Phacodynamics: an aspiration flow vs vacuum comparison

PURPOSE

To compare actual flow and the vacuum necessary to generate that flow for the Advanced Medical Optics Sovereign (Advanced Medical Optics, Santa Ana, California, USA) and the Alcon Legacy (Alcon, Fort Worth, Texas, USA) phacoemulsification machines.

DESIGN

In vitro laboratory study.

METHODS

Flow was collected and machine indicated vacuum noted from 12 ml/min to 40 ml/min in 2 ml/min steps (20-gauge). Nineteen and 20-gauge tips were also compared. Machine indicated vacuum was converted to actual tip vacuum.

RESULTS

Legacy flow (102.4 +/- 3.8% of indicated) was significantly more than Sovereign (96.5 +/- 3.9%; P < .0001). 20-gauge flow was less than 19-gauge flow (96.1% vs 98.6% of indicated, P < .0001). Sovereign had less unoccluded vacuum (70.3 +/- 3.2 mm Hg) than Legacy (89.4 +/- 1.2 mm Hg) at 36 ml/min of flow (P < .0001 for 26 to 36 ml/min of flow).

CONCLUSION

There is unoccluded vacuum at the phaco tip of these systems at 14 ml/min, of flow and at 40 ml/min, this was 112.0 mm Hg for the Legacy.

Use of the Unfolder Silver/Sapphire system to inject capsular tension ring during phacoemulsification in cases with subluxated cataract

Capsular tension rings (CTRs) have proved to be useful devices in cataract surgery in cases of zonular weakness and dialysis. They can be inserted with the help of forceps or commercially available injection systems. We describe use of the Unfolder Silver/Sapphire Series implantation system (Advanced Medical Optics, Inc.) to inject a CTR into the capsular bag during phacoemulsification in cases with subluxated cataract. The implantation system used for CTR insertion can subsequently be used for implantation of a foldable intraocular lens.

Effect of incisional friction and ophthalmic viscosurgical devices on the heat generation of ultrasound during cataract surgery

PURPOSE

To determine the thermal features of the Legacy (Alcon) and Sovereign (Advanced Medical Optics) phacoemulsification machines in a cadaver eye and with 7 ophthalmic viscosurgical devices (OVDs).

SETTING

In situ and in vitro study.

METHODS

Temperature without occlusion was recorded at the sleeve placed in the wound of a cadaver eye, and temperature over baseline was determined after 60 seconds. The result was then compared with the results in a previous study that used balanced salt solution (BSS) in artificial chambers. In the second portion of the experiment, with irrigation and aspiration lines occluded, temperature was recorded at the sleeve placed in an artificial chamber filled with sodium hyaluronate 2.3% (Healon5), sodium hyaluronate 1.4% (Healon GV), sodium hyaluronate 1.0% (Healon), sodium hyaluronate 1.6% (Amvisc Plus), sodium hyaluronate 1.0% (Provisc), sodium hyaluronate 3.0%-chondroitin sulfate 4.0% (Viscoat), or hyaluronate 3.0% (Vitrax). Temperature over baseline was also determined after 60 seconds. These results were compared with each set of OVD data and with the results in the prior BSS study.

RESULTS

In the eye-bank model, the Legacy machine had a 62% temperature increase from incisional friction and the Sovereign machine had a decrease of 8.6% over results in an artificial anterior chamber. The OVD temperature increases were greater for the Sovereign (P<.001) and followed the same general trend for the Legacy. The least temperature increase was with Amvisc Plus, Healon, and Healon GV; the intermediate increases were with Provisc and Vitrax; and the greatest increases were with Viscoat and Healon5. The OVD findings did not correlate with viscosity or pseudoplasticity.

CONCLUSIONS

Incisional friction alone increased heat generation in the Legacy, a stroke-length driven instrument, more than in the Sovereign, a power-driven instrument. Ophthalmic viscosurgical devices are not only a concern due to outflow occlusion but can also add up to 6 times the heat in comparison with BSS. The need to aspirate the OVD before using ultrasound is thus verified.

Modified flexible iris retractor to retract superior iris and support inferior capsule in eyes with iris coloboma and inferior zonular deficiency

Flexible nylon iris retractors are a useful adjunct to cataract surgery in cases of small pupil and subluxated lenses. A modification is presented of the standard application of iris hooks to retract the superior iris and support the inferior capsule during phacoemulsification in cases of iris coloboma with inferior zonular deficiency. Three iris hooks are applied to retract the iris, and 2 iris hooks are applied to the inferior capsule margin to support the crystalline lens in that quadrant. Clear corneal temporal phacoemulsification is then performed with adequate pupillary diameter and capsular support.

