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At least 127 records · Page 7Linked to original sources
PubMed2003

Role of the sclera in the development and pathological complications of myopia.

Myopia is one of the most prevalent ocular conditions and is the result of a mismatch between the power of the eye and axial length of the eye. As a result images of distant objects are brought to a focus in front of the retina resulting in blurred vision. In the vast majority of cases the structural cause of myopia is an excessive axial length of the eye, or more specifically the vitreous chamber depth. In about 2% of the general population, the degree of myopia is above 6 dioptres (D) and is termed high myopia. The prevalence of sight-threatening ocular pathology is markedly increased in eyes with high degrees of myopia ( > -6 D). This results from the excessive axial elongation of the eye which, by necessity, must involve the outer coat of the eye, the sclera. Consequently, high myopia is reported as a leading cause of registered blindness and partial sight. Current theories of refractive development acknowledge the pivotal role of the sclera in the control of eye size and the development of myopia. This review considers the major biochemical mechanisms that underlie the normal development of the mammalian sclera and how the scleral structure influences the rate of eye growth during development. The review will characterise the aberrant mechanisms of scleral remodelling which underlie the development of myopia. In describing these mechanisms we highlight how certain critical events in both the early and later stages of myopia development lead to scleral thinning, the loss of scleral tissue, the weakening of the scleral mechanical properties and, ultimately, to the development of posterior staphyloma. This review aims to build on existing models to illustrate that the prevention of aberrant scleral remodelling must be the goal of any long-term therapy for the amelioration of the permanent vision loss associated with high myopia.

Animals↗
PubMed1980

[Effect of a silicone band on the sclera of the human eye - morphological analysis].

Sixteen months after application of an encircling silicon band the morphological condition of the sclera was analysed. The findings were as follows: 1) The silicon band is highly compatible with the sclera and dose not produce a foreign body reaction. 2) The sclera is able to adjust to altered mechanical conditions produced by degenerative and regenerative processes. 3) The polyamide suture material was at least partially unchanged 16 months after implantation but had led to a strong foreign body reaction. The large number of cells containing enlarged polymorphic lysosomes indicate an attempt to break down the polyamide fiber enzymatically by localized cell reactions.

Humans↗
PubMed2005

Enucleation with reverse replacement of sclera as an alternative to conventional evisceration.

BACKGROUND AND OBJECTIVE: To objectively review the results of a technique combining enucleation with evisceration in patients listed for traditional evisceration with preservation of the rectus muscles. MATERIALS AND METHODS: Ten patients who underwent combined enucleation and evisceration with 3 to 36 months of follow-up were identified (average follow-up 14 months). Three eyes were phtihisical, 1 microphthalmic, 1 buphthalmic, 1 a secondary implant following conventional evisceration and 4 non-phtihisical painful eyes. The technique involved enucleation followed by evisceration of the eye contents. Implants, either coral or acrylic, were wrapped in the eviscerated sclera and replaced in the orbit with the posterior pole of the sclera facing anteriorly. The rectus muscles were then resutured onto the sclera. The patients were subsequently recalled and volume replacement, cosmesis and complications were assessed. RESULTS: Three coral and 7 acrylic implants were placed, 2 of 22 mm, 7 of 20 mm and 1 of 18 mm. No complications were encountered, in particular no implant extrusions. Cosmesis was graded good in 9 out of 10 patients. CONCLUSION: Combined enucleation and evisceration allows the selection and placement of an appropriately large-sized implant to achieve good volume replacement with no extrusions in our series. This technique is particularly pertinent as an alternative to standard evisceration in phtihisical eyes.

Adolescent↗
PubMed2000

A comparative study of bovine pericardium (periguard) and homologous sclera as lower eyelid spacer graft analogs in New Zealand white rabbits.

PURPOSE: To compare bovine pericardium (Periguard; Bio-Vascular, Inc., St. Paul, MN, U.S.A.) and homologous sclera as spacer graft analogs in a rabbit model. METHODS: A nonrandomized experimental animal study was conducted. Elliptical subconjunctival implants were placed in one lower eyelid each of 10 rabbits. Five rabbits received homologous sclera implants, and five received bovine pericardium implants. The rabbits were killed 7 weeks later, and the lower eyelids were examined clinically and histopathologically. RESULTS: Rabbit eyelids implanted with Periguard had a more marked inflammatory reaction and more significant collagen lamellar disruption than eyelids implanted with homologous sclera, although clinically they appeared quite similar. CONCLUSIONS: Although bovine pericardium elicited a more intense inflammatory response at the histopathologic level, both implants were similarly tolerated at the clinical level. These findings are consistent with animal and human investigations of bovine pericardium in other parts of the body, and warrant further studies into its potential use in the human eyelid.

