[Retinal damage by perfluorocarbon liquids - a question of specific gravity? Intraocular pressure peaks and shearing forces]. / Retinale Schäden durch flüssige Perfluorkarbone - eine Frage des spezifischen Gewichts? Intraokulare Druckspitzen und Scherkräfte.

BACKGROUND: Perfluorocarbon liquids (PFCL) cause retinal damage when used as long-term ocular endotamponades. Whether these changes are related to the mechanical or to the chemical properties of PFCL is unclear. The purpose of this study was to evaluate pressure spikes or shearing forces during endotamponade with PFCL and standardised eye movements. MATERIAL AND METHODS: Part 1: In an eye model the resulting pressure forces of 6 PFCL were measured at four different sites during standardised eye movements. Part 2: Shearing forces were determined in a plexiglass eye model and the resulting tangential forces at the PFCL-retina interface were calculated. Part 3: Rabbit eyes were vitrectomised and filled with light and heavy fluorocarbons for 6 weeks. Subsequently, the retina were examined histologically and by immunohistochemistry. RESULTS: With increasing filling of the eye model, the maximum of the pressure peaks moved from the inferior wall of the eye model to the lateral eye walls. For perfluorodecalin (PFD) the highest pressure peak was 407 Pa with a 75 % filling of the vitreous cavity. The lowest pressure peak was 314 Pa with a 50 % filling of hexafluoropropene oxide. Shearing forces for standardised accelerations were dependent on viscosity and ranged between 0.87 mN/m(2) (perfluorohexyloctane) and 8055 mN/m(2) (hexafluoropropene oxide). Part 3: Histological and immunohistochemical analyses did not reveal pressure-related damage or any difference between the effects of the different tamponades in vivo. CONCLUSION: In comparison with physiological dynamic and static pressure peaks, the measured mechanical forces induced by intraocular PFCL tamponades are low. Specific gravity and mechanical damage by intraocular PFCL as a cause of retinal damage seem unlikely. Animal studies underline these findings.

[The influence of a new surface treatment of silicone intracoular lenses with fluoralkylsitan on the adherence of endophthalmitic bacteria in vitro]]. / Effekt einer neuen Oberflächenbehandlung von Intraokularlinsen aus Silikon durch ein Fluoralkylsilan auf das Adhärenzverhalten Endophthalmitis-relevanter Bakterien in vitro.

INTRODUCTION: Dynasilan is a fluoroalkylsilan which is able to bind to surface active molecules of intraocular lenses (IOLs), thereby offering a new option for surface modification of silicone lenses. The purpose of this in vitro study was to investigate the influence of this new surface treatment on the adherence of two typical endophthalmitis-inducing bacteria ( Staphylococcus epidermidis, Propionibacterium acnes). MATERIALS AND METHODS: A total of 14 Dynasilan-treated and 14 untreated silicone lenses were incubated at 37 degrees C for 24 h in brain heart infusion broth (10(8) CFU/ml) either with Staphylococcus epidermidis or with Propionibacterium acnes for 1 h. Subsequently, the adherent bacteria were resuspended using ultrasonification at 35 kHz for 3 x 45 s. After a dilution series and incubation at 37 degrees C for 24 h or 3 days the colonies were counted. RESULTS: On untreated IOLs incubated with Staphylococcus epidermidis the average number of bacteria was 3.6 x 10(7)/ml, and on treated IOLs the number of counted colonies was reduced to 1.09 x 10(7)/ml. Incubated with Propionibacterium acnes the average number of adherent bacteria on untreated IOLs was 4.75 x 10(4)/ml and on modified IOLs the number was reduced to 2.94 x 10(4)/ml. CONCLUSION: Dynasilan surface treatment may reduce the adherence of Staphylococcus epidermidis and Propionibacterium acnes on silicone intraocular lenses. Further studies regarding the stability of this treatment, its biocompatibility and influence on lens epithelial cell adhesion are in progress.

Combined use of partially fluorinated alkanes, perfluorocarbon liquids and silicone oil: an experimental study.

