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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 -
Asia-Pacific Journal of Ophthalmology... 2017Intrascleral sutureless intraocular lens (IOL) fixation utilizes direct haptic fixation within the sclera in eyes with deficient capsular support. This has advantages of... (Review)
Review
Intrascleral sutureless intraocular lens (IOL) fixation utilizes direct haptic fixation within the sclera in eyes with deficient capsular support. This has advantages of long-term stability, good control of tilt and decentration, and lesser pseudophakodonesis. This review summarizes various techniques for intrascleral haptic fixation, results, complications, adaptations in special situations, modifications of the technique, combination surgeries, and intrascleral capsular bag fixation techniques (glued capsular hook).
Topics: Aphakia; Humans; Lens Implantation, Intraocular; Lenses, Intraocular; Refraction, Ocular; Retrospective Studies; Sclera; Suture Techniques; Sutures
PubMed: 28726356
DOI: 10.22608/APO.2017158 -
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 -
Experimental Eye Research Aug 2020Scleritis is a sight-threatening inflammation characterized by severe pain and redness of the eye. It can cause blindness by severe complications like scleral and... (Review)
Review
Scleritis is a sight-threatening inflammation characterized by severe pain and redness of the eye. It can cause blindness by severe complications like scleral and corneal necrosis, keratitis, and uveitis. The pathogenesis of scleritis is largely unknown due to a combination of the rarity of the disease, the little available human tissue-based research material, and the lack of animal models. The immune system is assumed to play a crucial role in the pathogenesis of scleritis. Multiple clues indicate probable antigenic stimuli in scleritis, and the involvement of matrix metalloproteinases in the destruction of scleral tissue. In this article we review the current insights into the pathogenesis of scleritis, and we suggest new hypotheses by implementing knowledge of systemic autoimmune disease pathogenesis. Understanding the pathogenesis of scleritis is crucial to improve the clinical management, as well as to find novel treatment modalities.
Topics: Autoimmunity; Diagnostic Imaging; Humans; Matrix Metalloproteinases; Sclera; Scleritis
PubMed: 32504648
DOI: 10.1016/j.exer.2020.108078 -
Indian Journal of Ophthalmology Jul 2021The aim of this study was to evaluate the application and safety of three-dimensional (3D) visualization system in varied anterior segment procedures and Scleral Buckle. (Observational Study)
Observational Study
PURPOSE
The aim of this study was to evaluate the application and safety of three-dimensional (3D) visualization system in varied anterior segment procedures and Scleral Buckle.
METHODS
This was a prospective observational study of 313 eyes. Patients undergoing phacoemulsification (PE) with intraocular lens (IOL), trabeculectomies, glaucoma triple procedure (GTP), scleral fixated (SF) IOL, and scleral buckle (SB) were included in the study. Cases were randomly distributed in 3D visualization system (learning and post-learning phase) and conventional microscope group. Parameters studied were complications (intraoperative and early postoperative), surgical outcomes, and surgeon's perspective on various parameters (through a validated questionnaire) like surgical time, time lag, learning curve, ease of doing various steps and its value as an educational tool, for both groups [Questionnaires 1 and 2].
RESULTS
Complications rates were not different in two groups. Surgical outcomes (anatomical and physiological) were similar in both the groups. Mean duration of surgery in PE+IOL, Trabeculectomy, GTP in learning stage by 3D was significantly higher than Microscope, which became insignificant in postlearning stage. For, SB and SFIOL, duration between two groups were insignificantly different. There was significant learning struggle in PE+IOL, SB, and Trabeculectomy. Image resolution, depth perception, illumination and postural comfort was graded higher for 3D surgery across the stages. Time lag, poor color contrast, and field of view were appreciated during the learning stage. Educational relevance of 3D was higher, as appreciated by resident and nurses.
CONCLUSION
3D surgery is as safe, faster, and predictable after initial learning struggle. Even in anterior segment procedure, no apparent lag was appreciated after learning curve.
Topics: Cataract Extraction; Humans; Lens Implantation, Intraocular; Lenses, Intraocular; Phacoemulsification; Postoperative Complications; Sclera
PubMed: 34146031
DOI: 10.4103/ijo.IJO_3111_20