HCs. NON eyes were distinguished from HCs by foveal shape parameters indicating widening. Orthogonal partial least squares discriminant analysis discriminated ON vs. NON with 76% accuracy. In a follow-up of 2.4 (20.85) years, no significant time-dependent foveal changes were found.

CONCLUSION

The parafoveal area is altered in AQP4-Ab seropositive NMOSD patients suggesting independent neuroaxonal damage from subclinical ON. Longer follow-ups are needed to confirm the stability of the parafoveal structure over time.

The dynamics of saliency-driven and goal-driven visual selection as a function of eccentricity

Both saliency and goal information are important factors in driving visual selection. Saliency-driven selection occurs primarily in early responses, whereas goal-driven selection happens predominantly in later responses. Here, we investigated how eccentricity affects the time courses of saliency-driven and goal-driven visual selection. In three experiments, we asked people to make a speeded eye movement toward a predefined target singleton which was simultaneously presented with a non-target singleton in a background of multiple homogeneously oriented other items. The target singleton could be either more or less salient than the non-target singleton. Both singletons were presented at one of three eccentricities (i.e., near, middle, or far). The results showed that, even though eccentricity had only little effect on overall selection performance, the underlying time courses of saliency-driven and goal-driven selection altered such that saliency effects became protracted and relevance effects became delayed for far eccentricity conditions. The protracted saliency effect was shown to be modulated by expectations as induced by the preceding trial. The results demonstrate the importance of incorporating both time and eccentricity as factors in models of visual selection.

The interplay of oxidative stress and ARMS2-HTRA1 genetic risk in neovascular AMD

Age-related macular degeneration (AMD) is the leading cause of vision loss in adults over 60 years old globally. There are two forms of advanced AMD: “dry” and “wet”. Dry AMD is characterized by geographic atrophy of the retinal pigment epithelium and overlying photoreceptors in the macular region; whereas wet AMD is characterized by vascular penetrance from the choroid into the retina, known as choroidal neovascularization (CNV). Both phenotypes eventually lead to loss of central vision. The pathogenesis of AMD involves the interplay of genetic polymorphisms and environmental risk factors, many of which elevate retinal oxidative stress. Excess reactive oxygen species react with cellular macromolecules, forming oxidation-modified byproducts that elicit chronic inflammation and promote CNV. Additionally, genome-wide association studies have identified several genetic variants in the age-related maculopathy susceptibility 2/high-temperature requirement A serine peptidase 1 (ARMS2-HTRA1) locus associated with the progression of late-stage AMD, especially the wet subtype. In this review, we will focus on the interplay of oxidative stress and HTRA1 in drusen deposition, chronic inflammation, and chronic angiogenesis. We aim to present a multifactorial model of wet AMD progression, supporting HTRA1 as a novel therapeutic target upstream of vascular endothelial growth factor (VEGF), the conventional target in AMD therapeutics. By inhibiting HTRA1’s proteolytic activity, we can reduce pro-angiogenic signaling and prevent proteolytic breakdown of the blood-retina barrier. The anti-HTRA1 approach offers a promising alternative treatment option to wet AMD, complementary to anti-VEGF therapy.

Mammalian Retinal Cell Quantification

Normal retina and its cell layers are essential for processing visual stimuli, and loss of its integrity has been documented in many disease processes. The numbers and the axonal processes of retinal ganglion cells are reduced substantially in glaucoma, leading to vision loss and blindness. Similarly, selective loss of photoreceptors in age-related macular degeneration and hereditary retinal dystrophies also results in the compromise of visual acuity. Development of genetically modified mice has led to increased understanding of the pathogenesis of many retinal diseases. Similarly, in this digital era, usage of modalities to quantify the retinal cell loss has grown exponentially leading to a better understanding of the suitability of animal models to study human retinal diseases. These quantification modalities provide valuable quantifiable data in studying pathogenesis and disease progression. This review will discuss the immunohistochemical markers for various retinal cells, available automated tools to quantify retinal cells, and present an example of retinal ganglion cell quantification using HALO image analysis platform. Additionally, we briefly review retinal cell types and subtypes, salient features of retina in various laboratory animal species, and a few of the main disease processes that affect retinal cell numbers in humans.