BACKGROUND: Partially fluorinated alkanes (FALKs) are a new class of substances which can be used in vitreoretinal surgery as an intraoperative tool and as a long-term tamponade. The aim of this in vitro study was (1) to investigate the solubility of FALKs in silicone oil during direct exchange, (2) to study their combined use and solubility in PFCLs, (3) to evaluate their lipophilic properties and (4) to investigate the possibility of preparing "heavy silicone oil". METHODS: (1) Four different FALKs (F6H6, F6H8, O44 and O62) were directly exchanged with silicone oil (5,000 mPas). The dissolved amount of fluorocarbons in the removed silicone oil was determined by gas chromatography and by gravimetry. Furthermore, the diffusion phenomena during the exchange process were studied. (2) The behaviour of FALKs in PFCLs was investigated and the solubility of the resulting mixtures in silicone oil was measured. (3) The solubility of FALKs and PFCLs in native olive oil was analysed. (4) Different FALKs were added to silicone oil and measurements of the resulting specific gravity and the viscosity were performed. RESULTS: (1) FALKs dissolved in silicone oil up to the following values: F6H6=45 m%, F6H8=54 m%, 044=100 m%, O62=18 m%. (2) FALKs dissolved in PFCL, thereby changing the physicochemical properties of PFCL depending on the type of FALK and ratio used. (3) The lipophilic properties of FALKs and PFCLs could be characterized by their dissolution in native olive oil (F6H8=23.4 m%, 044=16.7 m%, F6H6=12.3 m%, 062=5.3 m%, PFD=1.1 m%, PFO=0.6 m%). (4) It was possible to prepare "heavy silicone oil" e.g. by adding 30 vol% F6H8, resulting in a specific gravity of 1.08 g/ml, or by adding 80 vol% 044, resulting in a specific gravity of 1.25 g/ml, but decreasing the viscosity of the mixtures dramatically. CONCLUSION: (1) If FALKs are used as an intraoperative tool, a direct exchange with silicone oil should be avoided owing to their capacity to dissolve in silicone oil, resulting in a mixture with unpredictable properties. (2) A combined use with PFCLs and silicone oil is possible, if the right ratio is chosen. (3) The solubility of FALKs in native olive oil may be an indicator for their tissue penetration and may render feasible their use as a long-term tamponade. (3) "Heavy silicone oil" preparation using FALKs is possible, but the mixture needs further evaluation in terms of emulsification, mobilization of oligosiloxanes, tissue penetration and long-term stability.

Use of O44 as a solvent for silicone oil adhesions on intraocular lenses.

PURPOSE: To describe a solvent that removes silicone oil adhesions on intraocular lenses (IOLs). METHOD: The solvent O44 is a partially fluorinated alcane that dissolves silicone oil. Silicone oil adhesions on silicone and poly(methyl methacrylate) IOLs were treated with O44. The extent of silicone oil adhesions and the effectiveness of O44 were studied by gross microscopy. RESULTS: The solvent O44 removed silicone oil adhesions from both IOL types. CONCLUSION: The substance O44 may be a successful intraoperative tool to remove silicone oil IOL adhesions, avoiding IOL explantation.

[O44--a solvent for silicone oil adhesions on intraocular lenses]. / O44--ein Lösungsmittel für Silikonöladhäsionen auf Intraokularlinsen.

AIM: To examine the efficiency of O44, a partial fluorinated octane, as a solvent for silicone oil adhesions on intraocular lenses. MATERIALS AND METHODS: After placing silicone- and PMMA-lenses in silicone oil, the adhesions were treated with O44. The extent of silicone oil adhesions and the effectiveness of O44 were studied by gross microscopy by scanning electrone microscopy (SEM) and combined energy dispersive spectrometry (EDX). Furthermore an explanted silicone lens with oil adhesions was treated with O44 and examined. To simulate the effect of adhesion proteins PMMA- and silicone lenses were placed in silicone oil and human plasma. RESULTS: With EDX it was possible to prove that O44 is able to remove silicone oil adhesions from PMMA-lenses. The removal from an explanted silicone lens by O44 could be demonstrated by light microscopy. Silicone oil adhesions on intraocular lenses (IOL's) in vitro showed a different oil coverage than the IOL in vivo. Silicone lenses in vitro were often covered by a homogenous oil film and therefore the demonstration of the silicone adhesions and of the efficacy of O44 was difficult. The adhesions of IOL's placed additional in human plasma did not show any differences. CONCLUSIONS: O44 may be a successful intraoperative tool to remove silicone oil adhesions avoiding explantation of silicone oil contaminated IOL's. Silicone oil adhesions in vivo seem to be influenced by adhesive proteins.

Temporary vitreous gas tamponade by perfluoromethylcyclopentane.

Using perfluoromethylcyclopentane (FMCP; US patent no. 5,441,989, granted 1995) we have developed a new vitreous gas tamponade in a rabbit model that allows complete filling of the vitreous cavity without vitrectomy and without a significant increase in intraocular pressure. In humans this procedure would allow the blockage of inferior and posterior retinal holes without special positioning of the patient. Perfluoromethylcyclopentane (FMCP), a liquid perfluorocarbon with a boiling point slightly above body temperature, is injected in minute volumes into the vitreous cavity, where it vaporizes, thereby filling a gas volume approximately 500 times its liquid volume. FMCP was injected into the midvitreous in six rabbits (six eyes). After 2-3 days a complete gas tamponade was achieved in three eyes. Two eyes showed 75-90% filling, and one eye was filled only 50% with gas. Intraocular pressure was highest in the completely filled eyes, ranging from 26.6 to 38.8 mmHg. In all eyes the maximum expansion of the gas bubble lasted 2 weeks. One eye developed a retinal detachment. All eyes showed transient subcapsular cataracts. The results of this study showed that intravitreal injection of FMCP, a new perfluorocarbon liquid, results in a complete gas tamponade of the vitreous cavity which lasts 2 weeks without severe intraocular pressure rise and without vitrectomy. This procedure will be especially useful for eyes that have retinal detachment from inferior or posterior retinal holes. Injection of a conventional gas such as SF6 or C3F8 usually does not block retinal holes in inferior or posterior locations without tedious positioning and risk of (transient) glaucoma. Since the mechanism of transition of FMCP from liquid to gas in the vitreous is poorly understood, we are currently studying FMCP vaporization in an in vitro eye model.