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Anatomical Record (Hoboken, N.J. : 2007) Jan 2020The ocular skeleton, composed of the scleral cartilage and scleral ossicles, is present in many vertebrates. The morphology of the scleral cartilage and ossicles varies... (Review)
Review
The ocular skeleton, composed of the scleral cartilage and scleral ossicles, is present in many vertebrates. The morphology of the scleral cartilage and ossicles varies within different extant reptiles (including birds) and also varies dramatically from the morphology in extant teleosts. This incredible range of diverse morphologies is the result of millions of years of evolution. Both the position of these elements within the eye and the timing of development vary amongst different vertebrates. While the development of both the scleral cartilage and scleral ossicles is somewhat understood in reptiles and in teleosts, the functional advantage of these elements is still debated. Most reptiles have a multi-component scleral ossicle ring composed of a series of flat bone plates and a scleral cartilage cup lining the retina, some sharks have calcified cartilage plates, and some teleosts have two bones while most others only have a ring of scleral cartilage. The data presented shows that different vertebrates have adapted to similar selective pressures in different ways. However, the reason why sarcopterygians have a series of overlapping bones in the sclera remains unclear. A better understanding of the ocular skeletal diversity in Reptilia as well as a better understanding of the mechanisms of vision within different environments (i.e., air vs. water) and that used by secondarily aquatic organisms is needed. This review discusses the observed variation in morphology and development of the ocular skeleton in the context of evolution and highlights our knowledge gaps in these areas. Anat Rec, 2018. © 2018 American Association for Anatomy.
Topics: Animals; Biological Evolution; Bone and Bones; Eye; Reptiles; Sclera
PubMed: 30548203
DOI: 10.1002/ar.24043 -
ACS Biomaterials Science & Engineering Dec 2022Scleras are mainly used for the treatment of glaucoma, eyelid damage, and scleral ulcers. Given that the sclera and cornea collectively constitute the complete external...
Scleras are mainly used for the treatment of glaucoma, eyelid damage, and scleral ulcers. Given that the sclera and cornea collectively constitute the complete external structure of the eyeball and both have the same tissue and cell origin, we attempted to identify scleral materials to treat lamellar and penetrating corneal injuries. Based on research in our center, antigenic components in decellularized porcine sclera (DPS) were removed using a simplified decellularization method, leaving the collagen structure and active components undamaged. DPS preserved the mechanical properties and did not significantly inhibit the proliferation and replication of human corneal epithelial cells. In vivo, the graft epithelium healed well after lamellar and penetrating scleral grafting, and the graft thickness did not change evidently. DPS can resist suture traction during scleral transplantation and maintain anterior chamber stability until day 28 post-operatively, especially in penetrating repairs. No obvious immune rejection of lamellar or penetrating scleral grafts was found 28 days after DPS transplantation. This study shows that DPS could be used as an alternative material for the emergency repair of corneal perforations and lamellar injuries, representing another application of sclera.
Topics: Humans; Swine; Animals; Corneal Perforation; Sclera; Cornea
PubMed: 36454184
DOI: 10.1021/acsbiomaterials.2c00972 -
Experimental Eye Research May 2023Collagen is the main load-bearing component of cornea and sclera. When stretched, both of these tissues exhibit a behavior known as collagen fiber recruitment. In...
Collagen is the main load-bearing component of cornea and sclera. When stretched, both of these tissues exhibit a behavior known as collagen fiber recruitment. In recruitment, as the tissues stretch the constitutive collagen fibers lose their natural waviness, progressively straightening. Recruited, straight, fibers bear substantially more mechanical load than non-recruited, wavy, fibers. As such, the process of recruitment underlies the well-established nonlinear macroscopic behavior of the corneoscleral shell. Recruitment has an interesting implication: when recruitment is incomplete, only a fraction of the collagen fibers is actually contributing to bear the loads, with the rest remaining "in reserve". In other words, at a given intraocular pressure (IOP), it is possible that not all the collagen fibers of the cornea and sclera are actually contributing to bear the loads. To the best of our knowledge, the fraction of corneoscleral shell fibers recruited and contributing to bear the load of IOP has not been reported. Our goal was to obtain regionally-resolved estimates of the fraction of corneoscleral collagen fibers recruited and in reserve. We developed a fiber-based microstructural constitutive model that could account for collagen fiber undulations or crimp via their tortuosity. We used experimentally-measured collagen fiber crimp tortuosity distributions in human eyes to derive region-specific nonlinear hyperelastic mechanical properties. We then built a three-dimensional axisymmetric model of the globe, assigning region-specific mechanical properties and regional anisotropy. The model was used to simulate the IOP-induced shell deformation. The model-predicted tissue stretch was then used to quantify collagen recruitment within each shell region. The calculations showed that, at low IOPs, collagen fibers in the posterior equator were recruited the fastest, such that at a physiologic IOP of 15 mmHg, over 90% of fibers were recruited, compared with only a third in the cornea and the peripapillary sclera. The differences in recruitment between regions, in turn, mean that at a physiologic IOP the posterior equator had a fiber reserve of only 10%, whereas the cornea and peripapillary sclera had two thirds. At an elevated IOP of 50 mmHg, collagen fibers in the limbus and the anterior/posterior equator were almost fully recruited, compared with 90% in the cornea and the posterior sclera, and 70% in the peripapillary sclera and the equator. That even at such an elevated IOP not all the fibers were recruited suggests that there are likely other conditions that challenge the corneoscleral tissues even more than IOP. The fraction of fibers recruited may have other potential implications. For example, fibers that are not bearing loads may be more susceptible to enzymatic digestion or remodeling. Similarly, it may be possible to control tissue stiffness through the fraction of recruited fibers without the need to add or remove collagen.
