Robert W. Snyder

Treatment of Experimental Intravitreal Fibrin With Tissue Plasminogen Activator

We produced experimental intravitreal fibrin clots in rabbits that had previous gas compression of the vitreous or intact vitreous. Twenty-four hours after production of fibrin, the eyes were injected with 25 micrograms of tissue plasminogen activator or physiologic irrigation solution. In the gas compression group (n = 11), all tissue plasminogen activator-treated eyes cleared within six hours of injection; complete clearing was not seen until six days in the physiologic irrigation solution-treated eyes (n = 9). A similar response was seen in the intact vitreous group. No evidence of toxicity was observed as measured by slit-lamp biomicroscopy, intraocular pressure, corneal thickness, electroretinography, or histopathologic examination.

Resident Phacoemulsification Experience Using the In Situ Nuclear Fracture Technique

We retrospectively reviewed all of the 176 phacoemulsification procedures attempted by two third-year residents from July 1, 1991 to June 30, 1992. The in situ nuclear fracture technique was performed in 131 eyes; a nonfracture technique in 45. Overall, the rate of vitreous loss was 4.5% (8 of 176). The rate of vitreous loss associated with the in situ nuclear fracture technique was 3.1% (4 of 135); with the nonfracture technique, 8.9%. We conclude that phacoemulsification can be learned and performed by residents with vitreous loss rates comparable to those reported for extracapsular cataract extraction.

Evaluation of an Aqueous drainage glaucoma device constructed of ePTFE

Aqueous drainage devices for the treatment of glaucoma are subject to the same limitations as most polymeric implants, namely a healing response comprised of chronic inflammation and fibrosis. The most widely used devices are currently made of silicone or polypropylene, materials that exhibit biocompatibility difficulties when they are implanted on the sclera underneath the conjunctiva of the eye. Decreased outflow of aqueous fluid to the conjunctival space caused by the development of a fibrous capsule around the device accounts for at least 20% of aqueous shunts failures. Clearly, the need exists to improve the healing response to aqueous drainage devices, and one approach is to develop new polymers or polymer modifications. Improved devices would elicit a limited fibrotic response while increasing neovascularization around the implant. Previous studies have indicated that denucleation markedly improves the healing characteristics and biocompatibility of expanded polytetrafluoroethylene (ePTFE). We reasoned that altering the design of drainage devices to allow the use of denucleated ePTFE in vivo might minimize fibrosis, thereby improving shunt function. We found that after 8 weeks in vivo, experimental shunt function was equivalent to the Baerveldt shunt, while there was less scarring with increased neovascularizatin. These findings suggest that ePTFE has potential as an improved, long-term alternative material for use in constructing glaucoma shunts.

Transscleral Repair of Recalcitrant, Inadvertent, Postoperative Cyclodialysis Cleft

We present a patient with a cyclodialysis cleft in whom, after established medical, laser, and initial surgical interventions had failed to close the cleft, we successfully used ab externo suture placement to appose and close it. Although we present only one case, we believe this procedure, which may be useful in pseudophakic and aphakic eyes, is easier to perform than previously described techniques.

Respiratory distress after a Nadbath block.

Dysphagia and respiratory distress developed in three patients after administration of a Nadbath block. This complication may have resulted from inadvertent paralysis of the vagus, ipsilateral glossopharyngeal, and spinal accessory nerves causing pooling of oropharyngeal secretions and laryngospasm. Respiratory distress after a Nadbath block may be managed by properly positioning the patient. Short hypodermic needles (less than 12 mm), small volumes of anesthetic solution (less than 3 ml), and omission of hyaluronidase may reduce the incidence of this complication.

A Comparison of Gatifloxacin to Ciprofloxacin in the Prophylaxis of streptococcus pneumoniae in Rabbits in a Lasik Model

Purpose. To investigate the efficacy of the fourth-generation fluoroquinolone, gatifloxacin 0.3%, compared to ciprofloxacin 0.3%, in preventing Streptococcus pneumoniae keratitis in a rabbit laser in situ keratomileusis (LASIK) model. Methods. Twelve albino rabbits had bilateral lamellar flaps created. Group A (eight eyes) was given gatifloxacin 0.3%; group B (eight eyes) was given ciprofloxacin 0.3%; and group C (eight eyes) served as the controls. Groups A and B received one drop of antibiotic 20 minutes before the creation of the lamellar flap, at the conclusion of flap formation, and four times per day for 3 days. All corneas were inoculated with 0.1 mL of 4 × 105 organisms/mL of S. pneumoniae immediately after flap formation. On day 3, all corneas were examined and cultured. Results. Group A (gatifloxacin) had no infiltrates and three areas of 1-mm central corneal haze. On day 3, one of eight corneas had a positive culture. Group B (ciprofloxacin) had seven infiltrates, including one perforation, and six of eight corneas had positive cultures. Group C (control) had eight corneal infiltrates, and all eight corneas had positive cultures. The data show a statistically significant difference between gatifloxacin and ciprofloxacin and gatifloxacin and control for mean infiltrate size and mean culture scores. Conclusions. The fourth-generation fluoroquinolone, topical gatifloxacin 0.3%, is superior to topical ciprofloxacin 0.3% for prophylaxis against a clinical isolate of S. pneumoniae in a rabbit LASIK model.

Aqueous Penetration of Gatifloxacin and Levofloxacin into the Rabbit Aqueous Humor Following Topical Dosing

The aqueous penetration of the commercial preparations of the fluoroquinolone antibiotics ofloxacin, ciprofloxacin, levofloxacin, and gatifloxacin were compared following topical dosing in a rabbit model. Levofloxacin achieved the highest aqueous concentrations, with a mean aqueous level of 4.8014 microcg/mL (p = 0.002, p = 0.00002, p = 0.015.) Ofloxacin (2.5136 microcg/mL) and gatifloxacin (2.4817 microcg/mL) achieved statistically equal aqueous concentrations (p = 0.479). Ciprofloxacin reached the lowest levels in the aqueous humor (0.9616 microcg/mL, p = 0.00002, 0.00004, 0.008). Gatifloxacin alone achieved concentrations in excess of the MIC90s of gram-positive pathogens of concern.

Is tisseel a viable option in posterior lamellar keratoplasty

Purpose: It is well known that Tisseel Fibrin Sealant provides an excellent tissue adhesive. However, its thick and viscuous nature makes it nearly impossible to apply it in a uniform and thin layer. We propose applying the sealant phase as a dry powder and polymerizing it in-vivo by exposing it to thrombin solution after a graft has been placed. Methods: For each experiment two rabbit corneal buttons were affixed to each other using either Tisseel or thrombin plus dry fibrinogen component, the tensile strength of the bond was then tested in the tension box. Balanced salt solution was used as an aqueous substitute. Results: Tisseel was demonstrated to create significant adhesive tensile force (expressed as N/m2) between corneal buttons (P < 10−7). Using only the dry fibrinogen component followed by injection of the thrombin solution directly into the balanced salt solution did not significantly alter the strength of the bond (P = 0.18). Conclusion: The use of the dry fibrinogen component followed by injection of thrombin solution into the balanced salt solution, without the accompanying fibrinolysis inhibitor, is equally effective in adhesive strength when compared to complete Tisseel. This technique may be used in lamellar corneal surgery, although there would be potential difficulties with its application in the in vivo setting.