Acoustic cavitation in phacoemulsification: chemical effects, modes of action and cavitation index

Corneal endothelial cells and acoustic cavitation in phacoemulsification

Postoperative complications of phacoemulsification, such as corneal edema caused by human corneal endothelial cell (CEC) injury, are still a matter of concern. Although several factors are known to cause CEC damage, the influence of ultrasound on the formation of free radicals during surgery should be considered. Ultrasound in aqueous humor induces cavitation and promotes the formation of hydroxyl radicals or reactive oxygen species (ROS). ROS-induced apoptosis and autophagy in phacoemulsification have been suggested to significantly promote CEC injury. CEC cannot regenerate after injury, and measures must be taken to prevent the loss of CEC after phacoemulsification or other CEC injuries. Antioxidants can reduce the oxidative stress injury of CEC during phacoemulsification. Evidence from rabbit eye studies shows that ascorbic acid infusion during operation or local application of ascorbic acid during phacoemulsification has a protective effect by scavenging free radicals or reducing oxidative stress. Both in experiments and clinical practice, hydrogen dissolved in the irrigating solution can also prevent CEC damage during phacoemulsification surgery. Astaxanthin (AST) can inhibit oxidative damage, thereby protecting different cells from most pathological conditions, such as myocardial cells, luteinized granulosa cells of the ovary, umbilical vascular endothelial cells, and human retina pigment epithelium cell line (ARPE-19). However, existing research has not focused on the application of AST to prevent oxidative stress during phacoemulsification, and the related mechanisms need to be studied. The Rho related helical coil kinase inhibitor Y-27632 can inhibit CEC apoptosis after phacoemulsification. Rigorous experiments are required to confirm whether its effect is realized through improving the ROS clearance ability of CEC.

Medium-high frequency sonication dominates spherical-SiO2 nanoparticle size

Spherical SiO₂ nanoparticles (SSNs) have been inventively synthesized using the Stöber method with sonication at medium-high frequencies (80, 120, and 500 kHz), aiming to control SSN size and shorten reaction time. Compared to the conventional method, such sonication allowed the Stöber reaction complete in 20-60 min with a low molar ratio of NH₄OH/tetraethyl orthosilicate (0.84). The hydrodynamic diameters of 63-117 nm of SSNs were obtained under sonication with 80, 120, and 500 kHz of ultrasonic frequencies. Moreover, the SSNs obtained were smaller at 120 kHz than at 80 kHz in a multi-frequencies ultrasonic reactor, and the SSN size decreased with increasing ultrasonic power at 20 °C, designating the sonochemical unique character, namely, the SSN-size control is associated with the number of microbubbles originated by sonication. With another 500 kHz ultrasonic bath, the optimal system temperature for producing smaller SSNs was proven to be 20 °C. Also, the SSN size decreased with increasing ultrasonic power. The smallest SSNs (63 nm, hydrodynamic diameter by QELS, or 21 nm by FESEM) were obtained by sonication at 207 W for 20 min at 20 °C. Furthermore, the SSN size increased slightly with increasing sonication time and volume, favoring the scale-up of SSNs preparation. The mechanisms of controlling the SSN size were further discussed by the radical's role and effects of ammonia and ethanol concentration.

Histotripsy: the first noninvasive, non-ionizing, non-thermal ablation technique based on ultrasound

Histotripsy is the first noninvasive, non-ionizing, and non-thermal ablation technology guided by real-time imaging. Using focused ultrasound delivered from outside the body, histotripsy mechanically destroys tissue through cavitation, rendering the target into acellular debris. The material in the histotripsy ablation zone is absorbed by the body within 1-2 months, leaving a minimal remnant scar. Histotripsy has also been shown to stimulate an immune response and induce abscopal effects in animal models, which may have positive implications for future cancer treatment. Histotripsy has been investigated for a wide range of applications in preclinical studies, including the treatment of cancer, neurological diseases, and cardiovascular diseases. Three human clinical trials have been undertaken using histotripsy for the treatment of benign prostatic hyperplasia, liver cancer, and calcified valve stenosis. This review provides a comprehensive overview of histotripsy covering the origin, mechanism, bioeffects, parameters, instruments, and the latest results on preclinical and human studies.

