A Guide to the Removal of Heavy Silicone Oil

¹ Royal Liverpool University Hospital, United Kingdom
² Department of Clinical Engineering, School of Clinical Sciences, University of Liverpool, Liverpool, United Kingdom
³ St Paul's Eye Unit, United Kingdom
⁴ St Paul s Eye Unit, Royal Liverpool University Hospital, Prescot St., Liverpool, L7 8XP, UK, United Kingdom

^* To whom correspondence should be addressed. E-mail: theodorstappler{at}web.de.

Accepted 10 March 2008

	Abstract

Purpose: 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 (7.5mm) and smaller (20G) needle allowing its removal "from a distance".

Method: Active aspiration on a vacuum of 600mmHg 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 5mm for a steel and 7mm 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.