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PubMed2004

[Matrix metalloproteinase-2 mRNA expression in the posterior sclera of chick form-deprivation myopia].

OBJECTIVE: To investigate the dynamic changes of matrix metalloproteinase-2 (MMP-2) mRNA expression in the posterior sclera of chick form-deprivation myopia (FDM) and its possible molecular mechanism. METHODS: Fifty white 1-day-old leghorn chicks were divided randomly and equally into 5 groups. The right eye of each chick was covered with a plastic goggle at 4, 7, 14, 21, and 30 postborn days respectively to induce FDM, and the left eye served as a self-control. Meanwhile, normal age-matched chicks were provided as negative control speciments for each group. Removing the goggle at every experiment point, refractive status and axial length were determined with streak retinoscopy (without cycloplegia) and A-scan ultra-sonography under topical anaesthesia, respectively. Both eyes were collected after the chicks were killed. The total RNA in the posterior sclera was extracted traditionally using TRIZOL reagent, and then the expression levels of MMP-2 messenger RNA were analyzed by one step reverse transcriptiontase-polymerase chain reaction. RESULTS: Compared with the normal and self-control groups, the expression levels of MMP-2 mRNA in the deprived eyes significantly increased (P < 0.001). With the delay of form-deprivation duration, MMP-2 mRNA expression levels increased significantly and especially reached a highest point at the 14th day of monocular deprivation. After that the level decreased slightly, but maintained at a high level. Although there was no significant difference between the normal control group and the self-control one (P > 0.05), MMP-2 mRNA expressed slightly higher in the self-controlled eyes. CONCLUSION: As a primary element to trigger early active sclera extracellular matrix remodeling process, MMP-2 gene is probably involved in the development of FDM by excessive degradation of extraceller matrix which can make sclera thinner and the eye axis longer.

Animals↗
PubMed2006

[Experimental study of acellular xenogenic dermal matrix and allogeneic sclera as wrapping materials for hydroxy apatite implantation].

OBJECTIVE: To observe the experimental results and histopathological changes of acellular xenogenic dermal matrix (X-ADM) and allogeneic sclera used as wrapping materials of hydroxy apatite (HA) ocular implants in New Zealand white rabbits. METHODS: Twenty-four rabbits received unilateral eye enucleating and the sockets were implanted with HA spherical implants wrapped with either acellular xenogenic dermal matrix or allogeneic sclera at random. The rabbits were examined for inflammation and implant exposure and sacrificed at 1, 2, 4, 6, 8 and 12 weeks after implantation. The sockets with the grafts were exenterated and the specimens were assessed histopathologically and ultrastructurally with light or transmission electron microscopy for the changes in inflammation reaction and vascularization. RESULTS: Compared to allogeneic sclera at the same stage of implantation, acellular xenogenic dermal matrix demonstrated more active and earlier growth of fibroblasts and new vessels with abundant collagen deposition. There were few inflammatory cells and no rejection was found. CONCLUSION: This experiment showed that the acellular xenogenic dermal matrix, with fast neovascularization and low immunity, can be an ideal material of ocular implant and a good substitute for allogeneic sclera.

Animals↗
PubMed1991

Electron microscopic study of distribution of proteoglycans in bovine cornea and sclera.

To study differences in the distribution of proteoglycans and their relationships to collagen fibrils in the cornea and sclera, bovine cornea and sclera were examined histochemically using the ruthenium red (RR) staining method. RR-positive granules (30 nm in diameter) were present in association with fine filamentous materials (3 nm in diameter and 30-100 nm in length) in the interfascicular spaces of collagen bundles in both the corneal stroma and sclera. The amount of these materials was smaller in the sclera than in the cornea. The characteristic band-like arrangement of RR-positive granules connected by filamentous materials at intervals of 80-100 nm was found only in the cornea. In enzyme digestion experiments, tissue sections were treated by chondroitinase ABC, AC, and keratanase before RR staining. The RR-positive granules and their associated filamentous materials were darkly stained after chondroitinase AC or keratanase digestion, but displayed markedly lighter staining after chondroitinase ABC digestion. These results indicate that RR-positive granules and filamentous materials contain dermatan sulfate proteoglycan.

Actin Cytoskeleton↗
PubMed1990

Insulin and IGF-1 binding in chick sclera.