Topics: Humans; Intraocular Pressure; Glaucoma; Extracellular Matrix; Collagen; Tonometry, Ocular; Sclera; Biomechanical Phenomena
PubMed: 36935071
DOI: 10.1016/j.exer.2023.109446 -
Die Ophthalmologie Oct 2022
Topics: Cooperative Behavior; Interpersonal Relations; Sclera; Trabeculectomy
PubMed: 36214906
DOI: 10.1007/s00347-022-01727-y -
Nature Biomedical Engineering Aug 2023In myopic eyes, pathological remodelling of collagen in the posterior sclera has mostly been observed ex vivo. Here we report the development of triple-input...
In myopic eyes, pathological remodelling of collagen in the posterior sclera has mostly been observed ex vivo. Here we report the development of triple-input polarization-sensitive optical coherence tomography (OCT) for measuring posterior scleral birefringence. In guinea pigs and humans, the technique offers superior imaging sensitivities and accuracies than dual-input polarization-sensitive OCT. In 8-week-long studies with young guinea pigs, scleral birefringence was positively correlated with spherical equivalent refractive errors and predicted the onset of myopia. In a cross-sectional study involving adult individuals, scleral birefringence was associated with myopia status and negatively correlated with refractive errors. Triple-input polarization-sensitive OCT may help establish posterior scleral birefringence as a non-invasive biomarker for assessing the progression of myopia.
Topics: Adult; Humans; Animals; Guinea Pigs; Sclera; Birefringence; Cross-Sectional Studies; Myopia; Biomarkers
PubMed: 37365268
DOI: 10.1038/s41551-023-01062-w -
Contact Lens & Anterior Eye : the... Aug 2021To assess the correlation of the scleral shape and corneal tomographic parameters in keratoconus.
PURPOSE
To assess the correlation of the scleral shape and corneal tomographic parameters in keratoconus.
METHODS
Twenty eyes of 15 keratoconus patients with no previous specialty lens wear or ocular surgery were included in this study. Corneal imaging was obtained with the Pentacam HR and three-dimensional (3D) corneoscleral maps were acquired using the Eye Surface Profiler, ESP. Sagittal height was calculated at the central corneal level (annulus of 0-4 mm radius), peripheral cornea (annulus 4-6 mm radius) and sclera (annulus 6-8 mm radius) using ESP maps and Pentacam HR (exclusively for the central cornea). The flattest and steepest regions of each annulus and the circumferential scleral asymmetry were calculated based on custom-made software. The Pearson correlation coefficient (r) was used to evaluate the correlation between corneal parameters as measured by Pentacam HR and scleral asymmetry.
RESULTS
Anterior corneal parameters, such as flattest and steepest keratometry, were found to be correlated with scleral asymmetry in keratoconus (all r>0.5, p < 0.05). In contrast, anterior astigmatism showed poor correlation with the level of scleral irregularity (r=-0.11; p = 0.32). Other disease-specific parameters pertaining to the posterior corneal curvature and corneal thickness were not correlated with scleral asymmetry. The steepest regions of the central cornea, peripheral cornea, and sclera tended to share a common angle (r = 0.92; p < 0.001 for central cornea compared to sclera).
CONCLUSION
Anterior corneal parameters measured by corneal imaging are associated with the level of scleral asymmetry and the orientation of the steepest area of the sclera in eyes with keratoconus.
Topics: Astigmatism; Cornea; Corneal Topography; Humans; Keratoconus; Sclera
PubMed: 32938544
DOI: 10.1016/j.clae.2020.08.010 -
JAMA Ophthalmology Dec 2022
Topics: Humans; Sclera
PubMed: 36301520
DOI: 10.1001/jamaophthalmol.2022.4402 -
Microscopy Research and Technique Jun 2023The conjunctions of the cornea and sclera in the eyes of donkeys, cattle, dogs, sheep, pigs and rabbits, regardless of gender, were examined in this study. No animals...
