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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 -
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 -
The Ocular Surface Jan 2023Scleral melting, while rare, can lead to significant ocular morbidity. Several possible risk factors for scleral melt have been identified, such as infection, autoimmune... (Review)
Review
Scleral melting, while rare, can lead to significant ocular morbidity. Several possible risk factors for scleral melt have been identified, such as infection, autoimmune disease, trauma, and post-surgical state, and these may act in combination with each other. Treatment should be tailored according to the etiology and severity of the scleral melt. Medical management may be indicated, especially in cases of autoimmune-related melt; however, surgical procedures are often necessary due to compromised ocular integrity and limited penetration of medications into the avascular sclera. An understanding of the surgical options available and their operative outcomes is particularly important when choosing the appropriate treatment protocol for each patient.
Topics: Humans; Scleral Diseases; Sclera
PubMed: 36549583
DOI: 10.1016/j.jtos.2022.12.005 -
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 -
Current Opinion in Ophthalmology Jan 2020To review current, effective and more popular techniques for scleral fixation of intraocular lens (IOLs) and IOL-capsular bag complex. (Review)
Review
PURPOSE OF REVIEW
To review current, effective and more popular techniques for scleral fixation of intraocular lens (IOLs) and IOL-capsular bag complex.
RECENT FINDINGS
Scleral fixation of IOLs became popular, originally with sutured scleral fixated IOLs and later the Scharioth technique of intrascleral haptic fixation. This was further developed as the Glued IOL technique which enjoys widespread adoption all over the world. Recently the Yamane technique has also become popular and is being widely adopted as well.
SUMMARY
Scleral fixated IOLs have evolved in the last 2 decades with technical modifications, extended indications and improvised instrumentation. Though sutured and sutureless techniques have been growing equally, the sutureless scleral fixation techniques have attracted special interest. Reduced suture-related complications, technical ease and high-quality functional outcomes may be possible reasons. Sutureless capsular bag fixation also has distinct advantages.
Topics: Cataract Extraction; Humans; Lens Implantation, Intraocular; Lenses, Intraocular; Pseudophakia; Sclera; Suture Techniques; Visual Acuity
PubMed: 31789971
DOI: 10.1097/ICU.0000000000000632 -
Journal of Cataract and Refractive... Dec 2020To describe the indications, motivations, and outcomes of artificial iris exchange.
PURPOSE
To describe the indications, motivations, and outcomes of artificial iris exchange.
SETTING
Stein Eye Institute.
DESIGN
Consecutive case series.
METHODS
Review of medical records of patients implanted with an artificial iris device who underwent a subsequent artificial iris exchange.
RESULTS
Five patients were identified: 4 women and 1 man. Their ages ranged from 19 to 58 years at the time of the exchange. One patient had congenital aniridia; the other 4 had acquired iris defects. Three exchanges were simultaneous; 2 were consecutive. Corneal decompensation was the most common indication for the surgery precipitating the exchange. Explanted iris devices included models from Ophtec, Morcher, BrightOcular, and HumanOptics. Replacement models were from Morcher and HumanOptics. Three of the original irides were passively fixated in the capsular bag or ciliary sulcus. All of the replacement irides were suture-fixated to the sclera, either directly or secondarily by way of an intraocular lens. The motivation for the exchange was improved cosmesis in 4 patients and sustained cosmesis in 1 patient. Final visual acuities were 20/25 for 2 patients, 20/100 for 1 patient, and hand motion for 2 patients.
CONCLUSIONS
No 2 iris exchanges were similar. Clinical indications and outcomes varied considerably from patient to patient. A common thread was each patient's motivation to maintain or improve on the functional and cosmetic benefits of having been previously implanted with an artificial iris device. Final visual acuity results were often poor because of the effects of comorbidities, especially glaucoma and corneal decompensation.
Topics: Adult; Aniridia; Female; Humans; Iris; Lenses, Intraocular; Male; Middle Aged; Sclera; Visual Acuity; Young Adult
PubMed: 32842080
DOI: 10.1097/j.jcrs.0000000000000321 -
Retina (Philadelphia, Pa.) Aug 2020
Topics: Retina; Sclera
PubMed: 31895094
DOI: 10.1097/IAE.0000000000002735 -
Annals of Anatomy = Anatomischer... Jul 2020Most organs of the human body are supplied with a dense network of blood and lymphatic vessels. However, some tissues are either hypovascular or completely devoid of... (Review)
Review
PURPOSE
Most organs of the human body are supplied with a dense network of blood and lymphatic vessels. However, some tissues are either hypovascular or completely devoid of vessels for proper function, such as the ocular tissues sclera and cornea, cartilage and tendons. Since many pathological conditions are affecting the human sclera, this review is focussing on the lymphangiogenic and hemangiogenic privilege in the human sclera.
METHODS
This article gives an overview of the current literature based on a PubMed search as well as observations and experience from clinical practice.
RESULTS
The healthy human sclera is the outer covering layer of the eye globe consisting mainly of collagenous extracellular matrix and fibroblasts. Physiologically, the sclera shows only a superficial network of blood vessels and a lack of lymphatic vessels. This vascular privilege is actively regulated by balancing anti- and proangiogenic factors expressed by cells within the sclera. In pathological situations, such as open globe injuries or ciliary body melanomas with extraocular extension, lymphatic vessels can secondarily invade the sclera and the inner eye. This mechanism most likely is important for tumor cell metastasis, wound healing, immunologic defense against intruding microorganism, and autoimmune reactions against intraocular antigens.
CONCLUSIONS
The human sclera is characterized by a tightly regulated vascular network that can be compromised in pathological situations, such as injuries or intraocular tumors affecting healing outcomes Therefore, the molecular and cellular mechanisms underlying wound healing following surgical interventions deserve further attention, in order to devise more effective therapeutic strategies.
Topics: Eye Neoplasms; Humans; Lymphangiogenesis; Lymphatic Vessels; Macrophages; Sclera
PubMed: 32120002
DOI: 10.1016/j.aanat.2020.151485 -
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