Impact of torsional micropulse on phacoemulsification efficiency and chatter

OBJECTIVE

Evaluate the effect of increasing ultrasound (US) power on chatter events and efficiency under both continuous and micropulse torsional US to reduce total cataract extraction times.

DESIGN

In vitro laboratory study.

METHODS

Porcine lens nuclei were incubated in formalin for 2 hours and then cut into 2-mm cubes. Phacoemulsification was performed using the Centurion Vision System and Infiniti OZil handpiece with the balanced tip. Both US modalities were studied at 60%, 80%, and 100% power. Micropulse rate was 83 pulses per second with 50% on time. Each combination comprised 20 runs. Efficiency was considered as the total time for a cube to be emulsified; chatter was the number of times the lens fragment bounced off the tip.

RESULTS

There was significant decrease in efficiency when power was increased from 60% to 100% (1.33-1.97 s; p < 0.001) under micropulse US and significant increase in chatter when power was further increased to 100% from 60% (0.15-0.94 s; p < 0.001). There was no significant efficiency change with increased power under continuous US. Comparing the phacoemulsification efficiency between continuous and micropulse US, we found no significant difference at 60% and 80% power; at 100% power, continuous was significantly more efficient than micropulse (1.48 and 1.97 s, respectively; p = 0.001).

CONCLUSIONS

Increasing power above 60% decreased efficiency under torsional micropulse US. We believe that this was due to the chatter increase observed with increasing US power. Torsional continuous US was significantly more efficient than micropulse US at 100% power.

Determining optimal ultrasound percent on time with long-pulse torsional phacoemulsification

OBJECTIVE

To evaluate the optimum percent on time for the most efficient lens fragment removal using long-pulse torsional ultrasound (US).

DESIGN

In vitro laboratory study.

METHODS

Porcine lens nuclei were incubated in formalin for 2 hours and then cut into 2 mm cubes. Phacoemulsification was performed using the Centurion^® Vision System and Infiniti OZil handpiece with the balanced tip. Vacuum was set at 500 mm Hg, aspiration rate at 50 mL/min, and intraocular pressure (IOP) at 50 mm Hg. Pulse rate was 26 pulses/second. Studied parameters were percent power: 60%, 80%, and 100%, and percent on times: 50%, 60%, 70%, and 80%. Efficiency was the total time for a cube to be emulsified. Chatter was the number of times the lens fragment bounced off the tip.

RESULTS

There was no significant difference in efficiency between 50%, 60%, and 70 % on-time settings (p = 0.17 and 0.08, respectively); however, there was significant increase in efficiency when the on time was increased from 70% to 80% (p = 0.03). Increasing power from 60% to 100% showed a statistically significant efficiency increase (p = 0.001). There was no significant change in chatter with increasing on time; however, there was a statistically significant increase in chatter with every power level increase.

CONCLUSION

Increasing on-time percent does not improve efficiency under torsional long-pulse US. There is no significant change in chatter with increasing on-time percent. Increasing power increases efficiency despite chatter increase. Long-pulse US does not appear to influence torsional action in a clinically meaningful way.

Effects of intracameral ascorbic acid on the corneal endothelium of dogs undergoing phacoemulsification

OBJECTIVE

Cataracts are the most common ocular disorder in dogs. Phacoemulsification is the preferred treatment method among ophthalmologists, but the cellularity of the endothelium must be considered for its success, as endothelial lesions may produce permanent corneal decompensation. The objective of this study was to evaluate the effects of intracameral ascorbic acid, a known antioxidant, on the corneal endothelium of dogs undergoing phacoemulsification.

ANIMAL STUDIED

In all, 40 eyes from 20 dogs, males and females from 7 to 12 years of age, were assessed for mature cataracts.

