Murat V. Kalayoglu, M.D., Ph.D.
Vitreoretinal surgery has benefited greatly from the advent of select vitreous substitutes, substances that are injected into the vitreous intraoperatively to facilitate a given surgical procedure. A wide range of liquid and gaseous vitreous substitutes are available for Eye MDs. Perhaps the most versatile and useful such substance is Perfluorocarbon (PFC) liquid. PFC liquids have been used to facilitate intravitreal surgery ever since 1982, when Haidt et al. (IOVS Suppl. 22:223, 1982) first used PFC experimentally as a vitreous substitute. Since then, PFC liquids have been used in a myriad of ophthalmic surgical procedures, including during repair of retinal detachments and giant retinal tears, ocular trauma, drainage of suprachoroidal hemorrhage, surgery for proliferative retinopathy in diabetes, and even to protect the retina during removal of a dislocated crystalline or intraocular lens. PFC liquids are particularly advantageous in the surgical management of severe proliferative vitreoretinopathy, where even a minimal amount of PFC can be applied over the optic disc to aid in flattening a funnel detachment and reveal areas of vitreoretinal traction.
In many ways, PFC liquids are ideal substances to manipulate the retina. The three properties of PFC liquids that confer this benefit are their 1) high density; 2) moderate surface tension; and 3) low viscosity. PFC liquids’ specific gravity (up to 2.0) is twice that of water’s, which allows these substances to exert a relatively large force against the retina. This property therefore permits the retina to be weighed down by PFC liquids and helps fold out the retina in a controlled manner. PFC liquids’ surface tension also is a bonus; most PFCs (perfluoro-N-octane, perfluorophenanthrene, perfluoro-decalin, perfluoroethylcyclohexane, and others) have surface tensions around 15 dynes/cm at room temperature (in comparison, water’s surface tension is above 70 dynes/cm at room temperature). The tension at the interface between a given PFC liquid and water is therefore similar to that between silicone oil and water. Thus, PFC liquids remain cohesive and tend to not separate into small globules, a property that is of critical advantage to the vitreoretinal surgeon during a controlled flattening of a detached retina. The third highly appealing property of PFC liquids is their low viscosity. Unlike silicone oil, which has ranges of viscosity between 100 and 5000 centistrokes (cS) at room temperature, many PFC liquids have viscosities of approximately 2 to 3 cS. The low viscosity of PFC liquids allows these substances to be injected and aspirated with relative ease through small–gauge ports during vitreoretinal surgery.
PFC liquids have additional properties that make them desirable for use in a variety of ophthalmic surgeries. They are optically clear substances that do not absorb the wavelengths used for retinal photocoagulation. This property allows the surgeon to see the retina clearly through the PFC liquid and apply laser directly to lesions just under the PFC liquid. Moreover, PFC liquids are immiscible with water and layer below at a distinct interface (due to their slightly different index of refraction when compared to water or saline solution). This property allows the surgeon to easily identify and manipulate the PFC liquid intraoperatively in a highly controlled manner.
In principle, pure perfluorocarbon liquids are biologically inert substances due to a highly stable carbon–fluorine bond. However, in practicality, the minute quantities of impurities present within PFC solutions render many of these substances toxic. Impurities are often due to compounds that contain nitrogen bonds as well as fluoride/hydrogen bonds, and these bonds are thought to confer the long–term toxicity attributes to PFCs. As such, all PFCs are used intraoperatively and are then removed from the eye completely in order to prevent potential long–term damage to the retina. Some well–known complications resulting from the use of PFC liquids are corneal endothelial compromise, uveitis, increased intraocular pressure or hypotony, and photoreceptor cell death if the PFC liquid gains access to the subretinal space. In general, studies in animal models have shown that PFC liquids tend to be well tolerated for hours and even days. However, a multitude of reports have demonstrated poor tolerance for these substances in the long–term. As chemical synthesis and purification methods advance to consistently and reliably obtain pure PFC liquids, these “vitreous substitutes” are likely to find access to even a larger number of ophthalmic procedures.