Bimanual microphaco for posterior polar cataracts

We describe a technique in which bimanual microphacoemulsification technique through 2, 1.4 mm incisions is performed for posterior polar cataract extraction. The low-infusion and low-vacuum system provides good anterior chamber stability and followability. The irrigation and aspiration handpieces are interchangeable, enabling removal of the lens fragments without hydrodissection or nucleus rotation. Only 1 (12.5%) of the 8 cases presented here was complicated by posterior capsule rupture. This occurred after epinucleus removal without any vitreous disturbance. The bimanual microphacoemulsification technique appears to minimize the risk for complications, allowing posterior polar cataract extraction to be performed more safely.

Origin of intraocular metallic foreign bodies during phacoemulsification

This is the first report of a case of intraocular metallic foreign bodies retained after phacoemulsification in which the source was identified as silver emanating from the brazing of the irrigation tube as it entered the handpiece shell on its inner diameter. Although silver is considered to be inert in the eye and nonmagnetic, manufacturers should evaluate alternate methods of phacoemulsification handpiece design.

Thermal study of bare tips with various system parameters and incision sizes

PURPOSE

To identify major and minor surgeon-controlled parameters that affect incision temperature when performing microincision lens removal using the Alcon Infiniti Vision System.

SETTING

In vitro research and development laboratory, Alcon Research, Irvine, California, USA.

METHOD

Phacoemulsification was performed in eye-bank cadaver eyes and the following parameters evaluated: incision, duty cycle, ultrasound (US) power, aspiration flow rate (AFR), vacuum, pulse, bottle height and balanced salt solution temperature, and tip design/size. Each parameter was varied while the others remained constant. The resulting temperature of the incision and US tip was measured using a thermal camera.

RESULTS

Major contributors to elevated incision temperature included incision size, US power, duty cycle, AFR, vacuum setting, tip design, and presence of an ophthalmic viscosurgical device (OVD). Minor contributors included pulse frequency, bottle height, and temperature of the infusate.

CONCLUSION

Microincision lens removal can be performed at safe temperatures with the knowledgeable selection of surgeon-controlled parameters.

Anatomic evaluation of the Morcher capsular tension ring by ultrasound biomicroscopy

PURPOSE

To analyze the anatomic position of the Morcher capsular tension ring (CTR) by anterior segment ultrasound biomicroscopy.

SETTING

Academic institution.

METHODS

Fourteen pseudophakic eyes (13 patients) with placement of a Morcher CTR during cataract extraction had ultrasound biomicroscopy.

RESULTS

In all eyes, the CTR had a position between the intraocular lens haptics and the ciliary body without posterior iris touch.

CONCLUSIONS

In this small population of eyes, the Morcher CTR was found to be in a consistent, safe, and stable location in the capsular bag.

Retention and removal of a new viscous dispersive ophthalmic viscosurgical device during cataract surgery in animal eyes

AIMS

To assess the retention and removal properties of a new viscous dispersive ophthalmic viscosurgical device (OVD), DisCoVisc, in comparison with those of cohesive (Provisc), dispersive (Viscoat), and viscoadaptive (Healon5) OVDs.

METHODS

In 20 porcine eyes, cataract surgery was simulated using one of the four OVDs which were stained with fluorescein for better visualisation. Three parameters were measured. Firstly, the presence/absence of OVDs in the chamber at the completion of phacoemulsification was recorded. Secondly, the time until the OVDs were completely removed from the anterior chamber using the phaco needle was measured. Thirdly, after intraocular lens (IOL) implantation, the time needed to completely remove the OVDs from the chamber with irrigation/aspiration tip was recorded.

RESULTS

At the completion of phacoemulsification, the OVDs retained in 0% (0/5) for Provisc, 80% (4/5) for Healon5, 100% (5/5) for DisCoVisc, and 100% (5/5) for Viscoat. The retention of OVDs during phacoemulsification was greatest with Viscoat followed by, in descending order, DisCoVisc, Healon5, and Provisc. The removal of OVDs after IOL implantation took longest with Viscoat followed by Healon5, DisCoVisc, and Provisc.

CONCLUSION

The viscous dispersive DisCoVisc showed excellent retention during phacoemulsification, while its removal after IOL implantation was very easy. When compared with the viscoadaptive Healon5, DisCoVisc was retained better in the chamber and was easier to remove. These features of DisCoVisc should be highly advantageous when considering covering the entire cataract surgery procedure with a single OVD.

