Glycoproteins of trabecular meshwork, cornea and sclera

Is the human sclera a tendon-like tissue? A structural and functional comparison

Collagen rich connective tissues fulfill a variety of important functions throughout the human body, most of which having to resist mechanical challenges. This review aims to compare structural and functional aspects of tendons and sclera, two tissues with distinct location and function, but with striking similarities regarding their cellular content, their extracellular matrix and their low degree of vascularization. The description of these similarities meant to provide potential novel insight for both the fields of orthopedic research and ophthalmology.

Aspergillus Flavus Necrotising Scleritis following Pars Plana Vitrectomy

PURPOSE

To report a case of fungal necrotising scleritis following pars plana vitrectomy. Results: A 65-year-old lady underwent phacoemlsificication with posterior capsular rupture and posteriorly dislocated lens in her left eye. On the same day she underwent 20 gauge pars plana vitrectomy and phacofragmentation. Postoperative period was uneventful for up to 6 weeks when she developed necrotising anterior scleritis with suppurative nodules. Scraping from the suppuration confirmed the presence of Aspergillus flavus. She was treated with topical Voriconazole and oral Itraconazole. Conclusion: We describe the first case of fungal necrotising scleritis without intraocular inflammation following pars plana vitrectomy (PubMed Search). Infection should be kept in the differential diagnosis of post-operative necrotising scleritis even in the absence of risk factors like hypopyon or diabetes. Early recognition improves final outcome. Medical therapy should be continued even after presumed cure to take care of residual fungi and prevent recurrences.

The Effect of Cytokine-Stimulation and Pharmacologic Intervention on PGE2 Production in Primary Human Conjunctival and Corneal Cells

We studied the production of PGE2 by human conjunctival and corneal cells in response to inflammation, and reduction of inflammation with non-steroidal anti-inflammatory drugs. Primary cultures of human conjunctival epithelial cells, fibroblasts, corneal epithelial cells, and keratocytes were incubated with IL-4 and TNF-α. PGE2 and COX-2 levels were analyzed. Effects of anti-inflammatory and anti-immune drugs on PGE2 production were also investigated. IL-4 and TNF-α induced the generation of PGE2 and COX-2 in conjunctival and corneal cells. Epithelial PGE2 production was significantly lower than in keratocytes and fibroblasts, which was down-regulated by aspirin. IL-4 and TNF-α enhanced the inflammatory response via prostaglandin production which contributed to ocular surface inflammation. Prostaglandin production was higher in stromal cells than epithelial cells. These results suggest that the epithelial barrier disruption may contribute to ocular allergic inflammation by the PGE2 production from stromal cells. Moreover, NSAIDs were effective in suppressing PGE2 production in our experiment.

Acute Unilateral Anterior Ischemic Optic Neuropathy Secondary to Optic Nerve Head Drusen: Report of a Rare Coexistence

A 45-year-old white male noticed on awakening the painless loss of inferior vision in the left eye 2 days ago. He was otherwise well and his medical history was unremarkable. Visual acuity was 20/20 in OD and 20/32 in OS with a left inferior altitudinal defect and right blind spot enlargement demonstrable on visual field test. On fundus examination, both disc margins were blurred and the left disc was diffusely oedematous, with linear haemorrhages in the adjacent nerve fibre layer. Radiologic imaging and laboratory tests were unremarkable. Bilateral optic nerve head drusen (ONHD) was demonstrated by optical coherence tomography and fundus autofluorescence imaging. Unilateral acute non-arteritic anterior ischemic optic neuropathy (NAION) and concomitant bilateral ONHD were diagnosed. NAION may develop secondary to ONHD. Therefore, clinicians should be aware of this rare association and inform the patients about this risk. Patients with ONHD should be followed-up periodically in terms of possible ischemic complications.

Expression Profile of the Integrin Receptor Subunits in the Guinea Pig Sclera

PURPOSE

The ocular dimensional changes in myopia reflect increased scleral remodeling, and in high myopia, loss of scleral integrity leads to biomechanical weakening and continued scleral creep. As integrins, a type of cell surface receptors, have been linked to scleral remodeling, they represent potential targets for myopia therapies. As a first step, this study aimed to characterize the integrin subunits at the messenger RNA level in the sclera of the guinea pig, a more recently added but increasingly used animal model for myopia research.

METHODS

Primers for α and β integrin subunits were designed using NCBI/UCSC Genome Browser and Primer3 software tools. Total RNA was extracted from normal scleral tissue and isolated cultured scleral fibroblasts, as well as liver and lung, as reference tissues, all from guinea pig. cDNA was produced by reverse transcription, PCR was used to amplify products of predetermined sizes, and products were sequenced using standard methods.

