No need to dissect conjunctiva during posterior vitrectomy

October 15, 2004

San Diego-A system for performing a sutureless posterior vitrectomy uses 25-gauge cannula instruments that can be inserted directly through the conjunctiva and eliminates the need for its dissection. The transconjunctival sutureless vitrectomy system (TSV25, Bausch & Lomb) reduces the problems associated with performing surgery in eyes with a shallow anterior chamber, according to Rosa Braga-Mele, MD.

"Most of the challenging cases encountered in phacoemulsification are those that involve shallow anterior chambers, because there is very little room to maneuver within the anterior chamber," said Dr. Braga-Mele, assistant professor of ophthalmology, University of Toronto, and director, Cataract Unit, Mt. Sinai Hospital, Toronto. "These eyes tend to be small, with axial lengths of less than 22 mm, or true nanophthalmic eyes that are less than 19 mm long. These eyes tend to be hyperopic, poorly dilating, and may or may not have glaucoma."

The standard surgical approach for these eyes includes the use of a wire lid speculum, topical anesthesia rather than retrobulbar anesthesia, a temporal approach, and a viscoelastic agent. Studies that have tried to establish a new approach to surgery in these problematic eyes reported efforts to relieve the positive posterior pressure by deepening the anterior chamber with periocular compression, topical betaxolol application, and dehydration.

Previous approaches In the past, Dr. Braga-Mele performed a vitreous tap with a pars plana approach using a 21-gauge needle or a 20-gauge vitreous cutter. This required a scleral or conjunctival cut-down and both the sclera and the conjunctiva must be closed with sutures. The 21-gauge needle may cause vitreous traction, and the 20-gauge vitreous cutter can do only 800 cuts per second.

Due to these limitations, Dr. Braga-Mele now uses a new approach with the transconjunctival sutureless vitrectomy system.

"I have converted to using the TSV25 cannula system, which was developed for posterior segment surgery," Dr. Braga-Mele said. "It is a sutureless technique with a high cut rate that would theoretically make the procedure safer than it was previously. In these eyes, especially in nanophthalmic eyes, surgeons should be aware of choroidal hemorrhage developing during these cases."

In the case of a nanophthalmic patient with an axial length of 18 mm, a 40.5-D lens for emmetropia was implanted. The white- to-white corneal diameter was 10.5 mm. Dr. Braga-Mele demonstrated the new technique with a variety of 25-gauge instruments. A trochar is inserted with a 25-gauge cannula system. She pointed out that it is easy for the trochar to be inserted with a bit of pressure. The procedure is performed with the patient under topical anesthesia.

"Before the procedure is started, the surgeon measures 3.5 mm back from the limbus," Dr. Braga-Mele said. "The surgeon pushes down aiming toward the optic nerve to avoid touching the posterior capsule of the lens and avoid any associated complications. The trochar is removed and the cannula remains in place. The 25-gauge cutter is then inserted and visualization occurs through the pupil. There is no need for a light pipe."

When performing this procedure, she presses on the eye to remove vitreous and to avoid excessive softening of the eye. With a cut rate of 1,200 to 1,500 cuts per second and a vacuum of 200 to 300 mm Hg, the vitreous is removed very quickly. A potential complication in these cases is the removal of excessive amounts of vitreous and softening of the eye, Dr. Braga-Mele explained.

Following this, the cannula is removed and the conjunctiva slips over the point of insertion.

"There is no bleeding and no vitreous exiting," she explained. "In a case with the potential to be difficult, a deep anterior chamber forms and the case can proceed as a straightforward phacoemulsification procedure."