Comparative in vitro flow study of 3 different Ex-PRESS miniature glaucoma device models.

PURPOSE: To determine the flow characteristics of the 3 different models of the Ex-PRESS miniature glaucoma device in a controlled laboratory study. MATERIALS AND METHODS: The 3 different Ex-PRESS models (P-50, R-50, and P-200; Optonol Ltd; now Alcon Lab) were tested using a gravity-driven flow test. Three samples of each of the 3 Ex-PRESS models were subjected to a constant gravitational force of fluid at 5 different pressure levels (5 to 25 mm Hg). Four measurements per sample were taken at each pressure level. The main outcome measure was flow rate (Q) (µL/min). Resistance (R) was calculated by dividing pressure (P) by the measured flow (Q). RESULTS: The flow rate was primarily pressure dependent. The P-200 model (internal diameter 200 µm) showed a statistically significant higher flow rate and lower resistance compared with both the P-50 and R-50 models (internal diameter 50 µm) (P<0.0001). The P-50 and R-50 models demonstrated similar flow rates (P=0.08) despite their difference in tube length (2.64 vs. 2.94 mm). CONCLUSIONS: The 3 models of the Ex-PRESS mini shunt behaved in vitro as simple flow resistors by creating a relatively constant resistance to flow. Tube diameter was the only parameter with significant impact on flow and resistance. All models demonstrated flow rates per unit of pressure much higher than the outflow facility of a healthy human eye.

Novel technique for Nd:YAG posterior capsulotomy in pediatric patients.

A 7-year-old girl had posterior capsule opacification 2 years after cataract extraction without posterior capsulotomy. This report describes a novel technique for Nd:YAG posterior capsulotomy in pediatric patients for providers who do not have access to an overhead-mounted Nd:YAG laser.

From the bedside to the bench and back again: predicting and improving the outcomes of SLT glaucoma therapy.

PURPOSE: To determine whether selective laser trabeculoplasty (SLT) and prostaglandin analogues (PGAs) have a common mechanism of action that involves increasing conductivity across Schlemm's canal endothelial cells (SCEs) and inducing a similar decrease in intraocular pressure (IOP) in a given patient. METHODS: The intercellular junctions in SCEs were made visible by transfection of a plasmid containing a GFP-tagged gene for ZO-1 protein. Transfected SCEs were treated with media conditioned by lasered trabecular meshwork endothelial cells (TMEs), or with latanoprost, bimatoprost, or travoprost. Non-transfected SCEs were exposed to brimonidine, timolol, or brinzolamide. Confocal microscopy and conductivity measurements documented the in vitro treatment effects. Clinically, the IOP in the first SLT-treated eye of 24 patients was measured (1) while on PGA therapy, (2) at "baseline" several weeks after discontinuing PGA therapy, and (3) approximately 90 days after SLT treatment. RESULTS: Both the in vitro addition of any of the 3 PGAs and of media conditioned by lasered TMEs induced similar SCE effects involving junction disassembly, paracellular pathway widening, and increased conductivity. Clinically, PGAs decreased IOP by a mean of 5.58 mmHg and SLT decreased IOP by 6.60 mmHg from a baseline of 21.52 mmHg. CONCLUSIONS: Exposure to media conditioned by lasered TMEs, or the addition of PGAs, induces the disassembly of intercellular junctions opening up the SCE barrier. Clinically, a positive PGA response predicts both a successful SLT outcome and the magnitude of the decrease in IOP after SLT. We hypothesize that SLT and PGA therapies may share a common mechanism of action.

Ocular surface fluid contamination of sutureless 25-gauge vitrectomy incisions.

PURPOSE: To determine whether 25-gauge transconjunctival sutureless vitrectomy incisions are more likely to allow the inflow of ocular surface fluid than sutured vitrectomy incisions. METHODS: Four groups of cadaver eyes underwent three-port vitrectomy in a laboratory setup. Groups A and B had 25-gauge vitrectomy, with and without conjunctival displacement, respectively, and were left unsutured. Group C had 25-gauge vitrectomy with suturing of the sclerotomies. Group D had 20-gauge sutured vitrectomy. In all groups, India ink was applied to the ocular surface after the procedure, and the intraocular pressure (IOP) was varied to simulate postoperative IOP changes. Histology of the incisions was performed. RESULTS: Ink particles were identified in the wound in over two-thirds of eyes that underwent 25-gauge sutureless vitrectomy. Conjunctival displacement had no effect on ink ingress. Sutured 25- and 20-gauge incisions did not demonstrate ink particles in the wound. CONCLUSIONS: Twenty-five-gauge transconjunctival sutureless vitrectomy incisions, with or without conjunctival displacement, allowed the entry of ocular surface fluid into the eye in this laboratory model. Based on the limited number of eyes examined in this study, sutureless vitrectomy techniques may carry an increased risk of bacterial contamination that could predispose to endophthalmitis. Suturing may protect against ocular surface fluid ingress.