Performance of a Modified Vitrectomy Probe in Small - gauge Vitrectomy

S mall-gauge sutureless pars plana vitrectomy reduces postoperative inflammation at the sclerotomy sites in comparison with conventional 20-gauge sutured pars plana vitrectomy, thus decreasing patient discomfort postoperatively and hastening recovery.1-5 Despite the clinical advantages of smaller diameter vitrectomy systems, they pose significant challenges in vitreous removal as they decrease infusion and aspiration rates in comparison with 20-gauge systems. These factors may increase the time required for bulk vitreous removal, often counterbalancing the time saved in wound opening and closure. In fact, the aspiration rate generated by the 25-gauge vitreous cutter is proportionally decreased because of its smaller port and diameter by a mean factor of 6.62 because, in accordance with Poiseuille law, the flow in a pipe (therefore the aspiration in a vitrectomy probe) is proportional to 4 times the radius of the tube. To remedy part of this problem, we can use a higher aspiration (at least 600 mm of aspiration) or reduce the length of the cutter or the aspiration tubes or both. Also, increasing the port size of a vitreous cutter is an effective way to increase flow rates, as flow rapidly increases as the port diameter increases until it reaches a critical diameter. In fact, the flow begins to level off as the port diameter becomes larger than the inner lumen of the inner cutter. Beyond this diameter, the increase in port diameter appear to have less of an effect on overall flow rates.6 A vitrectomy probe, however, is not always open, as it is equipped with a guillotine that opens and closes continuously. Duty cycle is the percentage of time the cutter port is open relative to the complete cutting cycle. Duty cycle has a significant influence on flow. We know, however, that in this era of high-speed vitrectomy, duty cycle diminishes in the new generations of cutters.7 A duty cycle of 50%, therefore, will always result in a time in which the cutter mouth will be closed, as will the optimization of duty cycle. How does one solve the problem of the closure of the cutter? At our clinic in Pisa, Italy, our idea was to modify the cutter to include a “hole” in the internal guillotine blade that closes and opens in time. We made this modification on the vitrectomy probes for both the Stellaris PC (Bausch + Lomb, Aliso Viejo, CA) and the Performance of a Modified Vitrectomy Probe in Small-gauge Vitrectomy