Purpose
To investigate intraocular pressure (IOP) fluctuation during various vitrectomy maneuvers using the vitrectomy system (Alcon Constellation Vision System).
Design
An experimental study as laboratory investigation.
Methods
In porcine eyes, 23- and 25-gauge vitrectomy was performed, and IOP fluctuations were evaluated in vitreous cutting mode, in aspiration mode, and during scleral compression. The measurements were performed with the IOP control setting turned on or off.
Results
Using the 23-gauge system with the IOP control setting turned on, IOP decreased from 30 to 23.7 mm Hg after starting vitreous cutting, and then returned to 30 mm Hg in 2.6 seconds. When the IOP control setting was turned off, IOP decreased to 19.1 mm Hg in 0.9 seconds, and remained at that pressure. Under aspiration at 650 mm Hg without cutting, IOP showed a sharp depression from 30 to 12.2 mm Hg, and then returned to 30.6 mm Hg in 2.6 seconds with the IOP control setting turned on. When the IOP control setting was turned off, IOP decreased to 2.2 mm Hg in 9.7 seconds, and did not recover. When the sclera was compressed without aspiration, IOP rapidly increased to 70-100 mm Hg, and then slowly decreased to 30 mm Hg in 3.5-4.0 seconds, with or without the IOP control system. Similar data were obtained with 25-gauge vitrectomy.
Conclusions
The IOP control system can attenuate IOP fluctuations during vitrectomy maneuvers. There was no significant difference in IOP fluctuations between 23- and 25-gauge systems.
Intraocular surgery induces substantial fluctuations in intraocular pressure (IOP). Such IOP fluctuations can increase the risk of intraoperative and/or postoperative complications, including expulsive choroidal hemorrhage, vitreous hemorrhage, choroidal detachment, retinal ischemia, and optic nerve ischemia. Expulsive choroidal hemorrhage, which is one of the most serious complications of intraocular surgery, with a reported incidence of 0.41% during vitrectomy, is more likely to occur after a sudden drop in IOP. These IOP fluctuations may also adversely affect recovery of visual function after surgery. Especially, eyes with compromised retinal and/or optic nerve blood flow, such as those with proliferative diabetic retinopathy and cystoid macular edema attributable to retinal vein occlusion, are more susceptible to IOP fluctuation. Thus, recognizing intraoperative IOP fluctuations could improve the safety of vitrectomy.
Several reports have assessed IOP fluctuations during vitrectomy in an animal model and in human eyes. In an animal model, major IOP fluctuations up to 40 mm Hg during vitrectomy were demonstrated. Studies in human eyes have shown that IOP during vitrectomy ranged from 0-120 mm Hg. In these studies, either of the 2 infusion systems was used: the one dependent on the force of gravity or the vented gas-forced infusion (Alcon Accurus vitrectomy system; Alcon, Fort Worth, Texas, USA) system, which uses pressurized air.
Recently, the new vitrectomy system (Alcon Constellation Vision System; Alcon) has been developed. This device is equipped with a pressure control system and can maintain IOP at constant, independent of aspiration flow rates during vitrectomy. The intraoperative IOP fluctuations with this system, however, have not been assessed in detail. The purpose of this study was to measure changes in intraoperative IOP during vitrectomy with the Constellation Vision System, and to investigate IOP fluctuations during various maneuvers of vitrectomy.
Methods
Intraocular Pressure Monitoring System During Vitrectomy in Porcine Eyes
This is a preclinical study, and no patients or living animals were involved. Two fresh porcine eyes were obtained from a slaughterhouse less than 1 day after death. We performed 3-port 23-gauge vitrectomy in 1 eye and 25-gauge in the other eye. After core vitrectomy, vitreous gel around the irrigation cannula was removed with a vitrectomy cutter. Then, a 22-gauge cannula was inserted into the vitreous cavity via a scleral stab wound 4 mm posterior to the limbus and was connected to a pressure transducer (MLT0670; AD Instruments, Colorado Springs, Colorado, USA). After the pressure transducer was filled with balanced saline solution, it was connected via conditioning modules to a chart recorder (PowerLab; ADInstruments) for continuous monitoring of intraoperative IOP. The transducer was held at the level of the porcine eye and the liquid level of the bottle of balanced saline solution, and zeroed to atmospheric pressure. The set-up for this experiment is illustrated in Figure 1 .
Intraocular Pressure Monitoring During Surgical Maneuvers
Three surgical maneuvers were assessed in terms of IOP fluctuations during the procedures. All procedures were conducted with the 23- and 25-gauge systems.