Phacoemulsification in a patient with a deep brain stimulator

We describe a 62-year-old man with a deep brain stimulator who had cataract surgery performed by phacoemulsification. Representatives of Medtronic and Alcon Laboratories would not sanction our proceeding with cataract surgery because of the possible interaction between the ultrasound and the device. Simulated cataract surgery 1 week before the scheduled operation failed to produce any consequences. One week later, the patient had uneventful cataract surgery. Although a single case does not guarantee the lack of interference between the ultrasound used in phacoemulsification and the deep brain stimulator, our safe outcome may warrant a place in the ophthalmic literature.

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.

Thermal imaging study comparing phacoemulsification with the Sovereign with WhiteStar system to the Legacy with AdvanTec and NeoSoniX system

PURPOSE

To assess intraoperative thermal levels at the wound site during divide-and-conquer phacoemulsification with the Sovereign with WhiteStar (SWS) system or the Legacy with AdvanTec and NeoSoniX (LAD) system.

DESIGN

Prospective, randomized, parallel-group, comparative study.

METHODS

Twenty-six subjects from a private clinical practice underwent divide-and-conquer phacoemulsification with either the SWS system or the LAD system. CB/CF settings (60%/33% duty cycles) were utilized with SWS and 12 pulses per second with the LAD system. Key criteria assessed were peak wound-site temperature, mean temperature change at the wound site, effective phaco time, average phaco power, procedure time, amount of BSS used, and surgical complications.

RESULTS

Mean temperature change at the wound site was greater for the LAD than the SWS group. There was a statistically significant difference (P=.0002) in mean peak wound temperatures, with the LAD group having higher mean peak temperatures (42.47+/-5.33 degrees C) than the SWS group (36.59+/-1.33 degrees C). Highest wound-site temperature was 51 degrees C for the LAD group and 39.3 degrees C for the SWS group. A statistically significant difference (P=.0031) in mean peak temperature was found between the LAD and SWS systems for subjects with a cataract density of 4: higher mean peak temperatures were observed for LAD patients with a cataract density of 4.

CONCLUSIONS

Our findings show that phacoemulsification using the SWS system results in lower peak temperatures and less temperature change at the phaco wound site compared with the LAD system.

Comparison of thermal features associated with 2 phacoemulsification machines

PURPOSE

To determine the thermal characteristics of the Legacy Advantec and Sovereign WhiteStar phacoemulsification machines during different clinically relevant scenarios.

SETTING

In vitro study.

METHODS

In water, temperature was recorded continuously on the sleeve in an artificial chamber, and the increase in temperature over baseline after 60 seconds of ultrasound was determined. This was done for continuous ultrasound, 50 ms on and 50 ms off (pulse), 6 ms on and 12 ms off (WhiteStar; Sovereign only) with aspiration blocked and not blocked, and with 100 g and 200 g weights suspended from the sleeve.

RESULTS

Comparing temperature increase per 20% machine power increments, Sovereign ran hotter than Legacy Advantec for continuous ultrasound (2.31x) and pulse (2.23x). Blocking aspiration increased temperature over the unblocked state. Pulsing decreased temperature by 51% (Legacy Advantec, pulse), 52% (Sovereign, pulse), and 64% (WhiteStar). Weights had much more effect on the Legacy Advantec: 3.5 times more going from baseline to 100 g weights and 3.2 times more going from 100 to 200 g weights. For all these comparisons, the P value was less than 0.0001.

CONCLUSIONS

The machines behaved fundamentally differently, with the Legacy Advantec controlling stroke length and Sovereign controlling a fixed power at any setting. Therefore, workload had a much bigger impact on Legacy Advantec thermal characteristics. Pulsing decreased heat produced directly related to the duty cycle. The most dangerous incision burn scenario is with continuous ultrasound, aspiration blocked, and a heavy workload.

Advances in microincision cataract surgery intraocular lenses

PURPOSE OF REVIEW

This review provides an update of recent advances in understanding the quality and functional significance of contrast sensitivity for the clinician regarding cataract, intraocular lenses and refractive surgery that goes beyond the measurement of visual acuity.

RECENT FINDINGS

New American National Standards Institute standards for contrast sensitivity based on linear sine-wave gratings are discussed that promise rapid advances of understanding and quantifying visual quality and function by unifying clinical results reported using contrast sensitivity. Increased sensitivity of linear sine-wave gratings over proposed bull's-eye radial gratings is discussed. Digital-image-processing software uses contrast sensitivity data to process images to help understand the quality of what the patient sees. Contrast sensitivity measurement is compared with wavefront aberrometry. Contrast sensitivity measures the total visual system quality in terms of contrast, whereas wavefront aberrometry measures the optical quality in terms of spatial distortion. Both measurements are needed to more fully understand the quality of vision.

