Vitrectomy for proliferative vitreoretinopathy

When performing vitrectomy for proliferative vitreoretinopathy, surgeons might consider using an ophthalmic viscoelastic device (OVD) in a 'soft shell technique' to prevent subretinal migration of perfluorocarbon liquid (PFCL) through seen or unseen small retinal holes, according to David Wong MD. Dr Wong, Consultant Ophthalmologist, Royal Liverpool University Hospital, Liverpool, UK, credited Yamakiri et al for first describing the technique (Graefes Arch Clin Exp Ophthalmol. 2016;254(6):1069-73), in which the OVD is placed over the area of anticipated retinal breaks before injecting the PFCL. He demonstrated its efficacy in videos and presented experimental findings supporting the hypothesis that the technique works because the OVD increases the interfacial tension of the PFCL at the retina hole.

Our experimental findings suggest that the efficacy of the soft shell technique may be limited based on the size of the retinal break

“We think the PFCL migrates into the subretinal space when the hydrostatic pressure overcomes the interfacial tension of the heavy liquid at the retina hole,” explained Dr Wong. “Our experimental findings suggest that the efficacy of the soft shell technique may be limited based on the size of the retinal break. And in my experience, it is good for preventing PFCL migration through small posterior breaks,” he added. The experiment investigating the mechanism of action of the soft shell technique used an ex vivo model to analyse the PFCL-OVD interface at the retinal hole. Needles of various gauges were used to create pairs of equally sized holes in a series of porcine retinas mounted over aqueous on a transwell insert. One hole in each retina was covered with hyaluronate, and then perfluoro-n-octane (PFO) was added incrementally. Data were recorded when the heavy liquid passed through each hole. Calculations of the height of PFO overlying the retina when the heavy liquid passed through the holes showed the level reached was significantly higher for the openings pre-coated with hyaluronic acid compared with the control sites. With the holes stratified by area, the difference between the pre-coated and control sites was greatest for holes <1mm2. Interfacial tension between the PFO and aqueous solution present below the retinas was also determined, and the mean value was significantly higher for the group of holes coated with HA than for the untreated sites. Dr Wong noted that, while his hypothesis on the mechanism of the soft shell technique may be correct, other factors may also be involved, including the possibility that because of its cohesive, adhesive and viscous properties, the hyaluronate might provide a physical barrier at the retina hole. David Wong: shdwong@hku.hk