Review

Authors: Elsa Wilma Böhm, Francesco Buonfiglio, Anna Maria Voigt...

Oxidative stress occurs through an imbalance between the generation of reactive oxygen species (ROS) and the antioxidant defense mechanisms of cells. The eye is particularly exposed to oxidative stress because of its permanent exposure to light and due to several structures having high metabolic activities. The anterior part of the eye is highly exposed to ultraviolet (UV) radiation and possesses a complex antioxidant defense system to protect the retina from UV radiation. The posterior part of the eye exhibits high metabolic rates and oxygen consumption leading subsequently to a high production rate of ROS. Furthermore, inflammation, aging, genetic factors, and environmental pollution, are all elements promoting ROS generation and impairing antioxidant defense mechanisms and thereby representing risk factors leading to oxidative stress. An abnormal redox status was shown to be involved in the pathophysiology of various ocular diseases in the anterior and posterior segment of the eye. In this review, we aim to summarize the mechanisms of oxidative stress in ocular diseases to provide an updated understanding on the pathogenesis of common diseases affecting the ocular surface, the lens, the retina, and the optic nerve. Moreover, we discuss potential therapeutic approaches aimed at reducing oxidative stress in this context.

Topics: Antioxidants; Reactive Oxygen Species; Eye; Oxidative Stress; Lens, Crystalline

PubMed: 38006824
DOI: 10.1016/j.redox.2023.102967

Review

Authors: Xiaobo Zhang, Vimalin Jeyalatha M, Yangluowa Qu...

Dry eye can damage the ocular surface and result in mild corneal epithelial defect to blinding corneal pannus formation and squamous metaplasia. Significant progress in the treatment of dry eye has been made in the last two decades; progressing from lubricating and hydrating the ocular surface with artificial tear to stimulating tear secretion; anti-inflammation and immune regulation. With the increase in knowledge regarding the pathophysiology of dry eye, we propose in this review the concept of ocular surface microenvironment. Various components of the microenvironment contribute to the homeostasis of ocular surface. Compromise in one or more components can result in homeostasis disruption of ocular surface leading to dry eye disease. Complete evaluation of the microenvironment component changes in dry eye patients will not only lead to appropriate diagnosis, but also guide in timely and effective clinical management. Successful treatment of dry eye should be aimed to restore the homeostasis of the ocular surface microenvironment.

Topics: Cellular Microenvironment; Conjunctiva; Cornea; Dry Eye Syndromes; Eye; Eyelids; Homeostasis; Hormones; Humans; Lacrimal Apparatus; Lubricant Eye Drops; Meibomian Glands; Microbiota; Tears

PubMed: 28661456
DOI: 10.3390/ijms18071398

Authors: Tavé van Zyl, Wenjun Yan, Alexi M McAdams...

The anterior segment of the eye consists of the cornea, iris, ciliary body, crystalline lens, and aqueous humor outflow pathways. Together, these tissues are essential for the proper functioning of the eye. Disorders of vision have been ascribed to defects in all of them; some disorders, including glaucoma and cataract, are among the most prevalent causes of blindness in the world. To characterize the cell types that compose these tissues, we generated an anterior segment cell atlas of the human eye using high-throughput single-nucleus RNA sequencing (snRNAseq). We profiled 195,248 nuclei from nondiseased anterior segment tissues of six human donors, identifying >60 cell types. Many of these cell types were discrete, whereas others, especially in the lens and cornea, formed continua corresponding to known developmental transitions that persist in adulthood. Having profiled each tissue separately, we performed an integrated analysis of the entire anterior segment, revealing that some cell types are unique to a single structure, whereas others are shared across tissues. The integrated cell atlas was then used to investigate cell type-specific expression patterns of more than 900 human ocular disease genes identified through either Mendelian inheritance patterns or genome-wide association studies.

Topics: Adult; Anterior Eye Segment; Aqueous Humor; Atlases as Topic; Ciliary Body; Eye Diseases; Genome-Wide Association Study; Humans; Iris; Organ Specificity

PubMed: 35858321
DOI: 10.1073/pnas.2200914119

Authors: E Stefánsson, M P Snead

Topics: Aqueous Humor; Eye; Humans; Rheology; Tears; Vitreous Body

PubMed: 29417938
DOI: 10.1038/eye.2017.311

Authors: Richard D Semba, Jan J Enghild

Topics: Eye; Humans; Proteomics

PubMed: 24729286
DOI: 10.1002/prca.201470024

Review

Authors: Yoshiyuki Yamamoto

Topics: Animals; Biological Evolution; Environment; Eye; Fishes; Gene Expression Regulation, Developmental; Hedgehog Proteins; Trans-Activators

PubMed: 15556847
DOI: 10.1016/j.cub.2004.10.035

Review

Authors: Josef Flammer, Katarzyna Konieczka, Rosa M Bruno...