SUMMARY

Recent advances provide the clinician with an awareness of why the new contrast-sensitivity standards are based on linear sine-wave gratings and how image-processing software can be used to better understand the quality of functional vision of the patient.

Comparative clinical trial of ultrasound phacoemulsification with and without the WhiteStar system

PURPOSE

To compare the postoperative outcomes of cataract surgery performed with the Sovereign 4.0 system or the Sovereign system with WhiteStar power modulation.

SETTING

Ambulatory surgery centers at 4 sites in the United States.

METHODS

This was a 3-month, open-label, randomized, parallel-group comparative clinical trial in patients with visually interfering cataract. Surgeons used the divide-and-conquer phacoemulsification technique for nuclear removal. An intraocular lens was implanted using the recommended insertion system. Primary operative outcome measures were equivalent phaco time (EPT), percentage of phaco power, amount of balanced salt solution used, and surgical complications. Patients were seen 1 day and 3 months after surgery. Postoperative outcome measures were the change in endothelial cell count from the preoperative visit to 3 months, corneal clarity, inflammation, and corneal thickness.

RESULTS

The Sovereign with WhiteStar group had 48 patients and the Sovereign 4.0 group, 49 patients. Mean EPT and mean percentage of power were significantly lower in the Sovereign with WhiteStar group. Mean EPT was 6.67 seconds +/- 8.2 (SD) in the Sovereign with WhiteStar group and 8.59 +/- 9.3 seconds (P = .01) in the Sovereign 4.0 group. Mean percentage of phaco power was 6.41% +/- 3.3% in the Sovereign with WhiteStar group and 8.51% +/- 4.9% in the Sovereign 4.0 group (P = .01). The Sovereign with WhiteStar group lost significantly fewer endothelial cells (-319.6 +/- 634.2 cells/mm(2)) than the Sovereign 4.0 group (-430.3 +/- 594.6 cells/mm(2)) (P = .01). Corneal clarity, cells and flare, and pachymetry were comparable with the exception of the 3-month visit. The mean change in baseline central pachymetry showed significantly less corneal thickening in the Sovereign with WhiteStar group.

CONCLUSIONS

The Sovereign with WhiteStar power modulation system provides effective lens removal at lower levels of phaco power and ultrasound energy than the Sovereign 4.0 system. Lower ultrasound levels may reduce the risk for endothelial cell loss during phacoemulsification.

Optimization of biometry for intraocular lens implantation using the Zeiss IOLMaster

PURPOSE

To compare the accuracy of biometry using conventional A-scan ultrasonography and partial coherence interferometry, and to improve the accuracy of biometry by sequential audit of postoperative refractive error.

METHODS

The study was performed in three phases. In phase 1, 20 consecutive patients undergoing routine phacoemulsification underwent biometry using both A-scan ultrasonography and the Zeiss IOLMaster (ZIOLM). A single experienced optometrist refracted all patients 2 weeks after surgery. The errors between expected and achieved refraction were calculated and compared between the two methods. In phases 2 and 3, a further 22 and 20 patients, respectively, were recruited and only the ZIOLM was used for biometry. The manufacturer's suggested A-constant was refined and the error between expected and achieved refraction was calculated.

RESULTS

In phase 1, the median unexpected error for the ZIOLM was +0.63 (interquartile range +0.368 to +1.015) and for A-scan biometry was - 0.24 (interquartile range - 1.335 to +0.802). In phase 1 65% of patients' postoperative refractions were found to be within 1.0 D of emmetropia using the ZIOLM (55% using A-scan biometry). Refinements to the A-constant improved this to 95% by phase 3.

CONCLUSION

An error was identified in IOL power estimation with the ZIOLM, when using the manufacturer's recommended A-constant (recommended and previously optimized ultrasound A-constant 118.0; ZIOLM optimized A-constant 118.6). Serial modifications to the A-constant were successful in reducing the unexpected error to well within the tolerance limits of published international standards.

New classification of ophthalmic viscosurgical devices—2005

PURPOSE

To revise the generally accepted classification of ophthalmic viscosurgical devices (OVDs) to include cohesion data and the new class of viscous dispersive OVDs.

SETTING

York Finch Eye Associates, Toronto, Ontario, Canada, and Alcon Research Limited, Fort Worth, Texas, USA.

METHODS

Pseudoplasticity and cohesion-dispersion (CDI) data of DisCoVisc (hyaluronic acid 1.6%-chondroitin sulfate 4%), a new viscous dispersive OVD, were determined and compared with existing OVDs. The existing classification of OVDs was unable to accommodate its properties, so the classification was modified to include a new class and other potential new classes which currently remain unoccupied.

