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T. Stappler, R. Williams, H. Heimann, S. Liazos, D. Wong; Removal of Heavy Oil: The Long and Short of it . Invest. Ophthalmol. Vis. Sci. 2006;47(13):5255.
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The removal of 'heavy oil' is however slightly more complicated in that Densiron obviously sinks and traditionally, the its removal involves the use of high suction via a 18–gauge cannula long enough to reach the optic disc. Whereas there is no theoretical limit to the pressure of injection, with aspiration, the maximum suction is one atmosphere (pure vacuum). We observed that it was possible to remove silicone oil against all expectation using a 20–gauge cannula of 0.75 cm in length using a suction of 600 mmHg generated by the Accurus (Alcon). The purpose of the project is to demonstrate this in vitro.
Material and Methods: :
We used Densiron (1480 mPas and 1.06 g/ml) and a model eye chamber made of surface modified PMMA with a diameter of 2.30 cm. We also used 20–gauge metal cannula of 0.75 cm in length and 20–gauge plastic cannula cut to the same length. Injection: Densiron from a syringe driver was used to inject it into a balanced salt solution. A series of still photographs were taken to capture the maximum size of the droplet before it broke off from the cannula. Aspiration: A large bubble of Densiron was placed inside the model eye chamber and was then aspirated with the short cannula and photographed.
Injecting through a plastic cannula a droplet of cannula reached a maximum size of 6 mm in diameter and using the metal cannula, 4.5 mm. This effectively increased the 'reach' of the cannula from 0.75 to over 1 cm. Aspirating with a plastic or metal cannula, the bubble of Densiron was distorted from a rounded to a conical shape. This again resulted in an increased 'reach'. This 'stretching–out' of the bubble demonstrated the cohesiveness of Densiron under suction.
We have demonstrated that by using a short needle, it is possible to remove Densiron in normal–sized eye despite it being heavier–than–water and its viscosity. We have shown that this is due to the interfacial tension between the cannula and the oil and partly to the cohesiveness of the Densiron bubble under suction.
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