Dr. Viraj
Abhayakumar Vasavada, V11115, Dr. Shail, Dr.
Vaishali Abhaykumar Vasavada, Dr. Vasavada
Abhaykumar Raghukant
Authors : Viraj Vasavada, Shail Vasavada, Vaishali Vasavada, Samaresh Srivastava, Abhay Vasavada
Realtime,Dynamic,Intraocular Pressure during Microaxial Phacoemulsification using two phacoemulsification systems: Randomized, Clinical Trial
Abstract
Purpose: To record realtime, dynamic intraocular pressure (IOP) changes during phacoemulsification using an IOP-based fluidic system, and to compare it with a gravity-based fluidics system
Methods:
Prospective,randomized,clinical trial.50 eyes undergoing phacoemulsification randomized to Centurion Vision System,Alcon(Group 1,n=25)or Infiniti Vision System,Alcon(Group 2,n=25).Fluidic parameters were standardized. Centurion works on active fluidics with ability to preset IOP during surgery,in Group I it was set at 50 mmHg(65cm bottle height(BH)) and BH in Group II was set at 80 cm.Realtime IOP was recorded.Maximum,minimum IOP and % reduction from maximum during fragment removal were compared.
Results:
Minimum and Maximum IOP in the Centurion group was 40±4.0 and 55.5±6.8 mm Hg(P<0.05).Minimum and Maximum IOP in the Infiniti group was 30±3.0 and 60±1.2 mmHg(P< .002).Mean reduction from maximum was 59% in Group II compared to 35% in Group I,which was statistically significant(P<.002).Fluctuations in IOP were much less in the Centurion group.
Conclusion:
Absolute IOP rise and fluctuations in the IOP were much less with the IOP-based (Centurion Vision) fluidics system with active fluidics compared to the gravity-based fluidic system(Infiniti Vision System)
Introduction:
Modern phaco machines provide the benefit of improved fluidics and more user-controlled parameters, enabling surgeons to use different combinations of vaccum levels, aspiration rates and irrigation flow rates. While higher fluid settings offer the advantage of reduced surgical time as well as ultrasound energy dissipation in the eye, lower fluidic settings are known to reduce turbulence of fluid and thereby increase safety of the procedure. This translates into clearer corneas, lesser corneal thickness and anterior segment inflammation on postoperative day 1.16
Additionally, different bottle heights and fluid parameters are known to affect intraoperative IOP fluctuations. In a previous randomized clinical trial6, the mean IOP as well as the range between minimum and maximum IOP was shown to be significantly higher with higher bottle heights. The implications of continuous elevated or abrupt fluctuations in IOP could be manyfold, affecting vascular perfusion pressure and compromising blood flow to the optic nerve and retina1-5, or may even disrupt the anterior hyaloid membrane barrier during surgery.7
The concept of IOP-modulated active fluidics is relatively new. The Centurion Vision System (Alcon, USA) works on the active fluidics principle, with an ability to maintain a preset ‘IOP level’ during surgery. It does not depend on gravity-based infusion, but, rather, has a modulated fluidic system that is controlled to maintain the level of IOP within the anterior chamber that the surgeon decides. This has the advantage of allowing the surgeon to work at much lower intraocular pressure levels and still maintain stable anterior chambers.
We decided to measure real-time, the IOP fluctuations with the active fluidics-based system (Centurion Vision, Alcon) and compare it with the real-time IOP fluctuations with a gravity-based fluidic system(Infiniti Vision, Alcon).
Discussion:
Our study validates the claim of active fluidic-based systems that the actual IOP throughout the surgery is quite satisfactorily maintained very close to the IOP preset by the surgeon. It also shows that the surgeon can work with much lower preset IOP levels, without the fear of anterior chamber fluctuations or surge. This capability is unique and different from gravity-based systems, where the fluid input is fixed and determined by the bottle height, irrespective of the aspiration flow rate in the eye. Therefore, working at very low bottle height levels becomes difficult for chamber maintenance in gravity-based fluidic systems.
In a previous study comparing higher versus lower aspiration flow rates and bottle heights in a gravity-based system, we reported that when using an AFR of 20cc/min with a bottle height of 80cm, the maximum IOP achieved was 59 + 4 mmHg, and the minimum was 29 + 5 mmHg (mean + SD), with a mean percentage reduction of 40% . This maximum IOP went up to 62 + 4 mmHg, with a percentage fluctuation of 54% when using an AFR of 35cc/min with a BH of 100cm. The absolute maximum and minimum IOPs, as well as the % reduction of IOP were significantly higher when using a higher AFR and BH. In an experimental study, Suzuki and coauthors13 reported that the maximum IOP attained was as high as 60 mmHg when simulated phacoemulsification was performed in porcine eyes at a bottle of 65 cm.
