The neurovascular retina in retinopathy of prematurity

Rodent Models of Retinal Degeneration: From Purified Cells in Culture to Living Animals

Rodent models of retinal degeneration are essential for the development of therapeutic strategies. In addition to living animal models, we here also discuss models based on rodent cell cultures, such as purified retinal ganglion cells and retinal explants. These ex vivo models extend the possibilities for investigating pathological mechanisms and assessing the neuroprotective effect of pharmacological agents by eliminating questions on drug pharmacokinetics and bioavailability. The number of living rodent models has greatly increased with the possibilities to achieve transgenic modifications in animals for knocking in and out genes and mutations. The Cre-lox system has further enabled investigators to target specific genes or mutations in specific cells at specific stages. However, chemically or physically induced models can provide alternatives to such targeted gene modifications. The increased diversity of rodent models has widened our possibility to address most ocular pathologies for providing initial proof of concept of innovative therapeutic strategies.

Photoreceptors inhibit pathological retinal angiogenesis through transcriptional regulation of Adam17 via c-Fos

Pathological retinal angiogenesis profoundly impacts visual function in vascular eye diseases, such as retinopathy of prematurity (ROP) in preterm infants and age-related macular degeneration in the elderly. While the involvement of photoreceptors in these diseases is recognized, the underlying mechanisms remain unclear. This study delved into the pivotal role of photoreceptors in regulating abnormal retinal blood vessel growth using an oxygen-induced retinopathy (OIR) mouse model through the c-Fos/A disintegrin and metalloprotease 17 (Adam17) axis. Our findings revealed a significant induction of c-Fos expression in rod photoreceptors, and c-Fos depletion in these cells inhibited pathological neovascularization and reduced blood vessel leakage in the OIR mouse model. Mechanistically, c-Fos directly regulated the transcription of Adam17 a shedding protease responsible for the production of bioactive molecules involved in inflammation, angiogenesis, and cell adhesion and migration. Furthermore, we demonstrated the therapeutic potential by using an adeno-associated virus carrying a rod photoreceptor-specific short hairpin RNA against c-fos which effectively mitigated abnormal retinal blood vessel overgrowth, restored retinal thickness, and improved electroretinographic (ERG) responses. In conclusion, this study highlights the significance of photoreceptor c-Fos in ROP pathology, offering a novel perspective for the treatment of this disease.

Inhibition of NLRP3 inflammasome by MCC950 under hypoxia alleviates photoreceptor apoptosis via inducing autophagy in Müller glia

NLRP3 inflammasome activation has emerged as a critical initiator of inflammatory response in ischemic retinopathy. Here, we identified the effect of a potent, selective NLRP3 inhibitor, MCC950, on autophagy and apoptosis under hypoxia. Neonatal mice were exposed to hyperoxia for 5 days to establish oxygen-induced retinopathy (OIR) model. Intravitreal injection of MCC950 was given, and then autophagy and apoptosis markers were assessed. Retinal autophagy, apoptosis, and related pathways were evaluated by western blot, immunofluorescent labeling, transmission electron microscopy, and TUNEL assay. Autophagic activity in Müller glia after NLRP3 inflammasome inhibition, together with its influence on photoreceptor death, was studied using western blot, immunofluorescence staining, mRFP-GFP-LC3 adenovirus transfection, cell viability, proliferation, and apoptosis assays. Results showed that activation of NLRP3 inflammasome in Müller glia was detected in OIR model. MCC950 could improve impaired retinal autophagic flux and attenuate retinal apoptosis while it regulated the retinal AMPK/mTOR/ULK-1 pathway. Suppressed autophagy and depressed proliferation capacity resulting from hypoxia was promoted after MCC950 treatment in Müller glia. Inhibition of AMPK and ULK-1 pathway significantly interfered with the MCC950-induced autophagy activity, indicating MCC950 positively modulated autophagy through AMPK/mTOR/ULK-1 pathway in Müller cells. Furthermore, blockage of autophagy in Müller glia significantly induced apoptosis in the cocultured 661W photoreceptor cells, whereas MCC950 markedly preserved the density of photoreceptor cells. These findings substantiated the therapeutic potential of MCC950 against impaired autophagy and subsequent apoptosis under hypoxia. Such protective effect might involve the modulation of AMPK/mTOR/ULK-1 pathway. Targeting NLRP3 inflammasome in Müller glia could be beneficial for photoreceptor survival under hypoxic conditions.

4D label-free proteomics analysis of oxygen-induced retinopathy with or without anti-VEGF treatment

Oxygen-induced retinopathy (OIR) animal model is widely used for retinopathy of prematurity (ROP) researches. The purpose of this study was to identify proteins and related pathways of OIR with or without anti-vascular endothelial growth factor (VEGF) treatment, for use as biomarkers in diagnosing and treating ROP. Nine samples were subjected to proteomic analysis. Retina specimens were collected from 3 OIR mice, 3 OIR mice with anti-VEGF treatment and 3 normal mice (control group). Liquid chromatography-tandem mass spectrometry analysis was performed using the 4D label-free technique. Statistically significant differentially expressed proteins, gene ontology (GO) terms, Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway representations, InterPro (IPR) and protein interactions were analyzed. In total, 4585 unique proteins were identified as differentially expressed proteins (DEPs). Enrichment analysis of the GO and KEGG indicated functional clusters related to peptide biosynthetic and metabolic process, cellular macromolecule biosynthetic process and nucleic acid binding in OIR group. For anti-VEGF treatment group, DEPs were clustered in DNA replication, PI3K/Akt signaling pathway and Jak/STAT signaling pathway. Proteomic profiling is useful for the exploration of molecular mechanisms of OIR and mechanisms of anti-VEGF treatment. These findings may be useful for identification of novel biomarkers for ROP pathogenesis and treatment.

Automated diagnosis of plus disease in retinopathy of prematurity using quantification of vessels characteristics

The condition known as Plus disease is distinguished by atypical alterations in the retinal vasculature of neonates born prematurely. It has been demonstrated that the diagnosis of Plus disease is subjective and qualitative in nature. The utilization of quantitative methods and computer-based image analysis to enhance the objectivity of Plus disease diagnosis has been extensively established in the literature. This study presents the development of a computer-based image analysis method aimed at automatically distinguishing Plus images from non-Plus images. The proposed methodology conducts a quantitative analysis of the vascular characteristics linked to Plus disease, thereby aiding physicians in making informed judgments. A collection of 76 posterior retinal images from a diverse group of infants who underwent screening for Retinopathy of Prematurity (ROP) was obtained. A reference standard diagnosis was established as the majority of the labeling performed by three experts in ROP during two separate sessions. The process of segmenting retinal vessels was carried out using a semi-automatic methodology. Computer algorithms were developed to compute the tortuosity, dilation, and density of vessels in various retinal regions as potential discriminative characteristics. A classifier was provided with a set of selected features in order to distinguish between Plus images and non-Plus images. This study included 76 infants (49 [64.5%] boys) with mean birth weight of 1305 ± 427 g and mean gestational age of 29.3 ± 3 weeks. The average level of agreement among experts for the diagnosis of plus disease was found to be 79% with a standard deviation of 5.3%. In terms of intra-expert agreement, the average was 85% with a standard deviation of 3%. Furthermore, the average tortuosity of the five most tortuous vessels was significantly higher in Plus images compared to non-Plus images (p ≤ 0.0001). The curvature values based on points were found to be significantly higher in Plus images compared to non-Plus images (p ≤ 0.0001). The maximum diameter of vessels within a region extending 5-disc diameters away from the border of the optic disc (referred to as 5DD) exhibited a statistically significant increase in Plus images compared to non-Plus images (p ≤ 0.0001). The density of vessels in Plus images was found to be significantly higher compared to non-Plus images (p ≤ 0.0001). The classifier's accuracy in distinguishing between Plus and non-Plus images, as determined through tenfold cross-validation, was found to be 0.86 ± 0.01. This accuracy was observed to be higher than the diagnostic accuracy of one out of three experts when compared to the reference standard. The implemented algorithm in the current study demonstrated a commendable level of accuracy in detecting Plus disease in cases of retinopathy of prematurity, exhibiting comparable performance to that of expert diagnoses. By engaging in an objective analysis of the characteristics of vessels, there exists the possibility of conducting a quantitative assessment of the disease progression's features. The utilization of this automated system has the potential to enhance physicians' ability to diagnose Plus disease, thereby offering valuable contributions to the management of ROP through the integration of traditional ophthalmoscopy and image-based telemedicine methodologies.

Choroidal measurements in decision making for retinopathy of prematurity: a decision tree analysis

BACKGROUND

To compare the choroidal thickness and vascular profile of premature infants with ROP (retinopathy of prematurity) using a handheld SD-OCT device.

METHODS

We performed horizontal SD-OCT scans through the fovea in 115 eyes of 66 premature infants. Premature infants included 2 groups [infants with ROP requiring treatment (as treatment group) vs. infants without ROP or with ROP not- requiring treatment (as no-treatment group)] Choroidal thicknesses (CT) were measured at 5 points, including the fovea, 250 µm, and 500 µm mm nasal and temporal to the fovea. The choroidal vascularity index (CVI) and choroidal stromal index (CSI) were also calculated. The classification and regression tree (CRT) algorithm was used to predict the need for treatment based on all OCT characteristics.

