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Experimental Eye Research Dec 2023The collagen fibers of the corneoscleral shell play a central role in the eye mechanical behavior. Although it is well-known that these fibers form a complex...
The collagen fibers of the corneoscleral shell play a central role in the eye mechanical behavior. Although it is well-known that these fibers form a complex three-dimensional interwoven structure, biomechanical and microstructural studies often assume that the fibers are aligned in-plane with the tissues. This is convenient as it removes the out-of-plane components and allows focusing on the 2D maps of in-plane fiber organization that are often quite complex. The simplification, however, risks missing potentially important aspects of the tissue architecture and mechanics. In the cornea, for instance, fibers with high in-depth inclination have been shown to be mechanically important. Outside the cornea, the in-depth fiber orientations have not been characterized, preventing a deeper understanding of their potential roles. Our goal was to characterize in-depth collagen fiber organization over the whole corneoscleral shell. Seven sheep whole-globe axial sections from eyes fixed at an IOP of 50 mmHg were imaged using polarized light microscopy to measure collagen fiber orientations and density. In-depth fiber orientation distributions and anisotropy (degree of fiber alignment) accounting for fiber density were quantified over the whole sclera and in 15 regions: central cornea, peripheral cornea, limbus, anterior equator, equator, posterior equator, posterior sclera and peripapillary sclera on both nasal and temporal sides. Orientation distributions were fitted using a combination of a uniform distribution and a sum of π-periodic von Mises distributions, each with three parameters: primary orientation μ, fiber concentration factor k, and weighting factor a. To study the features of fibers that are not in-plane, i.e., fiber inclination, we quantified the percentage of inclined fibers and the range of inclination angles (half width at half maximum of inclination angle distribution). Our measurements showed that the fibers were not uniformly in-plane but exhibited instead a wide range of in-depth orientations, with fibers significantly more aligned in-plane in the anterior parts of the globe. We found that fitting the orientation distributions required between one and three π-periodic von Mises distributions with different primary orientations and fiber concentration factors. Regions of the posterior globe, particularly on the temporal side, had a larger percentage of inclined fibers and a larger range of inclination angles than anterior and equatorial regions. Variations of orientation distributions and anisotropies may imply varying out-of-plane tissue mechanical properties around the eye globe. Out-of-plane fibers could indicate fiber interweaving, not necessarily long, inclined fibers. Effects of small-scale fiber undulations, or crimp, were minimized by using tissues from eyes at high IOPs. These fiber features also play a role in tissue stiffness and stability and are therefore also important experimental information.
Topics: Animals; Sheep; Collagen; Cornea; Extracellular Matrix; Sclera; Microscopy, Polarization; Biomechanical Phenomena
PubMed: 37898229
DOI: 10.1016/j.exer.2023.109701 -
Klinische Monatsblatter Fur... Aug 2023Early (< 3 months) intraocular lens (IOL) dislocation occurs due to insufficient fixation in the capsular bag, while late dislocation (≥ 3 months) is due to...
Early (< 3 months) intraocular lens (IOL) dislocation occurs due to insufficient fixation in the capsular bag, while late dislocation (≥ 3 months) is due to increasing insufficiency of the zonular apparatus. Iris-fixated IOL (IFIOL) and suture- or sutureless-fixated scleral IOL (SFIOL) are currently the most commonly used methods when IOL exchange is indicated. Different methods of scleral fixation with or without sutures have been described. The most important techniques are summarised in this paper. IFIOL and SFIOL allow comparable visual outcomes but differ in their risk profile. The decision of which method to use should be made case by case and in accordance with the surgeon's preference.
Topics: Humans; Lens Implantation, Intraocular; Lenses, Intraocular; Iris; Causality; Lens Capsule, Crystalline; Sclera; Suture Techniques; Retrospective Studies; Postoperative Complications
PubMed: 37494272
DOI: 10.1055/a-2074-9028 -
Biomedicines Sep 2023Endogenous ochronosis, also known as alkaptonuria, is a rare disease known for its bluish-black discoloration of the skin, sclerae, and pinnae, as well as urine that...
Endogenous ochronosis, also known as alkaptonuria, is a rare disease known for its bluish-black discoloration of the skin, sclerae, and pinnae, as well as urine that turns black upon standing. Though rarely fatal, joint degradation is a common sequela, and many patients require multiple large joint arthroplasties throughout their lifetime. Though many aspects of the pathophysiological mechanisms of the disease have been described, questions remain, such as how the initiation of ochronotic pigmentation is prompted and the specific circumstances that make some tissues more resistant to pigmentation-related damage than others. In this report, we present the case of an 83-year-old female previously diagnosed with alkaptonuria including high-quality arthroscopic images displaying the fraying of articular cartilage. We also offer a summary of the latest literature on the pathophysiological mechanisms of the disease, including cellular-level changes observed in ochronotic chondrocytes, biochemical and mechanical alterations to the cartilaginous extracellular matrix, and patterns of pigmentation and joint degradation observed in humans and mice models. With these, we present an overview of the mechanisms of ochronotic chondropathy and joint degradation as the processes are currently understood. While alkaptonuria itself is rare, it has been termed a "fundamental disease," implying that its study and greater understanding have the potential to lead to insights in skeletal biology in general, as well as more common pathologies such as osteoarthritis and their potential treatment mechanisms.
