Our experience with perfluorohexyloctane (F6H8) as a temporary endotamponade in vitreoretinal surgery

Vitreous Substitutes as Drug Release Systems

Vitreous substitutes are traditionally used to stabilize the retina after vitrectomy. In recent years, various approaches have been developed for using the vitreous substitute not only as a tamponade but also as a drug release system to tackle ocular diseases. This review provides an overview of the requirements for vitreous substitutes and discusses the current clinically applied as well as novel polymer-based vitreous substitutes as drug delivery systems, including their release mechanisms, efficiencies, challenges, and future perspectives.

Heavy silicone oil and intraocular inflammation

In the past two decades, many advances have been made in vitrectomy instrumentation, surgical techniques, and the use of different tamponade agents. These agents serve close retinal breaks, confine eventual retinal redetachment, and prevent proliferative vitreoretinopathy (PVR). Long-acting gases and silicone oil are effective internal tamponade agents; however, because their specific gravity is lower than that of the vitreous fluid, they may provide adequate support for the superior retina but lack efficacy for the inferior retina, especially when the fill is subtotal. Thus, a specific role may exist for an internal tamponade agent with a higher specific gravity, such as heavy silicone oils (HSOs), Densiron 68, Oxane HD, HWS 45-300, HWS 46-3000, and HeavySil. Some clinical evidence seems to presume that heavy tamponades are more prone to intraocular inflammation than standard silicone if they remain in the eye for several months. In this review, we discuss the fundamental clinical and biochemical/molecular mechanisms involved in the inflammatory response after the use of heavy tamponade: toxicity due to impurities or instability of the agent, direct toxicity and immunogenicity, oil emulsification, and mechanical injury due to gravity. The physical and chemical properties of various HSOs and their efficacy and safety profiles are also described.

Vitreous substitutes: the present and the future

Vitreoretinal surgery has advanced in numerous directions during recent years. The removal of the vitreous body is one of the main characteristics of this surgical procedure. Several molecules have been tested in the past to fill the vitreous cavity and to mimic its functions. We here review the currently available vitreous substitutes, focusing on their molecular properties and functions, together with their adverse effects. Afterwards we describe the characteristics of the ideal vitreous substitute. The challenges facing every ophthalmology researcher are to reach a long-term intraocular permanence of vitreous substitute with total inertness of the molecule injected and the control of inflammatory reactions. We report new polymers with gelification characteristics and smart hydrogels representing the future of vitreoretinal surgery. Finally, we describe the current studies on vitreous regeneration and cell cultures to create new intraocular gels with optimal biocompatibility and rheological properties.

Oxygen-charged HTK-F6H8 emulsion reduces ischemia-reperfusion injury in kidneys from brain-dead pigs

BACKGROUND

Prolonged cold ischemia is frequently associated with a greater risk of delayed graft function and enhanced graft failure. We hypothesized that media, combining a high oxygen-dissolving capacity with specific qualities of organ preservation solutions, would be more efficient in reducing immediate ischemia-reperfusion injury from organs stored long term compared with standard preservation media.

METHODS

Kidneys retrieved from brain-dead pigs were flushed using either cold histidine-tryptophan-ketoglutarate (HTK) or oxygen-precharged emulsion composed of 75% HTK and 25% perfluorohexyloctane. After 18 h of cold ischemia the kidneys were transplanted into allogeneic recipients and assessed for adenosine triphosphate content, morphology, and expression of genes related to hypoxia, environmental stress, inflammation, and apoptosis.

RESULTS

Compared with HTK-flushed kidneys, organs preserved using oxygen-precharged HTK-perfluorohexyloctane emulsion had increased elevated adenosine triphosphate content and a significantly lower gene expression of hypoxia inducible factor-1α, vascular endothelial growth factor, interleukin-1α, tumor necrosis factor-α, interferon-α, JNK-1, p38, cytochrome-c, Bax, caspase-8, and caspase-3 at all time points assessed. In contrast, the mRNA expression of Bcl-2 was significantly increased.