RESULTS

Current OVD classification, although based on the clinically significant rheologic parameters of zero-shear viscosity and cohesion, only uses zero-shear viscosity because of the high correlation of these 2 parameters in existing OVDs. The appearance of DisCoVisc forces modification of the existing scheme because it does not fit into a preexisting category. The new proposed broadened classification is changed from a 1-dimensional list into a 2-dimensional table and considers CDI independently from viscosity for all OVDs. Expansion of the classification of OVDs in this manner predicts further possible new innovative OVDs for surgical use.

CONCLUSION

The surgical behavior of OVDs can be predicted by their position in a classification of OVDs based upon zero-shear viscosity and cohesion.

Optimization of biometry for intraocular lens implantation using the Zeiss IOLMaster

PURPOSE

To compare the accuracy of biometry using conventional A-scan ultrasonography and partial coherence interferometry, and to improve the accuracy of biometry by sequential audit of postoperative refractive error.

METHODS

The study was performed in three phases. In phase 1, 20 consecutive patients undergoing routine phacoemulsification underwent biometry using both A-scan ultrasonography and the Zeiss IOLMaster (ZIOLM). A single experienced optometrist refracted all patients 2 weeks after surgery. The errors between expected and achieved refraction were calculated and compared between the two methods. In phases 2 and 3, a further 22 and 20 patients, respectively, were recruited and only the ZIOLM was used for biometry. The manufacturer's suggested A-constant was refined and the error between expected and achieved refraction was calculated.

RESULTS

In phase 1, the median unexpected error for the ZIOLM was+0.63 (interquartile range+0.368 to+1.015) and for A-scan biometry was --0.24 (interquartile range--1.335 to+0.802). In phase 1 65% of patients' postoperative refractions were found to be within 1.0 D of emmetropia using the ZIOLM (55% using A-scan biometry). Refinements to the A-constant improved this to 95% by phase 3.

CONCLUSION

An error was identified in IOL power estimation with the ZIOLM, when using the manufacturer's recommended A-constant (recommended and previously optimized ultrasound A-constant 118.0; ZIOLM optimized A-constant 118.6). Serial modifications to the A-constant were successful in reducing the unexpected error to well within the tolerance limits of published international standards.

Illuminated endochopper in the management of posteriorly dislocated lens nucleus

We describe the use of an illuminated endochopper (a prototype instrument produced by DORC International) in the management of a posteriorly dislocated lens nucleus or lens particles. This instrument helps to divide the lens nucleus or its fragments into small pieces and thus reduces time and ultrasound energy.

In-air thermal imaging comparison of Legacy AdvanTec, Millennium, and Sovereign WhiteStar phacoemulsification systems

PURPOSE

To compare the temperature profiles of 3 popular phacoemulsification units (Alcon Legacy AdvanTec, Bausch & Lomb Millennium, and AMO Sovereign WhiteStar) under similar operating conditions in air.

SETTING

Jules Stein Eye Institute and the Department of Ophthalmology, David Geffen School of Medicine at UCLA, Los Angeles, California, USA.

METHODS

Phacoemulsification probes from the 3 units were placed side by side in air and imaged in the infrared region using model P60 ThermaCAM (Flir Systems). The highest temperature produced by each probe was measured 10 seconds and 30 seconds after power application. Testing was performed under conditions that might produce a corneal burn during cataract surgery. Irrigation flow was set at the low rate of 1 cc/min to simulate a tight incision. Aspiration flow was set at 0 cc/min to simulate occlusion of the needle lumen. Wound compression was simulated in some tests by suspending 22.6 g weights by rubber bands from the silicone sleeves. Manufacturers' specific and identical silicone sleeves were used to evaluate possible variations in thermal conductivity. The AdvanTec Legacy and Millennium were operated in pulse mode at 15 Hertz; 50% duty cycle; and 10%, 30%, and 50% power. The Sovereign WhiteStar was operated in both C/F (56 Hz, 33% duty cycle) and C/L (33 Hz, 20% duty cycle) modes at the same console power settings. Temperature profiles were determined at a variety of power settings with each system operating in continuous and pulse mode.

RESULTS

Under all experimental conditions (at 10%, 30%, and 50% powers; with and without external weights suspended from the phacoemulsification probes; with manufacturers' and identical silicone sleeves; and in continuous and pulse modes), the Millennium and the Sovereign WhiteStar generated higher temperatures than the Legacy AdvanTec.

CONCLUSIONS

Under controlled operating conditions in air and under a variety of power, load, and duty-cycle settings, the Millennium and the Sovereign WhiteStar, operating in both pulse and continuous modes, generated higher peak temperatures than the Legacy AdvanTec.