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PubMed1993

The collagen architecture of the sclera--SEM and immunohistochemical studies.

The arrangement of the collagen fibrils of the sclera was analyzed at defined areas by using SEM with regard to morphological alterations in cases of glaucoma and to postoperative astigmatism after cataract operations. Adult eyes with no apparent pathological changes were studied. In the lamina cribrosa the collagen fibrils are arranged circularly around the points of passage of the axons and vessels. In the region of the muscle attachments the tendinous collagen fibrils intersect the bundles of collagen fibrils of the sclera at right angles. The collagen fibrils form a reticular structure on the external surface of the sclera. A main route of alignment can only be identified in a few places. The collagen fibrils are aligned in a rhombic pattern on the internal surface of the sclera. The immunohistochemical analysis revealed collagen types I and III in the sclera, while collagen types I, III and IV were found in the lamina cribrosa.

Aged↗
PubMed1996

Anterior segment prosthesis development: evaluation of expanded polytetrafluoroethylene as a sclera-attached prosthetic material.

To further the development of a sclera-attached anterior segment prosthesis we investigated the biocompatibility of expanded polytetrafluoroethylene following its surgical implantation into the rabbit sclera. Thin sheets (250 microns) of expanded polytetrafluoroethylene were cut into pieces measuring either 2 x 2, 2 x 4, 2 x 8, or 4 x 8 mm. The pieces were sterilized and placed individually within surgically prepared pockets in the sclera of rabbit eyes. Animals were sacrificed for routine histopathologic evaluation and transmission electron microscopic study of the eyes at 7 days, 14 days, 1 month, and 4 months following surgical implantation. The implants demonstrated excellent compatibility with the sclera and, by 14 days following implantation surgery, exhibited histiocytes, fibroblasts, and blood vessels infiltrating the internodal spaces of the highly porous material. The number of cells and the amount of extracellular matrix material deposited in the implants appeared to increase with time. Transmission electron microscopic studies revealed deposition of collagen within the implants. Our results suggest that expanded polytetrafluoroethylene has potential for use in the development of a sclera-attached prosthetic device.

Animals↗
PubMed2001

Surface ultrastructure of collagen fibrils and their association with proteoglycans in human cornea and sclera by atomic force microscopy and energy-filtering transmission electron microscopy.

PURPOSE: We aimed to investigate the possible association of proteoglycans with D-periodic collagen fibrils in the human cornea and sclera, using energy-filtering transmission electron microscopy (EF-TEM) and atomic force microscopy (AFM). METHODS: Human cornea and sclera were digested with keratanase to eliminate keratan sulfate proteoglycans (KSPGs). For EF-TEM observation, surface proteoglycans were detected by cupromeronic blue (CB) staining. For AFM observation, cornea and sclera were treated with sodium hydroxide before and after keratanase digestion, and the surface topology of collagen fibrils was analyzed. RESULTS: With CB staining, numerous CB-positive short filaments of surface proteoglycans (proteoglycan filaments) were observed in the interfibrillar spaces of cornea and sclera associated with collagen fibrils. AFM imaging showed that the depth and periodicity of D-periodic collagen fibrils in keratanase-treated corneal collagens were deeper and more regular than in untreated ones. Moreover, the depth and periodicity of keratanase-untreated corneal collagens were shallow and irregular in comparison with keratanase-untreated scleral collagens. On the other hand, there was no difference in depth or regularity between keratanase-treated and -untreated scleral collagen fibrils. Using AFM imaging, additional thin grooves sub-bands were detected on the surface of keratanase-treated corneal collagen fibrils. The grooves were not detected in keratanase-untreated collagen fibrils nor in scleral collagen fibrils with or without keratanase digestion. Comparing densitometry waves, the grooves of D-periodic corneal collagen sub-bands corresponded to a and c bands. CONCLUSION: Using AFM and EF-TEM to study corneal and scleral collagen fibrils and their association with proteoglycans, we conclude that KSPG is found in ample amounts in the human cornea in comparison with sclera. Moreover, we topologically detected KSPG attached to a and c bands of collagen fibrils.