PubMed: 37892999
DOI: 10.3390/biomedicines11102625 -
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 -
International Journal of Molecular... May 2024Macrophages form a crucial component of the innate immune system, and their activation is indispensable for various aspects of immune and inflammatory processes, tissue... (Review)
Review
Macrophages form a crucial component of the innate immune system, and their activation is indispensable for various aspects of immune and inflammatory processes, tissue repair, and maintenance of the balance of the body's state. Macrophages are found in all ocular tissues, spanning from the front surface, including the cornea, to the posterior pole, represented by the choroid/sclera. The neural retina is also populated by specialised resident macrophages called microglia. The plasticity of microglia/macrophages allows them to adopt different activation states in response to changes in the tissue microenvironment. When exposed to various factors, microglia/macrophages polarise into distinct phenotypes, each exhibiting unique characteristics and roles. Furthermore, extensive research has indicated a close association between microglia/macrophage polarisation and the development and reversal of various intraocular diseases. The present article provides a review of the recent findings on the association between microglia/macrophage polarisation and ocular pathological processes (including autoimmune uveitis, optic neuritis, sympathetic ophthalmia, retinitis pigmentosa, glaucoma, proliferative vitreoretinopathy, subretinal fibrosis, uveal melanoma, ischaemic optic neuropathy, retinopathy of prematurity and choroidal neovascularization). The paradoxical role of microglia/macrophage polarisation in retinopathy of prematurity is also discussed. Several studies have shown that microglia/macrophages are involved in the pathology of ocular diseases. However, it is required to further explore the relevant mechanisms and regulatory processes. The relationship between the functional diversity displayed by microglia/macrophage polarisation and intraocular diseases may provide a new direction for the treatment of intraocular diseases.
Topics: Infant, Newborn; Humans; Microglia; Retinopathy of Prematurity; Retina; Macrophages; Phenotype
PubMed: 38551157
DOI: 10.3892/ijmm.2024.5369 -
Journal of Autoimmunity Apr 2024Scleritis is a severe and painful ophthalmic disorder, in which a pathogenic role for collagen-directed autoimmunity was repeatedly suggested. We evaluated the presence...
Scleritis is a severe and painful ophthalmic disorder, in which a pathogenic role for collagen-directed autoimmunity was repeatedly suggested. We evaluated the presence of sclera-specific antibodies in a large cohort of patients with non-infectious scleritis. Therefore, we prospectively collected serum samples from 121 patients with non-infectious scleritis in a multicenter cohort study in the Netherlands. In addition, healthy (n = 39) and uveitis controls (n = 48) were included. Serum samples were tested for anti-native human type II collagen antibodies using a validated enzyme-linked immunosorbent assay (ELISA). Further, sclera-specific antibodies were determined using indirect immunofluorescence (IIF) on primate retinal/scleral cryosections. Lastly, human leukocyte antigen (HLA) typing was performed in 111 patients with scleritis. Anti-type II collagen antibodies were found in 13% of scleritis patients, in 10% of healthy controls and in 11% of uveitis controls (p = 0.91). A specific reaction to scleral nerve tissue on IIF was observed in 33% of patients with scleritis, which was higher than in healthy controls (11%; p = 0.01), but similar to uveitis controls (25%; p = 0.36). Reactivity to the scleral nerve tissue was significantly associated with earlier onset of scleritis (48 versus 56 years; p < 0.001), bilateral involvement (65% versus 42%; p = 0.01), and less frequent development of scleral necrosis (5% versus 22%; p = 0.02). HLA-B27 was found to be twice as prevalent in patients with scleritis (15.3%) compared to a healthy population (7.2%). In conclusion, scleral nerve autoantibody reactivity was more common in scleritis and uveitis patients in contrast to healthy controls. Further research is needed to characterize these scleral-nerve directed antibodies and assess their clinical value.
Topics: Animals; Humans; Autoimmunity; Cohort Studies; Sclera; Scleritis; Uveitis
PubMed: 38368769
DOI: 10.1016/j.jaut.2024.103178 -
Diagnostics (Basel, Switzerland) Jan 2024Since its introduction, optical coherence tomography (OCT) has revolutionized the field of ophthalmology and has now become an indispensable, noninvasive tool in daily... (Review)
Review
Since its introduction, optical coherence tomography (OCT) has revolutionized the field of ophthalmology and has now become an indispensable, noninvasive tool in daily practice. Most ophthalmologists are familiar with its use in the assessment and monitoring of retinal and optic nerve diseases. However, it also has important applications in the assessment of anterior segment structures, including the cornea, conjunctiva, sclera, anterior chamber, and iris, and has the potential to transform the clinical examination of these structures. In this review, we aim to provide a comprehensive overview of the potential clinical utility of anterior segment OCT (AS-OCT) for a wide range of anterior segment pathologies, such as conjunctival neoplasia, pterygium, scleritis, keratoconus, corneal dystrophies, and infectious/noninfectious keratitis. In addition, the clinical applications of AS-OCT (including epithelial mapping) in preoperative planning and postoperative monitoring for corneal and refractive surgeries are discussed.