It has been reported that high bottle heights can adversely affect the health of the corneal endothelium within a short duration,15 and cause exaggerated anterior chamber inflammation.16 Recently, there have been concerns over integrity of the posterior capsule – anterior hyaloid membrane barrier integrity with high IOPs. It has been shown in experimental studies, that there is disruption of the anterior hyaloid face even with an intact posterior capsule whenever there is prolonged inflation and deflation of the eye, and when high IOPs are maintained in the anterior chamber.7
Techniques like the “slow-motion phacoemulsification” approach19 and “step down technique”20 have shown the clinical benefits of using low fluidic parameters and graded reduction in parameters during phacoemulsification. Although high flow rates can increase the speed of nuclear removal, they also require raising the bottle height to maintain anterior chamber stability, thus leading to higher and more fluctuating IOPs. In a previous clinical study, we reported that the use of higher AFR and BH resulted in more Descemet’s folds, anterior segment inflammation and thicker corneas in the early postoperative period.14 This finding was consistent in the present study as higher proportion of eyes had descemet’s folds and anterior segment inflammation on the first post-operative day when using AFRs of 35cc/min. This study, for the first time, gives evidence that higher proportion of clear corneas on postoperative day 1 with the use of low fluidic parameters is partly as a result of lower IOP fluctuations.
This study highlights that during phacoemulsification, the surgeon must be conscious of his parameters, as they affect intraoperative IOP fluctuations and will ultimately decide the corneal clarity on postoperative day 1. While this is relevant in all eyes, it would be even more relevant in eyes with weak corneas, small pupils, glaucoma26, 27 and compromised ocular blood flow. Measurement of realtime IOP during phacoemulsification allows a better understanding of the surgical technique, technology and machine parameters. It also helps the surgeon as well as industry to modify their techniques and their fluidic systems so as to provide better intraoperative safety and postoperative outcomes.
A limitation of our study is that we have not measured the fluid leakage from the incisions as well as the duration for which maximum IOP levels were maintained.
To conclude, our study shows in a clinical scenario that using active fluidic system allows us to preset a lower IOP during surgery, without compromising chamber stability as compared to gravity based fluidic system. This results in lesser IOP rise and lesser IOP fluctuations in the eye during phacoemulsificaiton.
Materials and Methods :
This prospective, randomized clinical trial included 50 eyes of 50 patients with age-related cataract who underwent microcoaxial phacoemulsification at Iladevi Cataract & IOL Research Center from March to October 2010. Patients with nuclear sclerosis grades 2 and 3 as per the LOCS III classification7 were included. The following exclusion criteria were exercised: presence of glaucoma, shallow anterior chamber (ACD < 2.1 mm), pupillary dilatation of < 6mm, extremely soft or dense cataracts (grades 1, 4 and above according to the LOCS III classification), posterior polar cataract, subluxated cataract, white mature cataract, diabetic retinopathy, high myopia (defined as AL > 25 mm), uveitis, or previous ocular trauma. Only one eye of each patient was randomly included in the study.
The Institutional Review Board approved the study and informed consent was obtained from all patients. Randomization was done using computer generated random number tables. An unscrubbed nurse in the operating room informed the surgeon just before the surgery about the parameters to be employed. All surgeries were performed by a single surgeon using a standardized technique. No attempt was made to mask the surgeon to the fluidic system being used.
Patients were randomized to one of two groups, Group I (Active Fluidics with the Centurion Vision System, n = 25) or Group II (Gravity Fluidics with the Infiniti Vision System, n = 25). In Group I, the IOP was set at 50 mmHg(equivalent to 65cm bottle height(BH)) and Bottle Height in Group II was set at 80 cm. The aspiration flow rate was kept at 20 cc / minute in both groups, whereas standardized vacuum and preset torsional ultrasound were used in both groups.
The IOP measurement setup:
The IOP measurement system was first reported and validated in 2006 (Vasavada et al: A preliminary trial to establish a simple setup to measure intraocular pressure during phacoemulsification; paper presented at ESCRS, Stockholm, 2006) and has 4 components: a pressure sensor connected to a transducer, a signal amplifier, an IOP recording device, and a display unit. It was later published in 2014.6
Recording the IOP
Following nuclear fragment division, the sensor cannula was introduced into the anterior chamber through the superior paracentesis. At the end of fragment removal, the cannula was removed from the eye.
Analyzing the IOP
A single observer reviewed the recorded IOP tracings during the fragment removal phase of each patient outside the operating room. For every eye the maximum IOP and the minimum IOP were noted. Percentage reduction from maximum IOP was calculated as: [maximum IOP – minimum IOP] / maximum IOP x 100. For analysis, the maximum IOP, minimum IOP and percentage reduction in IOP from maximum during nuclear fragment removal were compared between the groups.