PROCEDURES

Two groups were formed (n = 20): Group 1 (G1) received a balanced salt solution (BSS), whereas Group 2 (G2) received sterile ascorbic acid diluted in a BSS, at a final concentration of 0.001 m ascorbic acid. The corneal endothelium was assessed via non-contact specular microscopy at multiple time points before and after phacoemulsification. Cell density (cells/mm² ) and area (mm² ), corneal thickness (mm), hexagonality, and the coefficient of variation of cell size were all assessed. P values equal to or less than 0.05 were considered significant.

RESULTS

With respect to the density of endothelial cells, both groups showed losses, but they were less severe in G2. There were no differences in corneal thickness. Hexagonality decreased significantly in the postoperative period in G1. Also in G1, the coefficient of variation of cell size increased significantly.

CONCLUSION

According to the results obtained, ascorbic acid minimizes cellular losses in the corneal endothelium.

Bent versus straight tips in micropulsed longitudinal phacoemulsification

OBJECTIVE

The aim of this study was to evaluate bent and straight phacoemulsification tips to determine which tip is more efficient in removal of lens fragments, using micropulsed longitudinal ultrasound in phacoemulsification.

DESIGN

In vitro laboratory study.

METHODS

The John A. Moran Eye Center Laboratories, University of Utah, Salt Lake City, Utah, was the study setting. Pig lenses hardened in a manner comparable with dense human cataracts were cut into 2-mm cubes and removed with micropulsed longitudinal ultrasound using settings previously shown to be optimally efficient (6 milliseconds on and 6 milliseconds off for a bent tip). To verify this time as most efficient for a straight tip, we also tested times of 5, 6, and 7 milliseconds time on and off. The tips were either straight or with a 20-degree bend. Twenty cubes were used for each comparative run.

RESULTS

For the straight tip, 6 milliseconds on (1.56 ± 0.815 seconds) was significantly more efficient than 7 milliseconds on (2.45 ± 1.56 seconds, p = 0.001) and not significantly more efficient than 5 milliseconds on (1.69 ± 0.86 seconds, p = 0.43). Five milliseconds off time (1.45 ± 0.76s) was more efficient than 6 milliseconds (2.06 ± 1.37 seconds, p = 0.004) and 7 milliseconds off (2.18 ± 1.24s, p = 0.001). The straight tip was more efficient than the bent tip (1.38 ± 0.83 versus 2.93 ± 2.14 seconds, p = 0.006).

CONCLUSIONS

Results are contrary to accepted common belief. Micropulsed longitudinal phacoemulsification is more efficient with a straight rather than a bent tip.

On the efficiency of water soluble antioxidants

The wide use of high intensity ultrasound (HIU) in modern medicine raises the question of bio-safety. It has been shown that the effect of HIU in biological media may have similarity to the effects of ionizing radiation. Exposure of biological media to HIU field may lead to cavitation phenomenon followed by formation of free radicals such as hydroxyl radical (OH(·)) and the super-oxide ion (O(2)(·-)). These are highly reactive species that may cause harmful effects and induce oxidative stress. In the present study we employed electron spin resonance (ESR) spectroscopy together with spin traps to quantify the dynamics of hydroxyl radical formation during exposure to HIU field in the presence of different amounts of six antioxidants. Thus, the efficiency of water-soluble antioxidants, namely Allicin, Melatonin, Deoxyribose, Trolox, Nuphlutine and Hermidin, to suppress accumulation of OH radicals was examined. The results show that among the six, Trolox and Allicin reduce hydroxyl concentration with the highest efficiency.

