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Indian Journal of Ophthalmology Feb 2024High myopia is often associated with local ectasia and scleral thinning. The progression of myopia depends upon scleral biochemical and biomechanical properties. Scleral...
High myopia is often associated with local ectasia and scleral thinning. The progression of myopia depends upon scleral biochemical and biomechanical properties. Scleral thinning is associated with decreased collagen fiber diameter, defective collagen fibrillogenesis, and collagen cross-linking. Reversing these abnormalities may make the sclera tougher and might serve as a treatment option for myopic progression. Collagen cross-linking is a natural process in the cornea and sclera, which makes the structure stiff. Exogenous collagen cross-linkage is artificially induced with the help of external mediators by using light and dark methods. In this systematic review, we discussed existing literature available on the internet on current evidence-based applications of scleral collagen cross-linking (SXL) by using different interventions. In addition, we compared them in tabular form in terms of their technique, mechanisms, cytotoxicity, and the stage of transition from preclinical to clinical development. Furthermore, we discussed the in-vivo technique to evaluate the post-SXL scleral biomechanical property and outcome in the human eye.
Topics: Humans; Collagen; Cornea; Cross-Linking Reagents; Myopia, Degenerative; Sclera
PubMed: 38153964
DOI: 10.4103/IJO.IJO_1392_23 -
Asia-Pacific Journal of Ophthalmology... 2017The choroid is the most vascular tissue in the eye and it has been implicated in the pathophysiology of a variety of ocular diseases. A new era of research in the... (Review)
Review
The choroid is the most vascular tissue in the eye and it has been implicated in the pathophysiology of a variety of ocular diseases. A new era of research in the choroid began with the improved ability to visualize this layer and its inner and outer boundaries using spectral domain optical coherence tomography (OCT) with enhanced depth imaging and swept source OCT. The accuracy and precision of qualitative and quan-titative assessments of the choroidal layer support the potential use of OCT-derived choroidal parameters for diagnosis, monitoring of disease progression, planning surgical access, and evaluating treatment response. Although there is increasing interest in measuring choroidal thickness, there is currently no consensus nomenclature to classify choroidal layers and boundaries. Furthermore, the definition and description of the choroidal scleral interface is inconsistent in the literature, contributing to interstudy variation in choroidal thickness measurements. The purpose of this review is to provide an overview of the literature on the definition of choroidal layers and choroidal scleral boundary, review the discrepan-cies, and harmonize the terminology so that a consensus nomenclature can be proposed.
Topics: Choroid; Eye; Humans; Myopia; Posterior Eye Segment; Sclera; Terminology as Topic; Tomography, Optical Coherence
PubMed: 28161920
DOI: 10.22608/APO.201698 -
Scientific Reports Nov 2022Tractional tethering by the optic nerve (ON) on the eye as it rotates towards the midline in adduction is a significant ocular mechanical load and has been suggested as...
Tractional tethering by the optic nerve (ON) on the eye as it rotates towards the midline in adduction is a significant ocular mechanical load and has been suggested as a cause of ON damage induced by repetitive eye movements. We designed an ocular finite element model (FEM) simulating 6° incremental adduction beyond the initial configuration of 26° adduction that is the observed threshold for ON tethering. This FEM permitted sensitivity analysis of ON tethering using observed material property variations in measured hyperelasticity of the anterior, equatorial, posterior, and peripapillary sclera; and the ON and its sheath. The FEM predicted that adduction beyond the initiation of ON tethering concentrates stress and strain on the temporal side of the optic disc and peripapillary sclera, the ON sheath junction with the sclera, and retrolaminar ON neural tissue. However, some unfavorable combinations of tissue properties within the published ranges imposed higher stresses in these regions. With the least favorable combinations of tissue properties, adduction tethering was predicted to stress the ON junction and peripapillary sclera more than extreme conditions of intraocular and intracranial pressure. These simulations support the concept that ON tethering in adduction could induce mechanical stresses that might contribute to ON damage.