Animals↗
PubMed2005

Long-term results after bare sclera pterygium resection with excimer smoothing and local application of mitomycin C.

PURPOSE: To evaluate the long-term results and complications after bare sclera pterygium excision with local application of mitomycin C and consecutive smoothing of the wound area with an excimer laser (PTK). METHODS: This was an observational case series of 133 eyes of 101 patients who underwent pterygium surgery using the bare sclera technique. Thirty-one of these treated eyes (23%) were recurrences with a mean of 3 previous operations. After pterygium surgery, phototherapeutic keratectomy with an ArF:excimer laser was performed in the area of the excision. Additionally, all patients were treated with mitomycin C 0.02% twice daily for 4 days. Median follow-up was 53 months (minimum, 36). RESULTS: In the group with primary pterygia, 3 recurrences occurred after 6, 12, and 28 months (recurrence rate, 2.9%). In the group with previous pterygium operations, 2 recurrences (recurrence rate, 6.4%) were recorded. Uncorrected visual acuity of all treated patients improved from 0.61 preoperatively to 0.79 postoperatively (P < 0.0001), best corrected visual acuity increased from 0.82 to 0.91 (P = 0.0001) [LogMAR]. Mean astigmatism was significantly reduced from 1.54 D preoperatively to 0.61 D postoperatively (P < 0.0001). In 7 eyes, discrete granulomas developed postoperatively (5.3%); in 3 cases (2.3%), dellen formation occurred that persisted for a maximum of 4 months. No further complications were recorded during the follow-up. CONCLUSIONS: Pterygium excision using the bare sclera technique, phototherapeutic keratectomy, and local application of mitomycin C 0.02% eyedrops is a safe method with good functional results and a low recurrence rate.

Corneal Diseases↗
PubMedDate not supplied

Mersilene mesh versus sclera in wrapping hydroxyapatite orbital implants.

PURPOSE: To compare Mersilene mesh versus sclera in wrapping hydroxyapatite orbital implants used in primary enucleation. METHODS: In a prospective, randomized, interventional comparative case series, 60 eyes from 60 consecutive patients were included and randomly allocated for primary enucleation and either Mersilene mesh-wrapped hydroxyapatite (MHA) orbital implant (30 cases, 50%) or sclera-wrapped hydroxyapatite (SHA) orbital implant (30 cases, 50%) under general anesthesia. Complete socket examination was performed at 1 week, 1 month, and then every 3 months after surgery. RESULTS: Mean age was not significantly different (P = 0.08) between patients with MHA (36.43 years) and SHA (28.50 years) orbital implants. The most common cause of enucleation was trauma in both groups (P = 0.09). Patients with MHA had significantly (P = 0.005) longer follow-up time (mean, 11.40 months) than those with SHA (mean, 9.40 months). No exposure was found at last follow-up in the MHA group, but one patient in the SHA group had a small exposure (1 x 1 mm) 1 month after surgery that was conservatively treated. There were no significant postoperative soft tissue complications in either group. CONCLUSIONS: Sclera and Mersilene mesh could be used as a wrapping material for hydroxyapatite orbital implants without significant complications. Absence of disease transmission, low cost, and availability are the main advantages of Mersilene mesh.

Adolescent↗
PubMed1994

Quantitative analysis of the microstructure of the human cornea and sclera using 2-D Fourier methods.

A two-dimensional (2-D) Fourier analysis was used to characterize the microstructure of the human cornea and sclera. The average centre-to-centre spacing of collagen fibrils was found to be 59 nm for the cornea and 285 nm for the sclera. These results agreed with those obtained by direct measurement using the electron micrographs, and those reported in the literature. The spatial order in the microstructure of the cornea was much greater when compared with that of the sclera. The results of the 2-D Fourier analysis were consistent with the theory of transparency of the eye. The 2-D Fourier analysis will be useful in quantitative characterization and analysis of the complex microstructure of biological cells and tissues in normal development and abnormal pathogenesis.

