PMID: 11884900

Issn Print: 0275-004X

Publication Date: 2002/02/01


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A NEW THREE-PORT CANNULAR SYSTEM FOR CLOSED PARS PLANA VITRECTOMY

KAH-GUAN AU EONG; GILDO Y. FUJII; EUGENE de JUAN; PATRICK S. JENSEN; DREW N. SOMMERVILLE; TERRY H. SHELLEY; AARON C. BARNES; MAURICIO MAIA

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Excerpt

The use of cannulas in sclerostomies during closed pars plana vitrectomy protects the entry sites, reduces vitreous base traction, and allows easy exchange of 20-gauge and 19-gauge (0.9 mm and 1 mm in diameter, respectively) intraocular instruments. 1 Repeated introduction of instruments through an unprotected sclerostomy may gradually enlarge the entry site, sometimes necessitating a succession of larger plugs to close the opening as the surgery proceeds. Certain oddly shaped instruments such as intraocular scissors, forceps, and picks pose a danger to the retina because of inadvertent traction on the vitreous near the vitreous base, especially if they are exchanged frequently. Other instruments, such as the delicate 41-gauge retinal hydrodissection cannula 2 (Microsurgery Advanced Design Laboratory retinal hydrodissection cannula; Bausch & Lomb Surgical, St. Louis, MO) for macular translocation with punctate retinotomies, 3–5 are difficult to introduce through an unprotected sclerostomy and may be inadvertently damaged in the process. With the cannular system, the third sclerostomy, which is often underutilized when it is used only for infusion with a sewn-on infusion cannula, can be used for other instruments by switching the infusion tubing to one of the other two existing sclerostomies. A metallic infusion tube (connected to the infusion tubing) with a collar locking into any of the cannulas, which allows instrument access from a new direction and greatly facilitates delicate peripheral surgery, easily achieves this.
One cannular system currently in use is the Grieshaber trocar–cannula set (Grieshaber & Company AG, Schaffhausen, Switzerland) (Figures 1, 2, and 3). The cannulas are inserted into the sclerostomy by means of a trocar after the sclerostomies are made in the pars plana with a microvitreoretinal (MVR) blade. When pushed into the cannula, the trocar forms a continuous bevel with the cannula (Figure 1B). A rotating movement is supposed to facilitate introduction of the trocar–cannula in an atraumatic manner 1; however, this movement is often not possible with the current system, because neither the trocar nor the handle is attached firmly to the cannula and rotation of the handle tends to spin the trocar within the cannula without rotating the cannula.
A plug, a tiny rod with a central locking collar, can be used to close the cannula temporarily (Figure 3). In the current system, the plug is held by slipping a plastic tubing attached over the other end of the trocar (sometimes called the “plug puller”) over the plug (Figure 2B). 1 This holding mechanism, which is dependent on the elasticity of the plastic tubing, is not satisfactory under certain circumstances. The tubing material degrades after repeated use and sterilization, causing the tubing to fail to grip the plug snugly. It then has to be replaced, but new tubing can sometimes be difficult to slip over the plug. In addition, the length of the tubing affects the ease in which it can slip over the plug. When the tubing is too long, it becomes more flexible and increases the difficulty of engaging the plug. When silicone oil is present in the operative field, the lubricative effect of the oil also reduces the grip of the plastic tubing on the plug. To dislodge the plug from the plastic tubing, a pair of forceps is used to hold the plug (or the cannula when the plug is locked into the cannula) for countertraction. Contact between the forceps and the tubing, especially when the forceps is toothed, may tear the tubing and impairs its ability to grip the plug subsequently. For these reasons, we have developed a new cannular system to overcome these problems.
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