Hydrodynamic analysis of intraocular pressure changes during anterior chamber procedures.

Variations in intraocular pressure (IOP), observed by us and other authors in closed-system anterior chamber procedures, are explained using a simple hydrodynamic analysis based on the Bernoulli equation. Calculations show that the sudden increases in IOP (pressure spikes) measured during anterior segment surgery are due primarily to the small size of the infusion cannulas and are exacerbated by high infusion rates. Accurate measurement of these IOP variations requires placement of the pressure sensors in situ and is not possible by remote pressure sensing at the infusion line or the console.

Injection of a silicone prepolymer system into the gallbladder of rabbits.

The aim of this study was to assess the feasibility of a new nonsurgical treatment for cholelithiasis. This involved injecting a liquid prepolymer into the gallbladder which would polymerize in situ, entrapping existing gallstones and permanently filling the gallbladder so as to prevent subsequent gallstone formation. Initially, several silicone prepolymer mixtures were tested in vitro for viscosity, cure time, radiopacity, and consistency when polymerized.

Evaluation of drug treatments for proliferative vitreoretinopathy using vitreous microtensiometry.

The effectiveness of antimetabolic and anticollagen agents against proliferative vitreoretinopathy (PVR) was assessed by vitreous microtensiometry, a new technique that measures in situ the tensile strength of vitreous membranes. Two PVR models were produced in rabbits by intravitreal injection of bovine retinal pigment epithelial (RPE) or fibroblast cells, and the animals subsequently were treated with 5-fluorouracil (5-FU) and beta-aminopropionitrile (BAPN), administered alone or in combination. The fibroblast PVR model produced high-strength membranes that did not respond significantly to these therapies.

Constant-volume polymerization of composites by addition of ammonia-modified montmorillonite.

Polymerization shrinkage is a major limitation of dental composites. It generates internal stresses within bonded restorations and leads to marginal leakage, sensitivity and recurrent decay in the absence of adequate bonding. A method is presented for formulating composites that cure at constant volume by adding to the resin system small amounts of the hydrated mineral montmorillonite (MMT), which has been modified by replacing part of its hydration water with ammonia (NH3).

Effect of incision length, location, and shape on local corneoscleral deformation during cataract surgery.

The effect of incision length, location, and shape on the structural integrity of the globe was examined using finite element analysis by comparing the radial deformation of the corneoscleral tissue adjacent to the incision. The results show that incision length had the greatest adverse effect, 12 mm incisions causing deformations an order of magnitude higher than the distension of the intact globe at 20 mm Hg. The least structural disturbance was produced by 3 mm scleral pocket incisions.