CONCLUSIONS

The present study has demonstrated that in brain-dead pigs the perfusion of kidneys with oxygen-precharged HTK-perfluorohexyloctane emulsion results in significantly reduced inflammation, hypoxic injury, and apoptosis and cellular integrity and energy content are well maintained. Histologic examination revealed less tubular, vascular, and glomerular changes in the emulsion-perfused tissue compared with the HTK-perfused counterparts. The concept of perfusing organs with oxygen-precharged emulsion based on organ preservation media represents an efficient alternative for improved organ preservation.

Vitreous substitutes: a comprehensive review

Vitreoretinal disorders constitute a significant portion of treatable ocular disease. Advances in vitreoretinal surgery have included the development and characterization of suitable substitutes for the vitreous. Air, balanced salt solutions, perfluorocarbons, expansile gases, and silicone oil serve integral roles in modern vitreoretinal surgery. Vitreous substitutes vary widely in their properties, serve different clinical functions, and present different shortcomings. Permanent vitreous replacement has been attempted with collagen, hyaluronic acid, hydroxypropylmethylcellulose, and natural hydrogel polymers. None, however, have proven to be clinically viable. A long-term vitreous substitute remains to be found, and recent research suggests promise in the area of synthetic polymers. Here we review the currently available vitreous substitutes, as well those in the experimental phase. We classify these compounds based on their functionality, composition, and properties. We also discuss the clinical use, advantages, and shortcomings of the various substitutes. In addition we define the ideal vitreous substitute and highlight the need for a permanent substitute with long-term viability and compatibility. Finally, we attempt to define the future role of biomaterials research and the various functions they may serve in the area of vitreous substitutes.

Histopathology and Ultrastructure of Rabbit Retina After Intravitreous Injection of Perfluorohexyloctane (F6H8)

PURPOSE

To describe changes in rabbit retina after intravitreous injection of perfluorohexyloctane (F6H8).

METHODS

Intravitreous injections of C3F8 were performed in the right eye of 48 male New Zealand albino rabbits. All 48 eyes were injected with C3F8. The animals were divided in three groups of 18 each. 18 eyes (6 in each group) were used as controls and 30 (10 in each group) were further injected with F6H8. Animals were sacrificed at days 15, 30, and 60 and the eyes processed for light and electron microscopy and immunohistochemistry.

RESULTS

Vitreous tracts were observed behind the lens in all groups. Epiretinal and retrolental membranes developed in most of the treated eyes. Light microscopy showed retinal vacuolization in all eyes. No significant ultrastructural changes appeared in any of them. Macrophages were observed in the inner limiting membrane.

CONCLUSIONS

Ultrastructural findings can be considered signs of good tolerance to F6H8, though the appearance of epiretinal membranes associated with the presence of macrophagic response suggests we should refrain from using F6H8 until results from clinical trials are available.

A new heavy internal tamponade in vitreoretinal surgery: an in vitro study

AimTo study the solubility of perfluorohexyloctane (F6H8) in silicone oil (polydimethylsiloxane (PDMS) 1000) and to measure the viscosity and the specific gravity of the mixture obtained (heavy silicone oil or HSO tamponade) to define the ideal ratio of these components.MethodsThe solubility diagram of the mixture was obtained with the turbidimetric method, indicating the miscibility of F6H8 and silicone oil 1000 at all the useful temperatures. The viscosity was measured in steady shear conditions by using a controlled stress rheometer (Haake RS150) and a double cone/plate (DC 60/4) system, both at 25 and 37 degrees C for different volume per cent compositions of the mixture. The specific gravity was measured at 37 degrees C using a digital densimeter.ResultsA mixture of F6H8 30 v% and PDMS 70 v% was found to be transparent and stable at all the useful temperatures. By combining these proportions of the two substances, a resultant density of 1.06 g/cm(3) was obtained. The viscosity of the 30% F6H8 mixture was 203 mPa.s at 25 degrees C and 163 mPa.s at 37 degrees C respectively.ConclusionsThe ideal F6H8 and silicone oil mixture can be obtained combining 30% of F6H8 with 70% of silicone oil 1000. This mixture seems to have rheological properties useful for its use as an alternative intraocular heavy tamponade.Eye (2008) 22, 1082-1088; doi:10.1038/eye.2008.144; published online 6 June 2008.

