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Biomedical subjects

M F Refojo

Publications and source records attributed to M F Refojo.

At least 19 recordsLinked to original sources
PubMed1992

Long-term complications of the MAI hydrogel intrascleral buckling implant.

Seven cases in which long-term complications developed from swelling of the MAI hydrogel intrascleral buckling implant are reported herein. Micro-Fourier transform infrared spectroscopic analysis of two recovered implants demonstrated the occurrence of chemical changes leading to increased swelling. Clinical problems with the implants appeared 7 to 11 years after surgery, suggesting the need for periodic, long-term follow-up. It is possible that the present-day MIRAgel implant, which has the same chemical composition as the MAI implant, may require similar precautions.

Adolescent↗
PubMed1992

In vitro adhesion of Pseudomonas aeruginosa and Staphylococcus aureus to surface passivated poly(methyl methacrylate) intraocular lenses.

Bacterial attachment to intraocular lenses (IOLs) can be a cause of infectious endophthalmitis following cataract surgery. In this study, Pseudomonas aeruginosa and Staphylococcus aureus adhered in vitro to untreated poly(methyl methacrylate) (PMMA) and to surface passivated PMMA lenses. The IOLs were placed in bacterial suspensions (1 x 10(7) cfu/ml) in vitro. Significantly fewer S. aureus attached (P < .05) to the normal PMMA IOLs (4,535 +/- [SD] 3,052 bacteria/mm2) and to passivated PMMA IOLs (8,720 +/- 10,040 bacteria/mm2) than did P. aeruginosa (normal PMMA: 67,808 +/- 45,070 bacteria/mm2, passivated PMMA: 85,795 +/- 70,647 bacteria/mm2). The differences in bacterial attachment to surface passivated IOLs and to untreated PMMA lenses were not significant.

Bacterial Adhesion↗
PubMed1992

Attachment of Pseudomonas to human-worn, disposable etafilcon A contact lenses.

After 7 days of continuous wear, Acuvue (Vistakon, Jacksonville, FL, U.S.A.; etafilcon A) lenses were soaked in a Pseudomonas aeruginosa suspension (1.4 x 10(8) cfu/ml). New Acuvue lenses served as controls. A single strain of P aeruginosa harvested from a human corneal ulcer was used throughout the experiment. Lenses were examined by culture and scanning electron microscopy (SEM). We found significantly greater (p less than 0.05) bacterial attachment to new Acuvue lenses [culture, 3.1 x 10(4) (+/- 0.82 x 10(4)) cfu/mm2; SEM, 2.6 x 10(4) (+/- 0.47 x 10(4)) bacteria/mm2] compared with those previously worn [culture, 1.0 x 10(4) (+/- 0.17 x 10(4)) cfu/mm2; SEM, 0.73 x 10(4) (+/- 0.21 x 10(4)) bacteria/mm2]. No statistical difference was found among the individuals. Our findings demonstrate that the biological coating resulting from 1 week of continuous contact lens wear restricts P. aeruginosa attachment to the Acuvue lens when comparing new and used lenses.

Bacterial Adhesion↗
PubMed1992

Intravitreal silicone and fluorosilicone oils: pathologic findings in rabbit eyes.

The effects of medical-grade intraocular silicone and commercial-grade fluorosilicone oils were studied in rabbit eyes. The experimental model consisted of lensectomized and vitrectomized eyes that did not undergo further treatment (Group 1), and three groups of lensectomized and vitrectomized eyes that were injected intravitreously 3 months earlier with medical-grade silicone oil of 1000 cs (Group 3), and 10,000 cs (Group 4). The silicone oil-injected eyes developed proliferative membranes. The fluorosilicone oil caused an intravitreous inflammatory reaction with vacuolated macrophages present around the oil that may have been due to the higher concentration of low-molecular-weight components found in the oil.

Animals↗
PubMed1991

Corneal edema after overnight lid closure of rabbits wearing silicone rubber contact lenses.