The sclera of embryonic (days 10 and 14) and young adult (2-week posthatching chicks) contains distinct binding sites for insulin and for insulin-like growth factor-1 (IGF-1). Since there is a nearly 50% decrease in insulin and IGF-1 binding between embryonic day 10 and the 2nd week posthatching, it is clear that these sites are developmentally regulated. The affinity of each binding site for its ligand is stable across development. This suggests that the developmental decrease in binding is the result of a decrease in the number of binding sites. The insulin binding site in the sclera is specific for insulin since it has a high affinity for insulin and a lower affinity for IGF-1 (IC50 for unlabeled insulin = 0.4 nM; unlabeled IGF-1 = 5.0 nM). The embryonic chick sclera also contains two high-affinity IGF-1 binding sites. One of these sites exhibits poor binding specificity since it has an equal affinity for insulin and IGF-1. However, the specificity of this site increases in the young adult. The second IGF-1 binding site exhibits a more conventional specificity in that it has a higher affinity for IGF-1 than for insulin. The specificity of this binding site also improves in the young adult. The presence of insulin and IGF-1 receptor binding site subtypes is not correlated with structurally different receptor binding subunits since only a single population of binding subunits is observed (apparent molecular weight of 125 +/- 2.7 kD) in embryonic and adult sclera.(ABSTRACT TRUNCATED AT 250 WORDS)

Aging↗
PubMed1995

[Changes of expression in matrix metalloproteinase and its inhibitor level in the sclera from axially elongated eyes].

We studied the gelatinolytic activity, caseinolytic activity and the level of tissue inhibitor of metalloproteinase-1 (TIMP-1) in the sclera from experimentally induced axially elongated eyes. The animal models were made by the injection of 250U alpha-chymotrypsin into the posterior chamber of young albino rabbits. Animals were killed with overdoses of intravenous pentobarbital and eyes were enucleated gently. Sclera from the equatorial area was then subjected to organ culture. The enzyme activity in the media was investigated by zymography using gelatin- or casein-containing gels together with an image analyzer system. TIMP-1 levels in each medium were measured by enzyme immunoassay (EIA). All samples showed three major bands of gelatinolytic activity at molecular weights of 87, 61, and 57 kDa. Gelatinolytic activity of 87 kDa increased 1.1 to 2.9 times compared with control sclera. All of the caseinolytic activity (87, 82, 52, and 50 kDa) was also elevated 1.8 to 6.6 times in samples from experimental eyes. TIMP-1 levels were mildly increased (up to 1.41 times) in the experimental eyes. These data suggest that degradation processes might be accelerated in the sclera from experimentally induced elongated eyes.

Animals↗
PubMed1994

Near-infrared Fourier transform Raman spectroscopic study of cornea and sclera.

Near-infrared excited Fourier transform Raman spectroscopy was applied in situ on intact rabbit cornea and sclera. High quality Raman spectra were obtained noninvasively from these tissues. The characteristic bands assigned to proline and hydroxyproline appeared in the region of 800-1000 cm-1. Raman spectra of purified type I collagen and other components of the cornea and sclera were also determined. The main elements of the spectra of the cornea and sclera originated from the collagen proteins, and other components such as proteoglycan contributed little. Near-infrared excited Fourier transform Raman spectroscopy can be used for biophysical study of the cornea and sclera in situ or in vivo.

Animals↗
PubMed1996

[Prospective study of surgical therapy of pterygium: bare sclera technique vs. free conjunctiva-limbus transplant].

Many techniques of pterygium surgery with various rates of recurrence are described in the literature. We report on the outcome after pterygium excision with bare-sclera technique compared with free transplantation of limbal conjunctiva. We used the bare-sclera technique in 21 eyes and performed free transplantation of conjunctiva in 34 eyes. The duration of follow-up was 14 months. In patients operated with the bare-sclera technique there were significantly more recurrences (eight vs four, P < 0.025) and cases of development of pyogenic granuloma (four eyes vs no eyes, P < 0.01). In patients with primary surgery and free limbal transplant we found no case of recurrence, but the bare-sclera technique was associated with a recurrence rate of 35.5% (P < 0.01). We recommend free limbal conjunctival transplantation even in patients with primary surgery of a pterygium.

Aged↗
PubMed1996

Repair of a giant scleral ulcer with preserved sclera and tissue adhesive.