Semifluorinated alkanes--primitive surfactants of fascinating properties

Semifluorinated alkanes (SFAs) are diblock molecules, in which two mutually immiscible moieties, namely the hydrocarbon segment and the perfluorinated segment are bound covalently. The presence of two opposing segments within one molecule makes semifluorinated alkanes a very interesting class of compounds, which show a particular behavior both in bulk and at interfaces. Their highly asymmetric structure, arising from the incompatibility of the both constituent parts, results in surface activity of these molecules (so-called primitive surfactants) when dissolved in organic solvents, and allows for the Langmuir monolayer formation if spread at the air/water interface, despite of the absence of any polar group. Since 1984 (when SFAs have been characterized for the first time by Rabolt et al. [Rabolt JF, Russell TP, Twieg RJ. Macromolecules 1984;17:2786]), semifluorinated alkanes have been subjected to many studies. The present article reviews the results obtained so far and covers the aspects of their synthesis, properties in bulk (solutions and solid state) and applications. Special emphasis is put on the Langmuir monolayer properties and self-organization of SFAs on solid substrates.

Heavy tamponade 1: a review of indications, use, and complications

BACKGROUND

Heavier than water intraocular tamponades have several theoretical advantages over conventional tamponades, especially in the treatment of complicated retinal detachments and proliferative viteroretinopathy of the lower fundus periphery. However, initial clinical series of various heavy tamponades have reported significant complication rates. Therefore, heavy tamponades have not found widespread acceptance. Three recently developed heavy silicone oil tamponades, Oxane HD, Densiron 68, and HWS 46-3000, are much better tolerated and presently seem to enter routine clinical practice.

MATERIALS AND METHODS

Literature review of 21 publications on the clinical application of 9 different heavy tamponades (fluorosilicone, C10F18, F6H8, OL62HV, Oxane HD, O62, F6H8-silicone oil mixture, Densiron 68, and HWS 46-3000).

RESULTS

The first generation (fluorinated silicone and perfluorocarbon liquids) and second generation (partially fluorinated alkanes) of heavy tamponades were associated with relatively high complication rates, for example, tamponade emulsification, intraocular inflammation, and rise in intraocular pressure. The complication spectrum of the new generation of heavy silicone oils (Oxane HD, Densiron 68, and HWS 46-3000) seems to be comparable to conventional silicone oil tamponades while providing better support for the inferior retina and the posterior pole.

CONCLUSION

The recently developed heavy silicone oil tamponades are safe and effective tools for the use of complicated retinal detachments of the inferior fundus.

A NEW HEAVY SILICONE OIL (HWS 46-3000) USED AS A PROLONGED INTERNAL TAMPONADE AGENT IN COMPLICATED VITREORETINAL SURGERY

PURPOSE

To report the results of a prospective pilot study using a new heavy agent, HWS 46-3000, as long-term endotamponade in complicated retinal detachment.

METHODS

Thirty-two consecutive patients were enrolled in the study. Indications for enrollment included retinal detachment with proliferative vitreoretinopathy arising from inferior or posterior tears. The patients underwent pars plana vitrectomy, membrane peeling, and HWS 46-3000 filling. Follow-up examinations were scheduled at 1 day to 7 days and 1 month to 3 months after initial surgery and 7 days and 1 month to 6 months after endotamponade removal.

RESULTS

At baseline examination, mean best-corrected Snellen visual acuity was 2.44 logarithm of the minimal angle of resolution (logMAR). HWS 46-3000 was removed after 45 days to 96 days. Initial retinal reattachment was achieved in all eyes. HWS 46-3000 endotamponade was associated with a success rate of 84.6% with a single surgery and an overall success rate of 100% at 6 months with the second operation and conventional silicone oil endotamponade. At 6 months, mean best-corrected visual acuity was +1.09 logMAR (P < 0.0001). Complications were posterior subcapsular cataract formation (100%), membrane formation (3 eyes, 9%), and increased intraocular pressure (1 eye). Emulsification and intraocular inflammation were not observed.

CONCLUSION

HWS 46-3000 was well tolerated, effective in the inferior quadrants with a low incidence of membrane development. The main complication was the high rate of tamponade-related cataract formation.