Elastofilcon A silcone rubber contact lenses induce less corneal swelling than no lens wear during sleep, and increasing the central thickness and volume of the lens does not influence its overnight performance. We sought to elucidate whether a silicone rubber lens can promote the distribution of atmospheric O2 on the cornea through a small interpalpebral opening under closed-eye conditions. Three groups of rabbit eyes comprised 12 eyes wearing Silflex (Dk 79.8 barrer) lenses, 12 with elastofilcon A (Dk 340 barrer) lenses, and 12 without lenses. All eyes were surgically closed overnight; six eyes in each group had a complete lid closure and six eyes had a partial tarsorrhaphy that left a small, central gap approximately 3 mm in length. When the lids were opened the next morning, the partially closed elastofilcon A eyes showed less corneal swelling (6.2 +/- 1.4%) than the partially closed no-lens eyes did (9.6 +/- 1.3%) (p less than 0.01), whereas the partially closed Silflex eyes were significantly more swollen (12.8 +/- 2.1%) (p = 0.01) than the other two partially closed groups were. The completely closed eyes showed no significant difference in corneal swelling among the groups. These results indicate that small lid gaps during sleep may lead to less corneal swelling when elastofilcon A lenses are used than with no lenses.

Animals↗
PubMed1991

Pseudomonas attachment to low-water and high-water, ionic and nonionic, new and rabbit-worn soft contact lenses.

The authors determined the attachment of a single strain of Pseudomonas aeruginosa to seven brands of hydrogel soft contact lenses (SCLs): nonionic, low-water (polymacon and crofilcon); nonionic, high-water (lidofilcon); ionic, high-water (bufilcon, etafilcon, and perfilcon); and surface-neutralized, high-water (bufilcon). The lenses were exposed to a 1 X 10(8) colony-forming units (CFU)/ml P. aeruginosa suspension either when new and sterile or after 24 hr of continuous wear in rabbit eyes. Quantitative scanning electron microscopy showed that, regardless of lens type, significantly fewer bacteria attached to worn than to new SCLs (P less than 0.05). The bacterial attachment on new, unworn SCLs was significantly lower (Wilcoxon rank-sum test) (P less than 0.05) on polymacon and crofilcon than on all other lenses tested except perfilcon; on etafilcon than on bufilcon; and on perfilcon than on all SCLs tested except polymacon. The bacterial attachment on rabbit-worn SCLs was significantly lower (P less than 0.05) on polymacon than on all other lenses tested except crofilcon and perfilcon; on crofilcon than on bufilcon; on lidofilcon and on surface-neutralized bufilcon than on crofilcon and perfilcon; on etafilcon than on crofilcon, bufilcon, and perfilcon; and on perfilcon than on crofilcon and bufilcon. The results did not show a consistent relationship between hydration and surface charge and P. aeruginosa adherence. Among the SCLs tested, no one lens had a decisive advantage over another, because all, both new and worn, can bind amounts of P. aeruginosa that could potentially produce bacterial keratitis on predisposed eyes.

Animals↗
PubMed1991

Ocular toxicity of low-molecular-weight components of silicone and fluorosilicone oils.

Silicone oil (SiO) and fluorosilicone oil (FSiO) are injected into the vitreous cavity in difficult cases of retinal detachment surgery. SiO and FSiO contain linear and cyclic low-molecular-weight components (LMWC) that are thought to cause ocular toxicity. Using the purified oils (without LMWC) and some of the individual LMWC, the authors evaluated the relation of the LMWC to the short-term ocular toxicity of the oils. When octamethylcyclotetrasiloxane or other single small species of linear and cyclic LMWC of SiO were injected into the rabbit anterior chamber, severe inflammation and corneal edema were induced. The ocular responses to the single species of the LMWC of SiO decreased with an increase of the molecular weights. Cyclic LMWC of FSiO (a mixture of trimethyl-3,3,3-trifluoropropylcyclotrisiloxane and tetramethyl-3,3,3-trifluoropropylcyclotetrasiloxane) also induced inflammation and corneal edema. However, unpurified SiO and FSiO, as well as purified oils (via solvent fractionation), did not cause significant adverse ocular response, presumably because the amounts of LMWC (especially the smallest species) in the oils were relatively small. Using gas chromatography, the authors analyzed SiO and FSiO recovered from rabbit and human vitreous cavities up to 2 yr after injection. In most of the cases, the concentrations of LMWC in SiO decreased after injection. This is consistent with the possibility that LMWC diffused from the oils into the ocular tissues. The long-term effect of LMWC in intraocular SiO and FSiO has not been determined. However, diffusion of LMWC into ocular tissues may relate to the chronic ocular toxicity of the oils.