Widefield topographical analysis of the retinal perfusion and neuroretinal thickness in healthy eyes: a pilot study

PURPOSE

In this pilot study we reported variation of superficial (SCP) and deep (DCP) capillary plexuses flow in macular and near/mid periphery regions in healthy subjects using widefield swept source-optical coherence tomography angiography (SS-OCTA).

METHODS

In this prospective, cross-sectional study, enroled subjects were imaged with an SS-OCTA system (PLEX Elite 9000, Carl Zeiss Meditec Inc., Dublin, CA, USA). OCTA scans were taken in primary and extremes of gaze and a montage was automatically created. Quantitative analysis was performed in the macular and peripheral regions. In addition, SCP and DCP variables were further investigated in distinct fields within these three different regions.

RESULTS

Fifty-five young healthy subjects (55 eyes) were enroled. The retinal periphery displayed a higher SCP perfusion density (39.6 ± 1.7% and 40.7 ± 1.4%, P < 0.0001) and SCP vessel diameter index (3.5 ± 0.2 and 3.6 ± 0.2, P < 0.0001), in comparison with the macular region. At the DCP level, the retinal periphery was characterized by a lower perfusion density (41.6 ± 3.7% and 37.9 ± 2.9%, P < 0.0001) and vessel length density (14.6 ± 6.0% and 9.9 ± 2.6%, P < 0.0001). In the analysis investigating the DCP in the retinal periphery, the temporal sector was characterized by a reduction in perfusion density, vessel length density, and vessel diameter index. In univariate analysis, the retinal thickness was found to have a significant direct relationship with DCP perfusion density (P < 0.0001), but not with SCP perfusion density (P = 0.712).

CONCLUSIONS

We report quantitative mapping of the SCP and DCP in healthy individuals. The DCP perfusion appears to have a wide topographical variation, which is strictly dependent on the retinal thickness.

Bilirubin in the Vitreous Body of the Eye of Human Fetuses

The bilirubin content in the vitreous body of the eye of human fetuses of gestation week 17-31 was measured. During gestation weeks 17-19, the mean bilirubin concentration was 8.67 μmol/liter; then, decreased to 1.37 μmol/liter (gestation weeks 20 to 31). Bilirubin, being an endogenous antioxidant, is probably involved in protection of the retina and lens from LPO processes that intensively develop in retinal neurons and lens fibers.

Developmental Changes in Retinal Microvasculature in Children: A Quantitative Analysis Using Optical Coherence Tomography Angiography

PURPOSE

To quantify the macular microvasculature in healthy children of various ages by using optical coherence tomography angiography (OCTA).

DESIGN

Prospective cross-sectional study.

METHODS

A total of 333 normal children from 4 to 16 years old were included. OCTA was performed on a 3- × 3-mm area centered on the macular region. Vascular density, perfusion density, fovea avascular zone (FAZ) area, FAZ perimeter, and FAZ acircularity index (AI) were measured and adjusted for axial length. Differences were compared among various ages.

RESULTS

Among the different age groups, both macular vascular density and perfusion density increased with age (P < .0001 and P = .0028, respectively). After adjustments were made for the spherical equivalent (SE) and axial length, macular vascular density was significantly associated with age (r = 0.183; P = .001) No factors were significantly correlated with the perfusion density after adjustment for the age, SE, or axial length. The FAZ area and FAZ perimeter did not change among groups of different ages. Nevertheless, the AI of FAZ in the 4.00-6.99-year-old group was smaller to that of the 13.00-15.99-year-old group (P = .03). Younger children had significantly higher rates of nonconsecutive vessels branched toward the macular center (P = .0002) and vascular loops contributing to irregular shapes of FAZ (P = .024).

