phacodynamics basics what you need to know
- 1. PHACODYNAMICS Dr Osama Albarghouthi MD JBOphth FICO MRSCed
- 2. history The invention of phacoemulsification by Charles Kelman in 1967 marked the beginning of the modern era of cataract surgery. this advance also coincided with the invention of ophthalmic viscosurgical devices (ovds), the evolution of intraocular lens design, and a change to performance of cataract surgery on an outpatient basis, resulting in a paradigm shift that allowed cataract surgery to be performed via relatively small corneal incisions, leading to lower incidence of wound-related and vitreous-related complications and more rapid rehabilitation of vision. First surgery 3 hours + aphakic + rigid iol + 4 liter of fluid )))
- 3. Important factors for cataract surgery Biometry Surgical Skills + Technique + cataract Application Of Principles Of Phacodynamics
- 4. Instrumentation There are several types of phaco machines, but their major components are essentially the same. These include : Console The handpiece Foot pedal Irrigation system Pump
- 6. 0.05-0.1 mm (0,15,30,45,60) A tip with a steeper bevel has an oval port with a larger surface area, which can generate more holding force and greater cutting efficiency. The disadvantage of steeper bevels is that the larger opening may be more difficult to occlude to achieve full vacuum.
- 7. occlusion 1.Orientation 2.Impede deep 3.Listen to machine VRT
- 8. position 1 produces irrigation (no aspiration, no u/s). No linear control (on/off) position 2 irrigation and aspiration at a constant (panel) or variable (linear) rate (no u/s). position 3 irrigation, aspiration and u/s at a fixed (panel) or a variable (linear) rate.
- 10. The surgeon uses the handpiece to simultaneously emulsify and aspirate the crystalline lens while keeping the tip cool and maintaining anterior chamber depth without damaging posterior capsule or endothelium. FLUIDICS
- 11. Phaco power Phaco power is the percentage % of stroke length Amplitude ( how far ) to-and-fro oscillation which generate main forces for nucleus disassembly 1. Jack hammer effect longitudinal (grooving and chopping) & tortional (segment) 2. Acoustic shock wave & Cavitations ( microbubbles ) (more power % >> more impact >>more heat >> more damage to nucleus and the eye )) Frequency ( how often ) 40 KHZ fixed
- 13. Phaco Modes 1. Continuous: power is delivered constantly and is either linear or panel controlled (more ultrasound power- good for sculpting)
- 14. 2. Pulse mode: The term pulse describes an interval of phaco power turned on alternating with an interval during which phaco power is off (duty cycle concept). The more the pedal is depressed, the higher the power in linear mode The delivery of phaco power for only a portion of the cycle reduces repulsion ( chatter ) of material by the vibrating tip and improves followability ideal for quadrant removal
- 15. Duty cycle refers to the ratio of on:off pulses. If the time of power on equals the time of power off, the duty cycle is 50%.
- 16. 3. Burst mode: Burst-mode phaco involves delivery of preset power (0%100%) in single bursts that are separated by decreasing intervals as the foot pedal is depressed through position 3. At the end of the position 3 excursion, the power is no longer delivered in bursts but is continuous. Burst mode allows the tip of the phaco needle to be buried into the lens, an essential step for chopping techniques.
- 17. Advanced phaco power mode delivery by J&J
- 18. Fluidics
- 19. Main concepts Maintain space (prevent collapse of AC by balancing inflow and outflow rates) Create currents (bring cataract pieces to phaco probe and remove them) Keep it cool (prevent thermal injury)
- 20. Fluidics parameters Mechanical Infusion/inflow/irrigation Aspiration and leakage Vacuum Clinical Incision size Vitreous pressure
- 21. Inflow/infusion BSS flows from bottle to irrigation port Infusion is passive by gravity or active by pressing BSS bag Bottle height above patient creates a pressure gradient Approximately 11 mmHg (above ambient atmospheric pressure produced intraocularly) for every 15 cm of bottle height above the patient's eye Optimal around 80-90 cm >>> iop (role of low tension phaco on the machine )
- 22. Aspiration flow rate (AFR) Measured in ml/min Is determined by speed of pump As flow increases : current in AC increases: this determines how well particulate matter is attracted to the tip 15-20 trenching or sculpting 30-45 quadrant 25-30 chop & epinecleus 30-50 I&A 5-10 polish
- 23. Vacuum Create holding power ( negative pressure ) to keep material in phaco tip Created by a pump: Peristaltic pump: vacuum develops slowly Venturi pump: rapid rise in vacuum 20-80 trenching or sculpting 400 quadrant 500 chop 300 epinecleus
- 24. AFR Vs Vacuum AFR is the rate at which fluid and emulsified nuclear particles are removed from the eye when the phaco tip is not occluded Vacuum is the negative pressure that builds up when the tip is occluded They are separate components that work hand in hand during outflow At low flow rates: gradual build up of vacuum (safe but slow) At high flow rates: faster vacuum build up (but less safe)
- 25. Pump Main function is to move fluid through the aspiration tubing Pump settings control rate of movement of fluid 1. Peristaltic pump (Flow based) Allows independent control of aspiration rate and vacuum level 2. Venturi pump (Vacuum based) Allows direct control of only vacuum level. Flow is dependent on vacuum level setting
- 27. Rollers move Compress the outflow tubing in a peristaltic manner milking action on fluid column The machine can control the flow level (flow based) A preset vacuum level is achieved once there is occlusion of outflow line (at low speed of rotation) By increasing the flow rate, vacuum is produced in the aspiration line without occlusion To build up vacuum without occlusion, you need to increase the flow rate (flow based pump)!!!! Active Control of Flow, Passive Change of Pressure
- 28. Venturi pump A Venturi pump creates a vacuum based on the Venturi principle: a flow of gas or fluid across a port creates a vacuum proportional to the rate of flow of the gas.