RESULTS

Mean CT was higher in 500 µm nasal to the fovea compared to temporal CT (275.8 ± 64.8 and 257.1 ± 57.07, P value < 0.03). No statistically significant difference was found regarding CVI, corrected CVI, and temporal and nasal CT in the treatment group versus the no-treatment group. The foveal CT was significantly lower in ROP patients with the plus disease compared to not-plus ROP (P value = 0.03. ANOVA, Bonferroni posthoc test). CT was not significantly different between plus and pre-plus patients (P-value = 0.9, ANOVA, Bonferroni posthoc test). No significant relationship was found between the stage of ROP and choroidal thickness (P value > 0.05, GEE). The decision tree analysis showed that in infants with ROP, the most important predictor for the need for treatment is CSI.

CONCLUSION

This study delineated the possible effectiveness of choroidal measurements as an additive to decision-making for ROP. We also demonstrated that choroidal involution is associated with the presence of plus disease, not with the stage of ROP. We demonstrated that choroidal measurements are very sensitive but not specific tools for assessing the need for treatment in ROP patients.

Biphasic change in retinal nerve fibre layer thickness from 30 to 60 weeks postmenstrual age in preterm infants

BACKGROUND/AIMS

The optic nerve development during the critical postnatal weeks of preterm infants is unclear. We aimed to investigate the change of retinal nerve fibre layer (RNFL) in preterm infants.

METHODS

We used an investigational handheld optical coherence tomography (OCT) system to serially image awake preterm infants between 30 and 60 weeks postmenstrual age (PMA) at the bedside. We assessed RNFL thickness in the papillomacular bundle and nasal macular ganglion cell layer+inner plexiform layer (GCL+IPL) thickness. We applied a segmented mixed model to analyse the change in the thickness of RNFL and GCL+IPL as a function of PMA.

RESULTS

From 631 OCT imaging sessions of 101 infants (201 eyes), RNFL thickness followed a biphasic model between 30 and 60 weeks, with an estimated transition at 37.8 weeks PMA (95% CI: 37.0 to 38.6). RNFL thickness increased at 1.8 μm/week (95% CI: 1.6 to 2.1) before 37.8 weeks and decreased at -0.3 μm/week (95% CI: -0.5 to -0.2) afterwards. GCL+IPL thickness followed a similar biphasic model, in which the thickness increased at 2.9 μm/week (95% CI: 2.5 to 3.2) before 39.5 weeks PMA (95% CI: 38.8 to 40.1) and then decreased at -0.8 μm/week (95% CI: -0.9 to -0.6).

CONCLUSION

We demonstrate the feasibility of monitoring RNFL and GCL+IPL thickness from OCT during the postnatal weeks of preterm infants. Thicknesses follow a biphasic model with a transition age at 37.8 and 39.5 weeks PMA, respectively. These findings may shed light on optic nerve development in preterm infants and assist future study designs.

Pathophysiology of Retinopathy of Prematurity

Retinopathy of prematurity (ROP) is a complex disease involving development of the neural retina, ocular circulations, and other organ systems of the premature infant. The external stresses of the ex utero environment also influence the pathophysiology of ROP through interactions among retinal neural, vascular, and glial cells. There is variability among individual infants and presentations of the disease throughout the world, making ROP challenging to study. The methods used include representative animal models, cell culture, and clinical studies. This article describes the impact of maternal-fetal interactions; stresses that the preterm infant experiences; and biologic pathways of interest, including growth factor effects and cell-cell interactions, on the complex pathophysiology of ROP phenotypes in developed and emerging countries.

Electroretinographic Responses in Retinopathy of Prematurity Treated Using Intravitreal Bevacizumab or Laser

PURPOSE

Intravitreal injection of bevacizumab (IVB) offers advantages over laser photoablation for treatment of type 1 retinopathy of prematurity (ROP). However, retinal function has not, to date, been quantitatively compared following these interventions. Therefore, electroretinography (ERG) was used compare retinal function among eyes treated using IVB or laser, and control eyes. In addition, among the IVB-treated eyes, ERG was used to compare function in individuals in whom subsequent laser was and was not required.

DESIGN

Prospective clinical cohort study.

METHODS

ERG was used to record dark- and light-adapted stimulus/response functions in 21 children treated using IVB (12 of whom required subsequent laser in at least 1 eye for persistent avascular retina [PAR]). Sensitivity and amplitude parameters were derived from the a-wave, b-wave, and oscillatory potentials (OPs), representing activity in photoreceptor, postreceptor, and inner retinal cells, respectively. These parameters were then referenced to those of 76 healthy, term-born controls and compared to those of 10 children treated using laser only.

RESULTS

In children with treated ROP, every ERG parameter was significantly below the mean in controls. However, these significant ERG deficits did not differ between IVB- and laser-treated eyes. Among children treated using IVB, no ERG parameter was significantly associated with dose or need for subsequent laser.

CONCLUSION

Retinal function was significantly impaired in treated ROP eyes. Function in IVB-treated eyes did not differ from that in laser-treated eyes. Functional differences also did not distinguish those IVB-treated eyes that would subsequently need laser for PAR.

The Development of Retinal Function and Refractive Error in Children With Retinopathy of Prematurity

Purpose

The purpose of this study was to test the hypothesis that retinopathy of prematurity (ROP) prolongs development of rod-mediated thresholds for detection of stimuli at 10 degrees but not 30 degrees eccentricity. In addition, to evaluate the thresholds at each site for an association with visual acuity (VA) and spherical equivalent (SE).

Methods

We estimated rod-mediated dark-adapted thresholds (DATs) for the detection of 2 degree diameter, 50 ms, blue (λ < 510 nm) flashes at 10 degrees and 30 degrees eccentric in former preterm subjects (n = 111), stratified by ROP severity: None (n = 32), Mild (n = 66), and Severe (n = 13). We also tested Term-born (n = 28) controls. To determine the age at half-maximal sensitivity (Agehalf) for each group and eccentricity, we fit DATs to logistic growth curves. We obtained VA and SE for Preterm subjects and evaluated the course of threshold development at 10 degrees and 30 degrees for significant association with VA and SE predicted at age 10 years.

Results

DAT development at 10 degrees was significantly delayed in ROP (Mild and Severe); ROP did not significantly alter DAT development at 30 degrees. At age 10 years, among Preterm subjects, both VA and SE were significantly associated with group (None,Mild, and Severe). SE was predicted by the course of DAT development at 30 degrees. VA was not associated with the course of DAT development at 10 degrees.

Conclusions

At 10 degrees, ROP-whether mild or severe-is associated with significant delays in DAT development, evidence that the late-maturing central retina is vulnerable to ROP. The association of 30 degree threshold and myopia are evidence that more peripheral retina is important to refractive development.

Nanocarriers for the Delivery of Neuroprotective Agents in the Treatment of Ocular Neurodegenerative Diseases

Retinal neurodegeneration is considered an early event in the pathogenesis of several ocular diseases, such as diabetic retinopathy, age-related macular degeneration, and glaucoma. At present, there is no definitive treatment to prevent the progression or reversal of vision loss caused by photoreceptor degeneration and the death of retinal ganglion cells. Neuroprotective approaches are being developed to increase the life expectancy of neurons by maintaining their shape/function and thus prevent the loss of vision and blindness. A successful neuroprotective approach could prolong patients' vision functioning and quality of life. Conventional pharmaceutical technologies have been investigated for delivering ocular medications; however, the distinctive structural characteristics of the eye and the physiological ocular barriers restrict the efficient delivery of drugs. Recent developments in bio-adhesive in situ gelling systems and nanotechnology-based targeted/sustained drug delivery systems are receiving a lot of attention. This review summarizes the putative mechanism, pharmacokinetics, and mode of administration of neuroprotective drugs used to treat ocular disorders. Additionally, this review focuses on cutting-edge nanocarriers that demonstrated promising results in treating ocular neurodegenerative diseases.

Insights into the developing fovea revealed by imaging

Early development of the fovea has been documented by histological studies over the past few decades. However, structural distortion due to sample processing and the paucity of high-quality post-mortem tissue has limited the effectiveness of this approach. With the continuous progress in high-resolution non-invasive imaging technology, most notably optical coherence tomography (OCT) and OCT angiography (OCT-A), in vivo visualization of the developing retina has become possible. Combining the information from histologic studies with this novel imaging information has provided a more complete and accurate picture of retinal development, and in particular the developing fovea. Advances in neonatal care have increased the survival rate of extremely premature infants. However, with enhanced survival there has been an attendant increase in retinal developmental complications. Several key abnormalities, including a thickening of the inner retina at the foveal center, a shallower foveal pit, a smaller foveal avascular zone, and delayed development of the photoreceptors have been described in preterm infants when compared to full-term infants. Notably these abnormalities, which are consistent with a partial arrest of foveal development, appear to persist into later childhood and adulthood in these eyes of individuals born prematurely. Understanding normal foveal development is vital to interpreting these pathologic findings associated with prematurity. In this review, we first discuss the various advanced imaging technologies that have been adapted for imaging the infant eye. We then review the key events and steps in the development of the normal structure of the fovea and contrast structural features in normal and preterm retina from infancy to childhood. Finally, we discuss the development of the perifoveal retinal microvasculature and highlight future opportunities to expand our understanding of the developing fovea.