Heavy silicone oil versus standard silicone oil as vitreous tamponade in inferior PVR (HSO Study): design issues and implications

PURPOSE

Proliferative vitreoretinopathy (PVR) is the most important reason for blindness following retinal detachment. Presently, vitreous tamponades such as gas or silicone oil cannot contact the lower part of the retina. A heavier-than-water tamponade displaces the inflammatory and PVR-stimulating environment from the inferior area of the retina. The Heavy Silicone Oil versus Standard Silicone Oil Study (HSO Study) is designed to answer the question of whether a heavier-than-water tamponade improves the prognosis of eyes with PVR of the lower retina.

METHODS

The HSO Study is a multicentre, randomized, prospective controlled clinical trial comparing two endotamponades within a two-arm parallel group design. Patients with inferiorly and posteriorly located PVR are randomized to either heavy silicone oil or standard silicone oil as a tamponading agent. Three hundred and fifty consecutive patients are recruited per group. After intraoperative re-attachment, patients are randomized to either standard silicone oil (1000 cSt or 5000 cSt) or Densiron((R)) as a tamponading agent. The main endpoint criteria are complete retinal attachment at 12 months and change of visual acuity (VA) 12 months postoperatively compared with the preoperative VA. Secondary endpoints include complete retinal attachment before endotamponade removal, quality of life analysis and the number of retina affecting re-operation within 1 year of follow-up.

RESULTS

The design and early recruitment phase of the study are described.

CONCLUSIONS

The results of this study will uncover whether or not heavy silicone oil improves the prognosis of eyes with PVR.

The combined use of perfluorohexyloctane (F6H8) and silicone oil as an intraocular tamponade in the treatment of severe retinal detachment

BACKGROUND

The purpose of this study was to investigate the combined use of perfluorohexyloctane (F6H8) and 1,000-centistoke silicone oil as a long-term intraocular tamponade in the treatment of complicated retinal detachment.

METHODS

Sixty consecutive eyes affected by complicated retinal detachment with (1) retinal breaks of the lower two quadrants and severe proliferative vitreoretinopathy, (2) inferior giant retinal tear, (3) penetrating trauma or (4) choroidal detachment underwent pars plana vitrectomy using a combined internal tamponade of F6H8 and silicone oil. The double filling (DF) was removed after 40-50 days. The anatomical outcome and the complications due to the DF are reported.

RESULTS

Retinal reattachment was achieved in all but one patient. Thirty-eight (63%) eyes needed further surgery with silicone oil tamponade. Silicone oil was successfully removed in 22 eyes. Sixteen (27%) eyes had retained silicone oil at the last follow-up examination. One eye showed persistent retinal detachment despite further surgery. Main complications of the DF were recurrent retinal detachment of the upper retina in six (10%) eyes and membrane formation in 25 (42%) eyes.

CONCLUSIONS

A combined internal tamponade of F6H8 and silicone oil may be a useful tool in the treatment of complicated retinal detachment involving the lower quadrants of the retina.

A pilot study on the use of silicone oil–RMN3 as heavier-than-water endotamponade agent

AIMS

This work was conducted to report an interventional non-comparative pilot study using Oxane HD, a mixture of ultra-purified silicone oil and RMN3, a partially fluorinated olefin, as heavier-than-water internal tamponade.

METHODS

Twenty-eight consecutive patients were recruited for this study. Indications included recurrent retinal detachment (RD) with proliferative vitreoretinopathy (PVR) (stage > or =C2) arising from inferior or posterior tears, recurrences after vitreoretinal surgery, penetrating trauma and combined rhegmatogenous and choroidal detachment. The patients underwent a pars plana vitrectomy, membrane peeling, and Oxane HD was used as long-term internal tamponade.

RESULTS

Oxane was removed after 88 days (range 45-96 days) and exchanged with BSS in five eyes, long-acting gas in 14 eyes and with silicone oil in nine eyes. Retinal reattachment was achieved in 15 eyes. The overall anatomical success rate obtained using Oxane HD was 53.5%. In 15 patients with previous marked scleral buckling, the success rate was 26%: in nine patients recurrent RD occurred in the inferior sector, in five patients new tears were detected in the lower sectors; membrane formation was observed in 15 eyes. In 13 patients without marked scleral indent, the success rate was 84.6%. There was no evidence of dispersion and excessive inflammation.

