EFFECT OF CUT RATES ON FLUIDIC BEHAVIOR OF CHOPPED VITREOUS

Purpose: To analyze the viscoelastic properties of the chopped vitreous at different cut rates to better understand complex fluidic behavior of chopped vitreous during vitrectomy. Methods: Twenty-and 25-gauge cutters were used to cut 107 porcine eyes at different cut rates of 500, 1000, 1500, 2000, and 2500 cuts per minute with a fixed vacuum pressure of 500 mmHg. Each sample was immediately tested using a shear rheometer to obtain its rheologic properties. Results: Chopped vitreous demonstrated significantly lower viscosity (0.039 +/- 0.01 Pa.s) than intact vitreous (908.1 +/- 210.8 Pa.s). However, cut rate did not have any significant impact on viscosity. In addition, chopped vitreous presented elastic behavior. It was shown that the compliance, the inverse of stiffness, of chopped vitreous is much higher than that of intact vitreous (1.83 +/- 0.31 Pa for intact vitreous and 85.3 +/- 14.4 Pa for chopped vitreous) and varies in a nonlinear fashion when cut at different cut rates. Conclusion: Cut rate affects the rheologic properties of the chopped vitreous and, therefore, its flow inside the vitrectomy system. It is essential to account for both viscosity and elasticity of chopped vitreous to understand flow behavior during vitrectomy. RETINA 33:166-169, 2013