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Indian Journal of Ophthalmology Feb 2018Important functions of cornea in the eye include protecting the structures inside the eye, contributing to the refractive power of the eye, and focusing light rays on... (Review)
Review
Important functions of cornea in the eye include protecting the structures inside the eye, contributing to the refractive power of the eye, and focusing light rays on the retina with minimum scatter and optical degradation. Considerable advances have taken place in understanding the organization of collagen in the corneal stroma and its clinical significance. In this review, the structure and function of various components of cornea and ocular surface are presented.
Topics: Cornea; Humans; Sclera
PubMed: 29380756
DOI: 10.4103/ijo.IJO_646_17 -
Progress in Retinal and Eye Research Jan 2020As the eye's main load-bearing connective tissue, the sclera is centrally important to vision. In addition to cooperatively maintaining refractive status with the... (Review)
Review
As the eye's main load-bearing connective tissue, the sclera is centrally important to vision. In addition to cooperatively maintaining refractive status with the cornea, the sclera must also provide stable mechanical support to vulnerable internal ocular structures such as the retina and optic nerve head. Moreover, it must achieve this under complex, dynamic loading conditions imposed by eye movements and fluid pressures. Recent years have seen significant advances in our knowledge of scleral biomechanics, its modulation with ageing and disease, and their relationship to the hierarchical structure of the collagen-rich scleral extracellular matrix (ECM) and its resident cells. This review focuses on notable recent structural and biomechanical studies, setting their findings in the context of the wider scleral literature. It reviews recent progress in the development of scattering and bioimaging methods to resolve scleral ECM structure at multiple scales. In vivo and ex vivo experimental methods to characterise scleral biomechanics are explored, along with computational techniques that combine structural and biomechanical data to simulate ocular behaviour and extract tissue material properties. Studies into alterations of scleral structure and biomechanics in myopia and glaucoma are presented, and their results reconciled with associated findings on changes in the ageing eye. Finally, new developments in scleral surgery and emerging minimally invasive therapies are highlighted that could offer new hope in the fight against escalating scleral-related vision disorder worldwide.
Topics: Aging; Animals; Biomechanical Phenomena; Glaucoma; Humans; Myopia; Sclera
PubMed: 31412277
DOI: 10.1016/j.preteyeres.2019.100773 -
Proceedings of the National Academy of... Jul 2018Worldwide, myopia is the leading cause of visual impairment. It results from inappropriate extension of the ocular axis and concomitant declines in scleral strength and...
Worldwide, myopia is the leading cause of visual impairment. It results from inappropriate extension of the ocular axis and concomitant declines in scleral strength and thickness caused by extracellular matrix (ECM) remodeling. However, the identities of the initiators and signaling pathways that induce scleral ECM remodeling in myopia are unknown. Here, we used single-cell RNA-sequencing to identify pathways activated in the sclera during myopia development. We found that the hypoxia-signaling, the eIF2-signaling, and mTOR-signaling pathways were activated in murine myopic sclera. Consistent with the role of hypoxic pathways in mouse model of myopia, nearly one third of human myopia risk genes from the genome-wide association study and linkage analyses interact with genes in the hypoxia-inducible factor-1α (HIF-1α)-signaling pathway. Furthermore, experimental myopia selectively induced HIF-1α up-regulation in the myopic sclera of both mice and guinea pigs. Additionally, hypoxia exposure (5% O) promoted myofibroblast transdifferentiation with down-regulation of type I collagen in human scleral fibroblasts. Importantly, the antihypoxia drugs salidroside and formononetin down-regulated HIF-1α expression as well as the phosphorylation levels of eIF2α and mTOR, slowing experimental myopia progression without affecting normal ocular growth in guinea pigs. Furthermore, eIF2α phosphorylation inhibition suppressed experimental myopia, whereas mTOR phosphorylation induced myopia in normal mice. Collectively, these findings defined an essential role of hypoxia in scleral ECM remodeling and myopia development, suggesting a therapeutic approach to control myopia by ameliorating hypoxia.