Topics: Humans; Finite Element Analysis; Optic Nerve; Optic Disk; Eye Movements; Sclera; Intraocular Pressure; Biomechanical Phenomena
PubMed: 36347907
DOI: 10.1038/s41598-022-22899-2 -
Journal of Biomechanical Engineering Jun 2022Elevated intraocular pressure (IOP) may cause mechanical injuries to the optic nerve head (ONH) and the peripapillary tissues in glaucoma. Previous studies have reported...
Elevated intraocular pressure (IOP) may cause mechanical injuries to the optic nerve head (ONH) and the peripapillary tissues in glaucoma. Previous studies have reported the mechanical deformation of the ONH and the peripapillary sclera (PPS) at elevated IOP. The deformation of the peripapillary retina (PPR) has not been well-characterized. Here we applied high-frequency ultrasound elastography to map and quantify PPR deformation, and compared PPR, PPS and ONH deformation in the same eye. Whole globe inflation was performed in ten human donor eyes. High-frequency ultrasound scans of the posterior eye were acquired while IOP was raised from 5 to 30 mmHg. A correlation-based ultrasound speckle tracking algorithm was used to compute pressure-induced displacements within the scanned tissue cross sections. Radial, tangential, and shear strains were calculated for the PPR, PPS, and ONH regions. In PPR, shear was significantly larger in magnitude than radial and tangential strains. Strain maps showed localized high shear and high tangential strains in PPR. In comparison to PPS and ONH, PPR had greater shear and a similar level of tangential strain. Surprisingly, PPR radial compression was minimal and significantly smaller than that in PPS. These results provide new insights into PPR deformation in response of IOP elevation, suggesting that shear rather than compression was likely the primary mode of IOP-induced mechanical insult in PPR. High shear, especially localized high shear, may contribute to the mechanical damage of this tissue in glaucoma.
Topics: Elasticity Imaging Techniques; Glaucoma; Humans; Intraocular Pressure; Optic Disk; Sclera
PubMed: 35001106
DOI: 10.1115/1.4053450 -
Investigative Ophthalmology & Visual... Aug 2014The structure and biomechanics of the sclera and cornea are central to several eye diseases such as glaucoma and myopia. However, their roles remain unclear, partly...
PURPOSE
The structure and biomechanics of the sclera and cornea are central to several eye diseases such as glaucoma and myopia. However, their roles remain unclear, partly because of limited noninvasive techniques to assess their fibrous microstructures globally, longitudinally, and quantitatively. We hypothesized that magic angle-enhanced magnetic resonance imaging (MRI) can reveal the structural details of the corneoscleral shell and their changes upon intraocular pressure (IOP) elevation.
METHODS
Seven ovine eyes were extracted and fixed at IOP = 50 mm Hg to mimic ocular hypertension, and another 11 eyes were unpressurized. The sclera and cornea were scanned at different angular orientations relative to the main magnetic field inside a 9.4-Tesla MRI scanner. Relative MRI signal intensities and intrinsic transverse relaxation times (T2 and T2*) were determined to quantify the magic angle effect on the corneoscleral shells. Three loaded and eight unloaded tendon samples were scanned as controls.
RESULTS
At magic angle, high-resolution MRI revealed distinct scleral and corneal lamellar fibers, and light/dark bands indicative of collagen fiber crimps in the sclera and tendon. Magic angle enhancement effect was the strongest in tendon and the least strong in cornea. Loaded sclera, cornea, and tendon possessed significantly higher T2 and T2* than unloaded tissues at magic angle.
CONCLUSIONS
Magic angle-enhanced MRI can detect ocular fibrous microstructures without contrast agents or coatings and can reveal their MR tissue property changes with IOP loading. This technique may open up new avenues for assessment of the biomechanical and biochemical properties of ocular tissues in aging and in diseases involving the corneoscleral shell.
