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.

Laboratory assessment of thermal characteristics of three phacoemulsification tip designs operated using torsional ultrasound.

PURPOSE: Ultrasound activation of phacoemulsification (phaco) tips can create considerable thermal energy that may increase the risk of tissue damage during cataract surgery. The purpose of this study was to define the thermal profiles of three phaco tip designs in simulated surgical conditions. METHODS: In this laboratory investigation, sleeved phaco tips (mini-flared Kelman(®) tip with aspiration bypass port and Intrepid(®) Balanced Tip with aspiration bypass port, and MST A1 bent-mini phaco tip (without aspiration bypass) were tested using an ultrasonic phaco device operated in torsional mode at power levels of 50%, 75%, and 100% amplitude. An automated fixture applied a 30 g load to simulate compression against the incision site, leading to friction between the silicone sleeve and the titanium tip. Temperature was recorded by high rate infrared imaging under conditions of free flow and occlusion, which was simulated by clamping the aspiration line. Data were summarized using descriptive statistics. RESULTS: Baseline temperatures of ~26°C were observed for all tips. During ultrasonic operation at 50%, 75%, and 100% amplitude, temperatures were lower for the mini-flared and balanced tips versus the bent-mini tip, both when load was applied and during occlusion. The bent-mini tip reached temperatures as high as 70°C during occlusion with load when operated at 100% amplitude, whereas the mini-flared tip remained <50°C, and the balanced tip remained <36°C in all test conditions. For the mini-flared and balanced tips, temperature increases during operation were not markedly different from free flow and no-load conditions when occlusion or frictional events were simulated. CONCLUSION: In all experiments for each tip design, increasing ultrasound power was associated with greater increases in tip temperature. Tip temperatures increased with applied load, but marked temperature increases during occlusion were observed only with the bent-mini tip. The balanced tip produced minimal thermal peaks in all tests.

Qualitative and quantitative analyses of stroke dynamics and microfluidics of phacoemulsification probes operating in different modes.

PURPOSE: To compare phacoemulsification (phaco) tip movement, microfluidic dynamics, and tip-to-load interaction between longitudinal, torsional, and elliptical ultrasound (US) modalities. SETTING: Phacodynamics Laboratory, Clínica Oftalmológica, Pasteur, Santiago, Chile. DESIGN: Experimental study. METHODS: All experiments were performed using a fluid-filled optical test chamber and phaco tips that were US power activated. Tip movement was evaluated using stroke tracing and stroboscopy imaging techniques. Qualitative and quantitative assessments of microfluidic behavior were performed using bead seeding and high-speed shadowgraphy imaging combined with particle-image velocimetry and vector analysis. Material load interaction was measured using a rubber sphere that represented lens material. RESULTS: Longitudinal and torsional US tips showed precise forward-and-backward and side-to-side (lateral) movement, respectively. Elliptical US tips scribed a 2-dimensional ellipsoid path that slightly changed in shape and orientation plane at higher powers. Longitudinal and lateral components of tip motion were evident in elliptical mode. Regular fluid flow was observed with longitudinal mode (forward-directed flow away from the aspiration port) and torsional mode (steady backflow into the aspiration port). In elliptical mode, bead repulsion, erratic bursts of acoustic streaming, oblique backflow, and areas of multidirectional flow were observed. The longitudinal mode caused the material load to bounce against the tip, whereas the torsional mode maintained a consistent load attraction. In elliptical mode, the material load rotated slightly and bounced away from the tip in irregular intervals when attraction was achieved. CONCLUSIONS: Tip movement, microfluidic behavior, and material load interaction were related within but varied across US modalities. The elliptical mode showed a movement pattern with longitudinal and lateral components and irregular microfluidic behaviors. FINANCIAL DISCLOSURE: Dr. Zacharias received research funding from Alcon Laboratories, Inc. He has no financial or proprietary interest in any material or method mentioned.

Thermal characterization of phacoemulsification probes operated in axial and torsional modes.

PURPOSE: To analyze temperature increases and identify potential sources of heat generated when sleeved and sleeveless phacoemulsification probes were operated in axial and torsional modes using the Infiniti Vision System with the Ozil torsional handpiece. SETTING: Phacodynamics Laboratory, Pasteur Ophthalmic Clinic, Santiago, Chile. DESIGN: Experimental study. METHODS: Two computer-controlled thermal transfer systems were developed to evaluate the contribution of internal metal stress and tip-to-sleeve friction on heat generation during phacoemulsification using axial and torsional ultrasound modalities. Both systems incorporated infrared thermal imaging and used a black-body film to accurately capture temperature measurements. RESULTS: Axial mode was consistently associated with greater temperature increases than torsional mode whether tips were operated with or without sleeves. In tests involving bare tips, axial mode and torsional mode peaked at 51.7°C and 34.2°C, respectively. In an example using sleeved tips in which a 30.0 g load was applied for 1 second, temperatures for axial mode reached 45°C and for torsional mode, 38°C. Friction between the sleeved probe and the incisional wall contributed more significantly to the temperature increase than internal metal stress regardless of the mode used. CONCLUSIONS: In all experiments, the temperature increase observed with axial mode was greater than that observed with torsional mode, even when conditions such as power or amplitude and flow rate were varied. Tip-to-sleeve friction was a more dominant source of phaco probe heating than internal metal stress. The temperature increase due to internal metal stress was greater with axial mode than with torsional mode. FINANCIAL DISCLOSURE: Dr. Zacharias received research funding from Alcon Laboratories, Inc., to conduct this study. He has no financial or proprietary interest in any material or method mentioned.

