Abstract
Purpose: :
Emulsification of silicone oil is caused by the shear force generated by eye movement. In the past, we investigated the effect of shear- and extensional-viscosities of silicone oil on the shear rate. We now study the extent of silicone oil filling and the presence of indentation within the vitreous cavity.
Methods: :
A model eye chamber made of surface-modified polymethymethacrylate (capacity 6ml) was driven by a stepper-motor to mimic large-amplitude eye movements (amplitude 90o, angular velocity 360o/s and a duration 300ms). Two indents made of agarose were introduced to simulate an encircling scleral buckling. Two silicone oils (1,300 and 5,000mPa.s), three volumes (3, 4 and 5ml) and two eye chambers (with and without indents) were tested. The movements of the oils inside the model chamber were captured by video recordings.
Results: :
The presence of indentation significantly reduced the velocity of the oil relative to the eye chamber. The extent of fill and the viscosity also had a significant but lesser effect. The peak velocity of the oil relative to the eye chamber was recorded at 349o/s. This occurred when there was no indentation in the chamber and when it was filled with 3 ml of 1,300mPa.s oil.
Conclusions: :
Of the three factors investigated, the presence of indent seemed to have the greatest influence on the shear rate. Scleral buckling and a more complete fill of an eye cavity may be as important as the use of high viscosity oils in preventing emulsification.
Keywords: vitreous substitutes • vitreoretinal surgery • eye movements