Phaco dynamics

Ophthalmology

1. PHACODYNAMICS Dr.Sharath Chandra Basa Dept.of Ophthalmology GREH Visakhapatnam

2. PHACOMACHINE The machine consists of the console, foot pedal, handpiece and their connections.

3. CONSOLE The console consists of a computer which controls all the functions of the machine. The setting for the various parameters, i.e. power, vacuum and flow rate are fed in here. These settings represent the maximum level of the parameter that will be achievable.

4. HANDPIECE The phaco handpiece contains the piezoelectric crystal, which is in contact with the tip. The tip is covered by a silicon sleeve. The infusion fluid flows between the tip and the sleeve cooling the former. There are two openings on the sleeve for the exit of this fluid. The proximal end of hand piece is connected to the console with an electric cord. There are two more connections: one each for the irrigation tubing and for connecting the aspiration system

5. 5 Silicon sleeve 80% of irrigating fluid enteres through this side port 20% Irrigation (Inflow) Aspiration( outflow) USG POWER

6. Phaco tip Most tips are made of titanium. All the tips must have a tapered hub. This reduces air bubble formation in the anterior chamber. The angulation of the tips may varyfrom 0–60°. Tips with 60°, 45°, 30°,15° and 0° angulation are available. More the angulation, the lesser the holding power but the cutting power is more The 45° tip has a very good cutting ability and was very popular initially as the emphasis was then on ‘Divide and Conquer’ in which trenching (thus cutting ability) was more important than occlusion. With the advent of aspiration phaco the most popular tip today is 30°. This has adequate holding and cutting power and is useful both for trenching and in chopping.

7. The Standard or regular tip is most commonly used. It has a 0.9 mm inner diameter and 1.1 mm outer diameter. The Microflow tip is useful in soft cataracts especially those lessthan grade 3. The internal diameter ranges from 0.45 to 0.6 mm,depending upon the manufacturer. As the fluid drawn out by the small bore is less, the amount of surge is decreased allowing one to work safely at higher vacuum levels. This tip is therefore not recommended for hard and hypermature cataracts. The Kelman tip has a downward angulation. This is ideal for sculpting in hard cataracts and eyes with deep AC Kelman flared tip is a modification of Kelman tip . The wider area of this tip allows more powertransmission and is, therefore, ideal for hard cataract. The Cobra tip has the base of micro flow tip proximally and that of regular tip distally. This configuration enables it to aspirate a big piece and emulsify it within its walls.

8. FOOT PEDAL it essentially consists of main central part and side kicks . The main part of the foot pedal controls infusion, aspiration and phaco power. The entire distance that the foot pedal traverses is divided by 2 dentations into 3 excursions Position 1 (I) --- Irrigation Position 2 (IA) --- irrigation+aspiration Position 3 (IAP)--- irrigation +aspiration+ US

9. Position 1 There is no linear control of the infusion —the infusion is either turned on or turned off. The height of the infusion bottle determines the relative infusion pressure and flow rate during the surgery. To keep the eye inflated during surgery, we need to ensure that the fluid inflow rate is greater than the fluid outflow rate. 9

10. Position 2 There is a linear control of vacuum and flow, so that the top of foot position 2 provides less vacuum or flow than the middle or bottom range of the same foot position 2. 10

11. Position 3 There is linear control of the ultrasound energy level so that more the pedal is depreesd in position 3, more ultrasound energy will be delivered. If the pedal is in position 3, we are already engaging the full function of both positions 1 and 2. The irrigation is on, and the vacuum and aspiration level is at its highest preset level. 11

12. Side kick fuctions of foot pedal The most important sidekick function of foot pedal is reflux. On kicking the side switch, aspiration flow rate is inverted and the material aspirated is expelled into the AC. Since it is not a continuous function, for further reflux, the switch needs to be kicked again. Inadvertent aspiration of wrong tissue (iris, capsule) can be released by this function especially by beginners. 12

13. Continuous infusion mode (CIM) In this mode, the infusion remains on regardless of the position of the foot pedal (i.e. even if the foot is accidentally lifted off the pedal the infusion remains on, and the chamber remains formed). It is started by kicking the side switch and remains on, till kicking the same switch again stops it.