Topics: Animals; Disease Models, Animal; Eukaryotic Initiation Factor-2; Extracellular Matrix; Eye Proteins; Guinea Pigs; Humans; Hypoxia; Hypoxia-Inducible Factor 1, alpha Subunit; Male; Mice; Myopia; Sclera; Signal Transduction; TOR Serine-Threonine Kinases
PubMed: 29987045
DOI: 10.1073/pnas.1721443115 -
Experimental Eye Research Jun 2022The global prevalence of myopia, or nearsightedness, has increased at an alarming rate over the last few decades. An eye is myopic if incoming light focuses prior to... (Review)
Review
The global prevalence of myopia, or nearsightedness, has increased at an alarming rate over the last few decades. An eye is myopic if incoming light focuses prior to reaching the retinal photoreceptors, which indicates a mismatch in its shape and optical power. This mismatch commonly results from excessive axial elongation. Important drivers of the myopia epidemic include environmental factors, genetic factors, and their interactions, e.g., genetic factors influencing the effects of environmental factors. One factor often hypothesized to be a driver of the myopia epidemic is environmental light, which has changed drastically and rapidly on a global scale. In support of this, it is well established that eye size is regulated by a homeostatic process that incorporates visual cues (emmetropization). This process allows the eye to detect and minimize refractive errors quite accurately and locally over time by modulating the rate of elongation of the eye via remodeling its outermost coat, the sclera. Critically, emmetropization is not dependent on post-retinal processing. Thus, visual cues appear to influence axial elongation through a retina-to-sclera, or retinoscleral, signaling cascade, capable of transmitting information from the innermost layer of the eye to the outermost layer. Despite significant global research interest, the specifics of retinoscleral signaling pathways remain elusive. While a few pharmacological treatments have proven to be effective in slowing axial elongation (most notably topical atropine), the mechanisms behind these treatments are still not fully understood. Additionally, several retinal neuromodulators, neurotransmitters, and other small molecules have been found to influence axial length and/or refractive error or be influenced by myopigenic cues, yet little progress has been made explaining how the signal that originates in the retina crosses the highly vascular choroid to affect the sclera. Here, we compile and synthesize the evidence surrounding three of the major candidate pathways receiving significant research attention - dopamine, retinoic acid, and adenosine. All three candidates have both correlational and causal evidence backing their involvement in axial elongation and have been implicated by multiple independent research groups across diverse species. Two hypothesized mechanisms are presented for how a retina-originating signal crosses the choroid - via 1) all-trans retinoic acid or 2) choroidal blood flow influencing scleral oxygenation. Evidence of crosstalk between the pathways is discussed in the context of these two mechanisms.
Topics: Animals; Disease Models, Animal; Myopia; Refraction, Ocular; Refractive Errors; Retina; Sclera
PubMed: 35447101
DOI: 10.1016/j.exer.2022.109071 -
Indian Journal of Ophthalmology Aug 2023This article explains a technique of scleral fixation of intraocular lens (SFIOL) by using a 30-gauge (g) needle.
UNLABELLED
This article explains a technique of scleral fixation of intraocular lens (SFIOL) by using a 30-gauge (g) needle.
BACKGROUND
The X-nit needle by "Aurolab" uses a 26-g needle, while in this technique, a 30-g needle is used, thus reducing the incision size and relevant complications.
PURPOSE
In this technique, glue or end-gripping forceps are not used, thus making it hassle free and more economical. There is no dependency on assistant; because of using 30 g needle, bleeding is minimal and wound healing is faster.