Bio-effects and safety of low-intensity, low-frequency ultrasonic exposure

Low-frequency (LF) ultrasound (20-100 kHz) has a diverse set of industrial and medical applications. In fact, high power industrial applications of ultrasound mainly occupy this frequency range. This range is also used for various therapeutic medical applications including sonophoresis (ultrasonic transdermal drug delivery), dentistry, eye surgery, body contouring, the breaking of kidney stones and eliminating blood clots. While emerging LF applications such as ultrasonic drug delivery continue to be developed and undergo translation for human use, significant gaps exist in the coverage of safety standards for this frequency range. Accordingly, the need to understand the biological effects of LF ultrasound is becoming more important. This paper presents a broad overview of bio-effects and safety of LF ultrasound as an aid to minimize and control the risk of these effects. Its particular focus is at low intensities where bio-effects are initially observed. To generate a clear perspective of hazards in LF exposure, the mechanisms of bio-effects and the main differences in action at low and high frequencies are investigated and a survey of harmful effects of LF ultrasound at low intensities is presented. Mechanical and thermal indices are widely used in high frequency diagnostic applications as a means of indicating safety of ultrasonic exposure. The direct application of these indices at low frequencies needs careful investigation. In this work, using numerical simulations based on the mathematical and physical rationale behind the indices at high frequencies, it is observed that while thermal index (TI) can be used directly in the LF range, mechanical index (MI) seems to become less reliable at lower frequencies. Accordingly, an improved formulation for the MI is proposed for frequencies below 500 kHz.

Visualization of irrigation fluid flow and calculation of its velocity distribution in the anterior chamber by particle image velocimetry

PURPOSE

To visualize irrigation fluid flow and calculate its velocity distribution in the anterior chamber during phacoemulsification by particle image velocimetry.

METHODS

Porcine eyes were fixed in a glass chamber filled with balanced salt solution. An ultrasound handpiece was fixed to the glass chamber, and its tip was inserted into the anterior chamber through a corneal incision. Irrigation fluid was mixed with fluorescein-labeled liposomes as tracer particles. During phacoemulsification without ultrasound, a sheet-like Nd-YAG pulsed laser beam was emitted and moved from the iris plane to the top of the cornea continuously. Images of illuminated liposomes in the anterior chamber were captured at short intervals with a CCD camera, and the velocity distribution of irrigation fluid flow was calculated by particle image velocimetry.

RESULTS

By particle image velocimetry, the flow velocity distribution could be calculated in any plane of the anterior chamber. Dynamic flow of the irrigation fluid, ejected from the tip of the ultrasound handpiece and returned to an aspiration port, was visualized clearly in the anterior chamber. The maximum flow velocity in the anterior chamber was 342 ± 131 mm/s.

CONCLUSIONS

Particle image velocimetry enabled the visualization of irrigation fluid flow and quantification of its velocity distribution in different planes of the anterior chamber during cataract surgery. These data are essential for evaluating the safety and efficacy of new surgical settings and devices during phacoemulsification.

New phacoemulsification tip with a grooved, threaded-tip construction

PURPOSE

To visually compare ultrasonic tip vibrations between a phaco tip with internal grooves (threaded tip) and a standard phaco tip during continuous-mode ultrasound (US) using ultra-high-speed digital video imaging.

SETTING

Watanabe Eye Clinic, Hyogo, Japan.

DESIGN

Experimental study.

METHODS

The threaded tip was constructed by creating grooves inside a standard phaco tip using a screw. An ultra-high-speed digital video camera was used to record the image during continuous-mode US. Samples used in the test chamber during phacoemulsification included a piece of chestnut as a representative human lens sample and actual human lens fragments.

RESULTS

Ultra-high-speed digital images showed that the threaded tip created a larger amount of cavitation than the standard phaco tip during US oscillation. Phacoemulsification of the sample using the standard phaco tip produced a chattering motion, making it difficult to maintain a steady tip position. The threaded tip produced little chattering motion, making it relatively easy to maintain a steady tip position. Once a piece of sample was gripped by the threaded tip, it was shaved and aspirated into the threaded tip without chattering motion. The mean effective phacoemulsification time (EPT) of the threaded tip was significantly shorter than that of the normal phaco tip (6.0 seconds ± 1.9 [SD] versus 15.4 ± 1.3 seconds; P=.002).

