Advanced Wound Management with a New Trocar/Cannula Entry System
A redesigned 23-gauge ESA system greatly reduces the amount of force needed to enter the eye.
By Philip Ferrone, MD
In addition to its new combined vitrectomy and phacoemulsification system, the Stellaris PC, Bausch + Lomb has introduced a redesigned 23-gauge Entry Site Alignment (ESA) system for vitrectomy. While the trocar/cannula entry system is not part of the Stellaris PC, per se, it is certainly an integral part of working with it.
The previously available 23-gauge ESA system created excellent wounds. As many of us know, it had a marker on one end, which was convenient, and it had a hypodermic needle-type blade along with a polyimide cannula. One criticism of that entry system, however, was that it required some extra force to enter the eye. The new 23-gauge ESA doesn't require that force. Entering the eye with the cannula requires only about half of the force, 377 grams compared with 750 grams (Figure 1). This vast improvement has been accomplished while the excellent wound and healing characteristics have been maintained. The required force of the ESA system is now approximately the same as what is required with the Alcon Edge Plus (Figure 2).
Figure 1. The redesigned 23-gauge Entry Site Alignment (ESA) system for vitrectomy requires far less force to enter the eye.
Figure 2. Comparison of force required to enter the eye using the B + L ESA system and the Alcon Edge Plus. The wounds pictured here are 90-degree entries, which are typically not done, but the images provide an idea of the resultant wound contours.
IMPROVED BLADE DESIGN
An enhanced blade design for the 23-gauge ESA system is largely responsible for easier insertion. The trocar tip is designed to create tighter sclerotomies, which provide better cannula retention. The cannula does not tend to migrate out of the wound as we've seen occur in the past with various systems.
The following additional new features also contribute to improved insertion:
■ The trocar tip has a longer taper that provides more cutting surface. This enables a more shallow entry for the very flat angles that we enter with now, with 23-gauge especially, so that we create a long tunnel for a nonleaking wound. The blade length, before it reaches the cannula, is approximately 4 mm, which is plenty of distance for making a tight wound.
■ The gap between the cannula and the trocar shaft has been closed, which minimizes potential tissue friction.
■ The chamfer on the leading edge of the polyimide cannula is very close to the edge of the blade. This allows the cannula to gently glide tissue away during insertion.
■ The cannula is 4 mm long, which is optimal for avoiding suprachoroidal infusion and not too long to prevent or hamper anterior vitreous manipulations.
■ The blade tip is rounded and made from a durable material that resists bending or dulling. New manufacturing techniques are being used so the consistency of the blades is better as well.
■ A solid needle has replaced the hollow needle and it displaces less tissue.
When the new entry system is tested in simulated eye medium, we can see how all of these new elements working together reduce the force required for entering the eye to levels comparable with other currently available systems (Figure 3). Of course, we see an increase in force as the tip penetrates the sclera. Another small blip occurs where the blade gets wider. Then right at the cannula junction the maximal force is required, but the value is low.
Figure 3. Insertion force with the 23-gauge Entry Site Alignment system. A) tissue entry as the trocar penetrates the sclera B) maximal tissue force as the tissue is cut C) shaft entry as the smooth shaft passes through the tunnel incision D) maximal insertion force as the cannula enters the eye.
Images of entries into rabbit eyes illustrate corresponding improvement in wound construction (Figure 4). At 1 week, the wounds are very well healed, with no avulsion of tissue and no blunting of the leading edge of wound tissue.
Figure 4. Wound in rabbit sclera one week after insertion of the 23-gauge ESA system. The wound has healed well, with no avulsion of tissue or blunting of the wound edges.
EARLY EXPERIENCES ARE POSITIVE
In my experience with the new 23-gauge ESA system, the changes in design make a noticeable difference. I can enter the eye smoothly and easily while holding it with only a cotton swab. I have only needed a cotton swab for disengaging the cannulas as well. Once I make my flat entry into the sclera and make the perpendicular incision, I haven't needed forceps to grasp the cannulas to unlock them from the trocars, which is very convenient. The cannula plugs are just snug enough and go in and out easily.
Also, it's not difficult to see the lumen of the cannulas without using the microscope. When the cannulas are removed from the eye at the end of a case, the wounds are barely visible and not leaking. I've been impressed with the fact that I can use only a Q-tip for counter-traction and make a very shallow, excellent wound with this new entry system.
Dr. Ferrone specializes in pediatric and adult retinal diseases at Long Island Vitreoretinal Consultants in New York.