BACKGROUND AND OBJECTIVE: Infectious scleral ulcer is a rare but severe late complication of pterygium surgery. Scleral grafts may be required in scleral ectasia with uveal exposure, corneal distortion, and severe anterior chamber reaction that are induced by scleral ulcer. The authors report a method for scleral grafting with preserved sclera and tissue adhesive. PATIENTS AND METHODS: Six cases of infectious scleral ulcers were repaired with this method. Preserved sclera was attached to the thinning sclera with tissue adhesive without sutures. The free or rotation conjunctival flap was placed over the graft area and sutured with 10-0 nylon. RESULTS: The six cases repaired by this method showed good results during the follow-up, except for one loss. The only complication was protrusion of the adhesive postoperatively. This protrusion can be easily removed with forceps on an outpatient basis. CONCLUSION: Tissue adhesive with preserved sclera is a useful method for repair of scleral thinning.

Aged↗
PubMed1993

Internal sclerostomy using laser ablation of dyed sclera in glaucoma patients: a pilot study.

Twelve eyes of 12 patients with refractory glaucoma were treated with internal sclerostomy using laser ablation of dyed sclera. The technique involves iontophoretic impregnation of the sclera at the limbal region with 1% methylene blue and subsequent delivery of a pulsed dye laser beam to the stained area through a goniolens. The red wavelength of 664 nm generated by the laser is maximally absorbed by the stained sclera and creates a through and through sclerostomy. Successful complete sclerostomy was achieved in seven eyes (58.3%) but there was some reduction of intraocular pressure (IOP) in all cases. Mean prelaser IOP (of all 12 eyes) was 36.6 mm Hg and 1 hour after therapy it was reduced to 20.0 mm Hg. At the end of the follow-up period (mean 16 months) the mean IOP was 23.7 mm Hg; five eyes (41%) maintained their IOP below 22 mm Hg, and the average number of medications per eye came down from 3.25 to 2.25 per eye. Transient corneal burns with Descemet's membrane folds adjacent to the laser impact zone were detected in eight eyes (67%). No major complications like IOP spike, hyphaema, iridodialysis, or retinal detachment have been detected. Clear cornea and dark blue scleral staining are essential for the mechanical success of this procedure. Gonioscopic laser internal sclerostomy of methylene blue dyed sclera is technically feasible and the preliminary results of IOP control in refractory glaucoma are promising. Modifications of the iontophoresis process and laser parameters are currently under investigation in order to improve these results.

Adult↗
PubMed1982

Nanophthalmic sclera. Ultrastructural, histochemical, and biochemical observations.

Scleral tissue from two cases of nanophthalmos was examined by amino acid analysis, light microscopy, histochemistry, and transmission electron microscopy. Perifibrillar aggregates, similar to proteoglycans, were prominent in the nanophthalmic sclera. The sclerae were thicker than normal and the bundles of collagen fibrils were less ordered. The clinical features of vortex vein compression seem causally related to the disordered and thickened sclera, which, in turn, may be caused by dysfunctional proteoglycans, or interaction with the scleral collagen, or both.

Adult↗
PubMed1990

Retinal influences on sclera underlie visual deprivation myopia.

Visual deprivation of chicks rapidly induces an increased growth of the vitreous chamber which results in axial myopia, even after a day or so. This experimental myopia provides an opportunity to trace the causal path from altered visual experience to altered eye growth. With respect to the visual factors involved, the gross activity of the retinal neurons seems an important variable. The eyes of animals raised wearing translucent occluders do not become myopic or elongated if stroboscopic illumination is present. Conversely, the eyes do become myopic and elongated if deprived of all form vision, if reared in a featureless environment or if deprived in only part of the visual field. The deprivation must, however, be continuous if myopia is to result; even as little as two hours of normal vision per day almost completely eliminates the effect of 12 hours of deprivation. The control of eye growth by vision seems to take place in local regions of the eye. Deprivation of various parts of the visual field produces myopia and elongation in only the deprived part, even in animals in which the optic nerve has been cut. It seems that at the level of the sclera ocular elongation (and thus myopia) results from local growth, because we find increases in synthesis of DNA and protein as well as more new cells. The protein synthesis increase is also local, in the sense that the posterior sclera grows much more than other parts, explaining why deprivation causes ocular elongation and myopia, rather than simply larger eyes. These results suggest that some factor in part of the retina can influence the growth of the subjacent sclera.

Animals↗
PubMed2004

NIR laser tissue welding of in vitro porcine cornea and sclera tissue.

