Article Date: 5/1/2007

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New Advances in Microincision Vitrectomy Benefit Patients and
Surgeons Physicians review 23-g and 25-g instrumentation.


ALLEN C. HO, MD • PETER K. KAISER, MD • STEVE CHARLES, MD • DAVID BOYER, MD

In recent years, significant progress has been made in the medical and surgical treatment of retinal disease. On the surgical side, microincision vitrectomy surgery (both 23- and 25-g) is providing improved comfort and faster visual recovery for patients. Alcon Laboratories, Inc. (Fort Worth, Texas) has developed microincision instruments in 23- and 25-g that provide a single-step entry system with the use of a sharp solid trocar blade, allowing cannulas to be inserted in 1 simple step.

Allen C. Ho, MD, is professor of ophthalmology, Wills Eye Hospital, Philadelphia; Peter K. Kaiser, MD, is in practice at the Cleveland Clinic Foundation Cole Eye Institute; Steve Charles, MD, is in private practice in Memphis, Tenn; and David Boyer, MD, is in private practice in Los Angeles. The authors of this article are consultants for Alcon.

MICROINCISION SURGICAL TECHNIQUES

Historically, with the 25-g system, surgeons were taught to displace the conjunctiva and then insert the sharp trocar directly into the eye.While this technique worked well in most cases, in some instances the displaced scleral fibers did not regain their alignment immediately, leaving open incisions at the end of the procedure. Some of these cases heal on their own and the scar will seal the opening. Other cases require a vitreous plug or suture to heal. Unfortunately, none of these options is ideal because they can lead to hypotony, shorter tamponade times, and endophthalmitis. In an attempt to find a safer technique, Dr. Kaiser and colleagues1 conducted a wound study to evaluate the 23-g and 25-g sutureless vitrectomy systems from Alcon, using either a straight or an angled incision. The study was conducted on white rabbits. A straight incision was made in the right eye and an incision with a very oblique angle was made in the left eye. Then, a 5-minute timed vitrectomy was performed with an intraocular pressure (IOP) of 30 mm Hg throughout the procedure. The cannulas were removed slowly to allow the scleras to displace back to their original positions. During cannula removal, the infusion was left on to help close the wound. The infusion cannula was removed with the infusion off. In humans, IOP is lowered to 20 mm Hg during cannula removal. After the surgery, trypan blue was injected into the rabbits’ eyes to assess for leakage through the sclerotomy sites. The eyes were assessed immediately postoperatively, at 6 hours postop, and at 1, 3, and 7 days postop.
STUDY FINDINGS

The study found that the angled incisions leaked half as much as the straight incisions; however, there was no difference in leakage between the 23-g and 25-g systems. The rabbit eyes were enucleated 7 days after surgery and the researchers noted that the straight incisions for both the 23- and 25-g systems had an amorphous, round-wound structure, while the angled incision had a unique chevronshaped incision. Interestingly, when the researchers examined the wounds from inside the eye, all incisions were chevron shaped, regardless of incision size and whether the incision was angled or straight. Upon histopathologic examination, the angled incisions were closed and nicely apposed, while the straight incisions were open. At 7 days postop, there was a significant difference between the straight and the angled 23-g incisions, but there was not a significant difference between the straight and angled 25-g incisions.With the 23-g system, surgeons should make the incision at a 15° to 20° angle, parallel to the limbus, and should remove the cannulas slowly with the infusion on.

FLUIDICS, FAST CUTTING, AND END-CUTTING DESIGN
Cutting on the highest speed can be done for all parts of the vitrectomy in all cases.While there is no evidence that faster speeds allow for cleaner and more efficient cutting of vitreous collagen , they are clearly better. In the past, the cutters and the fluidics were not ideal, so surgeons were taught to use caution to prevent the retina from entering the port.With the new systems, surgeons should continuously engage and advance.When using the highest cutting speeds, always keep the port in the vitreous and keep the port moving, and always advance the cutter. Fast cutting works because it interrupts the flow through the port. Alcon’s 23-g system does 2500 cuts per minute (CPM) and the 25-g does 1500 CPM. They are equal in terms of port-based flow limiting. However, if the 23-g cutter is reduced to 1500 CPM, there will not be sufficient port-based flow limiting. With this greater fluidic stability, the mobility of the retina is not increased every time the port opens and closes, and the cutter does not jerk on the vitreoretinal interface of an attached retina, which could cause a retinal detachment. Keep in mind that there are consequences to both low and high IOP.With low IOP, the cornea distorts when the instruments are moved around.While some surgeons try to maintain an IOP of 20 mm Hg, 45 mm Hg is preferred for most patients. This limits bleeding and maintains corneal rigidity.
IMPROVING ILLUMINATION AND VISUALIZATION
Many surgeons have tried 25-g surgery with previous systems and returned to 20-g surgery because of dim lighting and flexibility of handheld instrumentation. These surgeons should consider re-evaluating 25-g surgery with the new systems because advances in light sources and probes, as well as improved visualization systems, have made 23- and 25-g systems very safe and efficient. The initial light sources with 25-g surgery were halogen. Surgeons were unable to see because 25-g fibers are only half the diameter of 20-g fibers, and approximately 70% of the light was lost when using the 25-g fiber with halogen lighting. Alcon’s Xenon Illuminator offers enhanced illumination, providing surgeons with a 25-g chandelier option (the Tornambe Torpedo [Alcon]) that allows increased light during bimanual surgery. The second-generation fibers provide wider angles with no blind spot. Surgeons will notice a significant difference between the halogen and xenon light sources with 25-g xenon endoillumination. It is simply much brighter and better. The usual precautions apply for phototoxicity, but we have not had any cases with this unit or with other xenon illumination sources.

REFERENCE
1. Oswaloo Ferreira Moura B., Singh RP, Ufret-Vincenty RL, Kaiser PK. The integrity of
wound closure after 23- versus 25-gauge sutureless vitrectomy. Paper presented
at ASRS/EVRS Cannes Retina Festival. September 9-13, 2006; Cannes, France.



Retinal Physician, Issue: May 2007