Phaco-emulsification causes the formation of cavitation bubbles

Narrative review after post-hoc trial analysis of factors that predict corneal endothelial cell loss after phacoemulsification: Tips for improving cataract surgery research

PURPOSE

Identifying pre/perioperative factors that predict corneal endothelial-cell loss (ECL) after phacoemulsification may reveal ways to reduce ECL. Our literature analysis showed that 37 studies have investigated one or several such factors but all have significant limitations. Therefore, the data of a large randomized controlled trial (PERCEPOLIS) were subjected to post-hoc multivariate analysis determining the ability of nine pre/perioperative variables to predict ECL.

METHODS

PERCEPOLIS was conducted in 2015-2016 to compare two phacoemulsification techniques (subluxation and divide-and-conquer) in terms of 3-month ECL. Non-inferiority between the techniques was found. In the present study, post-hoc univariate and multivariate analyses were conducted to determine associations between ECL and age, sex, cataract density, preoperative endothelial-cell density, phacoemulsification technique, effective phaco time (EPT), and 2-hour central-corneal thickness. The data are presented in the context of a narrative review of the literature.

RESULTS

Three-month data were available for 275 patients (94% of the randomized cohort; mean age, 74 years; 58% women). Mean LOCSIII cataract grade was 3.2. Mean EPT was 6 seconds. Mean ECL was 13%. Only an older age (beta = 0.2%, p = 0.049) and higher EPT (beta = 1.2%, p = 0.0002) predicted 3-month ECL. Cataract density was significant on univariate (p = 0.04) but not multivariate analysis. The other variables did not associate with ECL.

CONCLUSIONS

Older age may amplify ECL due to increased endothelial cell fragility. EPT may promote ECL via cataract density-dependent and -independent mechanisms that should be considered in future phacoemulsification research aiming to reduce ECL. Our literature analysis showed that the average ECL for relatively unselected consecutively-sampled cohorts is 12%.

In vitro analysis of clinically relevant aspects of a polymer-coated phacoemulsification tip vs a traditional tip

PURPOSE

To compare the in vitro incisional temperature, acoustic energy, transient cavitation, and turbulence of the polymer-coated hybrid phacoemulsification tip with the balanced tip.

SETTING

Pasteur Ophthalmology Clinic, Vitacura, Santiago, Chile.

DESIGN

Laboratory study.

METHODS

The Centurion Vision System with Active Sentry handpiece was used with tips operated in torsional mode, and stroke was normalized. For thermal measurements, controlled loads were applied over the tip sleeve simulating the pressure applied at the expected level of the corneal incision. Heat generated was recorded on a blackbody filmstrip using infrared imaging. A directional hydrophone provided 360° mapping of acoustic pressure. Cavitation patterns with increasing ultrasound power were imaged with high-speed video recording. Particle image velocimetry was used to evaluate turbulence, streaming, and bubble formation.

RESULTS

The temperature rise for the hybrid and balanced tips was lower than with the control mini-flared Kelman tip ( P ≤ .0001). The hybrid tip generated reduced acoustic output compared with the balanced tip. Ultrasound threshold for cavitation was higher for the hybrid vs balanced tip (55% vs 25%). Fluid turbulence was more evident with the balanced tip compared with the hybrid tip at all flow conditions when normalized for stroke at 60% and 80% power for balanced and hybrid tip, respectively.

CONCLUSIONS

The polymer-coated hybrid tip showed reduced heat generation compared with the control mini-flared Kelman tip and had lower acoustic output, lower cavitation, and lower turbulence compared with the balanced tip, suggesting potential for improved clinical safety.

Effects of ultrasound energy on the porcine corneal endothelium - Establishment of a phacoemulsification damage model

PURPOSE

The purpose of this study was to establish a standardized in vitro phacoemulsification damage model for future investigations of the effects of phacoemulsification, surgical devices, protective ophthalmic viscoelastic devices (OVDs), irrigation solutions and other aspects related to cataract phacoemulsification surgery on the corneal endothelium using porcine eyes.

METHODS

Thirty-four porcine eyes were randomly assigned to three groups (phacoemulsification (n = 13), irrigation (n = 9), control (n = 12)). A total of 5 min of ultrasound energy with intermittent irrigation/aspiration was applied in the eyes of the phacoemulsification group. The eyes of the irrigation group received the identical treatment, but without the application of ultrasound energy. The control group was left untreated. All eyes were then prepared to split corneal buttons followed by 15 days of cultivation. Endothelial cell density (ECD) was assessed blinded on day 15.