Aged↗
PubMed1998

Meta-analysis on the recurrence rates after bare sclera resection with and without mitomycin C use and conjunctival autograft placement in surgery for primary pterygium.

BACKGROUND/AIMS: Bare sclera resection with and without use of mitomycin C and conjunctival autograft placement are three surgical techniques currently in use for the treatment of primary pterygium. The purpose of this study was to determine through a meta-analysis the risk for postoperative pterygium recurrence comparing the three surgical treatment modalities. METHODS: A search through Medline for randomised controlled clinical trials comparing at least two of the three surgical techniques in the treatment of primary pterygium, along with a hand search of all references in relevant papers, was conducted. All eligible clinical trials were graded for quality utilising the Detsky score; those studies with a score of 0.5 or greater were included. The main outcome measurements were the pooled odds ratios and 95% confidence intervals for the risk of pterygium recurrence. These were calculated utilising the Mantel-Haenszel method. RESULTS: Five eligible studies with an adequate quality score were retrieved, three comparing bare sclera resection with and without mitomycin C use, one comparing bare sclera resection with conjunctival autograft placement, and one comparing both. The pooled odds ratio for pterygium recurrence in patients who had only bare sclera resection was 6.1 (95% confidence intervals, 1.8 to 18.8) compared with the patients who had conjunctival autograft placement and 25.4 (9.0 to 66.7) compared with the patients who received mitomycin C. CONCLUSIONS: The odds for pterygium recurrence following surgical treatment of primary pterygium are close to six and 25 times higher if no conjunctival autograft placement is performed or if no intra/postoperative mitomycin C is used, respectively. Surgeons and clinical triallists should not be encouraged in the use of bare sclera resection as a surgical technique for primary pterygium.

Adult↗
PubMed2006

Measurement and prediction of lateral diffusion within human sclera.

PURPOSE: Drug delivery via the sclera is a promising approach to retinal disorder treatments that require access to the posterior segment of the eye. To complement existing studies of transverse diffusion across the sclera, this study examined lateral diffusion within the sclera parallel to the scleral surface. METHODS: Using sulforhodamine as a model hydrophilic drug, rates of diffusion were measured in strips of human cadaveric sclera for up to 1 week. Data were analyzed with a mathematical model based on theoretical expressions for one-dimensional diffusion. RESULTS: Measurable amounts of sulforhodamine were detected at distances of 5 and 10 mm from the sulforhodamine donor reservoir at 4 hours and 3 days, respectively. The effective lateral diffusivity of sulforhodamine was determined to be 3.82 x 10(-6) cm2/s, which is similar in magnitude to the transverse diffusivity. The theoretical model agreed with experimental values with an average error of 39%. CONCLUSIONS: This study shows that the lateral diffusion of sulforhodamine in human sclera is slow and localizes to the site of administration.

Biological Transport↗
PubMed2001

Steady state mRNA levels in tree shrew sclera with form-deprivation myopia and during recovery.

PURPOSE: In tree shrews, visual form deprivation induces myopia and tissue remodeling in the sclera, characterized by decreased levels of collagen and glycosaminoglycans (GAGs) and increased levels of matrix metalloproteinases (MMPs). Removal of the visual deprivation allows recovery. This study investigated whether these changes are accompanied by changes in steady state mRNA levels in the sclera. METHODS: Quantitative competitive reverse transcription-polymerase chain reaction (RT-PCR) was used to measure steady state levels of mRNA for collagen (alpha1(I) chain), decorin (core protein), gelatinase-A (MMP-2), stromelysin-1 (MMP-3), and a tissue inhibitor of metalloproteinase (TIMP-1) in the scleras of tree shrews that received either 11 days of monocular form deprivation (MD) or 11 days of MD followed by 4 days of recovery. A group of age-matched normal animals was also measured. RESULTS: After 11 days of MD, alpha1(I) collagen mRNA levels were 34% lower, and MMP-2 mRNA levels were 66% higher in the deprived eyes than in the control eyes. After 4 days of recovery, collagen mRNA levels were 33% higher, MMP-2 levels were 20% lower, and TIMP-1 levels were 43% higher in the recovering eyes than in the control eyes. Decorin and MMP-3 mRNA levels were not significantly different between the treated and control eyes after MD or after recovery. CONCLUSIONS: The tissue remodeling in mammalian sclera induced by altering the visual environment is accompanied by modulation of mRNA levels in the sclera. The levels of collagen and MMP-2 mRNA were modulated in a pattern generally consistent with observed changes in protein levels, suggesting that visual regulation of the levels of these scleral proteins may involve modulation of gene expression at the transcriptional level.