CONCLUSION

Oxane HD may be a useful tool in complicated RD with large inferior breaks, inferior PVR or combined rhegmatogenous, and choroidal detachment without marked scleral buckling, which put the eye profile out of shape, led to a higher failure rate and reduced the tamponading effectiveness of Oxane HD.

Long-Term Vitreous Replacement with Perfluorohexyloctane and Silicone Oil: Preliminary Reports of a Multicentric Study

AIM

To report on the use of a combined intra-ocular tamponade with silicone oil and perfluorohexyloctane (F(6)H(8)) in the treatment of complex retinal detachment.

DESIGN

A prospective consecutive interventional case series from seven study centres.

PARTICIPANTS

69 patients presenting a retinal detachment with proliferative vitreoretinopathy (PVR) and retinal breaks of the inferior two quadrants of the fundus.

METHOD

Patients were divided into two groups: (1) 28 eyes which had not been operated on before; (2) 41 eyes affected by recurrent retinal detachment that had had unsuccessful previous surgery with silicone oil or gas tamponade. A pars plana vitrectomy, membrane peeling and -- when necessary -- a retinotomy were performed; the vitreous cavity was filled with two thirds of F(6)H(8) and one third of silicone oil 1,000 mPas (double filling, DF). The endotamponade was removed after 30-45 days (median 38) and replaced by balanced salt solution or silicone oil according to the condition of the retina.

RESULTS

Retinal reattachment was achieved in 52 out of 69 cases (75%) 6 months after removal of the DF without any endotamponade.

CONCLUSION

The DF with F(6)H(8) and silicone oil allows a good endotamponading to the inferior retina and the posterior pole. The DF appeared to be well tolerated. Further studies are necessary to evaluate whether a DF is advantageous in respect to silicone oil filling alone in case of retinal breaks and PVR of the inferior retina.

Influence on membrane-mediated cell activation by vesicles of silicone oil or perfluorohexyloctane

PURPOSE

This study was conducted to investigate whether macrophage activation through cell membrane attachment might be supported by emulsified tamponade droplets of a certain vesicle size. It has been hypothesized that emulsification of vitreous tamponades might stimulate retinal membrane formation.

METHODS

In this laboratory investigation, similarly sized vesicles of silicone oil and the partially fluorinated alkane perfluorohexyloctane (F6H8) were produced by extrusion through polycarbonate membranes. Human neutrophils were obtained from blood donors. Human monocytes were negatively isolated from mononuclear cells by depletion of other cells. Cell activation status of phagocyting blood neutrophils was measured by a chemiluminescence assay. Fluorescent attached or internalized vesicles were monitored by fluorescent microscopy. The main outcome measures were the altered activation status of monocytes after vesicle incubation and the ability of human macrophages to attach and/or internalize vesicles in vitro.

RESULTS

Extruding silicone oil through a polycarbonate membrane resulted in the production of vesicles that remained stable for at least 2 days. F6H8 vesicles had to be stabilized with an emulsifier, in this case Pluronic PE6800 or Lipoid EPC. The mean vesicle diameter was similar with both components (F6H8: 13.08+/-2.95 microm, silicone oil: 10.05+/-4.6 microm). Neutrophil activation was not influenced by either emulsifier alone or by silicone oil vesicles without emulsifier. Stabilized F6H8 vesicles had a dose-dependent influence on blood neutrophil activation. Only silicone oil vesicles together with Lipoid EPC, not Pluronic PE6800, had a comparable influence on neutrophil activation. Neutrophil activation was influenced neither by 0.125% human serum albumin (HSA) alone nor by vesicles of F6H8 or silicone oil prepared with 0.125% HSA. Monocyte cell membrane attachment of silicone fluid was two times higher than that of F6H8 fluid. F6H8/Pluronic PE6800 vesicles enhanced this process 20-fold, whereas silicone oil vesicles did not enhance cell membrane attachment significantly.

CONCLUSIONS

These in vitro data do not support the hypothesis that emulsification of the tamponades silicone oil or F6H8 in the microenvironment of the eye might easily activate neutrophils or stimulate phagocytosis by monocytes. A prerequisite is the combination of a vesicle shape of the tamponades with specific stabilizing or modifying surfactants. Emulsified tamponades stabilized by artificial surfactants, but not by the naturally occurring protein HSA, favor cell activation by cell membrane attachment.