First, IOP was monitored during vitreous cutting with the following settings: the vented gas-forced infusion system–applied pressure was set at 30 mm Hg, cutting rate at 5000 cuts per minute (cpm), and the aspiration pressure at 650 mm Hg. The duty cycle, or the percentage of the time the cutter port was open relative to the complete cutting cycle, was set at “core mode” (actually 51%). Measurements were performed in these settings with the IOP control setting turned on or off. We inserted plugs to unused ports, confirming that balanced saline solution was not leaking from those ports. The foot pedal was quickly pressed to the floor, and the time necessary for IOP to reach a plateau and its IOP value were measured.
Second, IOP was monitored in the aspiration mode without cutting with the following settings: applied pressure was set at 30 mm Hg and the aspiration pressure at 650 mm Hg. Similar to the experiments in the vitreous cutting mode, measurements were performed with the IOP control setting turned on or off.
Third, IOP was monitored while scleral compression was applied. To measure IOP fluctuations during scleral compression for observation and shaving of the peripheral vitreous, we conducted the following experiments: applied pressure was set at 30 mm Hg, and the sclera 10 mm posterior to the corneal limbus was compressed with a scleral depressor. First, IOP fluctuations were recorded under rapid compression and release without aspiration. Next, IOP was recorded under gentle scleral compression for about 5 seconds with mild aspiration (approximately 100 mm Hg), and under gentle release for about 3 seconds without aspiration. Like the above experiments, measurements were performed with IOP control setting turned either on or off.
IOP measurements during cutting mode, aspiration mode, and scleral compression were repeated 10 times, respectively, and the mean was calculated. The time needed for IOP to reach ±10% of the vented gas-forced infusion–applied pressure was defined as “the time necessary for IOP change.” The mean and standard deviation were calculated for each variable. Unpaired t test was performed to investigate the relationship between the reached IOP with the IOP control setting turned on and off, during 3 surgical maneuvers. The analyses were carried out using Stat View (version 5.0; SAS Inc, Cary, North Carolina, USA).
Results
Monitoring Intraocular Pressure in Vitreous Cutting Mode
Using the 23-gauge system with the IOP control setting turned on, IOP showed a rapid decrease from 30 to 23.7 mm Hg after starting vitreous cutting under aspiration pressure of 650 mm Hg, and then quickly returned to approximately 30 mm Hg in 2.6 seconds ( Figure 2 , Top left). When the IOP control setting was turned off, IOP decreased from 30 to 19.1 mm Hg in 0.9 seconds, and remained at that pressure ( Figure 2 , Top right). Releasing of the foot pedal caused an IOP surge, the degree of which was smaller without the IOP control system (34.6 mm Hg) than with the IOP control system (50.2 mm Hg).
Using the 25-gauge system with the IOP control setting turned on, IOP exhibited a rapid depression from 30 to 22.9 mm Hg, and then quickly returned to approximately 30 mm Hg in 2.3 seconds ( Figure 2 , Bottom left). When the IOP control setting was turned off, IOP decreased from 30 to 16.7 mm Hg in 1.7 seconds, and stayed at that pressure level ( Figure 2 , Bottom right).
Monitoring Intraocular Pressure in Aspiration Mode
Using the 23-gauge system with the IOP control setting turned on, IOP showed a sharp depression from 30 to 12.2 mm Hg under aspiration of 650 mm Hg, and then recovered to 30.6 mm Hg in 2.6 seconds ( Figure 3 , Top left). When the IOP control setting was turned off, IOP decreased from 30 to 2.2 mm Hg in 9.7 seconds ( Figure 3 , Top right).
Using the 25-gauge system with the IOP control setting turned on, IOP similarly declined from 30 to 14.7 mm Hg, which returned to 34.5 mm Hg in 2.3 seconds ( Figure 3 , Bottom left). When the IOP control setting was turned off, it decreased from 30 to 2.2 mm Hg in 9.1 seconds ( Figure 3 , Bottom right).
Monitoring Intraocular Pressure With Scleral Compression
Using the 23-gauge system with the IOP control setting turned on, scleral compression without aspiration increased IOP rapidly from 30 to 75.8 mm Hg, and it took 3.5 seconds for IOP to lower to the preset level of 30 mm Hg. Then, by quick release, IOP decreased to 0 mm Hg in 0.2 seconds ( Figure 4 , Top left). When the IOP control setting was turned off, IOP rose sharply to 79.5 mm Hg and returned to around 30 mm Hg in 3.7 seconds. At the release of compression, it decreased to 0 mm Hg in 0.3 seconds ( Figure 4 , Top right).
