"When the 25-gauge technology was initially introduced, my colleagues and I had certain concerns," Dr. Charles said. "I thought the restricted fluidics would be a problem and I was convinced that dense subretinal membranes could not be removed, complex cases could not be performed, dense vitreous hemorrhages could not be removed, and we would not be able to manage silicone oil re-operations.
"All of these turned out to be untrue. I was also worried about wound leaks, and the conjunctival displacement concept of Eugene de Juan, in addition to my concept of fluid-air exchange, solved that," Dr. Charles said.
Concerning the issue of fluidics, Dr. Charles discussed the benefits of port-based flow limiting.
"Fast cutting is not about cutting, but rather about port-based flow limiting. The cutter interrupts the flow, as do small lumens. Fast cutting and 25-gauge lumens decrease pulse flow, which is the amount of fluid flow that goes to the port each time it opens and closes; pulse flow permits greater stability," said Dr. Charles, founder of the Charles Retina Institute, Memphis, TN.
"The advantage of 25-gauge flow limiting and therefore greater fluidic stability is less retinal movement and fewer iatrogenic breaks due to fluid surge after sudden elastic deformation of epiretinal membranes through the port. I prefer the 25-gauge system over the 23-gauge fluidics in these situations," he said.
He demonstrated that pulse flow is less with the 25-gauge system at 1,500 cuts per minute than it is with the 20-gauge system at 2,500 cuts per minute.
"The fluidic resistance in a 25-gauge system is an advantage on the aspiration side and a disadvantage on the infusion side, so, we compensate for it with higher infusion pressures," he said.
Some procedures that Dr. Charles performs combine 25-gauge techniques with one 20-gauge wound, which he refers to as 20/25 techniques, examples of which are silicone exchange and re-operation without silicone removal.
The latter is his preferred method over silicone removal and reinjection at the end of the case.
At the beginning of the case, silicone instead of saline is infused and the surgery is done "under silicone." This enables forceps membrane peeling, the use of scissors, retinectomy, and laser application, according to Dr. Charles.
Foreign bodies in the eye are usually larger than 25-gauge, which requires that one of the wounds be enlarged to accommodate forceps.
"In this situation, one wound will have a single suture, and the surgeon can have most of the benefits of the 25-gauge technology," he said.
The same applies to cases in which a fragmenter must be used for dislocated lens material. A vitrectomy is performed first, one wound is enlarged, the fragmenter is inserted, and the lens material is removed. This scenario also works for lensectomy, Dr. Charles explained.
When using the 25-gauge system, Dr. Charles advises two-thirds to nearly full fluid-air exchange to reduce wound leaks, which can carry dire consequences such as hypotony, suprachoroidal hemorrhage, and endophthalmitis. This produces a bubble that covers all three sclerotomies without a positioning requirement. He had previously recommended a partial (one-third) fluid-air exchange, which meant that the inferotemporal sclerotomy was uncovered when the patient was sitting or standing.
The primary limitation to the 25-gauge system is tool flexion, and this becomes evident in the cases of a tight orbit and in those cases in which the periphery must be visualized. He explained that using a contact-based wide-angle visualization allows the eye to remain near the primary position during vitrectomy, which reduces tool flexion. It is advantageous to have the patients rotate their heads from side to side or flex or hyperextend their necks to allow visualization of the periphery, according to Dr. Charles.
The second generation of instruments has eliminated some of this problem. The endoilluminator and the laser probe (Alcon Laboratories) are 57% stiffer than the previous-generation instruments and flexion is less of a problem.