Animals↗
PubMed2001

Structural and ultrastructural changes to the sclera in a mammalian model of high myopia.

PURPOSE: The development of high myopia is associated with scleral thinning and changes in the diameter of scleral collagen fibrils in humans. In the present study, the association between these scleral changes and the losses in scleral tissue that have previously been reported in animal models were investigated to determine the relationship between changes in collagen fibril architecture and thinning of the sclera in high myopia. METHODS: Myopia was induced in young tree shrews by monocular deprivation of pattern vision for short-term (12 days) or long-term (3-20 months) periods. Scleral tissue from normal animals over a wide age range (birth to 21 months) was also collected to provide data on the normal development of the sclera. Light and electron microscopy were used to measure scleral thickness and to determine the frequency distribution of collagen fibril diameters in the sclera. Tissue loss was monitored through measures of scleral dry weight. RESULTS: Significant scleral thinning and tissue loss, particularly at the posterior pole of the eye, were associated with ocular enlargement and myopia development after both short- and long-term treatments. However, collagen fibril diameter distribution was not significantly altered after short-term myopia treatment, whereas, from 3 months of monocular deprivation onward, significant reductions in the median collagen fibril diameter were noted, particularly at the posterior pole. CONCLUSIONS: The results of this study demonstrated that loss of scleral tissue and subsequent scleral thinning occurred rapidly during development of axial myopia. However, this initial tissue loss progressed in a way that did not result in significant alterations to the collagen fibril diameter distribution. In the longer term, there was an increased number of small diameter collagen fibrils in the sclera of highly myopic eyes, which is consistent with findings in humans and is likely to contribute to the weakened biomechanical properties of the sclera that have previously been reported.

Animals↗
PubMed2001

Detection of prostaglandin EP(1), EP(2), and FP receptor subtypes in human sclera.

PURPOSE: To examine the expression of five prostaglandin (PG) receptors, EP(1), EP(2), EP(3), EP(4), and FP and their corresponding mRNA transcripts in human sclera and cultured human scleral fibroblasts (HSFs). METHODS: Primary cultures of HSFs were established from donor eyes. Also, sclera from human donor eyes was snap frozen and sectioned. Immunocytochemistry was performed on HSFs and tissue sections with subtype-specific antibodies to the EP(1), EP(2), EP(3), EP(4), and FP receptors. The presence of mRNA for the receptor subtypes was examined from total RNA obtained from human sclera and confirmed with restriction digest analysis. RESULTS: Positive EP(1) and FP receptor immunoreactivity was observed in fibroblasts within the sections from human sclera. In primary cultures of HSFs, EP(1) and FP labeling was observed over the entire cell surface. EP(2) immunoreactivity within HSFs was mostly present in the juxtanuclear region. RT-PCR analysis of total RNA isolated from human sclera and HSFs confirmed the presence of EP(1), EP(2), and FP receptor subtypes. The identity of the polymerase chain reaction products was confirmed by restriction enzyme analysis. No mRNA or immunoreactivity above basal levels was detected for the EP(3) and EP(4) prostanoid receptor subtypes in tissue sections or primary cultures. CONCLUSIONS: The EP(1), EP(2), and FP receptor subtypes are present in HSFs, suggesting that these cells may respond to endogenous PGs and their structural analogues through interaction with these receptor subtypes.

Adult↗
PubMed2004

Microarray analysis of gene expression in human donor sclera.