Cornea↗
PubMed1985

Decreased scattering coefficient of blue sclerae.

The optical scattering properties of blue and normal sclerae were studied with a fiber optic scattering monitor. The scattering was clearly reduced in two osteogenesis imperfecta patients with blue sclerae, and low normal in one osteogenesis imperfecta patient without blue sclerae.

Adult↗
PubMed1985

A comparative analysis of the collagen type and distribution in the trabecular meshwork, sclera, lamina cribrosa and the optic nerve in the human eye.

A theory has been advanced (Tengroth et al 1984) that one common factor might be involved in the pathogenesis of chronic open angle glaucoma. The mechanical properties of the collagen could be one such factor. To characterize the collagen composition of the critical structures in cases with chronic open angle glaucoma i.e. the trabecular meshwork and the lamina cribrosa in the human eye, the following investigations were performed. Using immunoperoxidase technique and type specific antibodies to the genetically distinct collagen types I, III, IV and procollagen I along with the major non collagen proteins in the extracellular matrix laminin and fibronectin a light microscopic study was undertaken on the trabecular meshwork, cornea, sclera, lamina cribrosa and the optic nerve of the human eye. Furthermore biochemical analysis was performed on the collagen associated aminoacids hydroxyproline (Hyp), hydroxylysine (Hyl) and prolin (Pro) from microdissected samples of trabecular meshwork, sclera, lamina cribrosa and optic nerve. Both the immunohistological and the biochemical findings suggested similarities in the collagen composition between the trabecular meshwork and the lamina cribrosa. The immunohistochemical findings showed stronger staining of type III and IV in the trabecular meshwork and lamina cribrosa as compared to sclera or cornea while the opposite was true for type I and procollagen I. Fibronectin and laminin were present in both the trabecular meshwork and lamina cribrosa. These findings were in agreement with the amino acid analysis when the Hyp/Hyl ratio was calculated for each sample.(ABSTRACT TRUNCATED AT 250 WORDS)

Aged↗
PubMed1991

Collagen and uronic acid distribution in the human sclera.

In the normal adult eye the content of uronic acid, hydroxyproline, hydroxylysine and proline from different parts of sclera was examined. Scleral samples from the posterior eyeball showed a higher content of uronic acid than the scleral samples from papilla, equator and limbus. Apart from a lower concentration of hydroxyproline in sclera from equator, no major differences in concentration of hydroxyproline, hydroxylysine or proline was found in sclera samples.

Aged↗
PubMed2003

Viscoelastic characterization of peripapillary sclera: material properties by quadrant in rabbit and monkey eyes.

In this report we characterize the viscoelastic material properties of peripapillary sclera from the four quadrants surrounding the optic nerve head in both rabbit and monkey eyes. Scleral tensile specimens harvested from each quadrant were subjected to uniaxial stress relaxation and tensile ramp to failure tests. Linear viscoelastic theory, coupled with a spectral reduced relaxation function, was employed to characterize the viscoelastic properties of the tissues. We detected no differences in the stress-strain curves of specimens from the four quadrants surrounding the optic nerve head (ONH) below a strain of 4 percent in either the rabbit or monkey. While the peripapillary sclera from monkey eyes is significantly stiffer (both instantaneously and in equilibrium) and relaxes more slowly than that from rabbits, we detected no differences in the viscoelastic material properties (tested at strains of 0-1 percent) of sclera from the four quadrants surrounding the ONH within either species group.

Animals↗
PubMed2002

High precision subsurface photodisruption in human sclera.

BACKGROUND AND OBJECTIVES: Femtosecond pulses can generate high precision subsurface photodisruption in transparent tissues, such as the cornea. We used femtosecond laser technology to demonstrate early proof of concept for high precision subsurface photodisruption in the translucent sclera. This technique may ultimately enable novel surgical procedures for the treatment of glaucoma and/or presbyopia. STUDY DESIGN/METHODS AND MATERIALS: Microjoule femtosecond pulses from two different sources, 1060 and 775 nm, were used to make subsurface incisions in human sclera in vitro. Scleral tissue was dehydrated to improve translucency at these wavelengths. The beam was focused to a 1.5 (775 nm) or 5 microm spot size (1060 nm) and scanned below the tissue surface at various depths to produce four incision patterns. RESULTS: Photodisruption on the backsurface of the sclera was achieved without damage to overlying tissue. Several types of intrascleral incisions were made, including transcleral channels and grooves for scleral implants. CONCLUSIONS: High precision, subsurface scleral photodisruption can be achieved in vitro for a variety of intrascleral incisions. Further studies are required to determine if this technique is applicable in vivo for actual surgical applications.

