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Biomedical subjects

M F Refojo

Publications and source records attributed to M F Refojo.

At least 55 records · Page 3Linked to original sources
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↗
PubMed1988

Extraction of retinol and cholesterol by intraocular silicone oils.

According to their solubility parameters, retinol and its derivatives, as well as cholesterol and other lipophilic substances, are predicted to dissolve in intraocular silicone and fluorosilicone oils. Calf retinas were extracted in vitro with these oils and the oils then analyzed spectrophotometrically. The following levels were found after extraction for 4 and 48 hours, respectively: for retinol, silicone oil, 0.5 and 3.7 micrograms/ml, and fluorosilicone oil, 0.5 and 3.3 micrograms/ml; for cholesterol, silicone oil, 0.5 and 6.4 micrograms/ml, and fluorosilicone oil, 0.8 and 3.7 micrograms/ml. In in vivo experiments, intraocular oils were removed from rabbit eyes at 4 days to 10 weeks after injection. The retinol levels were 1.7 to 11.4 micrograms/ml in silicone oil and 2.4 to 7.3 micrograms/ml in fluorosilicone oil; the cholesterol levels were 2.7 to 12.6 micrograms/ml in silicone oil and 7.5 to 15.6 micrograms/ml in fluorosilicone oil. Fluorosilicone and silicone oils (1000 cs) removed from human eyes at 7.3 and 102.0 weeks postoperatively had a retinol content of 5.4 and 2.9 micrograms/ml, respectively. Silicone oil of 1000 cs removed from a patient 51 weeks postoperatively and silicone oil of 12,500 cs removed 96 weeks postoperatively gave reaction characteristics for cholesterol, 230 and 99 micrograms/ml, respectively.

Animals↗
PubMed1988

BCNU in silicone oil in proliferative vitreoretinopathy: I. Solubility, stability (in vitro and in vivo), and antiproliferative (in vitro) studies.

Various pharmacologic agents have been tried to control proliferative vitreoretinopathy (PVR). However, most are water soluble and cannot be used with silicone oil (SO), a tamponade agent also used in PVR management. We evaluated a lipophilic, antiproliferative drug, BCNU, in regard to its solubility and stability in SO, its release from SO into an aqueous solution, and its effect on cell cultures. BCNU is soluble in SO (peak concentration in micrograms/ml 1020, 750, and 294 at 37 degrees C, 21 degrees C, and 4 degrees C, respectively), and stable (half-life = 6.7 weeks at 37 degrees C, 17.9 weeks at 21 degrees C). At 4 degrees C, no significant decrease in concentration up to eight weeks was noted. BCNU is released from SO to water (partition coefficient = 10.28 +/- 2.16). Its median inhibitory doses (ID50) on bovine retinal pigment epithelial (RPE), rabbit RPE, and subconjunctival fibroblast cells are 13, 1.9, and 15.6 micrograms/ml, respectively. BCNU may be a useful pharmacologic tool to control PVR.

Animals↗
PubMed1987

Pseudomonas attachment to new hydrogel contact lenses.

The adhesion of two strains of Pseudomonas aeruginosa to unworn hydrogel contact lenses (CLs) was studied by scanning electron microscopy. New daily-wear polymacon lenses (38.6% water content) and extended-wear lidofilcon A lenses (70% water content) were exposed to a suspension of 10(8) colony-forming units per milliliter of P aeruginosa for 2, 5, 15, 30, and 60 minutes. Increasing numbers of bacteria were found to attach to the lenses with time, and no significant differences between CL types were demonstrated. Attachment was considered to be irreversible since washing did not remove the bacteria. We conclude that P aeruginosa can actively attach to new, unworn hydrogel CLs.

Bacterial Adhesion↗
PubMed1987

Effectiveness of silicone oil removal from rabbit eyes.

