In vivo comparison of three different porous materials intended for use in a keratoprosthesis.

AIM: The goal was to compare the biological response of the corneal stroma with three porous materials: a melt blown microfibre web of polybutylene:polypropylene (80:20); a polyester spun laced fabric (polyethylene terephthalate), and an expanded polytetrafluoroethylene. Fifty per cent of each of the materials were modified using argon radio frequency. METHODS: Discs (6 mm in diameter) were inserted into interlamellar stromal pockets and followed for a period of 12 weeks. Clinical evaluations were performed weekly. At 6 and 12 weeks, fibroplasia and the distribution of matrix proteins and growth factors (bFGF and TGF-beta) were evaluated immunohistochemically. The characterisation of glycosaminoglycans was determined after selective extraction and digestion. RESULTS: The response to the disc resembled that of a wound with a decrease in keratan sulphate and an increase in dermatan sulphate. Pretreatment of the disc reduced corneal oedema and neovascularisation. Heparan sulphate, not normally detected in the corneal stroma, was detected in the region immediately surrounding the disc and in the discs of some materials. The presence of glycosaminoglycans and collagens in the disc indicated that cells had migrated into the disc and deposited a complex matrix in all three materials. The collagen response was not surface specific. bFGF and TGF-beta were detected in the region between the disc and the stroma in the polybutylene material and became diffuse with time. CONCLUSION: Fibroplasia occurred most rapidly into the polyester discs but was accompanied by a large number of inflammatory cells. While the distribution of collagens was not altered by the material, the expression and distribution of growth factors was material dependent. bFGF was expressed transiently and occurred before that of TGF-beta. It is predicted that the transient expression of growth factors mediates the regulation of matrix proteins.

Advances in polyvinyl alcohol hydrogel keratoprostheses: protection against ultraviolet light and fabrication by a molding process.

Our goal was to: 1) modify poly(vinyl alcohol) hydrogels intended for use in a synthetic cornea to absorb ultraviolet light and 2) develop molding procedures for the fabrication of the device. Two ultraviolet light-absorbing monomers were incorporated by copolymerization. The resulting hydrogels protected against ultraviolet light, were not toxic to corneal fibroblasts, and the protection did not diminish during prolonged aqueous exposure. A novel keratoprosthesis molding procedure was developed that made use of the phase transition properties of mixtures of poly(vinyl-trifluoroacetate) and acetonitrile. In this procedure the keratoprosthesis was shaped and a fibrous skirt was bonded to it in a single operation. Composite keratoprostheses were designed and prepared for in vivo testing.

Intraocular pressure-raising potential of 1.0% rimexolone in patients responding to corticosteroids.

OBJECTIVE: To compare the intraocular pressure (IOP) elevating potential of 1.0% rimexolone and 0.1% fluorometholone alcohol ophthalmic suspensions in patients known to have responded to corticosteroids. DESIGN: In a double-masked, randomized, single-eye, crossover protocol, corticosteroid responsiveness initially was verified in 40 asymptomatic known steroid responders by challenge with either 0.1% dexamethasone sodium phosphate or 1.0% prednisolone acetate for up to 6 weeks. After a 1-month medication washout, subjects randomly received either rimexolone or fluorometholone for 6 weeks. Medications were again discontinued for 1 month, and subjects then received the alternate drug for 6 weeks. RESULTS: There was no significant difference between rimexolone and fluorometholone in the number of subjects demonstrating a 10-mm Hg increase in IOP or in the mean number of weeks required to achieve a 10-mm Hg response. Responses occurred in significantly more subjects receiving dexamethasone sodium phosphate (P = .001) or prednisolone acetate (P < .001) and in a significantly shorter interval than in subjects receiving rimexolone. CONCLUSIONS: Rimexolone has a low IOP-elevating potential, comparable to that of fluorometholone and less than that of dexamethasone sodium phosphate and prednisolone acetate.

Effect of pretreating porous webs on stromal fibroplasia in vivo.

