Retinal surgery — three new safety devices

Speakers at the symposium "Retinal Surgery — New Dimensions in Patient Safety," described three methods/instruments to help surgeons minimize complications during surgery including improved endotamponade applications, new cannula designs and microscope data projections.

Hakan Kaymak from Germany was on hand to sing the praises of a new 2000 mPas silicone oil. 1000 mPas and 5000 mPas silicone oil, which are widely used as long-term retinal tamponades suffer with a numbers of downsides; 1000 mPas has a tendency to emulsify and 5000 mPas can be difficult to inject and remove. Silicone oils behave like non-Newtonian fluids, altering their viscocity when shear forces act upon them. This is due to the decrease and increase of the interactions in the fluid resulting from the altered microscopic structure. "It's just like tomato ketchup," said Dr Kaymak, "when you try to pour ketchup out of the bottle by banging the bottom all the contents hit the plate at once. The hitting sets the shear forces into action. Shear viscosity is reduced and the flow limit is overcome. The ketchup comes out of the bottle all at once and behaves in what is described as a pseudoplastic manner."

The new Siluron 2000 acts differently to ketchup. It is a mixture of highly purified basic oils with different viscosities and has a viscosity of 2000 mPas. The intelligent combination of mixture ratio and varying viscosities of the basic oils leads to a higher dynamic viscosity of Siluron 2000. The higher dynamic viscosity enables the newly formulated silicone oil to better resist mechanically applied external force. Results from a pilot study of 20 eyes, followed-up for 4 months, were promising — with no emulsification or inflammatory reactions observed. Siluron can be applied with 20, 23 and 25 gauge instruments.

Dr P. Müther, also from Germany, described a new infusion cannula for vitreoretinal surgery. During surgery the standard infusion, centrally opened, creates a jet of fluid or air inside the eye hitting the retina on the opposite side, resulting in drying or stressing of the retina. One solution to this problem is an infusion which is centrally closed and has side ports to inject fluid or gas. Dr Müther demonstrated a new cannula design that diffuses the fluid or gas so that it does not cause damage to the retina.

The final presentation was made by Dr M. Becker who spoke about the importance of feedback on the parameters of the ophthalmic surgical system, which is to date given by the tactile feedback of the foot pedal and the acoustic feedback of the system. Currently, in order for a surgeon to get a visual confirmation, he/she must interrupt the surgical procedure to look up at the display. Dr Becker described a new system that eliminates this problem by showing the parameter display within the microscope field of vision. Clinical studies are planned midway 2009.