Effects of the Numbers and the Shapes of Venting Slits on Intraocular Pressure after Baerveldt Glaucoma Drainage Implant

Purpose: Venting slits are widely used as an effective method to avoid the high intraocular pressure (IOP) phase immediately after the implantation of non-valved glaucoma drainage devices. However, there have been no detailed reports comparing the types of needles used and the numbers of slits made. In this study we investigated the effects of different needle types and the number of venting slits.Methods: IOP was measured using a Keyence NR-600 transducer connected to the limbus of a pig eye with a 27G needle. A microsyringe pump was also connected to the corneal limbus using a 27G needle to make a continuous perfusion system at the rate of 200 mu l/hr. The silicone tube of a Baerveldt glaucoma drainage implant (BG101-350) was ligated near the plate and then implanted in the anterior chamber of the pig eye. The tube was covered with scleral tissue of another pig eye after 1 or 3 venting slits were created in the middle of the outer diameter using different types of needles (7-0 Vicryl (R), 7-0 PDS?(R), 5-0 PDS?(R), 3-0 PDS Plus (R)). IOP measurement was started from 50mmHg and then we monitored the chronological changes of IOP for 15minutes.Results: The IOPs at 15minutes after continuous perfusion with the venting slits made using 7-0 Vicryl needles were 29.02.5mmHg (1 slit) and 23.1 +/- 8.3mmHg (3 slits). The IOPs were 23.1 +/- 3.1mmHg and 23.5 +/- 4.7mmHg with 7-0 PDS needles (1 slit and 3 slits, respectively), 21.8 +/- 2.2mmHg and 20.8 +/- 4.3mmHg with 5-0 PDS needles (1 slit and 3 slits, respectively), and with 3-0 PDS needles they were 12.2 +/- 3.0mmHg for one slit and 13.2 +/- 3.5mmHg for 3 slits.Conclusions: Usage of a round (PDS) needles produces more predictable IOP than a spatulated (Vicryl) needle.