Late last year, 25-ga. instruments for retinal surgery hit the market. Though I was skeptical of them then, I'm now much happier with them, and I'm using them for about half my cases. Here's a look at 25-gauge's pros and cons.

My Experience
Fluidics. Surgeons were quite concerned with this in the beginning. In the past 10 months or so, however, Alcon and the Dutch Ophthalmic Research Center have built infusion cannulas with improved flow rates. I can now use infusion levels of 60 mmHg or occasionally less, and vacuum levels of around
400 mmHg.

The only issue with 25-ga. fluidics that's different than standard vitrectomies is that, once you stop removing vitreous, you have to reduce the infusion to a static pressure. My experience has been positive with the Accurus Vented Gas-Forced Infusion tubing (Alcon), which allows the surgeon to quickly toggle between a pressure of 25 mmHg and 50-70 mmHg.

Also, a 25-ga. handpiece limits the flow through the port. This produces fluidic stability that keeps the retina from lurching toward the port.

Leaks. I was worried about this complication with 25-ga. systems. I'm at ease now because of a technique I developed.

After each case, unless the patient already needs a gas tamponade, as in the case of a macular hole or a retinal detachment, I put in a one-third-fill air bubble. It takes just a second to do, and it seals up the sclerotomies just as air or gas seals retinal breaks. I've used this step for 50 cases, and haven't had any leaks, blebs, choroidal hemorrhages or a need for ocular volume enhancement.

Insertion force. In the Alcon/DORC cannula system with which I have experience, I also appreciate its low insertion force compared to other trocar systems.

Tool flexion. This is still an issue. The ways to address it are to use wide-angle visualization when viewing the periphery so you don't have to move the eye, and to pivot the instruments around the sclerotomy sites rather than rotating the eye. Also, carefully position the patient's head so you're not coming over the brow or a higher part of the nose.

I've found that the self-adherent DORC contact lenses work quite well in avoiding tool flexion. They avoid the need to have an assistant press a lens against the cornea.

Limitations. I've been able to do some diabetic traction detachments, but if a case is a difficult diabetic traction detachment for which I'll need a disposable endo-illuminator or the Chang endo-aspirating laser probe, then I'll use 20-ga. You can't do a lensectomy with a 25-ga. system unless it's a soft pediatric lens.

You can, however, use silicone oil: If you want to use oil, do the entire case with 25-ga. tools. Then, at the end, take a cannula out and insert a 24-ga. angiocath to put in 1,000-cs oil.

Though I was a bit apprehensive about 25-ga. vitrectomy at the outset, the advent of new techniques and better tools has made me much more comfortable. 

Dr. Charles is a vitreoretinal specialist and a clinical professor at the University of Tennessee. He is a consultant for Alcon.