Fluidics comparison between dual pneumatic and spring return high-speed vitrectomy systems.

BACKGROUND AND OBJECTIVE: To compare the water and vitreous flow rates and duty cycle (DC) between two ultrahigh-speed vitrectomy systems: pneumatic with spring return (SR) and dual pneumatic (DP) probes. MATERIALS AND METHODS: The flow rate was calculated using a high-sampling precision balance that measured the mass of water and vitreous removed from a vial by a vitreous cutter. Frame-by-frame analysis of a high-speed video of the cutter was used to determine the DC. Three cutters of each gauge (20, 23, and 25 G) were tested with an SR and a DP system using the standard DC setting (biased open) at 0 (water only), 1,000, 2,000, 3,000, 4,000, and 5,000 cuts per minute (CPM) with aspiration levels of 100, 200, 300, 400, 500, and 600 mm Hg. RESULTS: The DC was slightly higher with the SR system using most parameters and gauges although without statistical significance. The water flow rate was somewhat higher with the SR system, except for 25 G with 4,000 and 5,000 CPM. The vitreous flow rate was similar using most parameters, with the SR system showing higher flows at lower cut rates (1,000-3,000 CPM). CONCLUSIONS: SR and DP systems produced similar water and vitreous flow rates. Additional studies in human eyes are necessary to confirm these findings.

Performance analysis of ultrahigh-speed vitreous cutter system.

PURPOSE: To evaluate flow rates and duty cycle for different sizes of ultra-high-speed pneumatic vitreous cutters. METHODS: A precision balance measured the mass of water and vitreous removed from a vial. Porcine vitreous was obtained within 12 hours of killed at a local slaughterhouse and kept at 4 °C. Twenty-, 23- and 25-gauge (n = 3 of each gauge) pneumatic cutters were tested at 0 (water), 1,000, 2,000, 3,000, 4,000, and 5,000 cuts per minute with aspiration levels of 100, 200, 300, 400, 500, and 600 mmHg. Frame-by-frame analysis of high-speed video was used to determine the duty cycle. RESULTS: Larger gauge cutters associated with higher aspiration levels produced greater vitreous and water flow rates (P < 0.05). As the cut rate increased, the vitreous flow rate increased (maximum flow at 5,000 cuts per minute) and the water flow rate decreased (P < 0.05). The duty cycle of the new-generation cutters decreased as cut speeds increased, using all 3 gauges (P < 0.001). Vitreous flow rates averaged 10 times less than water flow rates using the same cutter at the same settings. CONCLUSION: Ultra-high-speed vitreous cutters produce consistent vitreous and water flow rates across the tested range of cuts per minute and aspiration levels.

Analysis of a 23-gauge ultra high-speed cutter with duty cycle control.

PURPOSE: The purpose of the study was to determine the performance of dual pneumatic ultra high-speed 23-gauge cutters operated with variable duty cycle (DC) settings. METHODS: Frame-by-frame analysis of high-speed video was used to determine the DC in core, 50-50, and shave modes. Using three cutters at various cycles per minute and aspiration levels, mass of water or vitreous removed from a vial was measured within a specified time period. Average flow rates were calculated for each aspiration level and cut rate with the different DC options. RESULTS: The DC increased with increasing cut rate in the shave mode was relatively stable in the 50-50 mode and decreased for the core mode. The DC converged at 5,000 cycles per minute for the 3 different modes. Water flow curves followed the DC variation. Vitreous flow rates for all the DC modes increased with increasing cut rates and peaked at 5,000 cycles per minute (P < 0.05). The results of the 50-50 mode, which had isolated the DC influence, showed that increasing aspiration and/or cut rate independently increased the vitreous flow rate. CONCLUSION: Progressive values of aspiration and/or cut rate increase the vitreous flow rate, independently of the DC. The DC control also has an important effect on the vitreous flow, but this effect was reduced at high cut rates because of convergence of the DC modes.

Fluidics in a dual pneumatic ultra high-speed vitreous cutter system.

BACKGROUND: Dual pneumatic systems use two separate air line tubes to open and close the cutter and can achieve high cut rates. The purpose of this study is to evaluate the influence of gauge size, cut rate and aspiration on the flow rate performance of ultra high-speed cutters operated with a commercially available dual pneumatic vitrectomy system. METHODS: Analysis of a high-speed video was used to determine duty cycle. Flow rates from 20-, 23- and 25-gauge cutters were calculated in predetermined conditions of aspiration levels and cut rates; water and fresh porcine vitreous samples were studied. RESULTS: For all three gauges of cutters, the duty cycle and water flow showed an inverse correlation with increasing cut rates and a direct correlation with increasing aspiration levels (p < 0.05). Vitreous flow rates from all gauges increased with increasing aspiration and cut rates (p < 0.05). CONCLUSION: Larger gauges of the cutters as well as higher aspiration and cut rate levels resulted in improvement of the vitreous flow rates. A good understanding of the different flow rate settings is essential for the surgeon and optimizes the safety of surgical procedures.

Association of complement factor H Y402H polymorphism and age-related macular degeneration in Brazilian patients.

PURPOSE: The aim of this study was investigate the association between complement Factor H polymorphism (Y402H) and age-related macular degeneration (AMD) in Brazilian patients. METHODS: Patients with AMD aged 50 or more and age-matched healthy controls were enrolled in the study. Genomic DNA was isolated from leucocytes of patients and controls; the Y402H polymorphism of complement Factor H gene (CFH) was determined by polymerase chain reaction directed sequencing. RESULTS: The frequency of 1277C allele of Factor H was 56.30% in patients with AMD compared with 36.51% in controls (p-value=0.001). The genotypic distribution differed significantly between the two groups (1277CC 36.98%, 1277CT 38.65% and 1277TT 24.37% for AMD group; 1277CC 13.16%, 1277CT 46.71% and 1277TT 40.13% for controls, p-value=0.001). The odds ratio for patients with AMD carrying only one 1277C allele was 1.36 and for those carrying two 1277C alleles was 4.63, when compared to the control group. CONCLUSIONS: These results suggest the Y402H polymorphism of CFH is a risk factor to the development of AMD in Brazilian patients. This is in accordance with findings from the majority of previous study population in Europe and North American.