- 29. Vacuum is created within a rigid drainage cassette connected to the aspiration tubing No milking of the aspiration line phaco tubing can be made rigid with low compliance Main advantage is the ability to create the preset vacuum level without occlusion of the phaco tip needle As the surgeon depresses the pedal, the preset vacuum is immediately created (vacuum based) Only the vacuum can be controlled. The flow rate is fixed and is a function of the vacuum Active Control of Pressure, Passive Change of Flow
- 31. Vacuum rise time The amount of time taken by the system to reach maximum vacuum setting once occlusion takes place Peristaltic pumps have a slower rise time (can be made faster by increasing the rotation of the wheel) Rise time 留 AFR 留 Pump Speed
- 32. AC stability Inflow=outflow at least but must be in>>out AC pressure has to be greater than vitreous pressure and atmospheric pressure (positive IOP) Under pressurization >>> collapse of AC forward movement of iris and lens and posterior capsule rupture of posterior capsule One indicator of AC pressure imbalance is bouncing movement of iris and lens Over pressurization can lead to deepening of AC and zonular stress
- 33. Clinical Parameters Incision size: affects: Leakage Infusion Depends on external diameter of phaco tip Small incision causes infusion flow obstruction: squeezing of infusion sleeve AC instability and build up of heat at the tip Big incision more leakage ,AC instability and more astigmatism Vitreous pressure Patient dependent myopia hyperopia small orbit anesthesia speculum PXF aqueous misdirection LIRDS >>>>>>>Affects AC depth during phaco
- 34. Surge disbalance between in/out When the phaco tip is occluded negative pressure builds in the tubing collapse of the aspiration tube occlusion breaks after eating the nucleus piece tube returns to original shape surge (sudden sucking effect of fluid with AC shallowing (until infusion fluid compensates)).
- 35. How to reduce surge? Lower levels of flow and vacuum Increased bottle height Reduce leakage Aspiration bypass port (ABS) Venting Fusion 息速
- 36. Fusion 息速 CASE Chamber Stabilization Environment
- 37. Deepest part of A/C Dont use 2nd instrument
- 38. Take home message Know your machine Know you skills Adopt your machine to your skills Accept the new technology Adopt your skills to new technology Pass knowledge & skills to juniors
Editor's Notes
- -fifth century bc.,COUCHING , was performed on mature cataracts. With the patient in a seated position, the surgeon inserted a needle or knife posterior to the corneoscleral junction and then pushed the lens inferiorly. -ICCE, was first performed in 1753 by Samuel Sharp. This procedure involved removing the lens with the capsule intact through a limbal incision by using a cryprobe. -17th century, Jacques Daviel (16961762), extracted the cataract -rather than simply displacing it- by Creating an incision through the inferior cornea, enlarging the wound with scissors, incising the lens capsule, expressing the nucleus, and removing the cortex by curettage. -Albrecht von Graefe (18281870) advanced this technique by developing a corneal knife CLEANER INCISION, BETTER HEALING.
- piezoelectriceffect, is the ability of certain materials (most commonly Quartz) to generate an AC (alternating current) voltage when subjected to mechanical stress or vibration, or to vibrate when subjected to an AC voltage, OR BOTH.
- Disatvanges are heat and chatter
- Followability: The ability of a fluidic system to attract and hold nuclear or cortical material onto the tip of an ultrasonic or irrigation/aspiration (I/A) handpiece until vacuum forces achieve evacuation.