PURPOSE: To develop gene expression profiles of human sclera to allow for the identification of novel, uncharacterized genes in this tissue-type, and to identify candidate genes for scleral disorders. METHODS: Total RNA was isolated from 6 donor sources of human sclerae, and reverse transcribed into cDNA using a T7-(dT) 24 primer. The resulting cDNA was in vitro transcribed to produce biotin-labeled cRNA, fragmented, and mixed with hybridization controls before a 16 h hybridization step with oligonucleotide probes on 6 Affymetrix U95A chips. The chips were scanned twice at 570 nM and the data collected using GeneChip software. Array analyses were carried out with Microarray Suite, version 5.0 (Affymetrix), using the expression analysis algorithm to run an absolute analysis after cell intensities were computed. All arrays were scaled to the same target intensity using all probe sets. Reverse-transcription polymerase chain reaction (RT-PCR) was performed to validate the microarray results. RESULTS: There were 3,751 genes with "present" calls assigned independently to all six human scleral samples. These genes could be clustered into 4 major categories; transcription (10%), metabolism (8.8%), cell growth and proliferation (5.4%), and extracellular matrix (2%). Many extracellular matrix proteins, such as collagens 6A3 and 10A1, thrombospondins 2 and 4, and dystroglycan have not previously been shown to be expressed in sclera. RT-PCR results confirmed scleral expression in 7 extracellular matrix genes examined. CONCLUSIONS: This study demonstrated the utility of gene microarray technology in identifying global patterns of scleral gene expression, and provides an extended list of genes expressed in human sclera. Identification of genes expressed in sclera contributes to our understanding of scleral biology, and potentially provides positional candidate genes for scleral disorders such as high myopia.

Adult↗
PubMed2004

[Ultrastructural changes in rabbits cornea and sclera caused by radio frequency burn].

OBJECTIVE: To assess the influence of radio frequency (RF) burn on the ultrastructure of rabbits cornea, sclera, lens and retina. METHODS: The cornea and sclera of 24 adult New Zealand rabbits were burned by RF (power 15 W) for 10 seconds. The specimens of cornea, sclera, lens and retina were collected and examined under transmission electron microscopy (TEM) at 2 hours, 24 hours, 3 days and 14 days after burning. RESULTS: The TEM showed corneal epithelial cells nuclear chromatin pyknosis, stromal partial colloid fibers rupture, endothelial cells mitochondria turgescence and vacuolization; scleral fibroblastic nuclear chromatin pyknosis, rough endoplasmic reticulum distention, mitochondria turgescence; lens normal; retinal pigment epithelial cells mitochondria turgescence, photoreceptor cells outer segment disarrangement, inner segment mitochondria turgescence, and outer nuclear layer cells' nuclear chromatin pyknosis, 2 hours after burning. Corneal epithelial cells structure was fairly clear, some mitochondria of endothelial cells were turgescent, scleral fibroblastic mitochondria were slightly turgescent, and retinal structure was almost normal, 3 days after burning. There were no significant changes of cornea, sclera and retina in ultrustructure when the burnt groups were compared with the control group, 14 days after burning. CONCLUSION: These findings suggest that RF can cause direct lesion of cornea, sclera and indirect lesion of retina by burning cornea and selera, but the ultrastructural changes will almost recover 14 days after RF burning.

Animals↗
PubMed1991

[Blue sclera in iron deficiency conditions].

The study involved 91 inpatients with anemia or/and blue sclera. Of them 66 proved iron-deficient: 59 with blue sclera against 7 without such. Twenty-three anemic patients free of iron-deficiency included 9 patients with blue sclera and 16 without them. Blue sclera were identified in 2 patients in the absence of anemia. Blue sclera as an indication of iron-deficiency has sensitivity of 89, specificity of 64 and accuracy of 82%. It is an additional sign in identification of anemia.

Anemia, Hypochromic↗
PubMed1989

[The late results of different methods of sclera-reinforcing operations on children and adolescents suffering from progressive myopia].