SYNOPSIS
A 30-g needle is bent at 3/4-1/4 junction (from the tip) and a piece of 240 silicon band is inserted into the needle to be used as a stopper. After completing vitrectomy, a 1.5-mm marking is done perpendicular to the limbus at 3'o clock and 9'o clock positions. Another marking is done 1.5 mm away from the first mark parallel to the limbus. A 30-g needle is inserted into partial-thickness sclera from the second mark toward the first marking, thus making a tunnel. The needle is penetrated into the sclera to enter in the vitreous cavity. The needle is then progressed toward the anterior vitreous cavity and brought out through the lip of previously made scleral tunnel in the superior quadrant. The tip of leading haptic of three-piece intraocular lens (IOL) is fed into the tip of needle and gradually, the needle is withdrawn. As soon as the tip of needle is visualized, the piece of band is gradually slipped into the haptic and the needle freed from the haptic. In a similar fashion, the trailing haptic is withdrawn from the opposite side. The bands are removed and the haptics are adjusted by pulling or pushing to centralize the IOL in the pupillary axis. Haptics are trimmed and ends are cauterized to make them blunt. Tunnel and conjunctiva are sutured with one or two (8-0) absorbable Vicryl sutures. The 25-g ports are removed and no suturing of ports is done.
HIGHLIGHTS
It is a minimally invasive and glueless technique in which end-gripping forceps is not used. So, it is very economical with faster wound healing and minimal bleeding and no post-op hypotony. Since the temporal scleral flaps are not made and 30 g needle is used so minimal invasive. Astigmatiam induced by scleral tunnel is seen i;e about 0.75- 1.15 D of cylinder.
VIDEO LINK
https://youtu.be/1msuS5KySOk.
Topics: Humans; Lens Implantation, Intraocular; Lenses, Intraocular; Sclera; Vitrectomy; Conjunctiva; Suture Techniques
PubMed: 37530297
DOI: 10.4103/IJO.IJO_125_23 -
EBioMedicine Jul 2020Myopia is a good model for understanding the interaction between genetics and environmental stimuli. Here we dissect the biological processes affecting myopia...
BACKGROUND
Myopia is a good model for understanding the interaction between genetics and environmental stimuli. Here we dissect the biological processes affecting myopia progression.
METHODS
Human Genetic Analyses: (1) gene set analysis (GSA) of new genome wide association study (GWAS) data for 593 individuals with high myopia (refraction ≤ -6 diopters [D]); (2) over-representation analysis (ORA) of 196 genes with de novo mutations, identified by whole genome sequencing of 45 high-myopia trio families, and (3) ORA of 284 previously reported myopia risk genes. Contributions of the enriched signaling pathways in mediating the genetic and environmental interactions during myopia development were investigated in vivo and in vitro.
RESULTS
All three genetic analyses showed significant enrichment of four KEGG signaling pathways, including amphetamine addiction, extracellular matrix (ECM) receptor interaction, neuroactive ligand-receptor interaction, and regulation of actin cytoskeleton pathways. In individuals with extremely high myopia (refraction ≤ -10 D), the GSA of GWAS data revealed significant enrichment of the HIF-1α signaling pathway. Using human scleral fibroblasts, silencing the key nodal genes within protein-protein interaction networks for the enriched pathways antagonized the hypoxia-induced increase in myofibroblast transdifferentiation. In mice, scleral HIF-1α downregulation led to hyperopia, whereas upregulation resulted in myopia. In human subjects, near work, a risk factor for myopia, significantly decreased choroidal blood perfusion, which might cause scleral hypoxia.
INTERPRETATION
Our study implicated the HIF-1α signaling pathway in promoting human myopia through mediating interactions between genetic and environmental factors.
FUNDING
National Natural Science Foundation of China grants; Natural Science Foundation of Zhejiang Province.
