Gut Microbiome in Retina Health: The Crucial Role of the Gut-Retina Axis

The term microbiome means not only a complex ecosystem of microbial species that colonize our body but also their genome and the surrounding environment in which they live. Recent studies support the existence of a gut-retina axis involved in the pathogenesis of several chronic progressive ocular diseases, including age-related macular disorders. This review aims to underline the importance of the gut microbiome in relation to ocular health. After briefly introducing the characteristics of the gut microbiome in terms of composition and functions, the role of gut microbiome dysbiosis, in the development or progression of retinal diseases, is highlighted, focusing on the relationship between gut microbiome composition and retinal health based on the recently investigated gut-retina axis.

Experimental infection of BALB/c mice with felid alphaherpesvirus 1

Felid alphaherpesvirus type 1 (FHV-1) is an important cause of respiratory and ocular diseases in cats worldwide. Mice have been widely used to study the pathogenesis of several human and animal viruses, especially herpesviruses. This study aimed to verify whether BALB/c mice are susceptible to FHV-1 infection. The animals were intranasally inoculated with FHV-1 and their clinical signs were observed from 3 days post-infection (dpi). At 10 dpi, the animals were euthanized and the lungs, liver, spleen, and kidneys were collected for histopathological examination and quantitative polymerase chain reaction. The results showed that mice were infected with FHV-1 and reproduced several features of the disease observed in its natural host. Histological lesions and viral DNA were found in all sampled tissues, with a higher frequency of FHV-1 DNA copies detected in the lungs. All mice were seroconverted to FHV-1 at 7 dpi. To our knowledge, this is the first report of experimental infection of BALB/c mice with FHV-1. Our findings demonstrate that this murine model can contribute to understanding of FHV-1 pathogenesis and may be useful for trials against this virus.

The interplay of autophagy and oxidative stress in the pathogenesis and therapy of retinal degenerative diseases

Oxidative stress is mainly caused by intracellular reactive oxygen species (ROS) production, which is highly associated with normal physiological homeostasis and the pathogenesis of diseases, particularly ocular diseases. Autophagy is a self-clearance pathway that removes oxidized cellular components and regulates cellular ROS levels. ROS can modulate autophagy activity through transcriptional and posttranslational mechanisms. Autophagy further triggers transcription factor activation and degrades impaired organelles and proteins to eliminate excessive ROS in cells. Thus, autophagy may play an antioxidant role in protecting ocular cells from oxidative stress. Nevertheless, excessive autophagy may cause autophagic cell death. In this review, we summarize the mechanisms of interaction between ROS and autophagy and their roles in the pathogenesis of several ocular diseases, including glaucoma, age-related macular degeneration (AMD), diabetic retinopathy (DR), and optic nerve atrophy, which are major causes of blindness. The autophagy modulators used to treat ocular diseases are further discussed. The findings of the studies reviewed here might shed light on the development and use of autophagy modulators for the future treatment of ocular diseases.

The Future of Virtual Reality and Deep Learning in Visual Field Testing

The visual field (VF) examination is a useful clinical tool for monitoring a variety of ocular diseases. Despite its wide utility in eye clinics, the test as currently conducted is subject to an array of issues that interfere in obtaining accurate results. Visual field exams of patients suffering from additional ocular conditions are often unreliable due to interference between the comorbid diseases. To improve upon these shortcomings, virtual reality (VR) and deep learning are being explored as potential solutions. Virtual reality has been incorporated into novel visual field exams to provide a portable, 3D exam experience. Deep learning, a specialization of machine learning, has been used in conjunction with VR, such as in the iGlaucoma application, to limit subjective bias occurring from patients' eye movements. This chapter seeks to analyze and critique how VR and deep learning can augment the visual field experience by improving accuracy, reducing subjective bias, and ultimately, providing clinicians with a greater capacity to enhance patient outcomes.

Pattern of ocular Diseases among Children under Five Years of Age in Southeast, Nigeria

Background: Children under 5 years are prone to ocular disorders which could be congenital or acquired. Early recognition of these conditions and timely intervention enhances optimum results. There is paucity of data on the pattern of ocular disorders among these children in Nigeria and this makes it difficult for policy makers to plan health systems that will target this very important group of the population. Aim: To determine the pattern of ocular diseases among children less than 5 years of age in Onitsha, Anambra state Nigeria. Methods: This was a retrospective study of children under 5 years of age that presented to City of Refuge Specialist Eye Clinic Onitsha, Nigeria between January 1st, 2016 to December 31st, 2020. Their case files were retrieved and relevant information extracted. Sociodemographics, month of presentation to the eye clinic and diagnoses were analyzed. Results: A total of 133 children were studied. The patients comprised 85 (63.9%) males and 48 (36.1%) females, with an approximate male to female ratio of 1.8:1. Eye diseases seen were both congenital 32(24.1%) and acquired 101 (75.9%). Of the congenital type, 20 (62.5%) were males, while 12 (37.5%) were females. Most common ocular morbidities recorded were allergic conjunctivitis 41(30.8%) and infective conjunctivitis 34(25.6%). Conclusion: Most of the causes of ocular morbidity in this study were preventable or treatable. Therefore, early detection and management of eye diseases in children will reduce complications in later life.

Immunity and pain in the eye: focus on the ocular surface

Most ocular diseases are associated with pain. While pain has been generally considered a mere (deleterious) additional symptom, it is now emerging that it is a key modulator of innate/adaptive immunity. Because the cornea receives the highest nerve density of the entire body, it is an ideal site to demonstrate interactions between pain and the immune response. Indeed, most neuropeptides involved in pain generation are also potent regulators of innate and adaptive leukocyte physiology. On the other hand, most inflammatory cells can modulate the generation of ocular pain through release of specific mediators (cytokines, chemokines, growth factors, lipid mediators). This review will discuss the reciprocal role(s) of ocular surface (and specifically: corneal) pain on the immune response of the eye. Finally, we will discuss clinical implications of such reciprocal interactions in the context of highly prevalent corneal diseases.

Role of Oxidative Stress in Ocular Diseases Associated with Retinal Ganglion Cells Degeneration

Ocular diseases associated with retinal ganglion cell (RGC) degeneration is the most common neurodegenerative disorder that causes irreversible blindness worldwide. It is characterized by visual field defects and progressive optic nerve atrophy. The underlying pathophysiology and mechanisms of RGC degeneration in several ocular diseases remain largely unknown. RGCs are a population of central nervous system neurons, with their soma located in the retina and long axons that extend through the optic nerve to form distal terminals and connections in the brain. Because of this unique cytoarchitecture and highly compartmentalized energy demand, RGCs are highly mitochondrial-dependent for adenosine triphosphate (ATP) production. Recently, oxidative stress and mitochondrial dysfunction have been found to be the principal mechanisms in RGC degeneration as well as in other neurodegenerative disorders. Here, we review the role of oxidative stress in several ocular diseases associated with RGC degenerations, including glaucoma, hereditary optic atrophy, inflammatory optic neuritis, ischemic optic neuropathy, traumatic optic neuropathy, and drug toxicity. We also review experimental approaches using cell and animal models for research on the underlying mechanisms of RGC degeneration. Lastly, we discuss the application of antioxidants as a potential future therapy for the ocular diseases associated with RGC degenerations.