CONCLUSIONS

Macular vascular density and perfusion density continuously increase with age in children. Despite the fact that FAZ area and perimeter did not change, the microstructure of FAZ pruned and tended to form a smooth and regular avascular area during development.

Paracentral acute middle maculopathy and the organization of the retinal capillary plexuses

The retinal capillary vasculature serves the formidable role of supplying the metabolically active inner and middle retina. In the parafoveal region, the retinal capillary plexuses (RCP) are organized in a system of three capillary layers of varying retinal depths: the superficial capillary plexus (SCP), intermediate capillary plexus (ICP) and deep capillary plexus (DCP). While the dynamic flow through these plexuses is complex and not completely understood, current research points to a hybrid model that includes both parallel and in series components in which blood flows in a predominantly serial direction between the superficial vascular complex (SVC) and deep vascular complex (DVC). Each capillary plexus autoregulates independently, so that under most conditions the retinal vasculature supplies adequate blood flow and oxygen saturation at varying depths despite diverse environmental stressors. When the flow in the deep vascular complex (i.e. ICP and DCP) fails, an ischemic lesion referred to as Paracentral Acute Middle Maculopathy (PAMM) can be identified. PAMM is an optical coherence tomography (OCT) finding defined by the presence of a hyperreflective band at the level of the inner nuclear layer (INL) that indicates INL infarction caused by globally impaired perfusion through the retinal capillary system leading to hypoperfusion of the DVC or specifically the DCP. Patients present with an acute onset paracentral scotoma and typically experience a permanent visual defect. Lesions can be caused by a diverse set of local retinal vascular diseases and systemic disorders. PAMM is a manifestation of the retinal ischemic cascade in which the mildest forms of ischemia develop at the venular end of the DCP, i.e. perivenular PAMM, while more severe forms progress horizontally to diffusely involve the INL, and the most severe forms progress vertically to infarct the inner retina. Management is targeted toward the identification and treatment of related vasculopathic and systemic risk factors.

MACULAR MICROVASCULAR NETWORKS IN HEALTHY PEDIATRIC SUBJECTS

PURPOSE

To report optical coherence tomography angiography (OCTA) values in healthy pediatric eyes and to identify factors that may modify these values.

METHODS

In this prospective observational cross-sectional study, macular OCTA images were acquired from healthy pediatric patients. Main outcome measures were 1) foveal avascular zone (FAZ) area at the level of the superficial retinal capillary plexus (SCP); 2) SCP and deep retinal capillary plexus (DCP) perfusion density (based on the area of vessels); 3) SCP and DCP vessel density (based on a map with vessels of 1-pixel width); and 4) CC perfusion density. Multiple regression analysis was performed to assess the effect of age, sex, ethnicity, refraction, and foveal macular thickness (FMT) on OCTA parameters.

RESULTS

Seventy-seven eyes from 52 subjects (23 male and 29 female) were included in analysis. Mean age was 11.1 ± 3.3 years (range = 5.0-17.0 years). Twenty-nine (55.8%) subjects were white, 14 (27.0%) Hispanic, 8 (15.4%) Asian, and 1 (1.8%) African-American. Mean refraction was -0.1 ± 2.4 diopters (D) (range = -5.75 to +9.0 D). Mean FMT was 248.6 ± 18.6 μm. Larger FAZ area was significantly associated with older age (P = 0.014). Furthermore, larger FAZ area was associated with reduced FMT (P < 0.0001). Male sex was associated only with increased SCP perfusion density (P = 0.042). Increased CC perfusion density was associated with younger age (P = 0.022).

CONCLUSION

We report data for pediatric OCTA parameters in healthy subjects. Several variables influence the density of macular microvascular networks, and these factors should be considered in the OCTA study of pediatric eye disorders.

