Self-retaining chandelier endoillumination can free one hand for scleral indentation, and thereby surgeons will achieve more controlled and smooth peripheral vitreous base shaving by themselves without the need for an assistant
In more challenging cases, the freed hand is helpful for holding forceps to grasp membranes for separation from the retina or for dissection using scissors or a cutter in a bimanual procedure. Setting the chandelier fiber superiorly is helpful, making the shadow go down to the inferior area, which can help in avoiding the instrument shadow coming into the working zone
The direction of the illumination focusing on the posterior pole (a) or periphery (b) can be optimized easily by changing the curvature of the chandelier fiber outside the eyeball with this flexible type of chandelier fiber
14.2 Technologies and Techniques in Vitreous Cutting
Most of the recently developed vitrectomy machines feature high-speed cutters with its cutting rates over 5,000 cpm. The high cutting speed keeping the duty cycle over 50 % has dramatically improved the vitreous cutting efficiency of small-gauge cutters even with 25 gauge or much smaller 27 gauge . This advancement has facilitated lots of surgeons making a transition to smaller-gauge instrumentation for MIVS in recent years (Fig. 14.4).
Global survey of surgeons’ preference of gauge over years
In addition to the improvement of the conventional spring pneumatic-driven vitreous cutter, the dual pneumatic valve-driven vitreous cutter (ULTRAVIT® probe, Alcon Laboratories) is a new concept for vitrectomy, which is currently capable to have a ultrahigh-speed cutting up to 7,500 cpm with duty cycle controls in a variety of situations (Fig. 14.5) in corporation with the CONSTELLATION Vision System® (Alcon Laboratories). The elegant mechanism that increases or decreases flow without changing the cut rate or vacuum parameters may facilitate more efficient core vitrectomy and safer peripheral vitreous shaving with less traction force to the retina . With the latest program featured in the CONSTELLATION Vision System®, two different cutting and aspiration settings can be set sequentially by the foot pedal control along with the percentage of step-in based on the surgeons’ preference as shown in Fig. 14.6. It is very convenient to perform efficient core vitrectomy with full step-in of the treadle and safer peripheral vitreous shaving sequentially by simply releasing the treadle slightly, especially suitable for the cases with retina detached or mobile even with the currently smallest small-gauge system of 27-gauge (Fig. 14.7).
Comparison of duty cycle changes of the dual pneumatic-driven cutter (5,000 cpm vs. 7,500 cpm). The definition of duty cycle is the ratio of the time the port is open in a cut cycle to the overall duration of the cut cycle, which is presented as a percentage. The CONSTELLATION Vision System® has three settings called “core” (port biased open), “shave” (port biased closed), and 50/50. The open biased setting renders the port mostly open in the cutting cycle, maximizing flow for the given cut rate and vacuum. The closed biased setting renders the port mostly closed in the cutting cycle, minimizing flow and traction force for the given cutting rate and vacuum. The reduced bite size at higher cut rates reduces the resistance to flow and increases the flow rates
A proposed 3D submode setting for efficient vitrectomy. Core vitrectomy is capable by full step-in of the foot pedal to keep the maximum aspiration of 650 mmHg with higher duty cycle cutting rates of 5,000 cpm, and a safer peripheral vitreous shaving is achievable sequentially by simply releasing the foot pedal to get a proportional control of the aspiration with the highest cutting rates of 7,500 cpm
A 27-gauge vitrectomy system for treating rhegmatogenous retinal detachment. (a) A 27+® valved cannula (purple) system with a 25-gauge cannula-compatible chandelier illumination fiber (light green). (b) Releasing the vitreous traction around the retinal break with a 27+ ULTRAVIT® probe at 7,500 cpm. (c) Peripheral vitreous shaving under scleral indentation. (d) Endophotocoagulation around the retinal break with a 27+ curved laser probe. (e) Fluid-air exchange performed with a 27+ soft-tip back-flush needle probe. (f) Surgical view at the occlusion of 27+ vitrectomy after cannula removal
Another concept of a double-port cutter featuring a second port in the internal guillotine blade of the cutter has been developed to incorporate into the spring pneumatic-driven cutter to improve the flow efficiency in a small-gauge cutter by keeping the duty cycle without attenuation along with increasing the cutting rate [4, 5]. This approach may be another step forward to improving the flow efficiency during small-gauge vitrectomy. However, further studies are still warrant to evaluate the potential risk of increasing the traction force on the vitreous with this type of cutter because of the cutting port almost being fully opened.
14.3 Techniques for Membrane Removal
14.3.1 Cutter Techniques
Several studies have proved transconjunctival MIVS to have several advantages over conventional 20-gauge instrumentations for diabetic vitrectomy [6–8]. The conjunctiva-preserving nature of MIVS allows repeated vitrectomy or filtering surgery that may be needed in patients with diabetes complicated with neovascular glaucoma, even after vitrectomy. The surgical techniques for removing diabetic fibrovascular membranes during MIVS differ from those in conventional 20-gauge vitrectomy. Because the distances from the ports to the tips in the small-gauge vitreous cutter are shorter than those of a conventional 20-gauge vitreous cutter, the cutters can serve as multifunctional tools during membrane removal. The port of the 23-, 25-, or 27-gauge cutters can be inserted readily between the fibrovascular membrane and retina, allowing successful membrane segmentation, dissection, and removal using a small-gauge vitreous cutter only. Therefore, we have lower chance to use complex instruments such as scissors, pick, and spatula for fibrovascular membrane removal in most cases.