BACKGROUND AND OBJECTIVE: The objective of this study was to test the hypothesis that an near infrared (NIR) laser system (1,455 nm) in combination with a motorized translational stage to control the position and speed of the laser beam and a shutter to control the laser exposure to the tissue being welded could be used to successfully weld ocular tissues. STUDY DESIGN/MATERIALS AND METHODS: Seventy-five porcine corneas and 23 porcine scleral tissues were welded in vitro in this study. The welded tissues were examined using histopathology and tensile strength analysis. Eight different welding conditions were analyzed for porcine cornea and one for sclera tissues. The tensile strength of the welded groups was compared to a sutured cornea control group. RESULTS: The NIR laser welding system provides strong, full thickness welds and does not require the use of extrinsic dyes, chromophores, or solders. Mean weld strengths of 0.15-0.45 kg/cm(2) were obtained for the cornea and 1.01 kg/cm(2) for sclera welds. The native H(2)O in the ocular tissue serves as an absorber of the 1,455 nm radiation and helps to induce the welds. CONCLUSIONS: We conclude that an NIR laser system using an optimal laser radiation wavelength of 1,455 nm can effectively weld cornea and sclera tissue and that this laser tissue welding (LTW) methodology typically causes minimal disruption of tissue, and thus, avoids opacities and irregularities in the tissue which may result in decreased visual acuity. The optimization of a laser welding system that leads to a strong full thickness tissue bond without tissue destruction, an instant seal that promotes wound healing, and the absence of a continued presence of a foreign substance like a suture, is of considerable importance to the ophthalmology medical community. This need is especially apparent with respect to corneal transplantation and fixing the position of corneal flaps in Laser-Assisted In Situ Keratomileusis (LASIK), a laser procedure used to permanently change the shape of the cornea.

Animals↗
PubMed1999

Isolated chick sclera shows a circadian rhythm in proteoglycan synthesis perhaps associated with the rhythm in ocular elongation.

In the growing chick, ocular elongation is rhythmic, increasing during the day and decreasing at night. Because experimentally induced changes in the rate of ocular elongation are associated with changes in the rate of synthesis of scleral proteoglycans, we asked whether there is a diurnal rhythm in scleral proteoglycan synthesis, whether the rhythm is endogenous, and whether scleras from normal eyes differed from those of faster growing form-deprived eyes. To assess proteoglycan synthesis, we measured the incorporation of labeled sulfate into glycosaminoglycans using two paradigms: (1) punches of sclera were cultured for either 2 or 10 h at various times of day, and (2) punches were cultured in a perifusion system for up to 80 h, and samples of the medium were collected for analysis at 2-h intervals. Synthesis of scleral proteoglycans is higher during the day than during the night. This rhythm persists for at least three cycles in vitro with a period of approximately 24 h. There are no significant differences between rhythms in scleras from normal and form-deprived eyes. Finally, biochemical analyses show the labeled molecule to be similar to aggrecan, the cartilage proteoglycan. We conclude that the synthesis of proteoglycans by scleral chondrocytes is circadian, and we speculate that this rhythm may influence the rhythm in ocular elongation.

Animals↗
PubMed1988

A comparison of the elastic properties of human choroid and sclera.

Multiple strips of choroid (56) and sclera (64) from eight pairs of human eye-bank eyes were subjected to simple tension in a test apparatus to determine the rigidity (modulus of elasticity) of these tissues. The modulus of elasticity of the chorodial complex (choroid-Bruch's membrane-pigment epithelium) was significantly greater in posteriorly located samples than in anteriorly located ones (7.5 +/- 7.0 vs. 2.2 +/- 1.5 x 10(5) N m-2, mean +/- S.D.). The modulus of elasticity for the complex averaged across all locations was 6.0 +/- 2.8 x 10(5) N m-2 and the average stress at failure was 3.3 +/- 1.3 x 10(5) N m-2. The modulus of elasticity for scleral strips also varied with location and averaged 2.9 +/- 1.4 x 10(6) N m-2 for anterior sclera and 1.8 +/- 1.1 x 10(6) N m-2 for posterior sclera at stress levels ranging from 20- to 260 x 10(4) N m-2. There was a significant correlation of scleral stiffness with age (P less than 0.05, r = 0.80). The elastic properties of the choroidal complex may be relevant to the pathogenesis of a variety of ocular diseases, including macular degeneration, angioid streaks, choroidal folds, and choroidal ruptures.