Outcome measures:
Results:
The main outcome measure was to measure intraoperative IOP during quadrant removal in real time between the 2 groups. The maximum IOP, minimum IOP and percentage(%) reduction in IOP were compared between groups. The number of times IOP reached maximum and minimum values in each eye with longitudinal ultrasound and torsional ultrasound was also compared.
Table 1 shows the values of maximum, minimum and % reduction of IOP in both the groups. The Maximum IOP attained was significantly lower in Group I. Moreover, the fluctuations in IOP, i.e. the % reduction in IOP was also significantly lower in Group I compared to Group II. The maximum IOP recorded was when the surgeon was in foot pedal position of irrigation only, or at the time of complete occlusion of the phaco tip. Similarly, minimum IOP recorded was at the time of occlusion break. Further, with the active fluidics system, the achieved IOP very closely matched the preset IOP level.
| Group | Maximum (+ SD) | Minimum (+ SD) | % Reduction of IOP |
| Group I – Centurion Vision System® | 53.6+7.2
|
34.7+6.2
|
35
|
| Group II – Infiniti Vision System® | 62.6 + 6.14 | 28.5 + 4.43 | 54 |
| P Value* | 0.03 | 0.04 | 0.04 |
Discussion:
Our study validates the claim of active fluidic-based systems that the actual IOP throughout the surgery is quite satisfactorily maintained very close to the IOP preset by the surgeon. It also shows that the surgeon can work with much lower preset IOP levels, without the fear of anterior chamber fluctuations or surge. This capability is unique and different from gravity-based systems, where the fluid input is fixed and determined by the bottle height, irrespective of the aspiration flow rate in the eye. Therefore, working at very low bottle height levels becomes difficult for chamber maintenance in gravity-based fluidic systems.
In a previous study comparing higher versus lower aspiration flow rates and bottle heights in a gravity-based system, we reported that when using an AFR of 20cc/min with a bottle height of 80cm, the maximum IOP achieved was 59 + 4 mmHg, and the minimum was 29 + 5 mmHg (mean + SD), with a mean percentage reduction of 40% . This maximum IOP went up to 62 + 4 mmHg, with a percentage fluctuation of 54% when using an AFR of 35cc/min with a BH of 100cm. The absolute maximum and minimum IOPs, as well as the % reduction of IOP were significantly higher when using a higher AFR and BH. In an experimental study, Suzuki and coauthors13 reported that the maximum IOP attained was as high as 60 mmHg when simulated phacoemulsification was performed in porcine eyes at a bottle of 65 cm.
It has been reported that high bottle heights can adversely affect the health of the corneal endothelium within a short duration,15 and cause exaggerated anterior chamber inflammation.16 Recently, there have been concerns over integrity of the posterior capsule – anterior hyaloid membrane barrier integrity with high IOPs. It has been shown in experimental studies, that there is disruption of the anterior hyaloid face even with an intact posterior capsule whenever there is prolonged inflation and deflation of the eye, and when high IOPs are maintained in the anterior chamber.7
Techniques like the “slow-motion phacoemulsification” approach19 and “step down technique”20 have shown the clinical benefits of using low fluidic parameters and graded reduction in parameters during phacoemulsification. Although high flow rates can increase the speed of nuclear removal, they also require raising the bottle height to maintain anterior chamber stability, thus leading to higher and more fluctuating IOPs. In a previous clinical study, we reported that the use of higher AFR and BH resulted in more Descemet’s folds, anterior segment inflammation and thicker corneas in the early postoperative period.14 This finding was consistent in the present study as higher proportion of eyes had descemet’s folds and anterior segment inflammation on the first post-operative day when using AFRs of 35cc/min. This study, for the first time, gives evidence that higher proportion of clear corneas on postoperative day 1 with the use of low fluidic parameters is partly as a result of lower IOP fluctuations.
This study highlights that during phacoemulsification, the surgeon must be conscious of his parameters, as they affect intraoperative IOP fluctuations and will ultimately decide the corneal clarity on postoperative day 1. While this is relevant in all eyes, it would be even more relevant in eyes with weak corneas, small pupils, glaucoma26, 27 and compromised ocular blood flow. Measurement of realtime IOP during phacoemulsification allows a better understanding of the surgical technique, technology and machine parameters. It also helps the surgeon as well as industry to modify their techniques and their fluidic systems so as to provide better intraoperative safety and postoperative outcomes.
A limitation of our study is that we have not measured the fluid leakage from the incisions as well as the duration for which maximum IOP levels were maintained.
To conclude, our study shows in a clinical scenario that using active fluidic system allows us to preset a lower IOP during surgery, without compromising chamber stability as compared to gravity based fluidic system. This results in lesser IOP rise and lesser IOP fluctuations in the eye during phacoemulsificaiton.
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