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Thicker than water
In this issue of BJO (p 662) Wong and colleagues present data from a prospective pilot study on the use of a long acting, heavier than water internal tamponade agent, Densiron-68, for retinal detachment (RD) repair. Some time ago1 we drew up a retinal surgeon’s wish list of vitreoretinal agents and adjuncts that are currently sorely lacking in surgical technology, including enzymatic vitreolysis, and antifibroproliferative drugs. Looming large on that wish list was a long acting heavier than water tamponade agent. Long coveted by vitrectomy surgeons, extended tamponade with heavy liquids would at last allow us to address the well recognised limitations of current tamponade agents, limitations that are for the most part imposed by gravity. Now, long acting inferior tamponade with “heavy oil” may soon be at hand, as described in this article.
The era of intraocular tamponade was ushered in with the introduction of air tamponade and then long acting gases (C3F8, SF6) and silicone oil. But these are all lighter than water agents that float upwards in the aqueous environment of the eye, leaving inferior retinal breaks exposed, at least with any feasible postoperative head positioning short of suspending patients upsidedown for days and weeks (yes, it has been tried). The inferior retina is critical in retinal detachment surgery, as it often harbours not only retinal tears but proliferative vitreoretinopathy (PVR) membranes, and is the typical site for performing large relaxing retinectomies. Heavier than water agents are available to us in the form of perfluorocarbon liquids such as perfluoro-n-octane (PFO) and perfluorodecalin. First developed by Chang and colleagues,2 perfluorocarbon liquids are invaluable tools for manipulating the retina and displacing subretinal fluid intraoperatively. But these agents are not left in the eye for postoperative tamponade because of risks of toxicity, suggested by animal studies but as yet unproved in human patients.3 Up to this point, there is simply been no way of getting around gravity, and tamponade of the inferior retina has been a frustrating gap in repair of retinal detachment.
Attempts to overcome this limitation are under way. For example, in a preliminary report of a prospective, uncontrolled pilot study, PFO has been tested in primary RD repair as a medium term tamponade agent for approximately 2 weeks in duration.4 Success rates with medium term PFO were encouraging, and significant retinal toxicity was not observed, but incomplete removal of PFO was an issue, as was cataract formation and glaucoma.
In their uncontrolled pilot study of 42 eyes, Wong and colleagues describe the use of Densiron-68 for complex RD cases with inferior retinal breaks and PVR. The surgical outcomes were promising, with 81% successful reattachment with a single surgery and mean duration of tamponade of 72 days. Densiron-68 is a novel tamponade agent composed of perfluorohexyloctane, a semifluorinated alkane with a specific gravity of 1.35 g/cm3, solubilised in 5000 cS silicone oil. This “heavy oil” has a specific gravity of 1.06 g/cm3, and has a higher viscosity than perfluorohexyloctane to reduce postoperative emulsification.
In a previous multicentre clinical study, perfluorohexyloctane used as a sole agent was reported to be effective for the management of complicated retinal detachments for up to 3 months of long term tamponade.5 However, significant emulsification of pure perfluorohexyloctane was observed, which can result in dispersion of the agent to undesired locations and inadequate tamponade as a result of underfilling of the vitreous cavity. For this reason, many retina surgeons currently use long term perfluorohexyloctane in combination with a standard perfluorohydrocarbon gas bubble. By comparison, this study using Densiron-68 found that dispersion of emulsified heavy oil was relatively infrequent, consisting of minor droplet formation in the anterior chamber and inferior vitreous cavity. Elevated intraocular pressure was associated with its use; short term glaucoma was seen in 14% of cases, and in 7% pressures remained elevated at the end of the study.
Ongoing trials based in Cologne, Germany, will compare the efficacy of Densiron-68 and standard silicone oil in the management of complicated retinal detachment. And novel applications may be developed once heavy oils are more widely used, such as for macular hole surgery to eliminate the need for face down head positioning postoperatively. In the meantime, further work will be necessary to evaluate potential issues of retinal toxicity, cataract formation, oil emulsification, and glaucoma risk with the use of this new class of compounds.
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Thicker than water
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