RESULTS

Endothelial cell density declined significantly more until day 15 in the phacoemulsification group (2567 ± 317/267 cells/mm² (median ± 25%/75%-quartiles), -32.5 ± 7.0/6.4%) compared to the irrigation (3450 ± 350/383 cells/mm², -11.8 ± 5.3/2.6%; p < 0.001) and the control group (3650 ± 288/258 cells/mm², -10.2 ± 3.2/4.6%; p < 0.001).

CONCLUSION

The phacoemulsification damage model presented in this study is sensitive to phacoemulsification energy and may reliably be used to investigate various factors involved in phacoemulsification with regard to their influence on corneal endothelial cells. This method is able to replace animal experiments or in vitro cell culture experiments that often do not translate well to the in vivo situation in humans.

Effects of Hydrogen in Prevention of Corneal Endothelial Damage During Phacoemulsification: A Prospective Randomized Clinical Trial

PURPOSE

Hydrogen (H₂) has been reported to scavenge free radicals, particularly the hydroxyl radical (·OH). Ultrasound oscillation in an aqueous solution produces ·OH. Our recent study demonstrated that H₂ dissolved in an irrigation solution prevented corneal endothelial damage during phacoemulsification in an animal model. We examined the effects of H₂ during clinical phacoemulsification.

DESIGN

A single-center, prospective, randomized, double-masked clinical trial.

METHODS

Thirty-two patients who had cataracts of similar nucleus hardness in both eyes (age: 75.4±7.68 years; 17 males, 15 females) were recruited. Phacoemulsification was performed using a solution of dissolved H₂ in one eye, and a conventional solution in the contralateral eye. Endothelial cell density (ECD) at the center of the cornea was measured using noncontact specular microscopy preoperatively and at 1 day, 1 week, and 3 weeks postoperatively.

RESULTS

Reduction rates of ECD (mean ± standard deviation) were 16.0%±15.7% at 1 day, 15.4%±16.1% at 1 week, and 18.4%±14.9% at 3 weeks in the control group, compared to 6.5%±8.7% at 1 day (P = .003), 9.3%±11.0% at 1 week (P = .039), and 8.5%±10.5% at 3 weeks (P = .004) in the H₂ groups. These rates were significantly smaller in the H₂ group at all time points.

CONCLUSIONS

H₂ dissolved in irrigation solution reduced corneal endothelial damage during phacoemulsification. This suggests that a considerable part of the corneal endothelial damage during phacoemulsification is caused by oxidative stress, and that H₂ is useful in clinical phacoemulsification.

Hydrogen prevents corneal endothelial damage in phacoemulsification cataract surgery

In phacoemulsification, ultrasound induces hydroxyl radical (·OH) formation, damaging corneal endothelium. Whether H2 can prevent such oxidative damage in phacoemulsification was examined by in vitro and in vivo studies. H2 was dissolved in a commercial irrigating solution. The effects of H2 against ·OH generation were first confirmed in vitro by electron-spin resonance (ESR) and hydroxyphenyl fluorescein (HPF). ESR showed a significantly decreased signal magnitude, and fluorescence intensity by oxidized HPF was significantly less in the H2-dissolved solution. The effects of H2 in phacoemulsification were evaluated in rabbits, comparing H2-dissolved and control solutions. Five hours after the procedure, the whole cornea was excised and subjected to image analysis for corneal edema, real-time semiquantitative PCR (qPCR) for heme oxygenase (HO)-1, catalase (CAT), superoxide dismutase 1 (SOD1), and SOD2 mRNA, and immunohistochemistry. Corneal edema was significantly less and the increases in anti-oxidative HO-1, CAT and SOD2 mRNA expressions were significantly suppressed in the H2 group. In addition, corneal endothelial cell expressions of two oxidative stress markers, 4-HNE and 8-OHdG, were significantly lower in the H2 group. In conclusion, H2 dissolved in the ocular irrigating solution protected corneal endothelial cells from phacoemulsification-induced oxidative stress and damage.

Computation of the temperature rise at the corneal endothelium during cataract surgery by modeling of heat generation inside the anterior chamber

The corneal endothelium sustaining the transparency of the cornea is a vulnerable cell layer. Thermal exposure during phacoemulsification is considered to be a potential cause of post-operative cell loss. Knowledge of the temperature rise and particularly of its dependence on region and system settings could deliver useful information about a potential correlation with cell damage. However, there exists a lack of understanding of the process and location of heat generation. Analytical calculations and experiments enabled the quantification of different mechanisms acting as heat sources during phacoemulsification. Heat generation caused by viscous friction was estimated using both an analytical approach and a numerical simulation. In contrast to absorption of sound and self-heating of the probe, this effect was ascertained to be the main heat source. Calorimetric measurement of the power input verified this modeling. On the basis of these results, the local temperature distribution inside a porcine eye was computed time dependently using the finite-element method. Two different amplitude settings were compared with respect to the temperature increase at the corneal endothelium. Various conclusions on the mitigation of thermal exposure during treatment can be drawn from this finite-element simulation.