Fiber Optic Technology↗
PubMed2000

The cutler-beard bridge flap technique with use of donor sclera for upper eyelid reconstruction.

We evaluated the Cutler-Beard bridge flap technique with the use of donor sclera for upper eyelid reconstruction. The right upper eyelid of a 22-year-old man (case 1) was bitten by a dog. A mass in the left upper eyelid of an 85-year-old man (case 2) was excised. Major full-thickness defects of the eyelid with small loss of tarsus were reconstructed with the use of donor sclera. Good cosmetic results were obtained. Major full-thickness defects of the upper eyelid with small loss of tarsus may be effectively reconstructed by the Cutler-Beard technique with use of donor sclera.

Adult↗
PubMed1996

Scanning electron-microscopic studies of the collagen architecture of the human sclera--normal and pathological findings.

The arrangement of the collagen fibrils of the human sclera was analyzed in the region of the limbus cornea, the corneoscleral trabeculum, at the zone of muscle insertion and at defined areas of the internal and external surface of the sclera. Adult eyes with no apparent pathological alterations and the sclera of a patient with staphyloma were examined by scanning electron microscopy. The investigations were performed to describe regularities in the collagen architecture in normal and pathologically altered eyes to understand pathomorphologic and pathophysiologic changes in scleral diseases.

Aged↗
PubMed2005

Viscoelastic material properties of the peripapillary sclera in normal and early-glaucoma monkey eyes.

PURPOSE: To test the hypothesis that changes in the viscoelastic material properties of peripapillary sclera are present within monkey eyes at the onset of early experimental glaucoma detected by confocal scanning laser tomography (CSLT). METHODS: Short-term (3-9 weeks), moderate (< or =44 mm Hg) intraocular pressure (IOP) elevation was induced in one eye of each of eight male monkeys by lasering the trabecular meshwork. This procedure generated early experimental glaucoma, defined as the onset of CSLT-detected optic nerve head (ONH) surface change, in the treated eye. Scleral tensile specimens from the superior and inferior quadrants of the eight early-glaucoma eyes were subjected to uniaxial stress relaxation and tensile tests to failure and the results compared with similar data obtained in a previous study of 12 normal (nonglaucomatous) eyes. Linear viscoelastic theory was used to characterize viscoelastic material property parameters for each specimen. Differences in each parameter due to quadrant and treatment were assessed by analysis of variance (ANOVA). RESULTS: Peripapillary sclera from the early-glaucoma eyes exhibited an equilibrium modulus (7.46 +/- 1.58 MPa) that was significantly greater than that measured in normal eyes (4.94 +/- 1.22 MPa; mean +/- 95% confidence interval, P < 0.01, ANOVA). Quadrant differences were not significant for the viscoelastic parameters within each treatment group. CONCLUSIONS: The long-term viscoelastic material properties of monkey peripapillary sclera are altered by exposure to moderate, short-term, chronic IOP elevations and these alterations are present at the onset of CSLT-detected glaucomatous damage to the ONH. Damage to and/or remodeling of the extracellular matrix of these tissues may underlie these changes in scleral material properties.

Animals↗
PubMed2004

Prostaglandin FP agonists alter metalloproteinase gene expression in sclera.