Topics: Animals; Collagen; Cornea; Humans; Intraocular Pressure; Magnetic Resonance Imaging; Models, Animal; Models, Biological; Sclera; Sheep
PubMed: 25103267
DOI: 10.1167/iovs.14-14561 -
Journal of Neurochemistry Jul 2011rho(1) GABA(C) receptor antagonists inhibit myopia in chick but the site of this effect is not known. The sclera ultimately determines the shape and size of the globe... (Comparative Study)
Comparative Study
rho(1) GABA(C) receptor antagonists inhibit myopia in chick but the site of this effect is not known. The sclera ultimately determines the shape and size of the globe and thus an untested possibility is that GABA agents have a scleral mechanism. Whether rho(1) GABA(C) receptors are expressed and located in chick sclera is unknown. Real-time PCR, western blot and immunohistochemistry were used to determine whether rho1 GABA(C) receptors are expressed and located in chick fibrous and cartilaginous sclera. Both layers of the chick sclera were positive for rho1 GABA(C) receptor mRNA (PCR) and protein (western blot) expression and labeling was observed in both fibroblasts and chondrocytes of the fibrous and cartilaginous layers (immunohistochemistry). These investigations clearly show that chick sclera possesses rho(1) GABA(C) receptors. The sclera is thus a potential previously unrecognized site for activity of rho(1) GABA(C) agents.
Topics: Animals; Cartilage; Chickens; Chondrocytes; Fibroblasts; Gene Expression Regulation; Receptors, GABA; Receptors, GABA-A; Sclera; rho-Associated Kinases
PubMed: 21554320
DOI: 10.1111/j.1471-4159.2011.07300.x -
Indian Journal of Ophthalmology Apr 2022Detaching a rectus muscle irreparably destroys its ciliary artery circulation which also supplies the anterior segment of the eye.
BACKGROUND
Detaching a rectus muscle irreparably destroys its ciliary artery circulation which also supplies the anterior segment of the eye.
PURPOSE
To educate strabismus surgeons about a method of detaching a muscle without compromising anterior segment circulation.
SYNOPSIS
A limbal based conjunctival incision is made. The muscle is identified, separated from its attachments and secured with 6-0 Vicryl. The anterior ciliary vessel supplying it is isolated by making a small snip incision in the muscle capsule with delicate blunt dissection parallel to the anterior ciliary artery The muscle is detached from its original insertion. The muscle is tied to sclera at the intended point of recession. The intact anterior ciliary artery, thus will continue to function, untouched.
HIGHLIGHTS
We recommend pre-placing the sutures in the muscle and also in the sclera at the point of reattachment to avoid possible stretching and breaking of anterior ciliary vessels at the time of muscle detachment and also to dissect the artery free from muscle several millimeters more than the intended recession in order to spare the anterior ciliary circulation in strabismus surgery.
VIDEO LINK
https://youtu.be/Bn050Ihu9rU.
Topics: Conjunctiva; Humans; Ischemia; Oculomotor Muscles; Sclera; Strabismus; Surgical Wound
PubMed: 35326085
DOI: 10.4103/ijo.IJO_629_22 -
Cell Communication and Signaling : CCS Oct 2022Frameshift mutations in LRPAP1 are responsible for autosomal recessive high myopia in human beings but its underlying mechanism remains elusive. This study aims to...
BACKGROUND
Frameshift mutations in LRPAP1 are responsible for autosomal recessive high myopia in human beings but its underlying mechanism remains elusive. This study aims to investigate the effect of LRPAP1 defect on ocular refractive development and its involved mechanism.
METHODS
A lrpap1 mutant zebrafish line with homozygous frameshift mutation was generated by CRISPR/Cas9 technology and confirmed by Sanger sequencing. The ocular refractive phenotype was analyzed by calculating the relative refractive error (RRE) with vivo photography and histological analysis at different development stages, together with examining ocular structure change via transmission electron microscopy. Further, RNA sequencing and bioinformatics analysis were performed. The potentially involved signaling pathway as well as the interacted protein were investigated in vivo.