Safety and efficacy of UltraShape Contour I treatments to improve the appearance of body contours: multiple treatments in shorter intervals

BACKGROUND

The UltraShape Contour I System (CE 0344; UltraShape Ltd., Yoqneam, Israel) is a noninvasive fat reduction and body contouring system currently approved for use outside the United States that utilizes focused ultrasound to selectively disrupt adipocytes.

OBJECTIVE

To evaluate the clinical safety and efficacy of the Contour I system when the intervals between treatments are shortened.

METHODS

Twenty-five healthy Caucasian women were selected from the patient population at two clinics in Paris, France, and received three 30- to 90-minute Contour I treatments in the abdominal region at two-week intervals. Safety parameters evaluated included adverse events, local skin reaction, and pain. Efficacy parameters evaluated included treatment area circumference, body weight, and comparison of before and after photos. Untreated thigh areas served as an internal control. Subjects were followed for 84 days after the last treatment (day 112).

RESULTS

No adverse events occurred. The majority of subjects (n = 23; approximately 90%) reported no pain. Mean midline circumference (2 cm below midline) was reduced by 2.47 cm (P < .001) on day 14 after the first Contour I treatment, 3.51 cm (P < .001) on day 56, and 3.58 cm (P < .001) on day 112. Peak midline circumference reduction was 3.12 cm on day 112. Most patients (n = 14; 63%) reported a positive change in body contour. Mean thigh circumference (the control area) was unchanged; the relative change between treated and untreated areas of the abdomen was significantly different at all time points. Circumference and weight reduction were significantly correlated (r = 0.42-0.71) at all time points; mean weight decrease was not statistically significant. Circumference reduction on day 112 positively correlated with patients' subjective satisfaction scores.

CONCLUSIONS

Our data showed that successive Contour I treatments at two-week intervals were safe and tolerable and also significantly reduced treatment area circumference.

Agents for intraocular surgery

No single viscoelastic material has all the properties required for every surgical procedure. Ophthalmic surgeons should be familiar with the advantages and disadvantages of several viscoelastics and realize the limitations encountered if the surgeon chooses to rely on a single viscoelastic. It is possible in the future that newer viscoelastics may become available offering aspects of cohesive and dispersive properties that make them easy to remove and not associated with postoperative hypertension. Investigation into other types of viscoelastic materials, such as poly-acrylamide (Orcolon) [33,51,52], human collagen [33,53], polytriethylene-glycol monomethacrylate, and polyglycerol monomethacrylate [48], may result in the availability of synthetic viscoelastic materials. Rethinking how we use viscoelastics may also be indicated. The approach of a single or repeat instillation of a viscoelastic only to have it aspirated during the procedure could be modified by using a continuous infusion ofa dilute viscoelastic [54]. One study diluted hyaluronic acid to a concentration of 0.06% to 0.12% and maintained continuous infusion of the viscofluid through the PE irrigation line [54]. It has been suggested that this may reduce turbulence and improve tissue protection [54].

The role of cavitation microjets in the therapeutic applications of ultrasound

The dynamics of a gas bubble situated in a sound-irradiated liquid and near a rigid boundary was studied theoretically to get a better understanding of the role of cavitation microjets in the therapeutic applications of ultrasound (US). The boundary integral method was adopted to simulate the temporal development of the bubble shape, jet formation during bubble collapse and bubble migration. It was found that the dynamic behaviour of the jet and the migratory characteristics of the bubble depend not only on the distance between bubble and boundary but, also, on the properties of the acoustic field. For frequencies of sound fields smaller than or equal to the resonance frequency of the bubble, jet formation and bubble migration toward the boundary are the main features of the interaction. No jet formation was observed for frequencies of sound fields larger than the resonance frequency of the bubble, and the bubble kept its initial position from the boundary throughout its motion. The pressure generated by the impact of the jet developed during bubble collapse close to the boundary may result in the fragmentation of brittle objects, such as renal calculi, dental tartar or intraocular lens.

White Star technology

White Star micropulse technology is a software modification that allows extremely short bursts of ultrasound energy. Studies have shown that this decreases wound heat build-up with the retained efficiency of continuous ultrasound. Decreased energy utilization with improved corneal function and improved nuclear fragment followability appear to be additional benefits.

Development of glaucoma after cataract surgery in dogs: 220 cases (1987-1998)

OBJECTIVE

To examine postoperative ocular hypertension (POH) and other variables as predictors of the risk of developing glaucoma after cataract surgery in dogs.

DESIGN

Retrospective study.

ANIMALS

220 dogs that had cataract surgery.