CONCLUSIONS

The threaded tip created larger amounts of cavitation and had strong destructive and holding power. This threaded construction is simple to produce and appears to be very effective for phacoemulsification.

Protective effect of different ophthalmic viscosurgical devices on corneal endothelium during severe phacoemulsification model in rabbits

BACKGROUND AND OBJECTIVE

To evaluate the protective effect of different ophthalmic viscosurgical devices (OVDs) on corneal endothelial cells against relatively severe phacoemulsification damage in a rabbit model.

MATERIALS AND METHODS

Twenty-four rabbit eyes were randomly assigned to four similar groups: in three groups the aqueous humor was completely replaced by Visiol (TRB CHEMEDICA, München, Germany), Biolon (Bio-Technology General Ltd., Kiryat Malachi, Israel), and Viscoat (Alcon, Puurs, Belgium) and in the control group no OVD was applied. Endothelial cell counts were performed prior to initiating the study. All eyes were exposed to continuous 5 minutes of phacoemulsification. Endothelial cell counts were repeated 4 days postoperatively.

RESULTS

Viscoat showed the highest endothelial cell loss (30%), followed by Biolon (25%), Visiol (22%), and the control group (19%). None of the differences between the groups were found to be statistically significant, although they were within each group (P = .028).

CONCLUSION

None of the tested OVDs demonstrated protective effect on corneal endothelial cells in comparison to the control group. This model was found to be too aggressive for the demonstration of the protective effect of different OVDs even for hard cataract.

Pretreatment with low-energy shock waves induces renal vasoconstriction during standard shock wave lithotripsy (SWL): a treatment protocol known to reduce SWL-induced renal injury

OBJECTIVE

To test the hypothesis that the pretreatment of the kidney with low-energy shock waves (SWs) will induce renal vasoconstriction sooner than a standard clinical dose of high-energy SWs, thus providing a potential mechanism by which the pretreatment SW lithotripsy (SWL) protocol reduces tissue injury.

MATERIALS AND METHODS

Female farm pigs (6-weeks-old) were anaesthetized with isoflurane and the lower pole of the right kidney treated with SWs using a conventional electrohydraulic lithotripter (HM3, Dornier GmbH, Germany). Pulsed Doppler ultrasonography was used to measure renal resistive index (RI) in blood vessels as a measure of resistance/impedance to blood flow. RI was recorded from one intralobar artery located in the targeted pole of the kidney, and measurements taken from pigs given sham SW treatment (Group 1; no SWs, four pigs), a standard clinical dose of high-energy SWs (Group 2; 2000 SWs, 24 kV, 120 SWs/min, seven pigs), low-energy SW pretreatment followed by high-energy SWL (Group 3; 500 SWs, 12 kV, 120 SWs/min + 2000 SWs, 24 kV, 120 SWs/min, eight pigs) and low-energy SW pretreatment alone (Group 4; 500 SWs, 12 kV, 120 SWs/min, six pigs).

RESULTS

Baseline RI (approximately 0.61) was similar for all groups. Pigs receiving sham SW treatment (Group 1) had no significant change in RI. A standard clinical dose of high-energy SWs (Group 2) did not significantly alter RI during treatment, but did increase RI at 45 min after SWL. Low-energy SWs did not alter RI in Group 3 pigs, but subsequent treatment with a standard clinical dose of high-energy SWs resulted in a significantly earlier (at 1000 SWs) and greater (two-fold) rise in RI than that in Group 2 pigs. This rise in RI during the low/high-energy SWL protocol was not due to a delayed vasoconstrictor response of pretreatment, as low-energy SW treatment alone (Group 4) did not increase RI until 65 min after SWL.

CONCLUSIONS

The pretreatment protocol induces renal vasoconstriction during the period of SW application whereas the standard protocol shows vasoconstriction occurring after SWL. Thus, the earlier and greater rise in RI during the pretreatment protocol may be causally associated with a reduction in tissue injury.

