Ralph Kerns

Vitreous dynamics: vitreous flow analysis in 20-, 23-, and 25-gauge cutters.

Purpose: To evaluate porcine vitreous flow and balanced saline solution (BSS) flow rates in different vitrectomy systems. Methods: Porcine vitreous was obtained within 24 hours of slaughter. A high-speed (2 samples/s) balance, precise to 0.01 g, was used. Variable cut rates and vacuum pressures were analyzed in vitreous and BSS. The vitreous was labeled with glass microspheres and triamcinolone acetonide. A high-speed (400 frames/s) camera was used to record cutting for each condition. Results: For all cutters, there was no vitreous flow at zero cut rates (off). In 25-gauge cutters, at 500 mmHg of vacuum, the electric cutter produced higher average flow rates at high cut rates (600 cpm, 0.004 mL/s, and 1500 cpm, 0.013 mL/s) than pneumatic, which demonstrated a decreased flow at speeds higher than 1000 cpm (1000 cpm, 0.015 mL/s, and 1500 cpm, 0.006 mL/s). The percentage of vitreous flow rate/BSS flow rate in different aspiration and cut rates showed an ascending curve. This demonstrates evidence of flow obstruction in 25- (all cut rates), 23- (all cut rates), and 20-gauge (all cut rates). Flow obstruction and surge movements were seen in the high-speed videos. Conclusions: The vitrectomy systems each illustrate different performances of vitreous removal. The physical characteristics of vitreous resulted in nonuniform flow in all vitreous cutters.

Vitreoretinal Traction Created by Conventional Cutters during Vitrectomy

PURPOSE To quantify the vitreous traction created by pneumatic (20-, 23-, and 25-gauge) and electric cutters (20- and 25-gauge) during vitrectomy. DESIGN Experimental study. PARTICIPANTS This is a preclinical study, and no patients were involved. METHODS Five separate cutters for each drive mechanism and gauge (20-, 23-, and 25-gauge pneumatic and 20- and 25-gauge electric) were used for each cut speed at predetermined aspiration rates. The retinal layers of fresh porcine eyes were transfixed with a 0.15-mm steel wire and fixed to the load cell of a strain gauge. The cutter to be assessed was introduced into the eye by a micromanipulator at a 45-degree angle adjacent to the retina. The traction force was determined and evaluated at a distance of 3 and 5 mm from the retina with different vacuum and cut rates. MAIN OUTCOME MEASURES Vacuum, cut speed, force (dynes), distance (millimeters), vitreoretinal traction, and gauge. RESULTS The 20-, 23-, and 25-gauge pneumatic cutters have a range of traction from 2.06 to 37.22 dynes, 3.85 to 15.38 dynes, 5.13 to 27.91 dynes, respectively. The 20- and 25-gauge electric cutters have a range of traction from 3.60 to 41.78 dynes and 5.28 to 27.91 dynes, respectively. All results are related to distance, cut, and aspiration rate. With an increase of 100 mmHg of vacuum/aspiration, the traction increased from 7.89 to 3.14 dynes (e.g., 4.96 for 20-gauge pneumatic). The traction decreased as the cut rate was increased, from 5.71 to 2.51 dynes (e.g., 3.41 for 20-gauge pneumatic). CONCLUSIONS The results indicate that retinal traction increased with increasing aspiration vacuum and proximity to the retina; conversely, retinal traction decreased with increasing cut rate. The present study demonstrates that the effects of aspiration, distance from the retina, and cut rate are crucial factors in the amount of retinal traction created by vitreous cutters. FINANCIAL DISCLOSURE(S) Proprietary or commercial disclosure may be found after the references.

Port geometry and its influence on vitrectomy.

Purpose: To determine the influence of port geometry on water and vitreous flow rates and test novel vitreous cutter tips in specific surgical situations. Methods: Custom 20-gauge and 25-gauge vitreous cutter tips with different sized ports were evaluated through porcine vitreous and water flow rates. Five cutter tips were designed and fabricated for specific surgical functionalities. Tips were compared with a normal control tip and evaluated by water and porcine vitreous flow rates, vacuum level required to cut porcine retina, time required to cut and aspirate a porcine lens, and surgical evaluation in enucleated porcine eyes. Results: Both vitreous and water flow asymptotically approached a maximum flow as the port diameter increased. Some tips removed water faster than the normal control tip, but none removed vitreous or lens faster. Several tips required higher vacuum levels to cut retina than the normal tip. Conclusions: Increasing the port diameter of a vitreous cutter to increase flow becomes less effective as the port becomes larger. Furthermore, modifying the port geometry of a vitreous cutter affects its surgical interactions with tissue. In the future, combinational instruments or surgery specific instruments may allow the surgeon to use an optimal port for a specific surgical task.

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.

An experimental protocol of the model to quantify traction applied to the retina by vitreous cutters.