The paper analyses immediate and remote results of different methods of sclera-enhancing operation in the posterior segment and equatorial zone of the eye in 362 children and juveniles (407 eyes) with progressive myopia, aged from 5 to 15 years. It is shown that for enhancement of the sclera in the posterior segment of the eye it is more advisable to use X-and Y-shaped grafts after the method of N. A. Puchkovskaia, A. S. Seniakina, G. G. Melikov or V. S. Beliaev. Stabilization of the myopic process within 6-7 years was recorded in 83.4% of cases. The method of scleroplasty after the N. N. Pivovarov's method is more preferable for enhancement of the sclera in the equatorial zone of the eye. Stabilization of the process within 3 years was recorded in 77.7%. Administration of autologous blood with hydrocortisone into the tenon's space after the A. S. Novokhatskiĭ stabilizes the myopic process within a year in 83.3% of cases. Donor material can be successfully replaced by a bioinert artificial synthetic Texplant for sclera-enhancing operations in dystrophic changes of the sclera in any part of localization. Stabilization of the myopic process within 5 years was recorded in 97.2% of cases.

Adolescent↗
PubMed1988

The complement system in sclera.

Sclera from donor globes was eluted in phosphate-buffered saline at 4 degrees C for 24 hr. Hemolytic assays were used to measure functional C1, C4, C2, C3, C5 and C6 in scleral eluates. Radial immunodiffusion was used to measure Factor B, a component of the alternative complement pathway, and albumin in scleral eluates. Molecular weight appeared to be a factor in determining the hemolytic activities of complement components C1-C6 in the sclera, because complement components with higher molecular weights had lower percentages of hemolytic activity in sclera relative to serum, while complement components with lower molecular weights had higher levels of hemolytic activity in sclera relative to serum. The sclera contains complement which could be activated by immune complexes that may be important in the pathogenesis of scleritis.

Adult↗
PubMed1995

Form deprivation myopia: elastic properties of sclera.

Thinning of the posterior sclera may imply that stretching and/or weakening of the sclera plays a role in axial elongation of myopic eyes. We investigated the elastic stress-strain properties of sclera from developing tree shrew eyes made myopic by monocular deprivation (MD) of form vision. Five days of MD induced a relative myopia (mean +/- SEM) of -5.6 D +/- 0.6 D (retinoscopy) and a vitreous chamber elongation (deprived minus control) of 106 +/- 14 microns, n = 10 (ultrasonography). Posterior scleral test samples (2 mm wide) cut from myopic eyes were significantly thinner than their contralateral eye controls (149 +/- 4 microns versus 164 +/- 4 microns, n = 10, P < 0.01) when measured with a force-controlled micrometer. However, posterior sclera from control eyes was significantly thicker than that from age-matched normal eyes (164 +/- 4 microns versus 149 +/- 3 microns, n = 10, P < 0.01). Under uniaxial tension, posterior scleral samples from myopic eyes failed at 18% lower load (162 g versus 198 g) and extended approximately 25% more than controls at a load corresponding to 20 mm Hg intraocular pressure. These differences were largely accounted for by the differences in scleral thickness. Finite element modelling of tree shrew eyes using the material properties summarised above, implies that simple elastic stretching of the sclera accounts for less than 20% of the observed difference in axial length between myopic and contralateral control eyes.

Animals↗
PubMed1998

Nonvascular contractile cells in sclera and choroid of humans and monkeys.

