Se. Brooks et al., MODIFICATIONS OF THE GLAUCOMA DRAINAGE IMPLANT TO PREVENT EARLY POSTOPERATIVE HYPERTENSION AND HYPOTONY - A LABORATORY STUDY, Ophthalmic surgery, 25(5), 1994, pp. 311-316
Hypotony or hypertension in the early postoperative period following i
mplantation of a nonvalved seton such as the Molteno tube is a common
problem. We conducted a laboratory investigation evaluating two modifi
cations of the silicone drainage tube. One involved a longitudinally-o
riented, pressure-sensitive slit-valve combined with an absorbable occ
luding ligature interposed between the valve and the episcleral plate.
Experiments examining the relationship between slit length, opening p
ressure, and flow rate were performed. The second modification involve
s focally constricting the lumen of the tube with an external ligature
in order to reduce flow rates. Our results indicate that a slit-valve
length of 2.0 mm appears to provide a reliable opening pressure of ar
ound 10 mm Hg, with relatively high flow when pressures exceed opening
pressure. Focally constricting the lumen of the tube, however, was sh
own to be both unpredictable and unsatisfactory for reducing the flow
of fluid to a range consistent with steady state aqueous production.