Subretinally injected semiconducting polymer nanoparticles rescue vision in a rat model of retinal dystrophy

Inherited retinal dystrophies and late-stage age-related macular degeneration, for which treatments remain limited, are among the most prevalent causes of legal blindness. Retinal prostheses have been developed to stimulate the inner retinal network; however, lack of sensitivity and resolution, and the need for wiring or external cameras, have limited their application. Here we show that conjugated polymer nanoparticles (P3HT NPs) mediate light-evoked stimulation of retinal neurons and persistently rescue visual functions when subretinally injected in a rat model of retinitis pigmentosa. P3HT NPs spread out over the entire subretinal space and promote light-dependent activation of spared inner retinal neurons, recovering subcortical, cortical and behavioural visual responses in the absence of trophic effects or retinal inflammation. By conferring sustained light sensitivity to degenerate retinas after a single injection, and with the potential for high spatial resolution, P3HT NPs provide a new avenue in retinal prosthetics with potential applications not only in retinitis pigmentosa, but also in age-related macular degeneration.

Retina in a dish: Cell cultures, retinal explants and animal models for common diseases of the retina

For many retinal diseases, including age-related macular degeneration (AMD), glaucoma, and diabetic retinopathy (DR), the exact pathogenesis is still unclear. Moreover, the currently available therapeutic options are often unsatisfactory. Research designed to remedy this situation heavily relies on experimental animals. However, animal models often do not faithfully reproduce human disease and, currently, there is strong pressure from society to reduce animal research. Overall, this creates a need for improved disease models to understand pathologies and develop treatment options that, at the same time, require fewer or no experimental animals. Here, we review recent advances in the field of in vitro and ex vivo models for AMD, glaucoma, and DR. We highlight the difficulties associated with studies on complex diseases, in which both the initial trigger and the ensuing pathomechanisms are unclear, and then delineate which model systems are optimal for disease modelling. To this end, we present a variety of model systems, ranging from primary cell cultures, over organotypic cultures and whole eye cultures, to animal models. Specific advantages and disadvantages of such models are discussed, with a special focus on their relevance to putative in vivo disease mechanisms. In many cases, a replacement of in vivo research will mean that several different in vitro models are used in conjunction, for instance to analyze and validate causative molecular pathways. Finally, we argue that the analytical decomposition into appropriate cell and tissue model systems will allow making significant progress in our understanding of complex retinal diseases and may furthermore advance the treatment testing.

Misaligned foveal morphology and sector retinal dysfunction in AKT1-mosaic Proteus syndrome

PURPOSE

Proteus syndrome arises as a result of a post-zygotic mosaic activating mutation in the AKT1 oncogene, causing a disproportionate overgrowth of affected tissues. A small number of ocular complications have been reported. We present the unique findings in a patient who had molecular confirmation of AKT1 mosaicism alongside fulfilling the clinical criteria for Proteus syndrome.

METHODS

Pattern electroretinography, visual evoked potentials and multifocal electroretinography testing were performed alongside detailed retinal imaging and clinical examination to detail the ophthalmic characteristics.

RESULTS

Electrophysiological findings characterised unilateral macular dysfunction alongside sector retinal dysfunction of the right eye. This was demonstrated through optical coherence tomography and ultra-wide-field imaging to be associated with a misaligned foveal morphology and sector retinal dysfunction extending into the temporal retina.

CONCLUSION

We propose this patient has asymmetric foveal development and concomitant sector retinal dysfunction as the result of the mosaic AKT1 mutation, either through disruption in the retinal PI3K-AKT1 signalling pathway or through mechanical distortion of ocular growth, resulting in disproportionate inner retinal development. The findings expand the ocular phenotype of Proteus syndrome and encourage early assessment to identify any incipient ocular abnormalities.

