Comparison of 3D Digitally Assisted Visualization System with Current Standard Visualization for the Removal of Vitreous in a Preclinical Model.

PURPOSE: Novel 3D digital display systems, such as NGENUITY 3D digitally assisted visualization system (DAVS), can provide enhanced illumination, depth of field, and digital filtering. This study compared vitreous removal using NGENUITY 3D DAVS with a standard surgical microscope. METHODS: This was an in vivo, 2-arm laboratory study in 15 Yorkshire pig eyes. The LuxOR LX3 microscope with NGENUITY 3D DAVS (arm 1) and the LuxOR LX3 microscope alone (arm 2) were used with 5× optical magnification and Oculus BIOM 200 mm optics. Standard core and peripheral vitrectomy without scleral depression was performed using the CONSTELLATION Vision System. Residual vitreous weight was assessed in enucleated eyes by a masked observer. Axial length and vitreous weight of contralateral eyes were compared from an additional 14 Yorkshire pigs to confirm that eyes from a single animal were essentially identical. RESULTS: After vitrectomy, mean ± SD residual vitreous was significantly smaller with NGENUITY versus standard microscope (0.143 ± 0.146 versus 0.580 ± 0.269 g, respectively; P < 0.0001). Based on a mean initial vitreous weight of 2.5 g, as determined by assessment in contralateral eyes from an additional 14 Yorkshire pigs, the mean percentage vitreous removal was 94% ± 6% versus 77% ± 11%, respectively. Further, vitreous weight and axial length for contralateral eyes from any single animal in these additional 14 animals were essentially identical, as mean differences were 0.046 ± 0.035 g and 0.11 ± 0.08 mm, respectively. CONCLUSION: Vitrectomy with NGENUITY 3D DAVS resulted in significantly less residual vitreous in pig eyes compared with standard microscopy. NGENUITY may improve vitreous removal during vitreoretinal surgery by enhancing visualization.

Simulation of Vitreous Traction Force and Flow Rate of High Speed Dual-Pneumatic 7500 Cuts Per Minute Vitrectomy Probes.

Purpose: To develop methods to simulate vitreous flow and traction during vitrectomy and qualify these methods using laboratory measurements. Methods: Medium viscosity and phase treatment were adjusted to represent vitreous (Eulerian two-phase flow) or saline solution (single-phase Navier-Stokes flow). Retinal traction was approximated using a one-way fluid-structure interaction simulating cut vitreous volume coupled to a structural simulation of elastic stretching of a cylinder representing vitreous fibers entrained in the flow. Results: Simulated saline solution flow decreased, but vitreous flow increased with increasing cut rate, consistent with experimental trends observed for the 50/50 duty cycle mode. Traction simulations reproduced all trends in variation of traction force with changes in conditions. Simulations reproduced the majority of traction measurements within experimental error. Conclusions: A scientific basis is provided for understanding how flow and traction vary with operational parameters. This model-based analysis serves as a "virtual lab" to determine optimal system settings to maximize flow efficiency while reducing traction. Translational Relevance: The model provides a better understanding regarding how instrument settings can help control a vitrectomy procedure so that it can be made as efficient as possible (maximizing the rate of vitreous removal) while at the same time being made as safe as possible (minimizing retinal traction).

Clinical comparison of 27-gauge and 23-gauge instruments on the outcomes of pars plana vitrectomy surgery for the treatment of vitreoretinal diseases.