PURPOSE: To investigate by histochemistry and immunohistochemistry the distribution and innervation of nonvascular contractile cells in the sclera and choroid of humans and monkeys. METHODS: Globes were obtained from 2 macaque monkeys and 19 human cadavers that ranged in age from fetal life to 94 years. Immunohistochemistry was performed using monoclonal antibody against human smooth muscle (SM) alpha-actin and tyrosine hydroxylase (TH). The nicotinamide-adenine dinucleotide phosphate (NADPH)- diaphorase reaction was used as a marker for nitric oxide synthase. RESULTS: The scleras of all but fetal, newborn, and infant globes exhibited myofibroblasts, amelanotic, fibroblastlike cells having SM alpha-actin immunoreactivity. In the choroid of all but fetal eyes, SM cells were present in the suprachoroidal layer, forming a reticulum of flattened laminae, and in the choriocapillaris where ovoid-to-spindle-shaped SM cells were arrayed in parallel layers immediately adjacent to Bruch's membrane. Contractile cells in the sclera and choroid were most concentrated subfoveally and were sparse anteriorly. Nerve terminals positive for NADPH- diaphorase were colocalized with SM alpha-actin-positive cells in the sclera and choroid, whereas TH-positive nerve terminals colocalized with SM cells in the choroid. Clusters of ganglion cells were present on the posterior surface of globes near SM cells. CONCLUSIONS: The posterior choroid and sclera of humans and monkeys contain nonvascular contractile cells. The presence of nerve terminals and adjacent ganglion cells suggests neural control of these contractile cells. The absence of such contractile cells in fetal, newborn, and infant eyes is an argument against a major role of these cells in promoting ocular enlargement. These contractile cells may instead participate in regulation of refractive state by maintenance of ocular size in the face of intraocular pressure or in intermediate-term regulation of choroidal thickness.

Actins↗
PubMed1979

Normal and staphylomatous sclera of high myopia. An electron microscopic study.

The posterior sclera of three normal eyes and five staphylomatous, myopic eyes was examined by electron microscopy. The following notable differences were found in myopic sclera: a predominantly lamellar, collagen fiber bundle arrangement; a reduction in the diameter of the fibrils; a greater dispersion for the range of fibril diameters; an increase in unusual star-shaped fibrils on cross section; and a greater prevalence of fibril groups with uniform but extremely fine diameters. These findings essentially agree with those in other studies of the myopic sclera. The ultramicroscopic changes encountered inpathologic myopia are judged to be compatible with an abnormal proteoglycan composition of the interfibrillary substance in the ectatic sclera.

Adult↗
PubMed1993

Natural history of blue sclerae in osteogenesis imperfecta.

Scleral hue is an important sign which distinguishes 2 broad groupings of patients, those with and those without blue sclerae with nonlethal osteogenesis imperfecta (OI). Individuals with OI type I have distinctly blue sclerae which remain intensely blue throughout life. In OI type III and OI type IV the sclerae may also be blue at birth and during infancy, but the intensity fades with time such that these individuals have sclerae of normal hue by adolescence and adult life.

Adolescent↗
PubMed2003

Melatonin receptor expression in the cornea and sclera.

The scornea and sclera have been shown to exhibit circadian rhythms in cellular proliferation, wound healing and extracellular matrix synthesis. The distribution of melatonin Mel1a and Mel1c receptors was examined in the cornea and sclera of the Xenopus laevis eye in order to determine whether melatonin may potentially influence the growth and/or development of these ocular tissues. Sections of adult X. laevis eyes were analyzed by immunocytochemistry and confocal microscopy, using antibodies prepared against specific peptide sequences of the Xenopus Mel1a and Mel1c receptor proteins. Antibodies were pre- incubated with their appropriate antigenic peptides to control for non-specific labelling. Analysis of the distribution of Mel1a and Mel1c receptor immunoreactivity in the Xenopus eye revealed that both the Mel1a and Mel1c receptors were located in the outer fibrous layer (OFL) of the sclera, with Mel1c labelling being the most prominent. Similarly, Mel1a and Mel1c (Mel1c mostly) were also located in cells of the inner fibrous layer (IFL) with Mel1c being most abundant. The chondrocytes of the cartilaginous layer also appeared to express Mel1a, Mel1c, or both receptors. Both Mel1a and Mel1c receptor immunoreactivity were observed in the corneal epithelium and endothelium. Whereas the Mel1a antibody labelled the entire corneal epithelial layer, the Mel1c antibody labelled only the most superficial layer of epithelial cells. Cell processes of fibroblasts of the corneal stroma were immunoreactive for either Mel1a or Mel1c receptors. The identification of Mel1a and Mel1c receptors in restricted distributions in the cornea and sclera suggests that melatonin may play a role in the cellular physiology of these ocular tissues.

Animals↗