Imaging lutein and zeaxanthin in the human retina with confocal resonance Raman microscopy

Lutein and zeaxanthin are xanthophyll carotenoids that are highly concentrated in the human macula, where they protect the eye from oxidative damage and improve visual performance. Distinguishing lutein from zeaxanthin in images of the human retina in vivo or in donor eye tissues has been challenging because no available technology has been able to reliably differentiate between these two carotenoids, which differ only in the position of one C = C bond. Here, we report the differential distributions of lutein and zeaxanthin in human donor retinas mapped with confocal resonance Raman microscopy. Zeaxanthin is highly concentrated in the fovea, extending from the inner to the outer limiting membranes, with especially high concentrations in the outer plexiform layer, while lutein is much more diffuse at relatively lower concentration. Our results imply that zeaxanthin may play a more important role than lutein in human macular health and disease.

Comparison of the Morphology of the Foveal Pit Between African and Caucasian Populations

Purpose

The purpose of this study was to characterize foveal pit morphology in an African (Ghanaian) population, to compare it to that of a Caucasian group and to determine if it varied with age in the two populations.

Methods

The depth, diameter, slope, and volume of the foveal pit were interpolated from optical coherence tomography volume scans recorded in 84 Ghanaian and 37 Caucasian individuals. Their association with age, sex, and ethnicity was investigated using multilevel regression models.

Results

The foveal pit differed significantly in width, slope, and volume between Ghanaian men and women (P < 0.001), but only in width and volume between Caucasian men and women (P < 0.01). In Ghanaians, age was associated with a narrowing of the foveal depression and a reduction of its volume. Overall, these changes were more pronounced in women as compared to men and were largely absent from the Caucasian group. When controlled for age, the foveal pit of Ghanaians was significantly wider and larger in volume as compared to the Caucasian group (P < 0.001).

Conclusions

The morphology of the foveal pit differs between African and Caucasian individuals. These anatomic differences should be considered when examining differences in prevalence and clinical features of vitreoretinal disorders involving the fovea between the two populations.

Translational Relevance

Differences in retinal anatomy may partly explain variations in the prevalence and clinical features of retinal diseases between Africans and Caucasians. Such differences should be adequately considered in diagnoses and monitoring of ocular diseases in patients with African ancestry.

Restoring vision at the fovea

In humans high quality, high acuity visual experience is mediated by the fovea, a tiny, specialized patch of retina containing the locus of fixation. Despite this, vision restoration strategies are typically developed in animal models without a fovea. While electrical prostheses have been approved by regulators, as yet they have failed to restore high quality, high acuity vision in patients. Approaches under pre-clinical development include regenerative cell therapies, optogenetics and chemical photosensitizers. All retinal vision restoration therapies require reactivation of inner retina that has lost photoreceptor input and that the restored signals can be interpreted at a behavioural level. A greater emphasis on tackling these challenges at the fovea may accelerate progress toward high quality vision restoration.

Retinogenesis of the Human Fetal Retina: An Apical Polarity Perspective

The Crumbs complex has prominent roles in the control of apical cell polarity, in the coupling of cell density sensing to downstream cell signaling pathways, and in regulating junctional structures and cell adhesion. The Crumbs complex acts as a conductor orchestrating multiple downstream signaling pathways in epithelial and neuronal tissue development. These pathways lead to the regulation of cell size, cell fate, cell self-renewal, proliferation, differentiation, migration, mitosis, and apoptosis. In retinogenesis, these are all pivotal processes with important roles for the Crumbs complex to maintain proper spatiotemporal cell processes. Loss of Crumbs function in the retina results in loss of the stratified appearance resulting in retinal degeneration and loss of visual function. In this review, we begin by discussing the physiology of vision. We continue by outlining the processes of retinogenesis and how well this is recapitulated between the human fetal retina and human embryonic stem cell (ESC) or induced pluripotent stem cell (iPSC)-derived retinal organoids. Additionally, we discuss the functionality of in utero and preterm human fetal retina and the current level of functionality as detected in human stem cell-derived organoids. We discuss the roles of apical-basal cell polarity in retinogenesis with a focus on Leber congenital amaurosis which leads to blindness shortly after birth. Finally, we discuss Crumbs homolog (CRB)-based gene augmentation.