PURPOSE OF REVIEW: To compare outcomes of 27-gauge and 23-gauge pars plana vitrectomy (PPV) for treatment of vitreoretinal diseases. RECENT FINDINGS: Sixty-eight patients undergoing microincisional PPV for treatment of vitreoretinal diseases were randomized 1 : 1 to 27-gauge or 23-gauge surgery with a 7500 cuts-per-minute vitrectomy probe. The most common reasons for vitrectomy were epiretinal membrane (49%) and vitreous hemorrhage (24%). Mean ±â€Šstandard deviation (SD) changes from immediate preoperative to immediate postoperative intraocular pressure were -0.40 ±â€Š6.60 mmHg in the 27-gauge and -3.05 ±â€Š7.64 mmHg in the 23-gauge group (adjusted mean difference 2.42 mmHg, 95% lower confidence limit 0.64, P = 0.013), but these changes were not associated with primary reason for vitrectomy (P = 0.065). Mean ±â€ŠSD conjunctival edema grades in the 27-gauge and 23-gauge groups 1 week after surgery were 0.02 ±â€Š0.124 and 0.10 ±â€Š0.246, respectively (least squares mean difference -0.09, 95% upper confidence limit -0.03, P = 0.004), and were 0.01 ±â€Š0.122 and 0.12 ±â€Š0.338, respectively, at the probe incision site. Conjunctival edema grades were similar in both groups at 1 and 3 months. Mean ±â€ŠSD pain ratings on postoperative day 1 - an indicator of patient comfort - were similar in the two groups. SUMMARY: Smaller diameter vitrectomy instruments are associated with smaller reductions in immediate postoperative intraocular pressure.

Porcine Vitreous Flow Behavior During High-Speed Vitrectomy up to 7500 Cuts per Minute.

PURPOSE: To evaluate the impact of high-speed cut rates (up to 7500 cuts per minute [cpm]) on vitreous flow through various gauge probes. METHODS: An open-sky vitrectomy technique was performed on porcine eyes using the CONSTELLATION Vision System with three different gauges of dual-pneumatic probes (27+-, 25+-, and 23-gauge UltraVit probes; n = 5 for each gauge). Flow rate was calculated by LabVIEW software that converted real-time mass measurements from an electronic scale into flow rate. RESULTS: Average vitreous flow rate increased slightly with increased cut rate in all probes with 50/50 duty cycle; more dramatic flow rate increases were observed for all probes with biased closed duty cycle. Under both conditions, maximum flow rate was observed at 7500 cpm for all gauges. Under the biased open duty cycle, average flow rate was inversely associated with cut rate. CONCLUSION: High-speed cut rate improved efficiency of vitreous aspiration. TRANSLATIONAL RELEVANCE: Increased vitreous aspiration of dual-pneumatic, high-speed vitrectomy probes may improve the efficiency of current vitrectomy techniques, allowing surgeons to take advantage of the benefits of high cut rates without sacrificing flow rate.

Performance Comparison of High-Speed Dual-Pneumatic Vitrectomy Cutters during Simulated Vitrectomy with Balanced Salt Solution.

PURPOSE: To measure flow rate of balanced salt solution and IOP during simulated vitrectomy using two sets of high-speed dual-pneumatic probes. METHODS: A closed-model eye system measured IOP and flow rate of a balanced salt solution through infusion cannula. The Constellation Vision System was tested with two sets of high-speed dual-pneumatic probes (UltraVit 23-gauge and enhanced 25+-gauge 5000-cpm probes; UltraVit 23-gauge and enhanced 25+-gauge 7500-cpm probes; n = 6 each) under different vacuum levels and cut rates in three duty cycle modes. RESULTS: In both probe sets, flow rates were dependent on cut rate with the biased open and biased closed duty cycles. Flow rates were highest with the biased open duty cycle, lower with the 50/50 duty cycle, and lowest with the biased closed duty cycle. IOP, as expected, was inversely associated with flow rate using both probe sets. CONCLUSIONS: The 7500-cpm probes offer greater control and customization compared with 5000-cpm probes under certain experimental conditions. At maximum cut rates, performance of 7500-cpm probes was similar to that of 5000-cpm probes, suggesting that 7500-cpm probes may be used without sacrifice of flow rate and IOP stability. TRANSLATIONAL RELEVANCE: Customization of vitrectomy parameters allows greater surgeon control during vitrectomy and may expand the usefulness of vitrectomy probes.

Vitreous flow rates through dual pneumatic cutters: effects of duty cycle and cut rate.