RESULTS
The lrpap1 homozygous mutant zebrafish line showed myopic phenotype. Specifically, the mutant lines showed larger eye axial length-to-body length in one-month old individuals and a myopic shift with an RRE that changed after two months. Collagen fibers became thinning and disordered in the sclera. Further, RNA sequencing and bioinformatics analysis indicated that apoptosis signaling was activated in mutant line; this was further confirmed by acridine orange and TUNEL staining. Moreover, the expression of TGF-β protein was elevated in the mutant lines. Finally, the treatment of wild-type embryos with a TGF-β agonist aggravated the degree of eyeball apoptosis; conversely, the use of a TGF-β inhibitor mitigated apoptosis in mutant embryos.
CONCLUSION
The study provides functional evidence of a link between lrpap1 and myopia, suggesting that lrpap1 deficiency could lead to myopia through TGF-β-induced apoptosis signaling. Video abstract.
Topics: Animals; Humans; Acridine Orange; Apoptosis; Collagen; Myopia; Sclera; Transforming Growth Factor beta; Zebrafish; LDL-Receptor Related Protein-Associated Protein; Zebrafish Proteins
PubMed: 36261846
DOI: 10.1186/s12964-022-00970-9 -
Indian Journal of Ophthalmology Nov 2020In this technique, the lamellar scleral tunnel is fashioned to cover IOL haptics and autologous blood is used to close the conjunctiva, which alleviates the need for...
In this technique, the lamellar scleral tunnel is fashioned to cover IOL haptics and autologous blood is used to close the conjunctiva, which alleviates the need for fibrin glue. The cornea is marked at four and 10'O clock meridian, and 2 mm incision is made on the conjunctiva. A lamellar scleral tunnel is fashioned 2 mm superior on one side and 2 mm inferior on the other side of this mark. The IOL is inserted into the anterior chamber and the haptics are exteriorized using bent 26-gauge hypodermic needle, flanged, and buried in the tunnel. A visible conjunctival blood vessel is punctured, allowing the blood to pool underneath the conjunctiva. The conjunctiva is approximated with the help of blood coagulum and allowed to remain dry for 3 min. Lamellar scleral tunnels give adequate cover to haptics, and autologous blood can be used to glue the conjunctival flaps instead of fibrin glue.
Topics: Humans; Lens Implantation, Intraocular; Lenses, Intraocular; Sclera; Sclerostomy; Suture Techniques; Visual Acuity
PubMed: 33120646
DOI: 10.4103/ijo.IJO_129_20 -
BioMed Research International 2014Time domain (TD) and spectral domain (SD) optical coherence tomography (OCT) are cross-sectional, noncontact, high-resolution diagnostic modalities for posterior and... (Review)
Review
Time domain (TD) and spectral domain (SD) optical coherence tomography (OCT) are cross-sectional, noncontact, high-resolution diagnostic modalities for posterior and anterior segment (AS) imaging. The AS-OCT provides tomographic imaging of the cornea, iris, lens, and anterior chamber (AC) angle in several ophthalmic diseases. In glaucoma, AS-OCT is utilized to evaluate the morphology of AS structures involved in the pathogenesis of the disease, to obtain morphometric measures of the AC, to evaluate the suitability for laser or surgical approaches, and to assess modifications after treatment. In patients undergoing surgery, AS-OCT is crucial in the evaluation of the filtering bleb functionality, permitting a combined qualitative and quantitative analysis. In this field, AS-OCT may help clinicians in distinguishing between functioning and nonfunctioning blebs by classifying their macroscopic morphology, describing bleb-wall features, bleb cavity, and scleral opening. This information is critical in recognizing signs of filtration failure earlier than the clinical approach and in planning the appropriate timing for management procedures in failing blebs. In this review, we summarize the applications of AS-OCT in the conjunctival bleb assessment.
Topics: Anterior Eye Segment; Diagnostic Imaging; Glaucoma, Open-Angle; Humans; Intraocular Pressure; Ophthalmologic Surgical Procedures; Radiography; Sclera; Tomography, Optical Coherence
PubMed: 25136603
DOI: 10.1155/2014/610623