The role of anti-vascular endothelial growth factor in treatment of retinopathy of prematurity-a current review

The review aims to evaluate the uses of conventional laser therapy and intravitreal injection of various anti-VEGF in terms of efficacy and side effects for the treatment of retinopathy of prematurity. A literature search of the publication, concerning conventional laser treatment and intravitreal injection of anti-VEGF for ROP. A total of 40 articles were reviewed after curation by the authors for relevance. Intravitreal anti-VEGF showed better ocular efficacy in zone I ROP while laser therapy had a lower recurrence rate in zone II. Comparing the two mainstay anti-VEGF agents, bevacizumab showed lower ROP recurrence rate than ranibizumab. Anti-VEGF has a higher chance in developing persistent peripheral avascularisation compared to conventional laser therapy, but a lower chance of developing high myopia. Ranibizumab has a lower systemic absorption than bevacizumab, despite having no difference in the incidence of persistent peripheral avascularisation. In conclusion, it is advised that intravitreal anti-VEGF should be used as the first-line treatment for zone I ROP while laser therapy should be the mainstay for zone II ROP owing to the different pathogenetic mechanisms. In patients with recurrence after initial anti-VEGF injection, that given ranibizumab may opt to repeat the injection while that given bevacizumab should consider supplement laser ablative treatment.

Neurosensory Alterations in Retinopathy of Prematurity: A Window to Neurological Impairments Associated to Preterm Birth

Retinopathy of prematurity (ROP) is one of the main blinding diseases affecting preterm newborns and is classically considered a vascular disorder. The premature exposure to the extrauterine environment, which is hyperoxic in respect to the intrauterine environment, triggers a cascade of events leading to retinal ischemia which, in turn, makes the retina hypoxic thus setting off angiogenic processes. However, many children with a history of ROP show persistent vision impairment, and there is evidence of an association between ROP and neurosensory disabilities. This is not surprising given the strict relationship between neuronal function and an adequate blood supply. In the present work, we revised literature data evidencing to what extent ROP can be considered a neurodegenerative disease, also taking advantage from data obtained in preclinical models of ROP. The involvement of different retinal cell populations in triggering the neuronal damage in ROP was described along with the neurological outcomes associated to ROP. The situation of ROP in Italy was assessed as well.

Therapeutic Potential of Microvesicles in Cell Therapy and Regenerative Medicine of Ocular Diseases With an Especial Focus on Mesenchymal Stem Cells-Derived Microvesicles

These days, mesenchymal stem cells (MSCs), because of immunomodulatory and pro-angiogenic abilities, are known as inevitable factors in regenerative medicine and cell therapy in different diseases such as ocular disorder. Moreover, researchers have indicated that exosome possess an essential potential in the therapeutic application of ocular disease. MSC-derived exosome (MSC-DE) have been identified as efficient as MSCs for treatment of eye injuries due to their small size and rapid diffusion all over the eye. MSC-DEs easily transfer their ingredients such as miRNAs, proteins, and cytokines to the inner layer in the eye and increase the reconstruction of the injured area. Furthermore, MSC-DEs deliver their immunomodulatory cargos in inflamed sites and inhibit immune cell migration, resulting in improvement of autoimmune uveitis. Interestingly, therapeutic effects were shown only in animal models that received MSC-DE. In this review, we summarized the therapeutic potential of MSCs and MSC-DE in cell therapy and regenerative medicine of ocular diseases.

Neurovascular abnormalities in retinopathy of prematurity and emerging therapies

Blood vessels in the developing retina are formed in concert with neural growth, resulting in functional neurovascular network. Disruption of the neurovascular coordination contributes to the pathogenesis of retinopathy of prematurity (ROP), a potentially blinding retinal neovascular disease in preterm infants that currently lacks an approved drug therapy in the USA. Despite vasculopathy as predominant clinical manifestations, an increasing number of studies revealed complex neurovascular interplays among neurons, glial cells and blood vessels during ROP. Coordinated expression of glia-derived vascular endothelial growth factor (VEGF) in spatio-temporal gradients is pivotal to the formation of well-organized vascular plexuses in the healthy retina, whereas uncoordinated VEGF expression triggers pathological angiogenesis with disorganized vascular tufts in ROP. In contrast with VEGF driving both pathological and physiological angiogenesis, neuron-derived angiogenic factor secretogranin III (Scg3) stringently regulates ROP but not healthy retinal vessels in animal models. Anti-VEGF and anti-Scg3 therapies confer similar high efficacies to alleviate ROP in preclinical studies but are distinct in their disease selectivity and safety. This review discusses neurovascular communication among retinal blood vessels, neurons and glial cells during retinal development and ROP pathogenesis and summarizes the current and emerging therapies to address unmet clinical needs for the disease.

Decoupling Oxygen Tension From Retinal Vascularization as a New Perspective for Management of Retinopathy of Prematurity. New Opportunities From β-adrenoceptors

Retinopathy of prematurity (ROP) is an evolutive and potentially blinding eye disease that affects preterm newborns. Unfortunately, until now no conservative therapy of active ROP with proven efficacy is available. Although ROP is a multifactorial disease, premature exposition to oxygen concentrations higher than those intrauterine, represents the initial pathogenetic trigger. The increase of oxygenation in a retina still incompletely vascularized promotes the downregulation of proangiogenic factors and finally the interruption of vascularization (ischemic phase). However, the increasing metabolic requirement of the ischemic retina induces, over the following weeks, a progressive hypoxia that specularly increases the levels of proangiogenic factors finally leading to proliferative retinopathy (proliferative phase). Considering non-modifiable the coupling between oxygen levels and vascularization, so far, neonatologists and ophthalmologists have "played defense", meticulously searching the minimum necessary concentration of oxygen for individual newborns, refining their diagnostic ability, adopting a careful monitoring policy, ready to decisively intervene only in a very advanced stage of disease progression. However, recent advances have demonstrated the possibility to pharmacologically modulate the relationship between oxygen and vascularization, opening thus the perspective for new therapeutic or preventive opportunities. The perspective of a shift from a defensive towards an attack strategy is now at hand.

Assessment and management of retinopathy of prematurity in the era of anti-vascular endothelial growth factor (VEGF)

The incidence of retinopathy of prematurity (ROP) continues to rise due to the improved survival of very low birth weight infants in developed countries. This epidemic is also fueled by increased survival of preterm babies with variable use of oxygen and a lack of ROP awareness and screening services in resource-limited regions. Improvements in technology and a basic understanding of the disease pathophysiology have changed the way we screen and manage ROP, educate providers and patients, and improve ROP awareness. Advancements in imaging techniques, expansion of telemedicine services, and the potential for artificial intelligence-assisted ROP screening programs have created opportunities to improve ROP care in areas with a shortage of ophthalmologists trained in ROP. To address the gap in provider knowledge regarding ROP, the Global Education Network for Retinopathy of Prematurity (GEN-ROP) created a web-based tele-education training module that can be used to educate all providers involved in ROP, including non-physician ROP screeners. Over the past 50 years, the treatment of severe ROP has evolved from limited treatment modalities to cryotherapy and laser photocoagulation. More recently, there has been growing evidence to support the use of anti-vascular endothelial growth factor (VEGF) agents for the treatment of severe ROP. However, VEGF is known to be important in organogenesis and microvascular maintenance, and given that intravitreal anti-VEGF treatment can result in systemic VEGF suppression over a period of at least 1-12 weeks, there are concerns regarding adverse effects and long-term ocular and systemic developmental consequences of anti-VEGF therapy. Future research in ophthalmology to address the growing burden of ROP should focus on cost-effective fundus imaging devices, implementation of artificial intelligence platforms, updated treatment algorithms with optimal use of anti-VEGF and careful investigation of its long-term effects, and surgical options in advanced ROP. Addressing these unmet needs will aid the global effort against the ROP epidemic and optimize our understanding and treatment of this blinding disease.

An imbalance in autophagy contributes to retinal damage in a rat model of oxygen-induced retinopathy

In retinopathy of prematurity (ROP), the abnormal retinal neovascularization is often accompanied by retinal neuronal dysfunction. Here, a rat model of oxygen‐induced retinopathy (OIR), which mimics the ROP disease, was used to investigate changes in the expression of key mediators of autophagy and markers of cell death in the rat retina. In addition, rats were treated from birth to postnatal day 14 and 18 with 3‐methyladenine (3‐MA), an inhibitor of autophagy. Immunoblot and immunofluorescence analysis demonstrated that autophagic mechanisms are dysregulated in the retina of OIR rats and indicated a possible correlation between autophagy and necroptosis, but not apoptosis. We found that 3‐MA acts predominantly by reducing autophagic and necroptotic markers in the OIR retinas, having no effects on apoptotic markers. However, 3‐MA does not ameliorate retinal function, which results compromised in this model. Taken together, these results revealed the crucial role of autophagy in retinal cells of OIR rats. Thus, inhibiting autophagy may be viewed as a putative strategy to counteract ROP.

