Showing papers by "Pratap Challa published in 2007"

Mechanisms of action and efficacy of argon laser trabeculoplasty and selective laser trabeculoplasty.

Abstract: Purpose of reviewSince the 1980s, laser trabeculoplasty has served as an effective way to lower intraocular pressure in patients with primary or secondary open angle glaucomas, both as an initial therapy or in conjunction with hypotensive medications. This manuscript will describe the proposed mecha

Transscleral diffusion of ethacrynic acid and sodium fluorescein

Abstract: Purpose One of the current limitations in developing novel glaucoma drugs that target the trabecular meshwork (TM) is the induced corneal toxicity from eyedrop formulations. To avoid the corneal toxicity, an alternative approach would be to deliver TM drugs through the sclera. To this end, we quantified ex vivo diffusion coefficient of a potential TM drug, ethacrynic acid (ECA), and investigated mechanisms of ECA transport in the sclera. Methods An Ussing-type diffusion apparatus was built to measure the apparent diffusion coefficient of ECA in fresh porcine sclera at 4 degrees C. To understand mechanisms of ECA transport, we quantified the transscleral transport of a fluorescent tracer, sodium fluorescein (NaF), that has a similar molecular weight but is more hydrophilic compared to ECA. Furthermore, we developed a mathematical model to simulate the transport processes and used it to analyze the experimental data. The model was also used to investigate the dependence of diffusion coefficients on volume fraction of viable cells and the binding of NaF and ECA to scleral tissues. Results The diffusion coefficients of ECA and NaF in the sclera were 48.5+/-15.1 x 10-7 cm(2)/s (n=9) and 5.23+/-1.93 x 10(-7) cm(2)/s (n=8), respectively. Both diffusion coefficients were insensitive to cell shrinkage caused by ECA during the diffusion experiments and cell damage caused by the storage of tissues ex vivo before the experiments. Binding of ECA to scleral tissues could not be detected. The apparent maximum binding capacity and the apparent equilibrium dissociation constant for NaF were 80+/-5 mM and 2.5+/-0.5 mM (n=3), respectively. Conclusions These data demonstrated that ECA diffusion was minimally hindered by structures in the sclera, presumably due to the lack of cells and binding sites for ECA in the sclera.

Exposure of Ex-PRESS Miniature Glaucoma Devices: case series and technique for tube shunt removal.

Abstract: Purpose To report a series of cases involving Ex-PRESS Miniature Glaucoma Device exposure and discuss the surgical techniques we used to remove the shunts. Methods A retrospective chart review was performed to identify all patients who were referred for Ex-PRESS Miniature Glaucoma Device exposure between January 2004 and December 2005. Demographic information, time to exposure, surgical technique for device implantation and removal, and patient outcomes after device removal were abstracted from the identified charts. In addition, we describe a surgical technique used to remove the exposed Ex-PRESS Miniature Glaucoma Devices. Results Six patients (8 eyes) experienced Ex-PRESS Miniature Glaucoma Device exposure. The average time to exposure was 8.5 months. In 2 eyes, the shunt had been inserted under a half-thickness scleral flap; in both these eyes and 1 additional eye, Mitomycin-C had been used during shunt insertion. At presentation with tube shunt exposure, all eyes had normal or elevated intraocular pressure. In 5 eyes, visual acuity worsened after the device was removed. All 8 patients required concomitant glaucoma surgery with device removal. Conclusions As an increasing number of patients undergo filtration surgery with Ex-PRESS Miniature Glaucoma Devices, anterior segment surgeons should be aware of the potential for device exposure and methods for device removal.