The vasculature of the eye and the heart share several common characteristics. The easily accessible vessels of the eye are therefore-to some extent-a window to the heart. There is interplay between cardiovascular functions and risk factors and the occurrence and progression of many eye diseases. In particular, arteriovenous nipping, narrowing of retinal arteries, and the dilatation of retinal veins are important signs of increased cardiovascular risk. The pressure in the dilated veins is often markedly increased due to a dysregulation of venous outflow from the eye. Besides such morphological criteria, functional alterations might be even more relevant and may play an important role in future diagnostics. Via neurovascular coupling, flickering light dilates capillaries and small arterioles, thus inducing endothelium-dependent, flow-mediated dilation of larger retinal vessels. Risk factors for arteriosclerosis, such as dyslipidaemia, diabetes, or systemic hypertension, are also risk factors for eye diseases such as retinal arterial or retinal vein occlusions, cataracts, age-related macular degeneration, and increases in intraocular pressure (IOP). Functional alterations of blood flow are particularly relevant to the eye. The primary vascular dysregulation syndrome (PVD), which often includes systemic hypotension, is associated with disturbed autoregulation of ocular blood flow (OBF). Fluctuation of IOP on a high level or blood pressure on a low level leads to instable OBF and oxygen supply and therefore to oxidative stress, which is particularly involved in the pathogenesis of glaucomatous neuropathy. Vascular dysregulation also leads to a barrier dysfunction and thereby to small retinal haemorrhages.

Topics: Blood Flow Velocity; Eye; Eye Diseases; Heart Diseases; Humans; Microcirculation; Retinal Vessels

PubMed: 23401492
DOI: 10.1093/eurheartj/eht023

Review

Authors: Adam D Baim, Asadolah Movahedan, Asim V Farooq...

This review describes a growing body of research on relationships between the microbiome and eye disease. Several groups have investigated the microbiota of the ocular surface; dysregulation of this delicate ecosystem has been associated with a variety of pro-inflammatory states. Other research has explored the effects of the gastrointestinal microbiota on ophthalmic diseases. Characterizing the ways these microbiotas influence ophthalmic homeostasis and pathogenesis may lead to research on new techniques for managing ophthalmic disease.

Topics: Environment; Eye; Eye Diseases; Host-Pathogen Interactions; Humans; Microbiota

PubMed: 30463439
DOI: 10.1177/1535370218813616

Review

Authors: Cintia S de Paiva, Anthony J St Leger, Rachel R Caspi...

The eye is a sensory organ exposed to the environment and protected by a mucosal tissue barrier. While it shares a number of features with other mucosal tissues, the ocular mucosal system, composed of the conjunctiva, Meibomian glands, and lacrimal glands, is specialized to address the unique needs of (a) lubrication and (b) host defense of the ocular surface. Not surprisingly, most challenges, physical and immunological, to the homeostasis of the eye fall into those two categories. Dry eye, a dysfunction of the lacrimal glands and/or Meibomian glands, which can both cause, or arise from, sensory defects, including those caused by corneal herpes virus infection, serve as examples of these perturbations and will be discussed ahead. To preserve vision, dense neuronal and immune networks sense various stimuli and orchestrate responses, which must be tightly controlled to provide protection, while simultaneously minimizing collateral damage. All this happens against the backdrop of, and can be modified by, the microorganisms that colonize the ocular mucosa long term, or that are simply transient passengers introduced from the environment. This review will attempt to synthesize the existing knowledge and develop trends in the study of the unique mucosal and immune elements of the ocular surface.

Topics: Humans; Dry Eye Syndromes; Meibomian Glands; Lacrimal Apparatus; Conjunctiva; Mucous Membrane; Tears

PubMed: 36002743
DOI: 10.1038/s41385-022-00551-6

Review

Authors: Pavan K Verkicharla, Ankit Mathur, Edward Ah Mallen...

PURPOSE

  We provide an account of the relationships between eye shape, retinal shape and peripheral refraction.

RECENT FINDINGS

  We discuss how eye and retinal shapes may be described as conicoids, and we describe an axis and section reference system for determining shapes. Explanations are given of how patterns of retinal expansion during the development of myopia may contribute to changing patterns of peripheral refraction, and how pre-existing retinal shape might contribute to the development of myopia. Direct and indirect techniques for determining eye and retinal shape are described, and results are discussed. There is reasonable consistency in the literature of eye length increasing at a greater rate than height and width as the degree of myopia increases, so that eyes may be described as changing from oblate/spherical shapes to prolate shapes. However, one study indicates that the retina itself, while showing the same trend, remains oblate in shape for most eyes (discounting high myopia). Eye shape and retinal shape are not the same and merely describing an eye shape as being prolate or oblate is insufficient without some understanding of the parameters contributing to this; in myopia a prolate eye shape is likely to involve both a steepening retina near the posterior pole combined with a flattening (or a reduction in steepening compared with an emmetrope) away from the pole.

SUMMARY

  In the recent literature, eye and/or retinal shape have often been inferred from peripheral refraction, and, to a lesser extent, vice versa. Because both the eye's optics and the retinal shape contribute to the peripheral refraction, and there is large variation in the latter, this inference should be made cautiously. Recently retinal shape has been measured independent of optical methods using magnetic resonance imaging. For further work on retinal shape, determining the validity of cheaper alternatives to magnetic resonance techniques is required.

Topics: Biometry; Disease Progression; Eye; Humans; Models, Biological; Myopia; Refraction, Ocular; Retina

PubMed: 22486366
DOI: 10.1111/j.1475-1313.2012.00906.x