What can visual electrophysiology tell about possible visual-field defects in paediatric patients

Recognising a potential visual-field (VF) defect in paediatric patients might be challenging, especially in children before the age of 5 years and those with developmental delay or intellectual disability. Visual electrophysiological testing is an objective and non-invasive technique for evaluation of visual function in paediatric patients, which can characterise the location of dysfunction and differentiate between disorders of the retina, optic nerve and visual pathway. The recording of electroretinography (ERG) and visual-evoked potentials (VEP) is possible from early days of life and requires no subjective input from the patient. As the origins of ERG and VEP tests are known, the pattern of electrophysiological changes can provide information about the VF of a child unable to perform accurate perimetry. This review summarises previously published electrophysiological findings in several common types of VF defects that can be found in paediatric patients (generalised VF defect, peripheral VF loss, central scotoma, bi-temporal hemianopia, altitudinal VF defect, quadrantanopia and homonymous hemianopia). It also shares experience on using electrophysiological testing as additional functional evidence to other tests in the clinical challenge of diagnosing or excluding VF defects in complex paediatric patients. Each type of VF defect is illustrated with one or two clinical cases.

Stress Signal Regulation by Na/K-ATPase As a New Approach to Promote Physiological Revascularization in a Mouse Model of Ischemic Retinopathy

Purpose

The identification of target pathways to block excessive angiogenesis while simultaneously restoring physiological vasculature is an unmet goal in the therapeutic management of ischemic retinopathies. pNaKtide, a cell-permeable peptide that we have designed by mapping the site of α1 Na/K-ATPase (NKA)/Src binding, blocks the formation of α1 NKA/Src/reactive oxygen species (ROS) amplification loops and restores physiological ROS signaling in a number of oxidative disease models. The aim of this study was to evaluate the importance of the NKA/Src/ROS amplification loop and the effect of pNaKtide in experimental ischemic retinopathy.

Methods

Human retinal microvascular endothelial cells (HRMECs) and retinal pigment epithelium (ARPE-19) cells were used to evaluate the effect of pNaKtide on viability, proliferation, and angiogenesis. Retinal toxicity and distribution were assessed in those cells and in the mouse. Subsequently, the role and molecular mechanism of NKA/Src in ROS stress signaling were evaluated biochemically in the retinas of mice exposed to the well-established protocol of oxygen-induced retinopathy (OIR). Finally, pNaKtide efficacy was assessed in this model.

Results

The results suggest a key role of α1 NKA in the regulation of ROS stress and the Nrf2 pathway in mouse OIR retinas. Inhibition of α1 NKA/Src by pNaKtide reduced pathologic ROS signaling and restored normal expression of hypoxia-inducible factor 1-α/vascular endothelial growth factor (VEGF). Unlike anti-VEGF agents, pNaKtide did promote retinal revascularization while inhibiting neovascularization and inflammation.

Conclusions

Targeting α1 NKA represents a novel strategy to develop therapeutics that not only inhibit neovascularization but also promote physiological revascularization in ischemic eye diseases.

Birth Weight Is a Significant Predictor of Retinal Nerve Fiber Layer Thickness at 36 Weeks Postmenstrual Age in Preterm Infants

PURPOSE

To assess retinal nerve fiber layer (RNFL) thickness in preterm infants.

DESIGN

Prospective observational study.

METHODS

We imaged 83 awake infants (159 eyes) at 36 ± 1 weeks postmenstrual age (defined as the time elapsed between the first day of the last maternal menstrual period and the time at imaging) using a handheld optical coherence tomography (OCT) system at the bedside. Blinded graders semi-automatically segmented RNFL in the papillomacular bundle (-15 to +15° relative to the fovea-optic nerve axis). We correlated RNFL thickness and 7 characteristics of interest (sex, race, ethnicity, gestational age, birth weight, stage of retinopathy at prematurity, and presence of pre-plus or plus disease) via univariable and multivariable regressions.

RESULTS

RNFL was 3.4 μm thicker in the right eyes than in the left eyes (P < .001). Among 7 characteristics, birth weight was the only independent predictor of RNFL thickness (P < .001). A 250-g increase in birth weight was associated with 5.2 μm (95% confidence interval: 3.3-7.0) increase in RNFL thickness. Compared with very preterm infants, extremely preterm infants had thinner RNFL (58.0 ± 10.7 μm vs 63.4 ± 10.7 μm, P = .03), but the statistical significance disappeared after adjustment for birth weight (P = .25). RNFL thickness was 11.2 μm thinner in extremely low birth weight infants than in very low birth weight infants (55.5 ± 8.3 μm vs. 66.7 ± 10.2 μm; P < .001). The difference remained statistically significant after adjustment for gestational age.

CONCLUSION

Birth weight is a significant independent predictor of RNFL thickness near birth, implying that the retinal ganglion cells reserve is affected by intrauterine processes that affect birth weight.

Dark-adapted threshold and electroretinogram for diagnosis of Usher syndrome

PURPOSE

To determine the utility of ophthalmology evaluation, dark-adapted threshold, and full-field electroretinogram for early detection of Usher syndrome in young patients with bilateral sensorineural hearing loss.

METHODS

We identified 39 patients with secure genetic diagnoses of Usher Syndrome. Visual acuity, spherical equivalent, fundus appearance, dark-adapted threshold, and full-field electroretinogram results were summarized and compared to those in a group of healthy controls with normal hearing. In those Usher patients with repeated measures, regression analysis was done to evaluate for change in visual acuity and dark-adapted threshold with age. Spherical equivalent and full-field electroretinogram responses from dark- and light-adapted eyes were evaluated as a function of age.

RESULTS

The majority of initial visual acuity and spherical equivalent results were within normal limits for age. Visual acuity and dark-adapted threshold worsened significantly with age in Usher type 1 but not in Usher type 2. At initial test, full-field electroretinogram responses from dark- and light-adapted eyes were abnormal in 53% of patients. Remarkably, nearly half of our patients (17% of Usher type 1 and 30% of Usher type 2) would have been missed by tests of retinal function alone if evaluated before age 10.

CONCLUSIONS

Although there is an association of abnormal dark-adapted threshold and full-field electroretinogram at young ages in Usher patients, it appears that a small but important proportion of patients would not be detected by tests of retinal function alone. Thus, genetic testing is needed to secure a diagnosis of Usher syndrome.

Translational Research in Retinopathy of Prematurity: From Bedside to Bench and Back Again

Retinopathy of prematurity (ROP), a vascular proliferative disease affecting preterm infants, is a leading cause of childhood blindness. Various studies have investigated the pathogenesis of ROP. Clinical experience indicates that oxygen levels are strongly correlated with ROP development, which led to the development of oxygen-induced retinopathy (OIR) as an animal model of ROP. OIR has been used extensively to investigate the molecular mechanisms underlying ROP and to evaluate the efficacy of new drug candidates. Large clinical trials have demonstrated the efficacy of anti-vascular endothelial growth factor (VEGF) agents to treat ROP, and anti-VEGF therapy is presently becoming the first-line treatment worldwide. Anti-VEGF therapy has advantages over conventional treatments, including being minimally invasive with a low risk of refractive error. However, long-term safety concerns and the risk of late recurrence limit this treatment. There is an unmet medical need for novel ROP therapies, which need to be addressed by safe and minimally invasive therapies. The recent progress in biotechnology has contributed greatly to translational research. In this review, we outline how basic ROP research has evolved with clinical experience and the subsequent emergence of new drugs. We discuss previous and ongoing trials and present the candidate molecules expected to become novel targets.

Roles of Exosomes in Ocular Diseases

Exosomes, nanoscale vesicles with a diameter of 30 to 150 nm, are composed of a lipid bilayer, protein, and genetic material. Exosomes are secreted by virtually all types of cells in the human body. They have key functions in cell-to-cell communication, immune regulation, inflammatory response, and neovascularization. Mounting evidence indicates that exosomes play an important role in various diseases, such as cancer, cardiovascular diseases, and brain diseases; however, the role that exosomes play in eye diseases has not yet been rigorously studied. This review covers current exosome research as it relates to ocular diseases including diabetic retinopathy, age-related macular degeneration, autoimmune uveitis, glaucoma, traumatic optic neuropathies, corneal diseases, retinopathy of prematurity, and uveal melanoma. In addition, we discuss recent advances in the biological functions of exosomes, focusing on the toxicity of exosomes and the use of exosomes as biomarkers and drug delivery vesicles. Finally, we summarize the primary considerations and challenges to be taken into account for the effective applications of exosomes.

Thyroid Activating Enzyme, Deiodinase II Is Required for Photoreceptor Function in the Mouse Model of Retinopathy of Prematurity

Purpose

Retinopathy of prematurity (ROP) is a severe complication of premature infants, leading to vision loss when untreated. Presently, the molecular mechanisms underlying ROP are still far from being clearly understood. This study sought to investigate whether thyroid hormone (TH) signaling contributes to the neuropathology of ROP using the mouse model of ROP to evaluate longitudinal photoreceptor function.

Methods

Animals were exposed to hyperoxia from P7 to P12 to induce retinopathy, thereafter the animals were returned to room air (normoxia). The thyroid-activating enzyme type 2 deiodinases (Dio2) knockout (KO) mice and the littermate controls that were exposed to hyperoxia or maintained in room air and were then analyzed. The retinal function was evaluated using electroretinograms (ERGs) at three and seven weeks followed by histologic assessments with neuronal markers to detect cellular changes in the retina. Rhodopsin protein levels were measured to validate the results obtained from the immunofluorescence analyses.