PROCEDURE

Medical records of 220 dogs (346 eyes) that had extracapsular cataract removal or phacoemulsification of cataracts were reviewed. With respect to glaucoma development, 8 variables were analyzed, which included development of POH, breed, sex, age at time of surgery, eye (right vs left), phacoemulsification time, intraocular lens (IOL) placement (yes or no), and stage of cataract development. Eyes developed glaucoma within 6 or 12 months of surgery or did not have signs of glaucoma at least 6 or 12 months after cataract surgery.

RESULTS

Of 346 eyes, 58 (16.8%) developed glaucoma after surgery. At 6 months, 32 of 206 (15.5%) eyes examined had glaucoma; at 12 months, 44 of 153 (28.8%) eyes examined had glaucoma. Median follow-up time was 5.8 months (range, 0.1 to 48 months). Mixed-breed dogs were at a significantly lower risk for glaucoma, compared with other breeds. Eyes with IOL placement were at a significantly lower risk for glaucoma, compared with eyes without IOL placement. Eyes with hypermature cataracts were at a significantly higher risk for glaucoma, compared with eyes with mature or immature cataracts.

CONCLUSIONS AND CLINICAL RELEVANCE

Multiple factors appear to contribute to the onset of glaucoma in dogs after cataract surgery. Complications prohibiting IOL placement during cataract surgery may lead to a high risk of glaucoma development.

The resiliency of the corneal endothelium to refractive and intraocular surgery

PURPOSE

To describe stress factors (phenylephrine and contact lenses) from the corneal epithelium that can affect the corneal endothelium, and to describe the effects of refractive and intraocular surgery on the corneal endothelial structure and function.

METHODS

Significant clinical and experimental publications are reviewed and recent experiments conducted in the author's laboratory to describe the corneal endothelial stresses.

RESULTS

The corneal epithelium serves as a barrier to topical phenylephrine (2.5-10%). In a compromised epithelium, topical phenylephrine will cause drug-induced stromal edema and endothelial vacuolization. Contact lenses are capable of stimulating the epithelial arachidonic acid cascade to release 12(R)hydroxyeicosatetraenoic acid (12(R)HETE) and 8(R)hydroxy-hexadecatrienoic acid (8(R)HHDTrE) to cause endothelial Na+/K+ adenosine triphosphatase (ATPase)-inhibition and polymegethism. Specular microscopy of the corneal endothelial cells after refractive surgery (photorefractive keratectomy [PRK], laser in situ keratomileusis [LASIK], intrastromal rings [INTACs]) has shown that there is minimal effect. However, laser ablation of the stroma within 200 microm of the corneal endothelium will result in endothelial cell structural changes and the formation of the amorphous substance deposited onto Descemet's membrane. Phacoemulsification with a high flow of the irrigation solution can alter the endothelial surface glycoprotein layer. Lidocaine hydrochloride (1%) used as intracameral anesthesia readily diffuses through the corneal endothelium, resulting in stromal uptake and endothelial cell swelling. With phacoemulsification, however, the washout of lidocaine from the cornea (T1/2, 5 minutes) and iris (T1/2, 9 minutes) occurs quickly. Corneal endothelial wound healing after keratoplasty occurs in the following sequence: migration of endothelial cells, development of tight junctions, and the formation of Na+/K+ ATPase pump sites.

CONCLUSIONS

Corneal endothelial resiliency is due to the increased peripheral endothelial cell number for migration, the ability of endothelial cells to form tight junctions to maintain the endothelial barrier, the increase in endothelial Na+/K+ ATPase pump sites under stress, and the ability of the corneal endothelial cells to shift their metabolism of glucose to the hexose monophosphate shunt for the production of nicotinamide adenine dinucleotide phosphate (NADPH) and membrane repair. All of these factors are important, along with the aqueous humor sodium concentration, which establishes the osmotic gradient for corneal deturgescence and transparency.

Phacoemulsification. Technology and fundamentals

The number one rule of phacoemulsification and aspiration cataract surgery is to know your machine. This chapter is designed to help the surgeon who is currently using phacoemulsification, or those who wish to understand more about technique, learn the basics and technology of the various types of phacoemulsification machines. Fluidics, pump design, handpiece mechanics, phacoemulsification needles, and fundamentals of phacoemulsification of cataracts will be reviewed.

Surgery for cataracts

The advent of phacoemulsification has substantially improved the success rate of cataract surgery in dogs, whereas the development of artificial lens implantation has equally improved postoperative visual acuity. In this chapter information pertaining to the etiology, diagnosis, and management of canine cataracts is provided for the general practitioner. More detailed information on phacoemulsification and artificial lens implantation is provided for residents in training or practicing ophthalmologists that may be converting from extracapsular extraction.