Fluid dynamics, cavitation, and tip-to-tissue interaction of longitudinal and torsional ultrasound modes during phacoemulsification.

PURPOSE: To describe the fluidic events that occur in a test chamber during phacoemulsification with longitudinal and torsional ultrasound (US) modalities. SETTING: Pasteur Ophthalmic Clinic Phacodynamics Laboratory, Santiago, Chile, and Nanyang Technological University, Singapore. DESIGN: Experimental study. METHODS: Ultra-high-speed videos of a phacoemulsifying tip were recorded while the tip operated in longitudinal and torsional US modalities using variable US power. Two high-speed video cameras were used to record videos up to 625,000 frames per second. A high-intensity spotlight source was used for illumination to engage shadowgraphy techniques. Particle image velocimetry was used to evaluate fluidic patterns while a hyperbaric environmental system allowed the evaluation of cavitation effects. Tip-to-tissue interaction at high speed was evaluated using human cataract fragments. RESULTS: Particle imaging velocimetry showed the following flow patterns for longitudinal and torsional modes at high US powers: forward-directed streaming with longitudinal mode and backward-directed streaming with torsional mode. The ultrasound power threshold for the appearance of cavitation was 60% for longitudinal mode and 80% for torsional mode. Cavitation was suppressed with pressure of 1.0 bar for longitudinal mode and 0.3 bar for torsional mode. Generation of previously unseen stable gaseous microbubbles was noted. Tip-to-tissue interaction analysis showed the presence of cavitation bubbles close to the site of fragmentation with no apparent effect on cutting. CONCLUSIONS: High-speed imaging and particle image velocimetry yielded a better understanding and differentiated the fluidic pattern behavior between longitudinal and torsional US during phacoemulsification. These recordings also showed more detailed aspects of cavitation that clarified its role in lens material cutting for both modalities.

Role of cavitation in the phacoemulsification process.

PURPOSE: To determine the role of cavitational energy as a mechanism responsible for the emulsification of the lens during phacoemulsification. SETTING: Clinica Ophthalmologica Pasteur, Santiago, Chile. METHODS: Cavitation and its relationship to phacoemulsification power were documented using a combination of light sources, high-speed video recording techniques, and computerized control and by monitoring environmental pressure. The suppression of cavitation from the phaco process was achieved by building an environmental hyperbaric system capable of retaining the phacoemulsification system's ability to provide irrigation, aspiration, and vacuum necessary at standard and elevated pressures. The pressure level was controlled and monitored through a computer interface alongside the simultaneous video monitoring of cavitation bubble creation changes during pressure rise or fall. Last, evaluation and measurement of phacoemulsification was performed on real cataract fragments in the presence and absence of cavitation. RESULTS: Cavitation around the phaco tip mainly occurred at longitudinal ultrasonic power levels of 30% or more. Cavitation bubble formation was observed during the backstroke or as the tip moved away from the lens material and collapsed during the forward displacement of the phaco tip. Cavitation at any power level was successfully suppressed when the pressure in the hyperbaric chamber increased beyond 2.0 bar (29.1 psi) above atmospheric pressure. Phacoemulsification performance in the presence or absence of cavitation was comparable. CONCLUSION: This study found strong evidence that cavitation plays no role in phacoemulsification, leaving the jackhammer effect as the only important mechanism responsible for the lens-disrupting power of phacoemulsification.

Volume-based characterization of postocclusion surge.

PURPOSE: To propose an alternative method to characterize postocclusion surge using a collapsible artificial anterior chamber to replace the currently used rigid anterior chamber model. SETTING: Fundación Oftamológica Los Andes, Santiago, Chile. METHODS: The distal end of a phacoemulsification handpiece was placed inside a compliant artificial anterior chamber. Digital recordings of chamber pressure, chamber volume, inflow, and outflow were performed during occlusion break of the phacoemulsification tip. The occlusion break profile of 2 different consoles was compared. RESULTS: Occlusion break while using a rigid anterior chamber model produced a simultaneous increase of chamber inflow and outflow. In the rigid chamber model, pressure decreased sharply, reaching negative pressure values. Alternatively, with the collapsible chamber model, a delay was observed in the inflow that occurs to compensate the outflow surge. Also, the chamber pressure drop was smaller in magnitude, never undershooting below atmospheric pressure into negative values. Using 500 mm Hg as vacuum limit, the Infiniti System (Alcon) performed better that the Legacy (Alcon), showing an 18% reduction in peak volume variation. CONCLUSIONS: The collapsible anterior chamber model provides a more realistic representation of the postocclusion surge events that occur in the real eye during cataract surgery. Peak volume fluctuation (mL), half volume recovery time(s), and volume fluctuation integral value (mL x s) are proposed as realistic indicators to characterize the postocclusion surge performance. These indicators show that the Infiniti System has a better postocclusion surge behavior than the Legacy System.

Osteoma de coroides / Choroidal osteoma

Se presentan 3 casos de osteoma de coroides en 3 mujeres jóvenes y sanas que consultan por la aparición de un escotoma positivo y pérdida de visión. El tumor coroideo, de color amarillo-anaranjado y de límites bien definidos, pero sinuosos, se situó en la región macular en 2 casos y supramacular en otro. La tomografía axial computarizada se demostró como el método más seguro en la confirmación diagnóstica. En dos pacientes se demostró la presencia de membranas neovasculares subretinales. En uno de ellos, la membrana era extramacular y fue tratada con éxito con láser de argón, normalizándose la visión