Results

In the ROP group, the photoreceptor ERG responses are considerably lower both in the control and the Dio2 KO animals at P23 compared to the non-ROP group. In agreement with the ERG responses, loss of Dio2 results in mislocalized cone nuclei, and abnormal rod bipolar cell dendrites extending into the outer nuclear layer. The retinal function is compromised in the adult Dio2 KO animals, although the cellular changes are less severe. Despite the reduction in scotopic a-wave amplitudes, rhodopsin levels are similar in the adult mice, across all genotypes irrespective of exposure to hyperoxia.

Conclusions

Using the mouse model of ROP, we show that loss of Dio2 exacerbates the effects of hyperoxia-induced retinal deficits that persist in the adults. Our data suggest that aberrant Dio2/TH signaling is an important factor in the pathophysiology of the visual dysfunction observed in the oxygen-induced retinopathy model of ROP.

[Results of long-term observation of extremely premature babies with retinopathy]

PURPOSE

To study the long-term clinical and functional outcomes of retinopathy in extremely premature infants.

MATERIAL AND METHODS

The study included 42 patients (84 eyes) with retinopathy of prematurity (ROP) at the age of 9-18 years. All patients underwent comprehensive ophthalmological examination, including morphometric (OCT), functional (ERG) and psycho-physical (computer perimetry) methods.

RESULTS

A high occurrence of low vision (67%) was revealed in extremely premature children with ROP during school years and adolescence, which depended on the severity of active ROP and the formation of pronounced residual changes in the fundus during the cicatricial phase of the disease, a high occurrence of refractive errors (92%), including high degree myopia (46%), late complications that develop with ROP of any degree (68%), impaired retinal electrogenesis - due to both ROP and deep morphological and functional immaturity of the retina.

CONCLUSION

Patients with any degree of cicatricial ROP born in the early stages of gestation and with extremely low body weight need regular complex ophthalmologic examination and lifelong follow-up.

Choroidal structural changes in preterm children with and without retinopathy of prematurity

PURPOSE

Evaluate choroidal structural changes in preterm children with and without retinopathy of prematurity (ROP) using image binarization technique on swept-source optical coherence tomography (SS-OCT) scans.

METHODS

Prospective case-control study. Forty-one (79 eyes) children aged 5-15 years with a history of preterm birth and 33 (63 eyes) age-matched full-term children were recruited. Demographics including gestational age at birth, birth weight and history of ROP were documented. All subjects had undergone complete eye examinations, including best-corrected visual acuity and SS-OCT imaging. Subfoveal choroidal thickness (SFCT) was calculated, and images were binarized to obtain stromal and luminal areas (LA). The choroidal vascularity index (CVI) was derived from the proportion of LA to the total subfoveal choroidal area.

RESULTS

There were no significant differences in SFCT between the preterm children with (286.63 ± 83.98 μm) or without (306.59 ± 77.29 μm) ROP and the full-term children (311.82 ± 42.87; p = 0.20 and 0.67, respectively). The CVI was significantly reduced in the preterm children with ROP (68.66 ± 3.24%; p = 0.005) compared with the CVI in the full-term control group (71.37 ± 3.63%); however, the CVI in the preterm children without ROP (71.68 ± 3.09%; p = 0.93) was not significantly affected.

CONCLUSION

The reduced CVI in preterm children with ROP may indicate compromised choroidal vascularity. The CVI was found to be a more sensitive OCT biomarker than the SFCT and may be helpful in evaluating associated choroidal structural changes in preterm children, especially those with a history of ROP.

The role of semaphorins in small vessels of the eye and brain

Small vessel diseases, such as ischemic retinopathy and cerebral small vessel disease (CSVD), are increasingly recognized in patients with diabetes, dementia and cerebrovascular disease. The mechanisms of small vessel diseases are poorly understood, but the latest studies suggest a role for semaphorins. Initially identified as axon guidance cues, semaphorins are mainly studied in neuronal morphogenesis, neural circuit assembly, and synapse assembly and refinement. In recent years, semaphorins have been found to play important roles in regulating vascular growth and development and in many pathophysiological processes, including atherosclerosis, angiogenesis after stroke and retinopathy. Growing evidence indicates that semaphorins affect the occurrence, perfusion and regression of both the macrovasculature and microvasculature by regulating the proliferation, apoptosis, migration, barrier function and inflammatory response of endothelial cells, vascular smooth muscle cells (VSMCs) and pericytes. In this review, we concentrate on the regulatory effects of semaphorins on the cell components of the vessel wall and their potential roles in microvascular diseases, especially in the retina and cerebral small vessel. Finally, we discuss potential molecular approaches in targeting semaphorins as therapies for microvascular disorders in the eye and brain.

Refractive status and optical components of premature babies with or without retinopathy of prematurity at 7 years old

BACKGROUND

This study aimed to investigate the refractive status and optical components of premature babies with or without retinopathy of prematurity (ROP) at 7 years old and to explore the influence of prematurity and ROP on the refractive status and optical components.

METHODS

From January 2009 to February 2011, premature babies receiving fundus photographic screening (FPS) were recruited and divided into non-ROP group and ROP group. Full-term babies matched in age were recruited as controls. Auto-refractometer was employed to detect the corneal refractive power, corneal radius (CR) of curvature and corneal astigmatism, A-scan ultrasonography was performed to detect the anterior chamber depth (ACD), lens thickness (LT), vitreous thickness (VITR) and ocular axial length (AL), and retinoscopy was done following cycloplegia with 1% cyclopentolate in these babies at 7 years old. These parameters were compared among groups, and the correlations of gestational age and birth weight with the refractive status and optical components were further evaluated.

RESULTS

Of 126 subjects, a total of 252 eyes were evaluated in this study, including 50 eyes of 25 subjects in ROP group (pre-threshold stage 1-3), 110 eyes of 55 subjects in non-ROP group and 92 eyes of 46 subjects in control group. The incidence of myopia was the highest in ROP group (9/50, 18%), followed by non-ROP group (11/110; 10%) and control group (6/92; 6.52%). The incidence of hyperopia was the highest in control group (21/92; 22.83%), followed by ROP group (8/50; 16%) and non-ROP group (10/110; 9.09%). The incidence of astigmatism was the highest in ROP group (18/50; 36%), followed by non-ROP group (25/110; 22.73%) and control group (12/92; 13.04%). The corneal astigmatism (-1.58, -1.11, -0.86 DC, P<0.01) and the mean degree of astigmatism (1.38, 1.17, 0.64 DC, P<0.05) in ROP group and non-ROP group were significantly higher than those in control group. The corneal refractive power in ROP group was more potent as compared to non-ROP group and control group (43.98, 43.16, 42.99 D, P<0.05); the corneal curvature in ROP group was significantly higher than that in non-ROP group and control group (7.87, 7.71, 7.67 mm, P<0.05); the ocular AL in ROP group and non-ROP group was significantly shorter than that in control group (2.41, 22.47, 22.78 mm, P<0.05). The LT in ROP group and non-ROP group was markedly thicker than that in control group (4.48, 4.45, 4.37 mm, P>0.05); the ACD in ROP group and non-ROP group was markedly deeper than in control group (3.16, 3.12, 3.21 mm, P>0.05). The gestational age was negatively related to corneal astigmatism (r=-0.208, P=0.013) and astigmatism (r=-0.226, P=0.004), but positively associated with ocular AL (r=0.252, P=0.005). The birth weight was negatively associated with corneal astigmatism (r=-0.30, P<0.001), astigmatism (r=-0.267, P=0.001), corneal refractive power (r=-0.255, P=0.001) and corneal curvature (r=0.242, P=0.001), but positively to ocular AL (r=0.243, P=0.001) and spherical equivalent refraction (SER) (r=0.151, P=0.028).

CONCLUSIONS

(I) Premature babies with or without ROP are susceptible to myopia and astigmatism; (II) low birth weight, prematurity and ROP synergistically influence the development of refractive status and optical components, resulting in myopia and astigmatism; (III) premature babies with or without ROP have increased corneal curvature and LT, which are related to the higher incidence of myopia and astigmatism.

Epac1 inhibition ameliorates pathological angiogenesis through coordinated activation of Notch and suppression of VEGF signaling

In this study, we investigated the roles of Epac1 in pathological angiogenesis and its potential as a novel therapeutic target for the treatment of vasoproliferative diseases. Genetic deletion of Epac1 ameliorated pathological angiogenesis in mouse models of oxygen-induced retinopathy (OIR) and carotid artery ligation. Moreover, genetic deletion or pharmacological inhibition of Epac1 suppressed microvessel sprouting from ex vivo aortic ring explants. Mechanistic studies revealed that Epac1 acted as a previously unidentified inhibitor of the γ-secretase/Notch signaling pathway via interacting with γ-secretase and regulating its intracellular trafficking while enhancing vascular endothelial growth factor signaling to promote pathological angiogenesis. Pharmacological administration of an Epac-specific inhibitor suppressed OIR-induced neovascularization in wild-type mice, recapitulating the phenotype of genetic Epac1 knockout. Our results demonstrate that Epac1 signaling is critical for the progression of pathological angiogenesis but not for physiological angiogenesis and that the newly developed Epac-specific inhibitors are effective in combating proliferative retinopathy.