Silicone oil (1000 and 12,500 cs) and fluorosilicone oil (1000 and 10,000 cs) were dyed red and injected into a gas-created space in the vitreous cavity of 51 rabbit eyes. Later the oils were removed from the vitreous cavity either by lavage with balanced salt solution (group 1, 27 eyes) or by injecting a sodium hyaluronate solution, followed by lavage with balanced salt solution (group 2, 24 eyes). The average amount of oil retained in the vitreous cavity in group 1 was 0.0675 ml, and occasionally a large amount of oil was found (more than 0.1 ml in 30% of eyes). The average amount of oil retained in group 2 was 0.0114 ml, and no eye retained more than 0.1 ml of oil. The difference between the two groups was statistically significant (p less than 0.02), but there was no significant difference in oil retention within either group between the different kinds of oils, or between different viscosities of oil. The data suggest that residual oil can persist in the vitreous cavity despite thorough lavage, and that removal of silicone oil with the use of a sodium hyaluronate solution significantly lowers the risk of a large amount of residual silicone oil that is occasionally seen with conventional removal methods.

Animals↗
PubMed1987

Hydrogel contact lens-induced Pseudomonas keratitis in a rabbit model.

Unused soft contact lenses (SCL) containing 38.6% water (polymacon) and 70% water (lidofilcon A) were exposed to Pseudomonas aeruginosa (10(8) CFU/ml) for 60 min and washed. The contaminated lenses were used on rabbit eyes under the following conditions: for 1 h on a scratched corneal epithelium (16 eyes, four infected), for 24 h on normal cornea (eight eyes, none infected), and for 7 days on normal cornea (eight eyes, three bacterial infections and two noninfected epithelial defects). A control group of rabbits used an uncontaminated lens for 7 days (eight eyes, four noninfected epithelial defects). The control group and groups that wore contaminated lenses for 24 h and 7 days underwent tarsorrhaphy to keep the contact lens in place. In addition, three drops of the bacterial suspension were instilled in eyes with normal corneal epithelium (eight eyes, none infected) and scratched corneal epithelium (16 eyes, 13 infected). Results suggest that Pseudomonas-contaminated SCL give rise to keratitis only on an injured corneal epithelium and that a bacterial suspension is more pathogenic to the rabbit cornea than is a similar amount of bacteria on an SCL.

Animals↗
PubMed1987

Use of high-density fluorosilicone oil in open-sky vitrectomy.

During prolonged open-sky vitrectomy, fluid accumulates in the suprachoroidal and subretinal spaces and the resultant ballooning of the choroid and of the retina interferes with the surgery. Fluorosilicone oil (polymethyl-3,3,3-trifluoropropylsiloxane) with a specific gravity of 1.28 was tested for use as a temporary vitreous substitute during open-sky vitrectomy. After open-sky vitrectomy and bullous retinal detachment in pigmented rabbits, fluorosilicone oil flattened the retina completely in nine of nine eyes, whereas 1% sodium hyaluronate solution flattened the retina completely in only four of nine eyes. The flattening effect of fluorosilicone oil on the retina was also better than that of 1% sodium hyaluronate in an experiment with retinal detachment and giant retinal tear after open-sky vitrectomy.

Animals↗
PubMed1986

Fluorinated oils as experimental vitreous substitutes.

Two kinds of fluorinated oils (a fluorosilicone oil and a perfluoroether [Freon E15]) that have a higher density than water were evaluated as long-term vitreous substitutes. Vitreous compression using perfluoropropane gas was performed to create a space for the vitreous substitute in rabbit eyes. Two fluorosilicone oils (1000 and 10 000 centistokes) induced edema of the inner retinal layers and occasionally of the outer retinal layers regardless of viscosity or period of observation up to six months, but they were well tolerated clinically. Control eyes injected with silicone oils of comparable viscosities showed similar histopathologic findings. Freon E15 induced formation of bubbles and precipitates by one month after injection, and retinal disorganization, formation of preretinal membranes, and tractional retinal detachment by six months. Thus, Freon E15 proved to be unsuitable, but fluorosilicone oil is a possible high-density vitreous substitute.

Animals↗