Protective effect of free-radical scavengers on corneal endothelial damage in phacoemulsification

PURPOSE

To examine the role of the water-soluble antioxidants glutathione and ascorbic acid in the irrigating solution on corneal endothelial cells following exposure to high-intensity ultrasound energy.

SETTING

Goldschleger Eye Research Institute, Sheba Medical Center, Tel-Aviv University, Tel Aviv, Israel.

METHODS

Thirty-two rabbit eyes were subjected to prolonged exposure to the phacoemulsification device in the anterior chamber. The eyes were divided into 4 groups that differed only in the composition of the irrigating solution applied to the eyes: balanced salt solution (BSS) BSS Plus BSS containing additional soluble components including glutathione, BSS with 10(-3) M of oxidized glutathione (GSSG), and BSS with 10(-2) M of ascorbic acid. Specular microscopy was performed preoperatively and 1 week after surgery.

RESULTS

The BSS group exhibited the highest endothelial cell loss (19.3%), followed by the BSS Plus group (10.6%), the GSSG group (5.2%), and the ascorbic acid group (0.9%). An overall difference was found between the groups (F = 11.046, P<.0001), and all groups demonstrated a statistically significant difference from the control BSS group (P<.02, P = .001, and P<.0001, respectively).

CONCLUSIONS

Damage to the cornea is largely due to the free radicals generated by high-intensity ultrasound energy during phacoemulsification. Adding the antioxidants ascorbic acid and GSSG to the irrigation solution significantly reduced the endothelial corneal cell damage. Ascorbic acid in the concentration of 10(-2) M had the highest protective effect; thus, it should be evaluated for clinical use.

The effect of elective phacofragmentation on central corneal thickness in the dog

OBJECTIVE

To characterize the short- and intermediate-term effects of elective phacofragmentation on central corneal thickness (CCT) in the dog.

METHODS

Forty-three dogs (66 eyes) undergoing elective phacofragmentation cataract surgery over an 8-month period at a single private ophthalmology referral clinic were enrolled in the study. Central corneal thickness was measured by ultrasonic pachymetry just prior to surgery, 1 day following surgery, 1 week postoperatively, 1 month postoperatively, and more than 2 months postoperatively. Statistical comparisons were made using descriptive and inferential statistical methods with a level of significance set at P < 0.05.

RESULTS

The initial mean CCT of 611 microm increased dramatically to 741 microm 1 day postphacofragmentation. Mean CCT remained slightly elevated (666 microm) at 1 week postoperatively, but became indistinguishable from preoperative measurements by 1 month postsurgery (626 microm) and remained so at the > 2-month time period (618 microm). The change over time and trends remained statistically significant and remarkably similar, even when adjusted separately for age, gender, surgeon status, diabetic status, cataract type, and total surgery time (all P < 0.0001). Corneas of diabetic dogs were thicker than those of nondiabetic dogs at all time periods, and the overall effect of diabetic status was significant (P = 0.016). There was a sharper increase from the preoperative to 1-day postoperative CCT in the diabetic group compared to the nondiabetic group. The mean CCT of the pseudophakic group took longer to return to baseline than the aphakic group. The mean CCT of the foldable intraocular lens (IOL) group took longer to return to baseline than both the rigid IOL and aphakic groups. Dogs with documented in-hospital postoperative intraocular pressure spikes (> 25 mmHg) developed a greater 1-day postsurgical increase in CCT. It appears that there was a sharper decrease in mean CCT from 1 month to more than 2 months postoperatively in the postoperative hypertension group.

CONCLUSIONS

Elective phacofragmentation cataract surgery results in an increase in CCT in dogs, but this increase is transient. Particular care may be indicated to protect the endothelium of diabetic patients undergoing phacofragmentation. These data do not clearly support an advantage of the small-incision cataract surgery made possible by the use of foldable IOLs.

Ultrasonic-generated fluid velocity with Sovereign WhiteStar micropulse and continuous phacoemulsification

PURPOSE

To evaluate and compare ultrasonic turbulence created by conventional and micropulse ultrasound technology.