Extracting the ON and OFF contributions to the full-field photopic flash electroretinogram using summed growth curves

Under cone-mediated (photopic) conditions, an "instantaneous" flash of light, including both stimulus onset and offset, will simultaneously activate both "ON" and "OFF" bipolar cells, which either depolarize (ON) or hyperpolarize (OFF) in response and, respectively, produce positive-going and negative-going deflections in the electroretinogram (ERG). The stimulus-response (SR) relationship of the photopic ON response demonstrates logistic growth, like that manifested in the rod-mediated (scotopic) b-wave, which is driven by a single class of depolarizing bipolar cell. However, the photopic b-wave SR function is importantly shaped by OFF responses, leading to a "photopic hill." Furthermore, both on and off stimuli elicit activity in both ON and OFF bipolar cells. This has made it difficult to produce meaningful parameters for ready interpretation of the photopic b-wave SR relationship. Therefore, we evaluated whether the sum of sigmoidal SR functions, as descriptors of the depolarizing and hyperpolarizing components of the photopic flash ERG, could be used to elucidate and quantitate the mechanisms that produce the photopic hill. We used a novel fitting routine to optimize a sum of simple sigmoidal curves to SR data in five groups of subjects: Healthy adult, 10-week-old infant, congenital stationary night blindness (CSNB), X-linked juvenile retinoschisis (XJR), and preterm-born, both without and with a history of retinopathy of prematurity (ROP). Differences in ON and OFF amplitude, sensitivity, and implicit time among the groups were then compared using parameters extracted from these fits. We found that our modeling procedure enabled plausible derivations of ON and OFF pathway contributions to the ERG, and that the parameters produced appeared to have physiological relevance. In adult subjects, the ON and OFF amplitudes were similar in magnitude with respectively longer and shorter implicit times. Infant, CSNB, and XJR subjects showed significant ON pathway deficits. History of preterm-birth, without or with a diagnosis of ROP, did not much affect cone responses.

Relationship between severe bronchopulmonary dysplasia and severe retinopathy of prematurity in premature newborns

BACKGROUND

Bronchopulmonary dysplasia (BPD) and retinopathy of prematurity (ROP) are two adverse sequelae of preterm birth associated with abnormal vascular development. The purpose of this study was to characterize the relationship between these two outcomes at a single institution.

METHODS

The medical records of infants screened for ROP at the University of Colorado Hospital between January 2012 and December 2017 were reviewed retrospectively. ROP was classified according to Early Treatment Retinopathy of Prematurity (ET-ROP) criteria; BPD, according to the 2010 Criteria from the National Institute for Child Health and Human Development. We examined the relationship between moderate-severe BPD and the development of severe ROP (type 1 or 2) using univariate analysis and multivariable logistic regression with the odds ratio as a measure of association. Covariates included gestational age and birth weight at delivery.

RESULTS

A total of 625 cases were reviewed. Of these, 64 infants (10%) developed severe ROP and 176 (28%) infants developed moderate-severe BPD. We found a significant relationship between these two outcomes following adjustments for gestational age, birth weight, and multiparity (OR = 3.2; 95% CI, 1.6-6.5 [P < 0.01]).

CONCLUSIONS

In our cohort of preterm infants, we found a significant relationship between moderate-severe BPD with severe ROP. We hypothesize that these two neonatal outcomes have links with a common pathogenesis.

Exosomes from Microglia Attenuate Photoreceptor Injury and Neovascularization in an Animal Model of Retinopathy of Prematurity

The role of microglia in the pathophysiology of ischemic retinal diseases has been studied extensively. Exosomes from microglial cells exert protective effects during several nervous system diseases, but their roles in hypoxia-induced retinopathy remain unclear. In our study, exosomes derived from microglial cells were injected into the vitreous body of mice with oxygen-induced retinopathy (OIR). Results showed that exosome-treated OIR mice exhibited smaller avascular areas and fewer neovascular tufts in addition to decreased vascular endothelial growth factor (VEGF) and transforming growth factor β (TGF-β) expression. Moreover, photoreceptor apoptosis was suppressed by exosome injection. Mechanistically, exosomes from microglial cells were incorporated into photoreceptors in vitro and inhibited the inositol-requiring enzyme 1α (IRE1α)-X-box binding protein 1 (XBP1) cascade, which contributes to hypoxia-induced photoreceptor apoptosis. Furthermore, the exosomes also downregulated the mRNA and protein levels of VEGF and TGF-β in hypoxia-exposed photoreceptors. A microRNA assay showed that microRNA-24-3p (miR-24-3p) levels were extremely high in exosomes from microglial cells, suggesting that this could be the key molecule that inhibits the hypoxia-induced expression of IRE1α in photoreceptors. These findings delineate a novel exosome-mediated mechanism of microglial cell-photoreceptor crosstalk that facilitates normal angiogenesis and visual function in OIR mice; thus, our results also suggest a potential therapeutic approach for retinopathy of prematurity.

An iTRAQ-Based Quantitative Proteomic Analysis of Plasma Proteins in Preterm Newborns With Retinopathy of Prematurity

Purpose

Retinopathy of prematurity (ROP) is a vision-threatening complication of a premature birth, in which the etiology still remains unclear. Importantly, the molecular processes that govern these effects can be investigated in a perturbed plasma proteome composition. Thus, plasma proteomics may add new insights into a better understanding of the pathogenesis of this disease.

Methods

The cord and peripheral blood of neonates (≤30 weeks gestational age) was drawn at birth and at the 36th postmenstrual week (PMA), respectively. Blood samples were retrospectively subdivided into ROP(+) and ROP(-) groups, according to the development of ROP.

Results

The quantitative analysis of plasma proteome at both time points revealed 30 protein abundance changes between ROP(+) and ROP(-) groups. After standardization to gestational age, children who developed ROP were characterized by an increased C3 complement component and fibrinogen level at both analyzed time points.

Conclusions

Higher levels of the complement C3 component and fibrinogen, present in the cord blood and persistent to 36 PMA, may indicate a chronic low-grade systemic inflammation and hypercoagulable state that may play a role in the development of ROP.

Fundus-Controlled Dark Adaptometry in Young Children Without and With Spontaneously Regressed Retinopathy of Prematurity

PURPOSE

We correlate dark adaptation course with foveal morphologic alterations in preterm and term-born children using a modified fundus-controlled perimeter and spectral domain-optical coherence tomography (SD-OCT) imaging.

METHODS

We performed fundus-controlled chromatic dark adaptometry in premature children aged 6 to 13 years without retinopathy of prematurity (no-ROP; n = 61) and with spontaneously regressed ROP (sr-ROP, n = 29), and in 11 age-matched term-born children. The degree of macular developmental arrest (MDA), defined as a disproportion of the outer nuclear layer to inner retinal layers in the fovea (ONL+/IRL-ratio), was analyzed with the DiOCTA tool in SD-OCT scans.

RESULTS

Children with MDA showed a flatter dark adaptation course progression with a significant rod-mediated sensitivity recovery delay (0.0113 vs. 0.0253 dB/s; P < 0.001). Preterm-born children with regular foveal morphology reached the final rod-mediated dark-adapted threshold at 12 minutes after bleach at 18.8 dB, compared to after 18.7 minutes at 17.6 dB in children with MDA (no significant difference in final threshold; P = 0.773). The cone-mediated dark adaptation progression showed a significant lower final threshold in children with MDA (6.0 vs. 8.1 dB; P = 0.004).

CONCLUSIONS

Changes in dark adaptation were seen in the presence of MDA observed in premature children in the no-ROP and sr-ROP groups. MDA in former premature children is associated with functional deficits of cone and rod photoreceptor visual pathways.

TRANSLATIONAL RELEVANCE

Morphologic alterations in the central retina of premature children, evident in SD-OCT, are associated with long-term functional deficits in the rod and cone pathways, particularly evident in the rod dark adaptation course measured at 12° eccentricity. This indicates a more widespread retinal functional pathology not limited to the fovea, but occurring together with foveal alterations best defined as MDA.

Wnt Signaling in vascular eye diseases

The Wnt signaling pathway plays a pivotal role in vascular morphogenesis in various organs including the eye. Wnt ligands and receptors are key regulators of ocular angiogenesis both during the eye development and in vascular eye diseases. Wnt signaling participates in regulating multiple vascular beds in the eye including regression of the hyaloid vessels, and development of structured layers of vasculature in the retina. Loss-of-function mutations in Wnt signaling components cause rare genetic eye diseases in humans such as Norrie disease, and familial exudative vitreoretinopathy (FEVR) with defective ocular vasculature. On the other hand, experimental studies in more prevalent vascular eye diseases, such as wet age-related macular degeneration (AMD), diabetic retinopathy (DR), retinopathy of prematurity (ROP), and corneal neovascularization, suggest that aberrantly increased Wnt signaling is one of the causations for pathological ocular neovascularization, indicating the potential of modulating Wnt signaling to ameliorate pathological angiogenesis in eye diseases. This review recapitulates the key roles of the Wnt signaling pathway during ocular vascular development and in vascular eye diseases, and pharmaceutical approaches targeting the Wnt signaling as potential treatment options.

Simultaneous assessment of aberrant retinal vascularization, thickness, and function in an in vivo mouse oxygen-induced retinopathy model

BACKGROUND

Retinopathy of prematurity is a condition of abnormal retinal vascularization in premature infants. The effect of abnormal vascularization on retinal structure and function is unclear. In vivo studies of retinal vascularization, thickness, and function were performed in mice with oxygen-induced retinopathy (OIR mice).

