A Guide to the Removal of Heavy Silicone Oil

Aim: Heavy silicone oil removal can be challenging and differs considerably from conventional oil. Traditionally, strong active aspiration had to be applied through a long 18G needle just above the optic disc. We present a novel technique using a much shorter (7.5 mm) and smaller (20G) needle allowing its removal "from a distance."

Method: Active aspiration on a vacuum of 600 mm Hg of the "viscous fluid injector" was applied using the 20G cannula in a polymethylmethacrylate model eye chamber that was surface-modified to mimic the surface properties of the retina. Measurements were taken using still photographs.

Results: Under injection the maximum diameter of a silicone oil bubble supported by interfacial tension alone was 5 mm for a steel and 7 mm for a polyurethane cannula. Under suction, the silicone bubble changed shape and became conical, thus further increasing the cannula's reach. This conical shape illustrated "tubeless siphoning," which is a physical property of non-Newtonian fluids.

Discussion: The use of shorter and smaller gauge cannula for removal of Densiron obviates the need to enlarge the sclerotomy beyond 20G or to apply suction in close proximity to disc and fovea. This potentially reduces the risk of iatrogenic damage such as entry site tears or postoperative hypotony.