14. PHACO DYNAMICS The various functions of the phaco machine and their inter relationship is called phacodynamics 14

15. POWER Phaco power is produced by theUltrasonic vibrations of the crystals in the hand piece. There maybe 2–6 crystals. The frequency is variable from 29–60 KHz in different machines. Higher frequency ensures a better cutting action but more heat is generated. In each machine, the frequency remains fixed—power is varied by varying the stroke length. stroke length is the to and fro movement of the tip

16. Control and delivery of power All machines provide 0–100% power and the power required can be chosen from the computer controlled panel. There are various modes— 1)surgeon/linear 2)panel.

17. In the surgeon mode , the power delivery varies from 0 to the maximum that one sets on the panel, by varying the foot pedal in phaco mode excursion of the foot in phaco mode will determine the amount of power being delivered

18. In the panel mode , as soon as you depress the foot pedal into the phaco mode (P0), you will immediately reach the maximum power that you have set on the panel. Here, there is no variation and full power is delivered. The hardness of the nucleus is not uniform,most surgeons prefer the linear mode so that they can control the power

19. Continuous mode All the time ultrasound is ON at gradual manner (LINEAR ) depending upopn foot pedal position 3 …….no OFF In Every second……. all second is full with ultrasound

20. Pulse mode pulse mode each pulse of energy is followed by a gap of equal duration. For effective power delivery, the nuclear fragment has to be held, so the interval between the pulses of phaco allow the vacuum to build up and thus a good hold is developed. Pulse mode is a variant of linear phaco mode where the frequency of the pulses is fixed and the phaco energy delivered in each pulse will depend on the amount the pedal is pressed. Thus the power is delivered at pre-set intervals, the frequency of which is pre-set and decided by the surgeon.

21. Phaco is not on throughout all part of 1 second With in 1 second …in part of second phaco is ON and in another part of second phaco is OFF ….there is pause in ultrasound Eg..1 If we have 2 pulses/sec… Means in 1 sec 2 on cycle and 2 off cycle ( i.e total 4 cycle) So each pulse is of 250 millisec ..( 1sec= 1000 millisec )

22. Burst mode Burst mode is a variant of panel mode where the energy is fixed and the frequency of phaco bursts will increase with increasing depression of the foot pedal in phaco mode.

23. Hyperpulse and Hyperbrust Hyperpulse allows the surgeon to choose from new, higher-range pulse settings that can exceed 100 pulses per second (compared with traditional pulse, which had a maximum of 20 pulses per second). Hyperburst technology allows you to use burst durations as short as 4 milli sec (compared with traditional burst, which had a minimum of 80 ms max 600ms).

24. Duty cycle Duty Cycle- --time during which power is on as % of cycle (traditionally 50%) Cycle time —pulse duration+interval duration Pulse duration- time of phaco power on (PYRAMID) Interval duration —time from one pulse to another

25. Mechanism of emulsification It is a combination of the bombarding action of the tip ( Jack-hammer ) and cavitation phenomenon caused by the high velocity of the tip moving backwards.

26. The Jack-hammer effect requires that the nucleus should be fixed as during trenching, or the nuclear fragment held by vacuum, during phaco -aspiration, for the bombarding action to be effective. This is the action that is primarily used during trenching. The rapid backward excursion of the tip creates a cavity into the area (as the tip moves faster than fluid) causing the surrounding fluid to fall into this space,virtually generating an ‘ implosion ’ thereby causing disintegration of the nuclear material.