Adolescent↗
PubMed2005

The sclera and myopia.

Myopia is a very common ocular problem, affecting perhaps one billion people worldwide. Most myopia is produced by lengthening of the vitreous chamber of the ocular globe. High myopia is characterized by scleral thinning and localized ectasia of the posterior sclera. The sclera is a dense, fibrous, viscoelastic connective tissue that forms the outer coat of the eye and consists of irregularly arranged lamellae of collagen fibrils interspersed with proteoglycans and non-collagenous glycoproteins. Scleral fibroblasts are located between scleral lamellae, and are responsible for synthesizing the extracellular matrix in which they reside. Research highlighted in this review clearly demonstrates that the sclera is not a static container of the eye, but rather is a dynamic tissue, capable of altering extracellular matrix composition and its biomechanical properties in response to changes in the visual environment to regulate ocular size and refraction. Based on these studies, a strategy directed at reversing myopia-associated scleral extracellular matrix remodeling events would be warranted, particularly in cases of high myopia in humans.

Animals↗
PubMed1998

A lattice model for computing the transmissivity of the cornea and sclera.

The method of photonic band structure is used to calculate the frequencies of light that propagate in lattice models of the cornea and sclera of the mammalian eye, providing an explanation for transparency in the cornea that first properly accounts for multiple scattering of light. Each eye tissue is modeled as an ordered array of collagen rods, and photonic band structure methods are used to solve Maxwell's equations exactly for these models, a procedure that automatically effectively includes all orders of multiple scattering. These calculations show that the dispersion relation for the cornea is linear in the visible range, implying that the cornea is transparent. We show that the transmissivity is approximately 97% by using an effective medium approximation derived from the photonic band structure results and applicable in the visible region. In contrast, the dispersion relation for the model in the sclera is not linear in the visible region, and there are band gaps in this region that could play an important role in the transmission of light in the sclera.

Animals↗
PubMed1999

Swelling studies on the cornea and sclera: the effects of pH and ionic strength.

The biophysical properties of the cornea and sclera depend on the precise maintenance of tissue hydration. We have studied the swelling of the tissues as a function of pH and ionic strength of the bathing medium, using an equilibration technique that prevents the loss of proteoglycans during swelling. Synchrotron x-ray diffraction was used to measure the average intermolecular and interfibrillar spacings, the fibril diameters, and the collagen D-periodicity. We found that both tissues swelled least near pH 4, that higher hydrations were achieved at lower ionic strengths, and that sclera swelled about one-third as much as cornea under most conditions. In the corneal stroma, the interfibrillar spacing increased most with hydration at pH values near 7. Fibril diameters and D-periodicity were independent of tissue hydration and pH at hydrations above 1. Intermolecular spacings in both tissues decreased as the ionic strength was increased, and there was a significant difference between cornea and sclera. Finally, we observed that corneas swollen near pH 7 transmitted significantly more light than those swollen at lower pH levels. The results indicate that the isoelectric points of both tissues are close to pH 4. The effects of ionic strength can be explained in terms of chloride binding within the tissues. The higher light transmission achieved in corneas swollen at neutral pH may be related to the fact that the interfibrillar fluid is more evenly distributed under these conditions.

Animals↗
PubMedDate not supplied

Surface topology of collagen fibrils associated with proteoglycans in mouse cornea and sclera.

PURPOSE: To clarify the histological basis for the optical difference in the cornea and sclera, we investigated the surface ultrastructure of D-periodic collagen fibrils. METHODS: The fibril arrangement and topology of D-periodic collagen fibrils from corneas and scleras of mice were examined by transmission and scanning electron microscopy, as well as by atomic force microscopy (AFM). The banding patterns were estimated by densitometry and compared with the profile made by computer simulation from the protein sequence of amino acids. RESULTS: Considerable association of proteoglycans/glycosaminoglycanson XI bands of corneal D-periodic collagen fibrils was seen with ruthenium red staining. Atomic force microscopy imaging showed that the depth of the groove in the D-periodicity of corneal collagen fibrils was shallow compared with that of the sclera. CONCLUSIONS: Corneal collagen fibrils are associated with many extracellular matrix components on both elevated and depressed surfaces of D-periodic bands, which may serve to maintain interfibrillar spaces, resulting in corneal transparency.

Animals↗