Animals↗
PubMed1990

Time course of experimental Pseudomonas aeruginosa keratitis in contact lens overwear.

New perfilcon contact lenses (71% water) were placed on one eye of 36 rabbits under complete tarsorrhaphy for 7 days. The lenses were then removed, and 18 were incubated for 1 hour with a suspension of 1 x 10(8) colony-forming units per milliliter of Pseudomonas aeruginosa and replaced on their respective corneas. The remaining 18 eyes were inoculated with 0.1 mL of the P aeruginosa suspension; the lenses were not replaced. All eyes were again closed by tarsorrhaphy for 4, 8, 16, 24, 36 , or 48 hours. Ulcerative keratitis occurred in contact lens-wearing eyes only, as P aeruginosa penetrated the epithelium at 8 to 36 hours, and polymorphonuclear leukocyte migration began at 24 hours. Compared with conventional abrasion-wound models, the time course of infectious keratitis in this model was delayed, possibly due to less preexisting corneal trauma, but our findings suggest that soft contact lens wear facilitates bacterial invasion and also inhibits the host inflammatory response.

Animals↗
PubMed1990

Experimental Pseudomonas aeruginosa keratitis from extended wear of soft contact lenses.

We used a rabbit model to investigate the pathogenesis of soft contact lens-induced bacterial keratitis. Rabbit eyes underwent complete tarsorrhaphy for 7 days either with (group A, n = 14) or without (group B, n = 13) new sterile soft contact lenses. On day 7, an increase in mean corneal thickness (20.3% in group A and 17.2% in group B) was detected. New or rabbit-worn soft contact lenses were then inoculated with 10(7) colony-forming units of Pseudomonas aeruginosa or by 0.1 mL of P aeruginosa suspension. On day 9, conjunctival cultures of all eyes yielded P aeruginosa. Corneal infection developed in 11 of 14 eyes wearing new or worn, contaminated soft contact lenses. Bacterial keratitis did not develop in any of the 13 eyes inoculated with P aeruginosa suspension. Light and electron microscopy of infected eyes showed abundant polymorphonuclear neutrophils destroying the epithelium, basement membrane, and stroma. Few bacteria could be detected and only in the deep stroma. Since bacterial suspension alone caused no inflammation, soft contact lens-wear appears crucial to corneal infection in this model.

Animals↗
PubMed1990

Evaluation of a viscoelastic solution of hydroxypropyl methylcellulose as a potential vitreous substitute.

Hydroxypropyl methylcellulose (HPMC), an inert polymer that forms a viscoelastic solution in aqueous media, is useful for anterior segment surgery. A 2.2% solution of HPMC (MW 86,000 daltons) of 6,000 centistokes viscosity was evaluated as a vitreous substitute in rabbit eyes. Four days after perfluoropropane gas compression of the vitreous, the gas was exchanged with 0.5 ml HPMC. The aqueous was removed 1 and 2 weeks postinjection and at sacrifice, the vitreous was removed at sacrifice. HPMC concentrations in aqueous humor were: 0 hr, 0%; 48 hr, 0.002%; 1 week, 0.004%; 2 weeks, 0.001%; 4 weeks, 0%. HPMC concentrations in vitreous were: 48 hr, 93% of amount injected; 2 weeks, 88%; 4 weeks, 78%; 10 weeks, 0%. Hyaluronidase injected in the vitreous enhanced HPMC elimination. The effect of HPMC also was assayed on a cultured retinal pigment epithelial monolayer. Compared with controls, HPMC-treated cells maintained normal morphology at 5 days, and 2, 3, and 4 weeks as observed by light microscopy. Because of rapid intraocular decrease in viscosity, HPMC is not a good long-term vitreous replacement to support retinal tears. However, HPMC might be useful short-term to avoid postoperative hypotony, and to remove intraocular silicone oil and peel retinal membranes.