The conjunctions of the cornea and sclera in the eyes of donkeys, cattle, dogs, sheep, pigs and rabbits, regardless of gender, were examined in this study. No animals were specifically sacrificed for this investigation. Scanning electron microscopy, light microscopy, and dissecting microscopy were used in this research. In the limbus of all the animals investigated, the cornea and sclera fused in accordance with a pattern. At the corneo-scleral junction, the sclera was situated anteriorly and the cornea posteriorly in the dorsal and ventral sections of the bulbus oculi. In the medial and lateral parts of the eyeball, the cornea and sclera were facing each other and interlaced. Pigmentation and the sulcus scleralis externus could be used to identify the macro-and micro-anatomical boundaries of the limbus. In addition, the cytoplasm of basal epithelial cells shrank, signaling the end of the corneal epithelium and the start of the conjunctival epithelium. The presence of Bowman's membrane in cattle and sheep eyes was definitely determined in histological examinations. Bowman's membrane in these animals came to an end at the limbus, which is where the conjunctival epithelium starts and the corneal epithelium ends. In all areas of the cornea, Bowman's membrane revealed irregular, abrupt thickening and thinning. The corneal epithelium was thick in the vertex and thinner towards the limbus, whereas Descemet's membrane was thin in the center (vertex) and thick in the periphery (near the limbus). In this study, pictures and diagrams were used to illustrate the general anatomical, histological, and morphometric characteristics of the limbus in the species under investigation. The data from our study showed that the limbus region of the bulbus oculi was narrow in the lateral and medial parts and wide in the dorsal and ventral parts. This was confirmed in the studied animals as a general rule. The width value will undoubtedly affect the number of cells covered by the regions. It is conceivable that these cells will play a significant role in the decision of where to perform surgical procedures in order to promote wound healing, giving doctors an advantage. In this circumstances, we think that the limbus should be studied in terms of clinical methods because it has different shapes depending on the species and the position of the bulbus.
Topics: Rabbits; Animals; Cattle; Sheep; Dogs; Swine; Sclera; Cornea; Epithelium, Corneal; Microscopy, Electron, Scanning; Epithelial Cells
PubMed: 36929228
DOI: 10.1002/jemt.24314 -
Journal of Cataract and Refractive... Dec 2021Current scleral suture fixation techniques pose challenges for highly complex eyes. A scleral suture fixation technique using a snare that is fashioned out of a 27-gauge...
Current scleral suture fixation techniques pose challenges for highly complex eyes. A scleral suture fixation technique using a snare that is fashioned out of a 27-gauge needle and 8-0 nylon suture is described. This technique is well-suited for scleral suture fixation in complex eyes because it reduces risk factors for intraoperative and postoperative complications, simplifies intraocular maneuvers, minimizes surgical trauma, and does not require specialized microinstrumentation.
Topics: Humans; Lens Implantation, Intraocular; Lenses, Intraocular; Postoperative Complications; Retrospective Studies; Sclera; Suture Techniques; Sutures
PubMed: 34433778
DOI: 10.1097/j.jcrs.0000000000000800 -
BMC Ophthalmology Mar 2020To study the morphologic and biochemical changes in the retina and sclera induced by form deprivation high myopia (FDHM) in guinea pigs and explore the possible... (Comparative Study)
Comparative Study
BACKGROUND
To study the morphologic and biochemical changes in the retina and sclera induced by form deprivation high myopia (FDHM) in guinea pigs and explore the possible mechanisms of FDHM formation.
METHODS
Forty 3-week-old guinea pigs were randomized into the blank control (Group I, 20 cases) and model groups (20 cases). In the model group, the right eyes of the guinea pigs were sutured for 8 weeks to induce FDHM (Group II) and the left eyes were considered a self-control group (Group III). The refractive errors were measured with retinoscopy. The anterior chamber depth (AC), lens thickness (L), vitreous chamber depth (V) and axial length (AL) were measured using ultrasonometry A. Retinal and scleral morphology and ultrastructural features were observed with light and electron microscopy. The malondialdehyde (MDA) content and superoxide dismutase (SOD) activity in the retina and sclera were detected with a chemical colorimetric assay.
RESULTS
After 8 weeks of stitching, the refractive errors of Group II changed from (+ 3.59 ± 0.33) D to (- 7.96 ± 0.55) D, and these values were significantly higher than those of Group I (+ 0.89 ± 0.32) D and Group III (- 0.55 ± 0.49) D (P < 0.05). The vitreous chamber depth (4.12 ± 0.13) mm and axial length (8.93 ± 0.22) mm of Group II were significantly longer than those of Group I [(3.71 ± 0.23) mm and (7.95 ± 0.37) mm, respectively] and Group III [(3.93 ± 0.04) mm and (8.01 ± 0.15) mm, respectively] (P < 0.05). With the prolongation of form deprivation (FD), the retina and scleral tissues showed thinning, the ganglion cell and inner and outer nuclear layers of the retina became decreased, and the arrangement was disordered. In Group II, the SOD activity was significantly lower than that in Group I and Group III; the MDA content was significantly higher than that in Group I and Group III. The differences were statistically significant (P < 0.05).
CONCLUSIONS
These findings suggested that in the FDHM guinea pigs model, the refractive errors, the vitreous chamber depth, and axial length increased significantly with prolongation of monocular FD time, and morphological structural changes in the retina and sclera were observed. Oxygen free radicals might participate in the formation of FDHM.
Topics: Animals; Disease Models, Animal; Eye Proteins; Guinea Pigs; Myopia, Degenerative; Retina; Retinoscopy; Sclera
PubMed: 32178637
DOI: 10.1186/s12886-020-01377-1