PURPOSE: The present study was undertaken to determine whether exposure of the sclera to prostaglandin (PG)F(2alpha) or to the PGF(2alpha) analogue latanoprost acid alters mRNA for matrix metalloproteinases. METHOD: Fifteen human eye bank eyes were studied. Circular pieces of sclera were either immediately preserved in a stabilization reagent or cultured in low-serum DMEM/F-12 medium. The cultures were treated for 24 hours with medium supplemented with PGF(2a), latanoprost acid, or vehicle. Total RNA was then isolated, and the expression of mRNA for matrix metalloproteinase (MMP)-1, -2, -3, -8, -9, -10, and -12 were determined by real-time PCR. All results were normalized according to the GAPDH mRNA in each sample. Altered mRNA expression after PG treatments also was evaluated with microarrays containing 19 MMP genes and 4 tissue inhibitor of matrix metalloproteinase (TIMP) genes. RESULTS: Real-time PCR results showed that 24 hours of exposure to 100 nM PGF(2alpha) significantly increased mRNA for MMP-1 and -9 (P < 0.06 Wilcoxon test) and that exposure to 100 nM latanoprost acid significantly increased mRNA for MMP-9 (P < 0.06 Wilcoxon test). Array analysis demonstrated increases of MMP-3 and -10 mRNA after exposure to 100 nM latanoprost and further increases after exposure to 200 nM latanoprost. The array results also showed that latanoprost induced dose-dependent increases in the expression of TIMP-1, -2, and -3 mRNA in the scleral cultures. CONCLUSIONS: PGF(2alpha) and latanoprost acid induce coordinated alterations of MMP gene transcription in scleral organ cultures. These results indicate that PGs can directly trigger MMP gene transcription changes within the sclera. These changes support a role for increased MMPs in the enhancement of uveoscleral outflow that occurs after topical treatment with latanoprost.

Aged↗
PubMed2006

Expression of collagen-binding integrin receptors in the mammalian sclera and their regulation during the development of myopia.

PURPOSE: The sclera has a collagen-rich extracellular matrix that undergoes significant biochemical and biomechanical remodeling during myopic eye growth. The integrin family of cell surface receptors play critical roles in extracellular matrix and biomechanical remodeling in connective tissues. This study identified the major collagen-binding integrin receptors in the mammalian sclera and investigated their mRNA expression during the development of and recovery from experimental myopia. METHODS: The presence of the alpha1, alpha2, and beta1 integrin subunits was examined by using tree-shrew-specific primers and RT-PCR. Scleral expression of alpha1beta1 and alpha2beta1 receptor proteins was further investigated by using Western blot analysis and immunocytochemistry. Myopia was induced monocularly by occluding pattern vision and scleral tissue collected after 24 hours and 5 days. In a subset of the 5-day treatment group, vision was restored for 24 hours before tissue was isolated. Total RNA was extracted, and integrin subunit expression levels were assessed with quantitative real-time PCR. RESULTS: The presence of the major collagen-binding integrin subunits alpha1, alpha2, and beta1 was confirmed by RT-PCR in both scleral tissue and cultured scleral fibroblasts. Both the alpha1 and alpha2 integrin subunit proteins were identified in tree shrew scleral tissues, and integrin receptor expression was localized to scleral fibroblast focal adhesions. After only 24 hours of myopia induction, a time when no structural elongation has occurred, significant decreases were observed in the expression of the alpha1 (-36%) and beta1 (-44%) integrin subunits. After 5 days of myopia induction, alpha1 integrin expression had returned to baseline levels, whereas the alpha2 subunit showed a significant decrease in expression (-52%). The 5-day integrin profiles were maintained during recovery from the induced myopia, with only alpha2 integrin showing a statistically significant relative decrease in expression (-41%). CONCLUSIONS: The mammalian sclera expresses the major collagen-binding integrin subunits. The alpha1 and beta1 subunit expression was decreased early during the development of myopia, whereas the regulation of alpha2 integrin occurred at a later time point. The differential regulation of alpha1beta1 and alpha2beta1 during the development of myopia may reflect specific roles for these receptors in the scleral extracellular matrix and biomechanical remodeling that accompanies myopic eye growth.

Animals↗
PubMedDate not supplied

Evaluation of sclera as a homograft in facial plastic and reconstructive surgery.

Augmentation of deficient soft tissue contours accounts for a large part of facial plastic and reconstructive surgery. An attempt to use homograft sclera in the feline animal model is presented. Augmentation of nasal dorsum and the chin contours was carried out in the cat model with preserved homograft sclera. Serial soft tissue radiographs and histologic study of the homografts demonstrated complete resorption of the grafts by six months. Further physical and chemical alterations of homograft sclera appear to be necessary prior to its implantation for the purpose of soft tissue augmentation.

Animals↗