PURPOSE The purpose of this study was to use a novel method to quantify the traction applied to the retina during vitrectomy. METHODS Five 20-gauge electric cutters were used. Fresh porcine eyes were positioned in a specially developed holder and transfixed to the retinal layers with a microwire, and the other end was fixed to the load cell of a strain gauge. The cutter to be assessed was introduced into the eye by a micromanipulator at a 45 degrees angle adjacent to the retina. The traction force was evaluated when the cutter was at 3 and 5 mm from the retina. As control, the experiment was repeated in eyes filled with water, and the results were compared to those when the eyes had vitreous gel. RESULTS Results from the eyes with vitreous gel indicate that retinal traction increased with increasing aspiration vacuum (7.90 dyn for each 100 mm Hg increased; P < 0.05) and proximity to the retina (2.17 dyn; P < 0.05) and decreased with increasing cut rate (2.51 dyn for each 500 cuts per minute increased; P < 0.05). In all eyes filled with water, traction was not observed. CONCLUSIONS The present study establishes a new reproducible technique to quantify vitreoretinal traction during vitrectomy and demonstrates that the effects of aspiration, distance from the retina, and cut rate are crucial factors in the amount of retinal traction created by vitreous cutters.

Novel method to quantify traction in a vitrectomy procedure

Aim To report a novel method to quantify traction applied to the retina using vitreous cutters during pars plana vitrectomy. Methods Fresh porcine eyes were positioned in a specially developed holder and transfixed to the retinal layers with a wire and the other end fixed to the load cell of a strain gauge. Five separate 20-gauge electrical drive mechanism vitrectors were introduced into the eye at a 45° angle and positioned at a distance of either 3 or 5 mm from the retina. Data from the strain gauge were acquired and the traction force computed. Results The analysis revealed that the vitreoretinal traction increased by 7.90 dynes for each 100 mm Hg increase in vacuum (p<0.05). The traction forces decreased by 2.51 dynes for each 500 cuts per minute increased (p<0.05) and the traction force increased by 2.17 dynes at 3 mm compared with 5 mm (p<0.05). Conclusion The traction was directly proportional to the aspiration vacuum and inversely proportional to the cut rate. The cutter traction force increased with proximity to the retina.

A new dual port cutter system for vitrectomy surgery.

Purpose: To evaluate and compare the performance of several designs of 20-gauge dual port (DP) vitreous cutter tips with a standard 20-gauge single port tip. Methods: Custom 20-gauge pneumatic vitreous DP cutter tips with different sizes and port positions were evaluated through porcine vitreous and water flow rates. Five designed and fabricated DP cutter tips were compared with a normal single port control tip and evaluated by the measurement of water and porcine vitreous flow rates, and surgical examination in enucleated porcine eyes. Results: Some DP tips approached a maximum vitreous and water flow rates, removing water and vitreous faster than the normal control tip. With reference to surgical evaluation, some DP tips performed better than the single port tip for bulk vitrectomy, but none shaved the vitreous base more effectively. Conclusion: The DP cutter system has the potential to increase the flow rates depending on the size and position of the extra port. In the future, the DP cutter may allow the surgeon to perform bulk vitrectomy more efficiently.

Performance Analysis of Millennium Vitreous Enhancer™ System

BACKGROUND AND OBJECTIVE This study evaluates water and porcine vitreous flow rates and duty cycle using the Millennium Vitrectomy Enhancer (MVE) system (Bausch & Lomb, St. Louis, MO). MATERIALS AND METHODS A precision balance measured mass of water or vitreous removed from a vial within a certain time by 20-, 23-, and 25-gauge MVE cutters at 800, 1,000, 1,500, 2,000, and 2,500 cuts per minute (CPM) with various aspiration levels was studied. Frame-by-frame analysis of high-speed video was used to determine duty cycle. RESULTS Larger cutter and higher aspiration levels produced greater flow rates. Water flow rate showed a parabolic trend peaking at 1,500 CPM and dropping moderately and vitreous flow rate increased moderately with cut-rate increased. The MVE system maintained a high flow rate and high duty cycle even at high cut-rates. CONCLUSION Flow rates for the MVE system are stable and predictable for all cutter gauges, which should aid the surgeon to select the optimal parameters for vitrectomy.

Guillotine performance: duty cycle analysis of vitrectomy systems.

PURPOSE To evaluate the duty cycle of different vitrectomy cutters and classify their blade movement. METHODS A precise weighing (0.01 g) high speed (2 samples/s) balance was used to study the 20-gauge and 25-gauge Bausch & Lomb Lightning-Millenium (St. Louis, MO), the 20-gauge (1500 cpm) and the 25-gauge Alcon Accurus (Fort Worth, TX), the 20-gauge Alcon Innovit, and the 23-gauge DORC (Netherlands) cutters. The weight of balanced saline solution (BSS) was recorded in real time using LabView software and then translated into a graph of volume removed versus time. Variable cut rates and vacuum pressures were analyzed in vitreous and BSS. A high-speed (400 frames/s) camera was used to record cutting for each condition. RESULTS Three types of duty cycle were investigated: parabolic incomplete (pneumatic), sinusoid (electric), and trapezoid (double pneumatic). The parabolic incomplete and trapezoid had a decreased duty cycle at 1500 cuts per minute when it was compared to 600 cuts per minute. The sinusoid had no statistical difference between cut rates. CONCLUSIONS Systems showed different performances of duty cycle. This new classification will be useful for improved understanding of vitrectomy in these different systems.