Comparison of Leakage Pressures in Tunnel versus Straight Sclerotomy Incisions Using a 23 Gauge Vitrectomy Trochar System

Abstract

Purpose:: Compare leakage pressure between two types of sclerotomy incisions in 23 gauge vitrectomy surgery.

Methods:: Ten freshly enucleated New Zealand white rabbit eyes underwent 23 gauge vitrectomy (Alcon Surgical, Ft Worth, TX). An infusion was placed 2 mm from the limbus at the 6 o'clock position. A second cannula was inserted with a trochar using a tunnel style sclerotomy incision at 10 o'clock by passing the trochar obliquely at a 15 degree angle with the bevel down. Vitrectomy was performed until free flow of fluid from the sclerotomy was achieved. The cannula was then removed with the intraocular pressure (IOP) set to zero. IOP was then increased progressively until leakage was noticed from the incision site, or the eye reached maximum machine IOP of 120mmHg. Balanced salt solution stained with Indocyanine Green (200mg/l) was infused into the eye to facilitate leak visualization. Subsequently a straight non-angled sclerotomy incision was performed at the 2 o'clock position and the same method of vitrectomy, cannula removal, and IOP testing was performed.

Results:: Ten incisions were performed in the tunnel group and 10 in the straight group. In 3 incisions of the tunnel group, leakage at low IOP was observed (2-7 mm Hg), at which time massage of the incision site with a cotton swab was performed and the infusion was raised to 35 mmHg to facilitate wound closure. All of these 3 eyes reached the maximum machine pressure of 120 mmHg after massage without any leakage observed. The maximum IOP of 120 mmHg was achieved for all other 7 incisions in the tunnel group. All 10 (100%) straight incisions were observed to leak at less than the maximum machine pressure of 120 mmHg. Without massaging, the average leakage IOP in the tunnel group was 85.1 mmHg (range 2-120 mmHg, SD=56.2 mmHg) and 20.2 mmHg (range 1-37 mmHg, SD=12.8 mmHg) for the straight incision group (p=0.002). Vitreous plugging the wound was visualized in 3 of the straight incisions. Two of those 3 incisions were noted to leak when the IOP was raised to the point of the vitreous plug expulsion (12-20 mmHg), at which point leakage was observed in those eyes even when IOP was lowered to 1 mmHg even after massage.

Conclusions:: Tunnel-style sclerotomy incisions showed increased integrity to elevated IOP when compared with straight incisions in 23 gauge vitrectomy.

Keywords: vitreoretinal surgery • wound healing • sclera