Editor, Since we have been using the novel tamponade agent perfluorohexyloctane, we have observed a few cases where it has passed into the anterior chamber. We report on its effects in the anterior chamber in a phakic eye. Pars plana vitrectomy was performed on a patient with rhegmatogenous retinal detachment and perfluorohexyloctane was injected. When the patient was referred to us again 22 days after surgery, slightly more than half of the anterior chamber was filled with perfluorohexyloctane, which formed a multitude of droplets, while the vitreous cavity was filled subtotally (Fig. 1). Perfluorohexyloctane had entered the anterior chamber between 2 and 5 days beforehand. Intraocular pressure (IOP) was found to be elevated to 32 mmHg. Aspiration and a second pars plana vitrectomy were used to remove the heavy liquid from the anterior chamber and vitreous cavity, respectively, and to replace it with balanced salt solution. Four days after surgery, IOP had returned to normal. Two days later, however, a significant level of perfluorohexyloctane was detected again in the anterior chamber (Fig. 2), whereas the vitreous cavity showed no sign of residual heavy liquid. Preoperative findings: more than half of the anterior chamber is filled with dispersed perfluorohexyloctane; the cornea appears to be clear. Postoperative findings: a significant level of perfluorohexyloctane was detected again 6 days after removal of the heavy liquid. The following conclusions can be drawn. (1) Even with intact anterior eye segments, perfluorohexyloctane can pass into the anterior chamber. The interface tension of perfluorohexyloctane against water – similar to those of perfluorocarbon liquids (Fluoron GmbH 2004) – makes passage through the zonular fibres difficult. Therefore, it appears likely that perfluorohexyloctane passes into the anterior chamber only after emulsification, which occurs within 3 weeks (Zeana et al 1999). (2) Perfluorohexyloctane can cause secondary glaucoma. It has already been proved that macrophages can phagocytize silicone oil, perfluorocarbons and perfluorohexyloctane alike (Vote et al. 2003). Therefore, the same mechanism as with silicone oil may apply here (i.e. obstruction of the trabecular meshwork by these macrophages) (Naumann 1997). (3) The short-term presence of perfluorohexyloctane in the anterior chamber does not necessarily have toxic effects on the cornea. Dispersion of perfluorohexyloctane may have improved the nutritive situation of the cornea and prevented known toxic effects on the corneal endothelium (Mertens et al. 2002). (4) It may be difficult to completely remove perfluorohexyloctane from the anterior chamber. Several mechanisms can account for this phenomenon, which was also observed by another group (Sampat et al. 2003). Because semifluorinated alkanes form a thin film on wet surfaces, remnants can remain in the eye and form small droplets. Dispersed perfluorohexyloctane may have remained, for example, between zonular fibres or within crypts of the iris. Unlike perfluorocarbons, semifluorinated alkanes are amphiphilic substances – like membrane-forming phospholipids – containing a lipophilic hydrogenated and a lipophobic fluorinated portion. Thus, it must be assumed that perfluorohexyloctane will be partly integrated into cell membranes. Although it has been proven that perfluorohexyloctane dissolves less than 0.2% by weight of the phospholipid lecithin (Meinert & Roy 2000), it should be borne in mind that the relationship between the weight of lipids and proteins in cell membranes may differ by a factor of 16 (Jungermann & Möhler 1980); this must have an effect on the integration of semifluorinated alkanes. As far as we know, data on the solubility of phospholipids other than lecithin in semifluorinated alkanes are not available. If perfluorohexyloctane were integrated into cell membranes, it would be more difficult to remove it. In addition, F–H bridges that form between adjacent fluorinated and unfluorinated molecular portions of semifluorinated alkanes may add to the difficulty of removing perfluorohexyloctane (Meinert & Roy 2000). Therefore, as the unfluorinated portion of the molecule is integrated into a cell membrane, the fluorinated portion may become attached to an unfluorinated portion of another molecule. Thus greater portions of the heavy liquid may be retained inside the eye despite attempts to remove them.