PURPOSE: We aimed to investigate effects of instrument settings on porcine vitreous flow rates through dual pneumatic high-speed vitrectomy probes. METHODS: The CONSTELLATION(®) Vision System was tested with 250, 450, and 650 mmHg of vacuum using six ULTRAVIT(®) vitrectomy probes of each diameter (25+(®), 25, 23, and 20 gauge) operated from 500 cuts per minute (cpm) up to 5,000 cpm. Duty cycle modes tested included biased open, 50/50, and biased closed. Flow rates were calculated by assessing the change in weight of porcine eyes during vitreous aspiration. Volumetric flow rate was measured with a computer-connected electronic scale. RESULTS: At lower cut rates, the biased open mode produced higher flow than did the 50/50 mode, which produced higher flow than did the biased closed mode. In the biased closed and 50/50 modes, vitreous flow rates tended to increase with increasing cut rate. Vitreous flow rates in the biased open duty cycle mode remained relatively constant across cut rates. CONCLUSION: Vitreous flow rates through dual pneumatic vitrectomy probes could be manipulated by changing the duty cycle modes on the vitrectomy system. Differences in duty cycle behavior suggest that high-speed cut rates of 5,000 cpm may optimize vitreous aspiration.

Comparison of the effects of 23-gauge and 25-gauge microincision vitrectomy blade designs on incision architecture.

PURPOSE: To compare the effects of different 23- and 25-gauge microincision vitrectomy trocar cannula entry systems on incision architecture. METHODS: We tested one ridged microvitreoretinal (MVR), one non-ridged MVR, one pointed beveled, and one round-tipped beveled blade (n=10 per blade design per incision type). Each blade's straight and oblique incision architecture was assessed in a silicone disc simulating the sclera. Wound leakage under pressure and endoscopic observations were conducted on sclerotomy sites of isolated porcine eyes (n=4 per blade design) after simulated vitrectomy. RESULTS: Differences in blade design created distinct incision architecture. Incisions were linear with the ridged MVR blade, flattened "M-shaped" with the non-ridged MVR blade, asymmetrical chevron-shaped with the pointed beveled blade, and curved with the round-tipped beveled blade. With the exception of oblique entry incision thickness, both MVR blade designs created thinner incisions than the beveled blades at entry and exit sites. Only the ridged MVR blade created incisions with no leakage. Vitreous incarceration was observed with all trocar cannula systems. CONCLUSION: Wound closure in porcine eyes was similar with all blades despite differences in incision architecture. Wound leakage occurred at low to moderate infusion pressures with most blades; no wound leakage was observed with ridged MVR blades.

Tissue attraction associated with 20-gauge, 23-gauge, and enhanced 25-gauge dual-pneumatic vitrectomy probes.

PURPOSE: To evaluate the influence of different vitrectomy probe gauge sizes and their fluidics, under various vacuum settings, on tissue attraction. METHODS: An apparatus was designed to model the retinal membrane during vitrectomy. A cantilever beam was constructed from a wire (diameter, 0.076 mm) with a latex strip (simulating ocular membranes) attached at a right angle to its tip. The beam was clamped vertically in a container of balanced salt solution. The port of the vitrectomy probe (20 gauge, 23 gauge, and enhanced 25 gauge) was aligned with the membrane. With the cutter off, the vacuum was increased until the membrane was attracted into the port. The aspiration flow rate was measured with a noninvasive flow meter. Attraction distance, vacuum pressure, and flow rate were recorded. RESULTS: For any given distance, the 20-gauge probe needed the lowest amount of vacuum and the highest aspiration flow, while the enhanced 25-gauge and 23-gauge probes needed larger vacuum and smaller aspiration flow rates to attract the membrane into the port. CONCLUSION: The sphere of influence on surrounding tissue was greatest with large-gauge vitrectomy probes. This laboratory model indicated that small-gauge probes could be used to target specific tissues while minimizing the effects on adjacent tissue structures.