27. The forward movement of the tip also generates an acoustic wave of fluid that can disintegrate the softer lens material. This shock wave is also responsible for some emulsification. The disadvantage of this wave is that it may push nuclear pieces away if the hold is not good

28. FLUDICS The fluidics of the machine refers to the integrated functions performed by infusion and aspiration systems by which a stable AC is maintained

29. Infusion system The infusion system consists of a bottle, the height of which provides the gradient for flow. The tubing from the bottle is run through a pinch valve which is controlled by the foot pedal. The infusion is gravity fed, 2 feet bottle height conforming to approximately 44 mmHg A bottle height of 3 ± 1 ft maintains a safe IOP with sufficient fluid entering the eye

30. Aspiration System The two functions of the aspiration system are lavage of the anterior chamber and creation of a hold for emulsification/crushing of the nucleus. Lavage is governed by the flow rate and the hold is a function of the vacuum generated by the system. The aspiration systems consist of a pump that is either flow based or vacuum based. The common type of flow pump is the Peristaltic pump . Venturi is the prototype of a vacuum-based machine.

31. Venturi System The swift movement of a compressed gas creates vacuum, inside a closed chamber which is then directly transmitted to the handpiece . The amount and speed of the gas decides the level of vacuum developed in the cassette. When the surgeon depresses the foot pedal, the preset vacuum level is immediately created. In the venturi system only the level of vacuum can be controlled and not the flow rate Here the flow rate is a fixed The advantage of the venturi pump is that it is able to create the preset vacuum level without occlusion of the phaco needle tip

32. Peristaltic System the rotation of the rollers by the pump pinches the soft, silicon tubing, creating a negative pressure by squeezing the fluid out of the tube. The faster the rollers rotate, more fluid is withdrawn and therefore there is a higher flow rate. In this system, vacuum will be built up only after the tip is occluded. Flow rate and vacuum can be set independently in a peristaltic system.

33. Flow rate It is the amount of fluid withdrawn from the anterior chamber per second The higher the flow rate,the sooner the debris in the AC is cleared.

34. Vacuum Vacuum is generated by the machine and is a measure of the strength of the ‘hold’ that the handpiece has on the nucleus. Level of vacuum and port size will determine how strong the grip is. The holding power is inversely proportional to the port size.

35. Rise Time (RT) The rise time is the time taken by a machine to reach maximum preset vacuum after occlusion has been achieved. Venturi system - the RT is fast, linear and dependent upon the highest preset vacuum peristaltic pump - RT depends on the FR of the machine. The higher the FR, the lesser the RT though the relationship is not absolutely linear. For a given flow rate, the initial rise time is more till a certain level has been achieved after which the vacuum build up is faster.

36. Followability It refers to the tendency of the nuclear fragments/cortical matter to come into the tip Zones of followability : The area just in front of the tip is the area of highest followability. All the fragments in this area will be attracted towards the tip. Followability decrease as you go further away (both horizontally and vertically) from the tip.

37. Compliance Change of the tubing shape and volume when put under negative pressure. When the tip of the phaco needle is occluded, negative pressure will build in the tubing. The higher the compliance the more change in the tube’s volume. When negative pressure is created highly compliant tubing collapses on itself reducing its inner volume’s capacity.

38. When occlusion breaks, the tubing returns to its original shape and a temporary imbalance exists causing rapid exit of fluid from the anterior chamber. This is called Surge The higher the compliance the greater the surge amplitude during occlusion break

39. SURGE Sudden withdrawal of fluid from AC after occlusion break is called surge.

40. CONTROL OF SURGE 1)Venting : In this, the machine has a sensor which detects occlusion break and releases fluid/air into the system to fill the volume of the re-expanding tubing. This prevents fluid being drawn out of the AC.

41. Occlusion of phacotip by nuclear fragment Vaccum created When vaccum reached to the maximum preset level Vent valve will open and some air or fluid will entres into the system (VENT)

42. 2) Delay in start of the motor following occlusion break Here, following occlusion break, start of the motor is delayed till the expansion of the tubings is complete. 3) Differential FR/vacuum settings before and after occlusion Some machines have an option of setting different FR and vacuum settings which the machine can switch to after occlusion break. The vacuum and AFR are decreased for a short period of time as soon as the occlusion breaks, to decrease the surge. Once the piece has been aspirated, the settings then revert to whatever had been previously set.

43. 3) Decreasing the effective flow rate: 4) Increasing the infusion 5) The use of an Anterior chamber maintainer 6) Proper wound construction: 7) Increased viscosity of the AC contents: 8) Partial occlusion of the tip 9) Foot control

44. Thank you