We have previously demonstrated that keratocytes penetrate and deposit collagen after a porous web is inserted into interlamellar corneal pockets. In these studies our goal was to determine whether pretreatment of the porous discs would enhance wound healing. We have evaluated four methods of pretreating the porous disc prior to its placement in the stroma. The pretreated discs were followed in vivo for a period of 42 days. The criteria we used to determine whether pretreatment affected wound healing were: collagen deposition, extent of fibroplasia, the synthetic rate of keratocytes within the disc, and lack of edema. Our results indicate that preseeding with stromal keratocytes enhanced the overall synthetic rate and specifically enhanced the amount of collage deposited within the web.

Comparative anti-inflammatory efficacy of topical corticosteroids with low glaucoma-inducing potential.

Fluorometholone and clobetasone butyrate have been developed as ophthalmic corticosteroids because of their lesser potential to elevate intraocular pressure. Nevertheless, their primary use is the inhibition of an inflammatory response. Quantification of their anti-inflammatory effect in the rabbit cornea indicates that 0.1% fluorometholone and 0.1% clobetasone butyrate are effective, but weak, anti-inflammatory agents. An increase in concentration of fluorometholone to 0.25% failed to enhance its anti-inflammatory effectiveness significantly, while an increase in concentration of clobetasone butyrate to 0.5% did significantly increase its anti-inflammatory effect. As with all other corticosteroid bases studied to date, formulation of fluorometholone as an acetate derivative significantly increased its effectiveness, rendering it as effective as 1.0% prednisolone acetate, the most effective of commercially available ophthalmic corticosteroids.

In vivo fibroplasia of a porous polymer in the cornea.

We have developed a melt-blown fibrous construction of polybutylene/polypropylene in which we previously demonstrated keratocyte ingrowth and collagen synthesis in vitro. In the present studies, we evaluated this material in vivo in interlamellar corneal pockets for periods of up to six months. By day 42, the porous interstices of the disc were heavily populated with keratocytes. Extracellular matrix deposition occurred and there was a 5000-fold increase in total protein and a 1000-fold increase in total collagen over background. The cells within the disc continued to be synthetically active for the six months of our study. Discs remained in corneas for periods of up to one year without any extrusion. This material has great promise as a porous peripheral component of a keratoprosthetic device.

Antibacterial effectiveness of ciprofloxacin 0.3% ophthalmic solution in the treatment of bacterial conjunctivitis.

Two hundred eighty-eight cases of culture-proven bacterial conjunctivities were evaluated as part of two multicentered, randomized, prospective clinical studies comparing the antibacterial efficacy of topically administered ciprofloxacin 0.3% either with a placebo or with tobramycin 0.3%. In the first study, ciprofloxacin was significantly (P less than .001) more effective than the placebo. It eradicated or reduced the various bacterial pathogens in 93.6% of patients, compared to 59.5% for the placebo. In the second study, ciprofloxacin (94.5%) and tobramycin (91.9%) were equally effective. Topically applied ciprofloxacin eradicated or reduced all isolated bacterial species, attesting to its broad antibacterial spectrum and its potential usefulness in treating external ocular infections.

Clinical evaluation of ciprofloxacin 0.3% ophthalmic solution for treatment of bacterial keratitis.

A multicenter, prospective clinical study of 148 culture-proven cases of bacterial keratitis, treated with ciprofloxacin 0.3% ophthalmic solution, compared its clinical and antibacterial efficacy with the standard therapy regimen of each investigator. Most often, this consisted of topically administered fortified cefazolin (33 mg/ml) and fortified gentamicin or tobramycin (14 mg/ml). Two control groups were studied: (1) patients treated while the ciprofloxacin study was ongoing (not enrolled group); and (2) patients treated during the year before initiation of the ciprofloxacin study (historical group). Treatment with ciprofloxacin yielded a 91.9% success rate. Standard therapy yielded an 88.2% success rate among not enrolled control patients and an 88.3% success rate among the historical control patients. No serious side effects accompanied ciprofloxacin administration. In vitro susceptibility testing showed ciprofloxacin to be highly effective against bacterial corneal pathogens. These findings suggest that ciprofloxacin 0.3% is safe and effective as a single agent for the treatment of bacterial keratitis.

Quantification of stromal destruction in the inflamed cornea.