METHODS

Eighteen mice were exposed to hyperoxia at postnatal day (P) 7, whereas 18 mice were raised in room air (RA). At P20 and 40, electroretinogram was performed for a-wave and b-wave amplitudes and peak times, followed by simultaneous fluorescein angiography for retinal avascular area, arterial tortuosity, and vein dilation assessments, and spectral domain optical coherence tomography for retinal thickness.

RESULTS

Capillary density appeared sparser in OIR mice, but retinal avascular area similar to RA mice. Retinal artery tortuosity was higher at P20 and P40 (P = 0.0001) in OIR than RA mice. OIR mice had dilated retinal veins at P20 and thinner inner retinas at P40. Retinal vein width positively correlated with inner retinal thickness (P = 0.008). b-wave amplitude was decreased in avascular retinal areas, and correlated with inner retinal thinning. b-wave peak time was prolonged in adult OIR mice at high intensities (P = 0.03).

CONCLUSIONS

Focal variations in retinal vascularization of OIR mice correlate with thickness and function. Adult OIR mice had increased retinal artery tortuosity, prolonged b-wave peak time, and decreased retinal vein width with inner retina attrition. These suggest abnormalities in inner retinal morphology or post-receptor signaling. Studying interactions between retinal vascular, structural, and functional changes could enhance knowledge of OIR pathogenesis and potential therapies.

Different effects of various anti-angiogenic treatments in an experimental mouse model of retinopathy of prematurity

BACKGROUND

Anti-vascular endothelial growth factor (VEGF) drugs are an option for the treatment of retinopathy of prematurity (ROP). Blocking of other angiogenic factors is also of interest. We therefore investigated in which effects would result blocking of placental growth factor (PlGF).

METHODS

C57BL/6 mice were exposed to 75% oxygen from P7 to P12. Intravitreal injections were performed at P12. Mice of control groups remained untouched after oxygen treatment, or phosphate buffered saline or neutral IgG molecules were injected. In the treatment groups, antibodies against VEGF or PlGF, a mixture of anti-VEGF and anti-PlGF, aflibercept or sunitinib were injected. On P17, electroretinographic (ERG) measurements were performed. Avascular zones and neovascularization were evaluated in retinal flat-mounts. Results are expressed as percent of total retinal area (median with median absolute deviation, MAD).

RESULTS

Eyes of control groups showed similar neovascularization (1.4-3.3%, MAD 0.4-0.9%). Neovascularization was significantly less (0.5-0.7%, MAD 0.1-0.3%) in all treatment groups. Avascular zones in the retinas of control groups showed similar values (18.3-25.7%, MAD 4.8-8.8%). Avascular zones were significantly reduced down to 3.6 ± 1.3% after anti-VEGF injection, but they were not reduced significantly in the other treatment groups (13.3-22%, MAD 3.6-6.1%). ERG measurements did not reveal significant differences between the controls and the treatment groups.

CONCLUSIONS

Blocking of PlGF or injection of sunitinib results in a similar inhibition of neovascularization as by anti-VEGF treatment in the mouse model of ROP. However, physiological angiogenesis that occurs after anti-VEGF treatment is blocked by anti-PlGF or sunitinib treatment, indicating that pathological neovascularization may follow different pathways than physiological angiogenesis.

Suppression of connexin 43 phosphorylation promotes astrocyte survival and vascular regeneration in proliferative retinopathy

Degeneration of retinal astrocytes precedes hypoxia-driven pathologic neovascularization and vascular leakage in ischemic retinopathies. However, the molecular events that underlie astrocyte loss remain unclear. Astrocytes abundantly express connexin 43 (Cx43), a transmembrane protein that forms gap junction (GJ) channels and hemichannels. Cx channels can transfer toxic signals from dying cells to healthy neighbors under pathologic conditions. Here we show that Cx43 plays a critical role in astrocyte apoptosis and the resulting preretinal neovascularization in a mouse model of oxygen-induced retinopathy. Opening of Cx43 hemichannels was not observed following hypoxia. In contrast, GJ coupling between astrocytes increased, which could lead to amplification of injury. Accordingly, conditional deletion of Cx43 maintained a higher density of astrocytes in the hypoxic retina. We also identify a role for Cx43 phosphorylation in mediating these processes. Increased coupling in response to hypoxia is due to phosphorylation of Cx43 by casein kinase 1δ (CK1δ). Suppression of this phosphorylation using an inhibitor of CK1δ or in site-specific phosphorylation-deficient mice similarly protected astrocytes from hypoxic damage. Rescue of astrocytes led to restoration of a functional retinal vasculature and lowered the hypoxic burden, thereby curtailing neovascularization and neuroretinal dysfunction. We also find that absence of astrocytic Cx43 does not affect developmental angiogenesis or neuronal function in normoxic retinas. Our in vivo work directly links phosphorylation of Cx43 to astrocytic coupling and apoptosis and ultimately to vascular regeneration in retinal ischemia. This study reveals that targeting Cx43 phosphorylation in astrocytes is a potential direction for the treatment of proliferative retinopathies.

Ischemic Retinopathies: Oxidative Stress and Inflammation

Ischemic retinopathies (IRs), such as retinopathy of prematurity (ROP), diabetic retinopathy (DR), and (in many cases) age-related macular degeneration (AMD), are ocular disorders characterized by an initial phase of microvascular changes that results in ischemia, followed by a second phase of abnormal neovascularization that may culminate into retinal detachment and blindness. IRs are complex retinal conditions in which several factors play a key role during the development of the different pathological stages of the disease. Increasing evidence reveals that oxidative stress and inflammatory processes are important contributors to the pathogenesis of IRs. Despite the beneficial effects of the photocoagulation and anti-VEGF therapy during neovascularization phase, the need to identify novel targets to prevent initial phases of these ocular pathologies is still needed. In this review, we provide an update on the involvement of oxidative stress and inflammation in the progression of IRs and address some therapeutic interventions by using antioxidants and anti-inflammatory agents.

The Beta Adrenergic Receptor Blocker Propranolol Counteracts Retinal Dysfunction in a Mouse Model of Oxygen Induced Retinopathy: Restoring the Balance between Apoptosis and Autophagy

In a mouse model of oxygen induced retinopathy (OIR), beta adrenergic receptor (BAR) blockade has been shown to recover hypoxia-associated retinal damages. Although the adrenergic signaling is an important regulator of apoptotic and autophagic processes, the role of BARs in retinal cell death remains to be elucidated. The present study was aimed at investigating whether ameliorative effects of BAR blockers may occur through their coordinated action on apoptosis and autophagy. To this aim, retinas from control and OIR mice untreated or treated with propranolol, a non-selective BAR1/2 blocker, were characterized in terms of expression and localization of apoptosis and autophagy markers. The effects of propranolol on autophagy signaling were also evaluated and specific autophagy modulators were used to get functional information on the autophagic effects of BAR antagonism. Finally, propranolol effects on neurodegenerative processes were associated to an electrophysiological investigation of retinal function by recording electroretinogram (ERG). We found that retinas of OIR mice are characterized by increased apoptosis and decreased autophagy, while propranolol reduces apoptosis and stimulates autophagy. In particular, propranolol triggers autophagosome formation in bipolar, amacrine and ganglion cells that are committed to die by apoptosis in response to hypoxia. Also our data argue that propranolol, through the inhibition of the Akt-mammalian target of rapamycin pathway, activates autophagy which decreases retinal cell death. At the functional level, propranolol recovers dysfunctional ERG by recovering the amplitude of a- and b-waves, and oscillatory potentials, thus indicating an efficient restoring of retinal transduction. Overall, our results demonstrate that BAR1/2 are key regulators of retinal apoptosis/autophagy, and that BAR1/2 blockade leads to autophagy-mediated neuroprotection. Reinstating the balance between apoptotic and autophagic machines may therefore be viewed as a future goal in the treatment of retinopathies.

Reduction on OFF-responses of Electroretinogram in Monkeys with Long-term High Intraocular Pressure

Background:

There are ON- and OFF-pathways in the normal vertebrate retina. Short- and long-flash electroretinogram (ERG) are suitable methods to observe the function of ON- and OFF-pathways in vivo, respectively. It is clear that high intraocular pressure (IOP) might cause dysfunction of cone-dominated photopic negative response (PhNR) in monkeys with high IOP in ON-pathway. However, whether cone-dominated OFF-responses are also affected is less known. The aim of this study was to observe photopic OFF-responses of ERG in monkeys with high IOP.

Methods:

Nine monkeys were involved in the experiment from January 2006 to December 2016. High IOP was induced in the right eye by laser coagulation of the mid-trabecular meshwork in five monkeys. Six years after the laser coagulation, both short- and long-flash of the photopic ERG were recorded. Stimulus light was red flashes superimposed on a blue background. Four normal monkeys were examined under the same ERG protocols as controls. Paired t-test was used to compare the difference of each ERG parameter between the lasered eye and the fellow eye. Analysis of variance (ANOVA) with Tukey adjustment was adopted to calculate the differences among the lasered eye, the fellow eye, and the eyes of normal monkeys.