SETTING

Sonora Medical Systems, Longmont, Colorado, USA.

METHODS

A high-resolution digital ultrasound probe imaged the zone around a phacoemulsification tip. Doppler analysis allowed determination of flow. The fluid velocity was measured at 4 levels of ultrasound power at a constant flow, comparing the ultrasonic conditions of continuous energy to WhiteStar micropulses.

RESULTS

In addition to the normal baseline irrigation and aspiration, fluid movement was detected directly below the phaco tip, produced by a nonlinear effect known as acoustic streaming. Acoustic streaming increased with increased phacoemulsification power for both conditions. At each of the 4 levels of power, fluid velocity away from the tip was less with micropulse technology than with continuous phacoemulsification.

CONCLUSIONS

The demonstrated decrease in acoustic streaming flow away from the phaco tip with Sovereign WhiteStar micropulse technology compared to conventional ultrasound provides an objective explanation for clinical observations of increased stability of nuclear fragments at the tip and less turbulence in the anterior chamber during phacoemulsification. This methodology can be used to examine and compare fluid flow and turbulence under a variety of clinically relevant conditions.

Extracellular ATP opposes thrombin-induced myosin light chain phosphorylation and loss of barrier integrity in corneal endothelial cells

Increased contractility of the actin cytoskeleton by phosphorylation of the regulatory myosin light chain (MLC) results in a loss of barrier integrity in corneal endothelial cells. This study has investigated the effect of extracellular ATP, which may influence both Ca2+ and cAMP signalling, on MLC phosphorylation and barrier integrity in cultured bovine corneal endothelial cells (BCEC) known to express A2B and P2Y purinergic receptors, and ecto-nucleotidases. Extracellular ATP (100 microM) promoted MLC dephosphorylation (pMLC=61.8% at 18 min; n=9). Pre-exposure to ARL-67156, an ecto-nucleotidase inhibitor, prevented ATP-induced dephosphorylation. Other P2Y agonists, UTP and ATPgammaS, also induced MLC dephosphorylation but to a lesser degree compared to ATP. Thrombin (2 U/ml), which activate Rho kinase through PAR-1 receptors in the endothelium, induced MLC phosphorylation (pMLC=129.2%; n=14). This phosphorylation was completely abolished by concomitant exposure to ATP. When cells were pretreated with adenosine (100 microM; A2B agonist) or forskolin (10 microM), thrombin-induced phosphorylation was suppressed. ATP also led to a significant increase in cAMP (> 3-fold compared to 10 microM adenosine). Thrombin-induced increase in trans-endothelial flux of horseradish peroxidase (44 kDa) and disruption of the cortical actin were suppressed by ATP. These findings indicate that in BCEC (1) ATP induces elevated cAMP through its metabolite adenosine leading to MLC dephosphorylation, (2) Stimulation of P2Y2 receptors also leads to activation of MLCP since UTP- and ATPgammaS caused MLC dephosphorylation, and (3) ATP is antagonistic to thrombin since the latter inhibits MLCP through increased activity of Rho kinase. These findings further emphasize the role of contractility of the actin cytoskeleton in regulating the barrier integrity of corneal endothelium.

Acoustic cavitation in phacoemulsification and the role of antioxidants

Cataract surgery by phacoemulsification generates acoustic cavitation, resulting in formation of reactive oxygen species. The aim of this study was to establish the mechanism of damage by phacoemulsification in an in vitro setting simulating cataract surgery and to assess the protective effects of water-soluble antioxidants. Electron paramagnetic resonance spectroscopy was used to analyze generation of radicals in an intraocular irrigating solution by phacoemulsification instrumentation, operating at an ultrasonic frequency range of 40--60 kHz. Hydroxyl radicals were generated by phacoemulsification under conditions simulating cataract surgery. The effects of water-soluble antioxidants in the irrigating solution on the amounts of radicals were evaluated by electron paramagnetic resonance spectroscopy. The water-soluble antioxidant glutathione, applied in either oxidized or reduced form, decreased hydroxyl radicals concentration measured in the sonicated medium. The effective concentrations of oxidized and reduced glutathione in irrigating solution that significantly eliminate the hydroxyl radical signal were determined in the range of 10(-3)-10(-2) M. Antioxidants should be applied clinically to reduce damage to the corneal endothelium induced by phacoemulsification, thereby improving biosafety.

