Time for a CataractQuiz: watch the video and you will see a tremendous amount of post-occlusion surge during phaco. When the cortex is removed with the IA probe there is far less surge. Why? Ask yourself what the potential causes could be. Look carefully at the tubing on the machine…
Dr. Dev⁸gan, thank you so much for this video. My name is John Weymouth and I teach phaco physics and fluidics. I can honestly tell you that occlusion break surge is created in the vacuum line, more than likely by the system that’s measuring the vacuum pressure. This occurs on almost every machine and almost every machine out there has some method to mask the occlusion break surge.
The Alcon Centurion uses active irrigation by squeezing the bag very hard after the occlusion starts to occur because it’s measuring the pressure in the infusion line. When it starts to drop, it just forces more fluid in. The same is true with all the AMO units, with the B&L units, JNJ units.
There’s one machine, however, out there that does not have this problem and it’s the OERTLI Cataract 3. You can actually disconnect the irrigation line, occlude the tip, and then push the foot pedal. The tip is clear of the lens material and there’ll be no occlusion break surge. Nothing! That’s because the measuring system that they use for the vacuum is so minute in variability of volume that it does not create the occlusion break surge.
In the eye surgical machine when the occlusion happens, when you trace the line, which is very rigid and is not collapsing all the way back to the cassette, there is a volume of fluid approximately the size of 3- 25 cent pieces (25 cent quarter). When vacuum occurs a metal plate flexes and as that metal plate is pulled in, the machine is measuring the vacuum. It just so happens that the amount of movement of that metal plate and the volume it’s displacing under that vacuum load is very close to the volume inside the anterior chamber.
As a result when the occlusion breaks, that metal piece flips back real hard and it sucks in all this fluid. You need something to replace what’s being pulled out of the eye at over 200 cc/min volume. It’s just outrageous how fast it comes out.
To sum it up, occlusion break surge is caused by the vacuum measuring system in the phaco units and there’s only one unit I know of out there today where that does not occur. The Alcon Centurion had it, the Infiniti had it, the Legacy unit had it before that, and all the phaco units that have a transducer that measures the volume have it, except for the Oertli. The way they do it is so precise and so minimal volume change that they have no occlusion break surge.
If you have questions, give me a call. I’d be happy to discuss this with you because once you understand how these machines create the problems they create, you can better fend off and have a safer, more accurate cataract surgery.