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O. Magalhaes, Jr., L. Chong, C. DeBoer, P. R. Bhadri, M. McCormick, S. Fang, R. Kerns, A. Barnes, M. Humayun; Vitreous Dynamics: The New Solid Development Concept. Vitreous Flow Analysis in 20, 23 and 25 Gauge Cutters. Invest. Ophthalmol. Vis. Sci. 2007;48(13):2243.
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To evaluate porcine vitreous flow and Balanced Saline Solution (BSS) flow rate and correlate these flows with variable parameters (vacuum and cutting rate), mechanisms of drive (pneumatic or electric), blade movement (partial rotation or axial), and overall probe size (20, 23 and 25 gauge) of the cutters.
The vitreous was removed en bloc from porcine eyes obtained within 24 hours of slaughter. A precise weighing (0.01g) high speed (2 samples/second) balance measured the 20 gauge and 25 gauge Bausch & Lomb Lightning-Millennium (St Louis, MO), the 20 gauge (Accurus 2500) and the 25 gauge Alcon Accurus (Fort Worth, TX), the 20 gauge Alcon Innovit, and the 23 gauge DORC (Netherlands) cutters. The vitreous and BSS weight was converted into a graph of volume removed versus time using LabView algorithm. Variable cut rates and vacuum pressures were analyzed. Vitreous was labeled with glass microspheres or Triamcinolone acetonide. A high speed (400 frames/second) camera was used to record cutting for each situation. Flow data was shown to correlate with prior high speed video analysis. Vitreous flow was normalized with respect to BSS to characterize vitreous removal.
There were three kinds of duty cycle: parabolic incomplete (pneumatic), sinusoid (electric) and trapezoid (partial rotation). The parabolic incomplete had a decreased duty cycle at 1500 cpm when it was compared to 600 cpm (p< 0,05 for all cutters). In 25 gauge cutters, at 500 mmHg of vacuum, the electric gave higher average flow rates at high cutting (600cpm- 0,004ml/sec and 1500cpm- 0,013 ml/sec) than that of pneumatic where a decreased flow at speeds higher than 1000 cpm (1000cpm- 0,015 ml/sec and 1500cpm- 0,006 ml/sec) was demonstrated. In the DORC 23-gauge system, at 1500 cpm and 500 mmHg, vitreous flow was low (0,0001 ml/sec). The percentage of vitreous flow rate/BSS flow rate showed an ascending curve for all instrumentation. It demonstrated an evidence of flow obstruction in 25 (all cut rates), 23 (all cut rates) and 20 gauge (small cut rates). Clog and surge movements seen confirmed these findings through high speed video analysis.
The systems showed diverse flow performances of vitreous removal. Vitreous (solid characteristics) demonstrated the complexity of a safe vitrectomy. Further studies along this research line are necessary to verify the physical aspects among the various systems in order to optimize different systems in different clinical situations.
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