Results:

The mean amplitude of a-wave (11.73 ± 2.05) and PhNR (8.67 ± 2.44) in lasered eyes was significantly lower than that of a-wave (21.47 ± 3.15) and PhNR (22.05 ± 3.42) in fellow eyes (P = 0.03 and P = 0.01, respectively) in response to short flash. The mean amplitude of d-wave (1.60 ± 0.59) and i-wave (3.13 ± 0.64) was significantly reduced in the lasered eyes than that of d-wave (4.01 ± 0.56) and i-wave (8.79 ± 1.75) in the fellow eyes (P = 0.02 and P = 0.02, respectively) in response to long flash.

Conclusions:

Reduced OFF-responses are recorded in monkeys with high IOP when dysfunction of photoreceptor is involved. The reduced OFF-responses to long-flash stimulus show evidence of anomalous retinal circuitry in glaucomatous retinopathy.

Pathophysiology, screening and treatment of ROP: A multi-disciplinary perspective

The population of infants at risk for retinopathy of prematurity (ROP) varies by world region; in countries with well developed neonatal intensive care services, the highest risk infants are those born at less than 28 weeks gestational age (GA) and less than 1 kg at birth, while, in regions where many aspects of neonatal intensive and ophthalmological care are not routinely available, more mature infants up to 2000 g at birth and 37 weeks GA are also at risk for severe ROP. Treatment options for both groups of patients include standard retinal laser photocoagulation or, more recently, intravitreal anti-VEGF drugs. In addition to detection and treatment of ROP, this review highlights new opportunities created by telemedicine, where screening and diagnosis of ROP in remote locations can be undertaken by non-ophthalmologists using digital fundus cameras. The ophthalmological care of the ROP infant is undertaken in the wider context of neonatal care and general wellbeing of the infant. Because of this context, this review takes a multi-disciplinary perspective with contributions from retinal vascular biologists, pediatric ophthalmologists, an epidemiologist and a neonatologist. This review highlights the latest insights regarding cellular and molecular mechanisms in the formation of the retinal vasculature in the human infant, pathogenesis of ROP, detection and treatment of severe ROP, the risks and benefits of anti-VEGF therapy, the identification of new therapies over the horizon, and the optimal neonatal care regimen for best ROP outcomes, and the benefits and pitfalls of telemedicine in the remote screening and diagnosis of ROP, all of which have the potential to improve ROP outcomes.

Retinopathy of prematurity: inflammation, choroidal degeneration, and novel promising therapeutic strategies

Retinopathy of prematurity (ROP) is an important cause of childhood blindness globally, and the incidence is rising. The disease is characterized by initial arrested retinal vascularization followed by neovascularization and ensuing retinal detachment causing permanent visual loss. Although neovascularization can be effectively treated via retinal laser ablation, it is unknown which children are at risk of entering this vision-threatening phase of the disease. Laser ablation may itself induce visual field deficits, and there is therefore a need to identify targets for novel and less destructive treatments of ROP. Inflammation is considered a key contributor to the pathogenesis of ROP. A large proportion of preterm infants with ROP will have residual visual loss linked to loss of photoreceptor (PR) and the integrity of the retinal pigment epithelium (RPE) in the macular region. Recent studies using animal models of ROP suggest that choroidal degeneration may be associated with a loss of integrity of the outer retina, a phenomenon so far largely undescribed in ROP pathogenesis. In this review, we highlight inflammatory and neuron-derived factors related to ROP progression, as well, potential targets for new treatment strategies. We also introduce choroidal degeneration as a significant cause of residual visual loss following ROP. We propose that ROP should no longer be considered an inner retinal vasculopathy only, but also a disease of choroidal degeneration affecting both retinal pigment epithelium and photoreceptor integrity.

Reduction of Rod and Cone Function in 6.5-Year-Old Children Born Extremely Preterm

Importance

The function of rods and cones in children born extremely preterm has not yet been fully investigated.

Objective

To compare retinal function via full-field electroretinographic (ffERG) recordings in 6.5-year-old children born extremely preterm with children born at term.

Design, Setting, and Participants

A subcohort study was conducted from July 1, 2010, to January 15, 2014, of the national Extremely Preterm Infants in Sweden Study, including preterm children (<27 weeks' gestational age) and children born at term, at 6.5 years of age and living in the Uppsala health care region in Sweden. Full-field electroretinography was performed binocularly, using DTL electrodes and electroretinographic (ERG) protocols with flash strengths of 0.009, 0.17, 3.0, and 12.0 candelas (cd)/s/m2, together with 30-Hz flicker and 3.0 cd/s/m2 single-cone flash.

Main Outcomes and Measures

The ffERG recordings were analyzed, and their associations with gestational age and retinopathy of prematurity were examined.

Results

Adequate ffERG recordings were obtained from 52 preterm children (19 girls and 33 boys; mean [SD] age at examination, 6.6 [0.1] years) and 45 children born at term (22 girls and 23 boys; mean [SD] age at examination, 6.6 [0.1] years). Lower amplitudes of the combined rod and cone responses (the a-wave of the dark-adapted ERG protocol of 3.0 cd/s/m2: mean difference, -48.9 μV [95% CI, -80.0 to -17.9 μV]; P=.003; the a-wave of the dark-adapted ERG protocol of 12.0 cd/s/m2: mean difference, -55.7 μV [95% CI, -92.5 to -18.8 μV]; P = .004), as well as of the isolated cone response (30-Hz flicker ERG: mean difference, -12.1 μV [95% CI, -22.5 to -1.6 μV]; P = .03), were found in the preterm group in comparison with the group born at term. The implicit time of the combined rod and cone responses (the a-wave of the dark-adapted ERG protocol of 12.0 cd/s/m2) was longer (mean difference, 1.2 milliseconds [95% CI, 0.3-2.0 milliseconds]; P = .01) in the preterm group, as were the isolated cone responses (30-Hz flicker ERG: mean difference, 1.2 milliseconds [95% CI, 0.5-1.8 milliseconds]; P < .001), than in the group born at term. No association was found between the ffERG recordings and gestational age or retinopathy of prematurity in the preterm group.

Conclusions and Relevance

Both rod function and cone function were reduced in children born extremely preterm when compared with children born at term. There was no association with retinopathy of prematurity in the preterm group, which suggests that being born extremely preterm may be one of the main reasons for a general retinal dysfunction.

Increment Threshold Functions in Retinopathy of Prematurity

PURPOSE

To assess scotopic background adaptation in subjects with a history of preterm birth and retinopathy of prematurity (ROP). Retinopathy of prematurity is known to have long-term effects on rod photoreceptor and rod mediated postreceptor retinal function.

METHODS

Rod-mediated thresholds for detection of 3° diameter, 50 ms stimuli presented 20° from fixation were measured using a spatial forced choice method in 36 subjects (aged 9-17 years) with a history of preterm birth and 11 age similar term-born subjects. Thresholds were measured first in the dark-adapted condition and then in the presence of 6 steady background lights (-2.8 to +2.0 log scot td). A model of the increment threshold function was fit to each subject's thresholds to estimate the dark-adapted threshold (TDA) and the Eigengrau (A0, the background that elevates threshold 0.3 log unit above TDA).

RESULTS

In subjects with a history of severe ROP, both TDA and A0 were significantly elevated relative to those in former preterms who never had ROP and term-born control subjects. Subjects who had mild ROP had normal TDA but elevated A0. Neither TDA nor A0 differed significantly between former preterms who never had ROP and term-born controls.

CONCLUSIONS

The results suggest that in severe ROP, threshold is affected at a preadaptation site, possibly the rod outer segment. In mild ROP, changes in the Eigengrau may reflect increased intrinsic noise in the photoreceptor or postreceptor circuitry or both.

The neural retina in retinopathy of prematurity

Retinopathy of prematurity (ROP) is a neurovascular disease that affects prematurely born infants and is known to have significant long term effects on vision. We conducted the studies described herein not only to learn more about vision but also about the pathogenesis of ROP. The coincidence of ROP onset and rapid developmental elongation of the rod photoreceptor outer segments motivated us to consider the role of the rods in this disease. We used noninvasive electroretinographic (ERG), psychophysical, and retinal imaging procedures to study the function and structure of the neurosensory retina. Rod photoreceptor and post-receptor responses are significantly altered years after the preterm days during which ROP is an active disease. The alterations include persistent rod dysfunction, and evidence of compensatory remodeling of the post-receptor retina is found in ERG responses to full-field stimuli and in psychophysical thresholds that probe small retinal regions. In the central retina, both Mild and Severe ROP delay maturation of parafoveal scotopic thresholds and are associated with attenuation of cone mediated multifocal ERG responses, significant thickening of post-receptor retinal laminae, and dysmorphic cone photoreceptors. These results have implications for vision and control of eye growth and refractive development and suggest future research directions. These results also lead to a proposal for noninvasive management using light that may add to the currently invasive therapeutic armamentarium against ROP.

Review of the mechanisms and therapeutic avenues for retinal and choroidal vascular dysfunctions in retinopathy of prematurity

Retinopathy of prematurity (ROP) is a multifactorial disease and the main cause of visual impairment and blindness in premature neonates. The inner retina has been considered the primary region affected in ROP, but choroidal vascular degeneration and progressive outer retinal dysfunctions have also been observed. This review focuses on observations regarding neurovascular dysfunctions in both the inner and outer immature retina, the mechanisms and the neuronal-derived factors implicated in the development of ROP, as well potential therapeutic avenues for this disorder.

CONCLUSION

Alterations in the neurovascular integrity of the inner and outer retina contribute to the development of ROP.