Topics: Animals; Disease Models, Animal; Female; Gene-Environment Interaction; Genetic Predisposition to Disease; Genome-Wide Association Study; Humans; Hypoxia-Inducible Factor 1, alpha Subunit; Male; Mice; Myopia; Sclera; Signal Transduction
PubMed: 32652319
DOI: 10.1016/j.ebiom.2020.102878 -
Drug Discovery Today Aug 2019The suprachoroidal space (SCS), a potential anatomical space between the sclera and choroid, is a novel route for drug delivery targeting the chorioretinal layers of the... (Review)
Review
The suprachoroidal space (SCS), a potential anatomical space between the sclera and choroid, is a novel route for drug delivery targeting the chorioretinal layers of the eye. The safety and efficacy of SCS drug delivery have been shown in multiple clinical trials. Recent studies have developed methods for more precise targeting within the SCS at sites of action at the posterior pole (e.g., macula), near the limbus (e.g., ciliary body), and throughout the SCS using iontophoresis, swollen hydrogels, high-density particle emulsions, highly viscous and non-Newtonian fluids, and microstents. Here, we review novel technologies targeting the posterior, anterior, or entire SCS.
Topics: Animals; Choroid; Choroidal Effusions; Drug Delivery Systems; Humans; Sclera
PubMed: 30953867
DOI: 10.1016/j.drudis.2019.03.027 -
Clinical & Experimental Optometry Mar 2014An examination of how intraocular pressure distending forces on the posterior sclera are an important mechanism in the development and progression of axial myopia has... (Review)
Review
An examination of how intraocular pressure distending forces on the posterior sclera are an important mechanism in the development and progression of axial myopia has been made. Papers were selected from the results of PubMed (143) and Science Direct (1,398) searches using the key word combinations of 'axial myopia' and 'intraocular pressure'. The main points include that the sclera is exposed to distending forces at all levels of physiological and pathological intraocular pressure. Reversible axial elongation is a common physiological response to elevated intraocular pressure in healthy eyes but more so in myopic eyes. Key variables, which appear to determine pathological (non-reversible) axial elongation include the thickness, rigidity and viscoelasticity of the posterior sclera and the associated increased susceptibility of it to distending forces. Intraocular pressure appears likely to have a greater role when it is above normal. Intraocular pressure elevations, which are not detected by clinical or experimental tonometry, may be significant contributors to axial elongation. Axial elongation can be pathological in myopic or myopically predisposed eyes, when elongation is not reversible. Axial elongation has also been associated with retinal defocus in both animals and humans, when thinning due to loss of scleral collagen and/or ground substance, which is driven by the retina, appears likely to be associated with increased scleral susceptibility to intraocular pressure. As myopia progresses, signs of retinal and choroidal stretching are an increasingly apparent consequence of the balloon-like expansion of the posterior sclera in response to intraocular pressure. Avoidance or moderation of activities which are known to elevate intraocular pressure may improve the prognosis for patients with genetic and/or environmental predisposition to myopic progression and may be an important consideration, even when other myopic control measures are being used.
Topics: Age Factors; Animals; Choroid Plexus; Elasticity; Humans; Intraocular Pressure; Myopia; Refractive Errors; Sclera; Tonometry, Ocular
PubMed: 23937058
DOI: 10.1111/cxo.12101 -
Advanced Drug Delivery Reviews Feb 2018The suprachoroidal space (SCS) is a potential space between the sclera and choroid that traverses the circumference of the posterior segment of the eye. The SCS is an... (Review)
Review
The suprachoroidal space (SCS) is a potential space between the sclera and choroid that traverses the circumference of the posterior segment of the eye. The SCS is an attractive site for drug delivery because it targets the choroid, retinal pigment epithelium, and retina with high bioavailability, while maintaining low levels elsewhere in the eye. Indeed, phase III clinical trials are investigating the safety and efficacy of SCS drug delivery. Here, we review the anatomy and physiology of the SCS; methods to access the SCS; kinetics of SCS drug delivery; strategies to target within the SCS; current and potential clinical indications; and the safety and efficacy of this approach in preclinical animal studies and clinical trials.
Topics: Administration, Ophthalmic; Animals; Choroid; Drug Delivery Systems; Humans; Kinetics; Sclera
PubMed: 29545195
DOI: 10.1016/j.addr.2018.03.001 -
Indian Pediatrics Mar 2005
Topics: Cornea; Corneal Opacity; Humans; Infant, Newborn; Sclera
PubMed: 15817979
DOI: No ID Found