Animals↗
PubMed1990

Factors contributing to the emulsification of intraocular silicone and fluorosilicone oils.

Silicone oil (SiO) and fluorosilicone oil (FSiO) are used as vitreous substitutes during retinal detachment surgery. Emulsification of these oils causes complications in oil-injected eyes. One factor contributing to emulsification is interfacial tension (gamma i) of the oils. In general, the lower the gamma i, the more easily the oils are emulsified. We measured the gamma i of SiO and FSiO by the ring method at 37 degrees C; corrected the measured values by the Harkins-Jordan table or the Zuidema-Waters equation; and found that the gamma i between the oils and liquefied bovine vitreous was low compared with the gamma i between the oils and water (eg, gamma i of 1000 centistokes [cs]SiO against liquefied vitreous and water was 16.0 and 42.8 dyne/cm, and that of 1000 cs FSiO was 14.7 and 38.7 dyne/cm, respectively). When SiO or FSiO and liquefied vitreous were shaken in a partially filled vial, both oils were emulsified regardless of viscosity and purity. However, when the vial was filled completely (a situation in which the hydrodynamic condition of the oils may be similar to that in the eye), SiO of 1000 and 12,500 cs and FSiO of 10,000 cs did not emulsify, although FSiO of 1000 cs did emulsify. SiO was less emulsified than FSiO of the same viscosity, possibly because the smaller density difference between SiO and intraocular fluids makes agitation difficult compared with FSiO. High viscosity of the oils restricted mechanical emulsification, which was not prevented by eliminating low-molecular-weight components of the oils. Residual catalysts may relate to spontaneous emulsification, which was observed occasionally with high-viscosity SiO in water.

Animals↗
PubMed1990

Analysis and fractionation of silicone and fluorosilicone oils for intraocular use.

Silicone oil (SiO) and fluorosilicone oil (FSiO) are useful in difficult cases of retinal detachment surgery. Unidentified low-molecular-weight components (LMWC) and residual catalysts in SiO and FSiO have been implicated in the adverse reactions of the oils in the eye. The authors analyzed LMWC of SiO and FSiO using a gas chromatograph (GC) equipped with a 6-ft x 2-mm column packed with 3% SP-2250 and a flame-ionization detector. By commercially available standards and a homologous series plot, MD3M to MD23M (linear LMWC) and D4 to D30 (cyclic LMWC) were positively identified in commercial-grade 1000-centistokes (cs) SiO. Commercial-grade 12,500-cs SiO contained GC-detectable LMWC (up to MD28M and D30) at higher concentrations than commercial-grade 1000 cs SiO, although the weight percent of acetone-extractable LMWC (including those larger than MD28M and D30) was less in the former than in the latter. The GC-detectable LMWC in most medical-grade SiO were less than those in commercial-grade SiO. Tetramethylammonium siloxanolate (a residual catalyst) and tributylphosphine oxide (a heat-decomposition product of a polymerization catalyst) were tentatively identified in commercial- and medical-grade 12,500-cs SiO, respectively. Commercial-grade 1000- and 10,000-cs FSiO also contained LMWC, including F3 and/or F4 (cyclic LMWC). To eliminate LMWC from the oils, the authors developed a solvent fractionation method using acetone for SiO and hexane for FSiO. After continuous solvent extraction of SiO for 2 weeks and FSiO for 3 weeks, all measurable LMWC were eliminated from the oils.

Catalysis↗
PubMed1989

Elimination of hydroxypropyl methylcellulose from the anterior chamber of the rabbit.

The elimination of hydroxypropyl methylcellulose (HPMC) of molecular weight 86,000 daltons (2%, viscosity 4,000 centipoises; 2.5%, 15,000 centipoises) and 120,000 daltons (2%, 15,000 centipoises) from the anterior chamber of rabbit eyes was determined colorimetrically and was nearly complete by 24 hours. The elimination rate was dependent on the viscosity of the HPMC injected into the eye. Elevation of the intraocular pressure by HPMC was detected three hours after injection, but the pressure was almost normal at six hours and was normal thereafter. This effect is independent of the molecular weight, the concentration, and the viscosity of the solutions used. Using an in vitro assay method, HPMC (86,000 daltons) at 2.5% concentration in tissue culture medium was innocuous to rabbit endothelial cells.