RESULTS

Guinea pig scleral tissue expressed all known integrin alpha subunits except αD and αE. The latter integrin subunits were also not expressed by cultured guinea pig scleral fibroblasts; however, their expression was confirmed in guinea pig liver. In addition, isolated cultured fibroblasts did not express integrin subunits αL, αM, and αX. This difference between results for cultured cells and intact sclera presumably reflects the presence in the latter of additional cell types. Both guinea pig scleral tissue and isolated scleral fibroblasts expressed all known integrin beta subunits. All results were verified through sequencing.

CONCLUSION

The possible contributions of integrins to scleral remodeling make them plausible targets for myopia prevention. Data from this study will help guide future ex vivo and in vitro studies directed at understanding the relationship between scleral integrins and ocular growth regulation in the guinea pig model for myopia.

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.

Trabecular cell expression of fibronectin and MMP-3 is modulated by aqueous humor growth factors

We investigated the mRNA and protein expression of fibronectin and stromelysin-1 (matrix metalloproteinase-3, MMP-3) by trabecular cells treated with growth factors present in primary and secondary aqueous humors. Serum-deprived trabecular cells were incubated for 48 hr or 7 days in medium containing either primary or secondary aqueous humor growth factors or in serum-free medium. We extracted total RNA, performed reverse transcription-polymerase chain reaction using primer pairs for fibronectin, stromelysin-1 and glyceraldehyde-3-phosphate dehydrogenase (GAPDH) and quantified the products. We utilized Western blotting to detect and quantify fibronectin and stromelysin-1 protein. Compared to controls, expression of fibronectin mRNA by trabecular cells was increased by 50 and 100% after incubation in primary aqueous humor growth factors for 48 hr or 7 days, respectively, and 50 and 130% after incubation in secondary aqueous humor growth factors. Stromelysin-1 mRNA expression was decreased by 25 and 50% after incubation in primary aqueous humor growth factors for 48 hr or 7 days, respectively, and 80 and 85% after incubation for 48 hr or 7 days, respectively, in secondary aqueous humor growth factors. Fibronectin protein increased 3.5-fold and 6-fold after incubation for 48 hr with primary or secondary aqueous humor growth factors, respectively; after 7 days, the level increased 4- and 7-folds, respectively. Stromelysin-1 protein was not detectable by western blotting. The up-regulation of fibronectin mRNA by trabecular cells exposed to growth factors present in secondary aqueous humor augmented by the down-regulation of stromelysin-1 mRNA contributed to the accumulation of fibronectin. Our findings open the possibility that induction of stromelysin-1 gene expression in the trabecular meshwork of glaucomatous eyes could effectively reduce buildup of fibronectin in the aqueous outflow pathway to decrease outflow resistance in glaucomatous states of the eye.

Transscleral drug delivery to the retina and choroid

Rapid advances in the molecular pathogenesis of retinal and choroidal disorders have highlighted the urgent need for innovative drug delivery modalities to the loci of pathology. In vitro and in vivo studies suggest that the transscleral route may offer a means to achieve the goal of sustained, targeted drug delivery to the posterior segment. Potentially therapeutic concentrations of macromolecules with retention of bioactivity can be attained in the choroid and retina via minimally invasive transscleral delivery.

The effect of hydration and matrix composition on solute diffusion in rabbit sclera

There is increasing interest in the possibility for drug delivery into the vitreous humor across the conjunctiva and sclera as an alternative route to the conjunctiva-cornea pathway. As a preliminary to human studies we have investigated the influence of scleral composition and hydration on solute transport in the rabbit sclera. Intermuscular sclera was excised from adult New Zealand rabbits. Tissue samples were either examined directly (controls), digested using chondroitinase ABC or crosslinked using glutaraldehyde. The effect of these treatments on the ultrastructural appearance of the sclera was assessed. Diffusion and partition coefficients for solutes of different molecular weights [sodium chloride (23 MW),(14)C sucrose (342 MW) and dextran-fluoresceins (3, 10, 40 and 70 kDa)] were measured in relation to tissue treatment. The results were used to determine the effect of tissue structure and composition on solute movement. We have found that: (1) diffusion and partition coefficients are sensitive to solute MW, decreasing as MW increases; (2) diffusion and partition coefficients are sensitive to tissue hydration, increasing as hydration increases; (3) crosslinking of the sclera by glutaraldehyde reduced the partition coefficients significantly for solutes with MW over 3 kDa; and (4) removal of glycosaminoglycans has only a small effect on either diffusion or the partition coefficient.