PubMed: 38248000
DOI: 10.3390/diagnostics14020122 -
International Ophthalmology Sep 2023We developed model eyes using six polymer materials to determine which materials were most appropriate in simulating real human sclera and extraocular muscle (EOM).
PURPOSE
We developed model eyes using six polymer materials to determine which materials were most appropriate in simulating real human sclera and extraocular muscle (EOM).
METHODS
Five three-dimensional (3-D) printed polymers (FlexFill, PolyFlex, PCTPE, Soft PLA, and NinjaFlex) and one silicone material were systematically tested by board-certified ophthalmologists and senior ophthalmology residents. Material testing included scleral passes with 6-0 Vicryl sutures through each eye model. Participants completed a survey designed to collect demographic data, subjective assessment of each material's accuracy in simulating real human sclera and EOM, and a ranking for each polymer material to identify which would be most suitable for an ophthalmic surgery training tool. The Wilcoxon signed-rank test was conducted to determine if there was a statistically significant difference in the distribution of ranks between the polymer materials.
RESULTS
The distribution of ranks for silicone material's "sclera" and "EOM" components were statistically significantly higher than that of all other polymer materials (all p < 0.05). Silicone material received the highest rank for both "sclera" and "EOM" components. Survey results indicated that the silicone material effectively simulated real human tissue.
CONCLUSION
Silicone model eyes performed better than 3-D printed polymers as an educational tool for incorporation into a microsurgical training curriculum. Silicone models provide a low-cost teaching tool that allows for independent practice of microsurgical techniques without requiring a wet-laboratory facility.
Topics: Humans; Internship and Residency; Polymers; Clinical Competence; Ophthalmology; Silicones
PubMed: 37217809
DOI: 10.1007/s10792-023-02736-9 -
Journal of Clinical Rheumatology :... Oct 2023
Topics: Humans; Arthritis, Rheumatoid; Sclera
PubMed: 37370216
DOI: 10.1097/RHU.0000000000001994 -
Acta Biomaterialia Mar 2024The contact and pull-off tests and finite element simulations were used to study the extraocular muscle-sclera adhesion and its variation with eye movement in this...
The contact and pull-off tests and finite element simulations were used to study the extraocular muscle-sclera adhesion and its variation with eye movement in this research. The effect of the adhesion on the eye movements was also determined using equilibrium equations of eye motion. The contact and pull-off tests were performed using quasi-static and non-quasi-static unloading velocities. Finite element models were developed to simulate these tests in cases with high unloading velocity which could not be achieved experimentally. These velocities range from the eye's fixation to saccade movement. The tests confirmed that the pull-off force is related to the unloading velocity. As the unloading velocity increases, the pull-off force increases, with an insignificant increase at the high ocular saccade velocities. The adhesion moment between the extraocular muscles and the sclera exhibited the same trend, increasing with higher eye movement velocities and higher separation angles between the two interfaces. The adhesion moment ratio to the total moment was calculated by the traditional model and the active pulley model of eye movements to assess the effect of adhesion behavior on eye movements. At the high ocular saccade velocities (about 461 deg/s), the adhesion moment was found to be 0.53% and 0.50% of the total moment based on the traditional and active pulley models, respectively. The results suggest that the adhesion behavior between the extraocular muscles and the sclera has a negligible effect on eye movements. At the same time, this adhesion behavior can be ignored in eye modeling, which simplifies the model reasonably well. STATEMENT OF SIGNIFICANCE: 1. Adhesion behavior between the extraocular muscles and the sclera at different indenter unloading velocities determined by contact and pull-off tests. 2. A finite element model was developed to simulate the adhesive contact between the extraocular muscles and the sclera at different indenter unloading velocities. The bilinear cohesive zone model was used for adhesive interactions. 3. The elastic modulus and viscoelastic parameters of the extraocular muscle along the thickness direction were obtained by using compressive stress-relaxation tests. 4. The influence of the adhesion moment between the extraocular muscles and the sclera on eye movement was obtained according to the equation of oculomotor balance. The adhesion moment between the extraocular muscles and the sclera was found to increase with increased eye movement velocity and increased separation angle between the two interfaces.
Topics: Eye Movements; Oculomotor Muscles; Movement; Face; Physical Phenomena
PubMed: 38296013
DOI: 10.1016/j.actbio.2024.01.028