An intrastromal injection of endotoxin lipopolysaccharide (LPS) in one eye of New Zealand albino rabbits induced a prominent keratitis characterized clinically and microscopically by edema and infiltration. Polymorphonuclear leukocytes (PMNs) constituted the primary invading leukocytic element. Collagen synthesis was measured by pulsing the corneas with 3H-proline before inducing inflammation. The invasion of the cornea by leukocytes did not alter the conversion of proline to hydroxyproline significantly in the stroma during the 14-day observation period, signifying that there were only negligible changes in the rate of collagen synthesis. However, the percentage of total stromal protein represented by collagen (ie, collagen/total protein) was only 50% of that in comparable corneas receiving an injection of phosphate-buffered saline. Some animals were rendered leukopenic by intravenous nitrogen mustard before intrastromal LPS injection caused a less severe corneal inflammatory response, characterized microscopically by fewer infiltrating leukocytes. Similarly, in nonleukopenic rabbits, topical therapy with 1% prednisolone acetate markedly reduced the corneal inflammatory response which also was characterized by fewer invading leukocytes. In neither instance was there extreme collagen loss, suggesting that the loss of stromal collagen is related to PMN infiltration.

Oncocytoma of the caruncle: a case report and ultrastructural study.

A case of oncocytoma of the lacrimal caruncle is reported, in which extensive ultrastructural studies were completed on the surgical specimen. Individual oncocytes were columnar in shape with apical surface microvilli. Their cytoplasm was filled with two types of mitochondria. Most were very large and ovoid with cristae arranged in a wide array of patterns. A smaller number of mitochondria were long and slender with more typical cristae. Two types of granular inclusions, presumed to represent alpha- and beta-glycogen deposits, were found within a small number of the large mitochondria. Poorly differentiated desmosomes joined the lateral surfaces of adjacent oncocytes. In some cases, these junctions had mitochondria attached to their cytoplasmic surfaces. A comparison is made between ultrastructural features of oncocytes in the caruncle and those found elsewhere. The relationship noted between mitochondria and desmosomes, which occurs predominantly in secretory epithelia, is also discussed.

In vitro evaluation of fibroplasia in a porous polymer.

We evaluated a polybutylene/polypropylene blend in a blown microfiber configuration in vitro for potential use as the peripheral area of a keratoprosthetic device. Material properties such as ultimate tensile strength and ultimate elongation were measured. Stromal fibroblasts were seeded onto the material in vitro, and cell proliferation between uncoated and Type I collagen coated discs did not differ significantly. Fibroblasts could be seen migrating along the fibers and also traversing the fibers. The synthesis of connective proteins was examined. Laminin, fibronectin, and Type I collagen were detected by day 8. The experiments demonstrate that stromal fibroblasts can adhere onto the fibers, proliferate, and synthesize connective tissue proteins. Experiments are now being conducted to further evaluate the material in vivo.

Effect of topically administered epidermal growth factor on corneal wound strength.

A 9-mm perforating corneal wound was created in one eye of New Zealand albino rabbits, sutured, and treated with mouse-derived epidermal growth factor (1 mg/L), human-derived epidermal growth factor (1.0 mg/L to 100 mg/L), or buffered saline, instilled once, twice, or four times daily. Both mouse-derived epidermal growth factor and human-derived epidermal growth factor significantly increased the tensile strength of full-thickness corneal wounds after 9 days of topical therapy. For human-derived epidermal growth factor, a concentration of 10 mg/L administered twice daily produced the maximal effect. An increase in either the concentration of epidermal growth factor or its frequency of administration failed to induce a further increase in wound strength. Indeed, at a concentration of 100 mg/L, human-derived epidermal growth factor appeared to lose its ability to accelerate healing of full-thickness corneal wounds.

Ultrastructural changes in the posterior layers of the cornea in Schnyder's crystalline dystrophy.

A case of central crystalline dystrophy of Schnyder is presented in which ultrastructural studies were performed on the corneal specimen after penetrating keratoplasty. Electron microscopic changes were documented not only in the anterior but in the posterior stroma and in the corneal endothelium. In the posterior stroma and at the interface between the stroma and Descemet's membrane, numerous ovoid, electron-lucent spaces were present that most likely represented foci of lipid deposition. In addition, rare, focal areas of endothelial cell degeneration were observed that produced minute discontinuities in the endothelial cell covering of Descemet's membrane. Changes in the posterior layers of the cornea in Schnyder's crystalline dystrophy may contribute to the comparatively poorer surgical results obtained with lamellar rather than full-thickness grafts in these cases.