Animals↗
PubMed1989

Keratopathy of the rabbit cornea following complete eyelid closure.

The corneal response to a complete tarsorrhaphy was studied in 46 rabbits for time periods up to 21 days. During the first 7 days of complete eyelid closure corneal thickness increased up to 18.4%, glycogen decreased 32.2%, and lactate rose 27.2%. A steep increase in corneal thickness to 89.8% appeared after 14 days, followed by decreasing values at 21 days, which was concomitant with the formation of extensive vascularized pannus. These results confirm previous findings that the partial pressure of O2 under closed eye conditions is substantially below physiologic requirements, affects endothelial pump capability, and results in major corneal swelling. When silicone contact lenses were fitted immediately before eyelid closure, corneal swelling 2 days after lid closure did not differ from that in eyes without lenses.

Animals↗
PubMed1989

Adherence of viable and nonviable bacteria to soft contact lenses.

Bacterial viability in bacterial adherence to new soft contact lenses (SCLs) was studied by exposing polymacon and lidofilcon A lenses to Pseudomonas aeruginosa: L, live, untreated bacteria; H, bacteria heated for 1 h at 100 degrees C; and P, bacteria treated with 3% hydrogen peroxide for 1 h. Cultures of groups L, H, and P showed heavy, no, and minimal bacterial growth, respectively. Scanning electron microscopy (SEM) showed significantly less bacteria on new SCLs in groups H and P. Transmission electron microscopy (TEM) showed that bacterial shape was mostly preserved in all groups, with marked intracellular and cell membrane changes and breaks (groups H and P), margination of intracellular electron-dense material (group H), and central and peripheral vacuolation (group P). Adherence to new SCLs appears to be an active process, as killed or altered bacteria adhere less.

Bacterial Adhesion↗
PubMed1989

Effects of hypertonic solutions on conjunctival epithelium and mucinlike glycoprotein discharge.

A simple, semiquantitative, histochemical method using periodic acid-Schiff (PAS) staining was developed to measure the mucinlike glycoprotein content of bathing solutions exposed to rabbit conjunctiva. Rabbit eyes were bathed in vivo in solutions of various tonicity (160, 260, 300, 330, and 363 mOsm/L). Eyes bathed in hypotonic or isotonic solutions (160, 260, and 300 mOsm/L) exhibited a steady-state glycoprotein secretion (50-100 micrograms/h). In hypertonic solutions (330 and 363 mOsm/L), glycoprotein discharge increased to 150-360 micrograms/h when the solutions were exchanged hourly for 6 h, but glycoprotein discharge increased to a much lower rate (100-167 micrograms/h) after prolonged bathing for 6 h without solution exchange. Periodic acid-Schiff--positive glycoprotein aggregates were noted more frequently on the filters of hypertonic solutions than on those of other tonicity. After eyes were bathed in hypertonic solutions, increased disruption of the surface epithelium, increased abnormal discharge of mucin granules, and decreased goblet cell density were noted in the biopsied conjunctiva. These data suggest that mucinlike glycoprotein secretion from the conjunctival goblet cells can be enhanced by the tonicity of the bathing solution, and that nonphysiological hypertonic solutions can also affect the conjunctival epithelium.

Animals↗
PubMed1988

Reevaluation of corneal complications after closed vitrectomy.

Corneal complications after closed vitrectomy were analyzed in patients treated by the same surgeon from January 1980 through December 1986. Of 428 eyes (400 patients), 64 (15%) had corneal complications, 58 (13.6%) had epithelial defects, and 12 (2.8%) had corneal edema. Among 206 diabetic eyes, 41 (19.9%) had corneal complications. Of 222 nondiabetic eyes, only 23 (10.4%) showed complications. Multiple regression analysis of possible contributing factors was performed. Diabetes, intraoperative lensectomy, and history of vitreous surgery were related significantly to the occurrence of all corneal complications combined. Our series showed a significantly decreased complication rate when compared with a previous study. Improved preoperative surgical preparation and intraoperative technique to minimize corneal trauma may have accounted for the decrease.

Cornea↗