Free radical development in phacoemulsification cataract surgery

Phacoemulsification and aspiration (PEA) has become the most popular cataract surgery, due to the establishment of safe surgical techniques and development of associated instruments. However, corneal endothelial damage still represents a serious complication, as excessive damage can lead to irreversible bullous keratopathy. In addition to causes such as mechanical or heat injuries, free radical formation due to ultrasound has been posited as another cause of corneal endothelium damage in PEA. Ultrasound in aqueous solution induces cavitation, directly causing water molecule disintegration and resulting in the formation of hydroxylradicals, the most potent of the reactive oxygen species. Considering the oxidative insult to endothelial cells caused by free radicals, their presence in the anterior chamber may represent one of the most harmful factors during these procedures. Indeed, some researchers have recently started to evaluate PEA from the perspective of oxidative stress. Conversely, the major ingredient in ophthalmic viscosurgical devices (OVDs), which are indispensable for maintaining the anterior chamber in PEA surgery, is sodium hyaluronate, a known free radical scavenger. OVDs can thus be expected to provide some anti-free radical effect during PEA procedures. In addition, since commercially available OVDs display different properties regarding retention in the anterior chamber during PEA, the anti-free radical effect of OVDs is likely to depend on behavior during irrigation and aspiration. The present study followed standard PEA procedures in an eye model and measured hydroxylradicals in the anterior chamber using electron spin resonance. The kinetics of free radical intensity and effects of several OVDs during clinical PEA were also demonstrated. These studies may be of significance in re-evaluating OVDs as a chemical protectant for corneal endothelium, since the OVD has thus far only been regarded as a physical barrier. In addition, many reports about corneal endothelium damage during PEA have been published, but objective evaluation of various damaging factors has been difficult. The present assay of free radicals in a simulation of clinical PEA offers the first method to quantitatively assess stress on the corneal endothelium.

The physics of phaco: a review

Despite its unparalleled success in the field of surgery, the precise mechanism of ultrasonic phacoemulsification cataract extraction remains controversial. We review the relevant peer-reviewed literature on the subject of power generation and tip-tissue interactions to clarify the current status of our knowledge. We conclude that phacoemulsification most likely operates by a combination of mechanisms, including direct action of the vibrating tip against tissue and indirect cavitational effects. Surgeons will benefit from understanding the physical principles underlying phacoemulsification because they will be better able to evaluate the performance of various parameters and different machine settings.

Visualization of fluid turbulence and acoustic cavitation during phacoemulsification

PURPOSE

To describe a technique for visualizing fluid turbulence and cavitational energy created by ultrasonic phaco tips.

SETTING

University Eye Clinic of Trieste, Trieste, Italy.

METHODS

Generation of cavitational energy by the phaco tip was visualized using an optical test bench comprising several components. The technique uses a telescope system to expand a laser light source into a coherent, collimated beam of light with a diameter of approximately 50.0 mm. The expanded laser beam shines on the test tube containing the tip activated in a medium of water or ophthalmic viscosurgical device (OVD). Two precision optical collimators complete the optical test bench and form the system used to focus data onto a charge-coupled device television camera connected to a recorder.

RESULTS

Images of irrigation, irrigation combined with aspiration, irrigation/aspiration, and phacosonication were obtained with the tip immersed in a tube containing water or OVD.

CONCLUSIONS

Optical image processing enabled acoustic cavitation to be visualized during phacosonication. The system is a possible means of evaluating a single phaco apparatus power setting and comparing phaco machines and techniques.