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.

The Pressure-Controlled Infusion System: a new instrument for closed-system surgery.

We present the new Pressure-Controlled Infusion System (PCIS), designed to automatically regulate intraocular pressure (IOP) during surgery. Studies were performed with rabbits in which we compared the true IOP during closed-system surgery using gravity-fed infusion with the automatic control provided by the PCIS. The results from irrigation/aspiration of the lens cortex, wound closure, and vitrectomy show that the PCIS performs two functions during closed surgery: it automatically maintains the baseline IOP at the pre-set level, and it dramatically decreases the pressure fluctuations that occur with gravity infusion.

Variations in intraocular pressure during closed-system surgical procedures.

True intraocular pressure (IOP) during closed-chamber anterior segment surgery and vitrectomy was measured in rabbits by inserting a miniature pressure sensor directly into the anterior chamber or into the vitreous. Infusion fluid pressure was also measured simultaneously with a sensor in the infusion line. Significant and rapid changes in IOP up to 110 mm Hg were observed during routine anterior segment and vitreous procedures.

Effects of topical treatment with beta-aminopropionitrile after radial keratotomy in the rabbit.

This study assessed the effect of beta-aminopropionitrile treatment on the long-term curvature and compliance of corneal tissue subjected to radial keratotomy (RK). beta-Aminopropionitrile is known to inhibit cross-linking of collagen and is expected to enhance the flexibility of scar tissue, thereby reducing wound contracture and regression after RK. Seventeen adult New Zealand rabbits, weighing about 4.

Investigation of the aggregation and activation of prothrombin using quasi-elastic light scattering.

The technique of quasi-elastic light scattering was used to measure the translational diffusion coefficient, D, of purified human prothrombin in buffered aqueous solutions and to monitor for the first time the fragmentation of this protein as it is converted to thrombin. The values of D20,w, measured at two different concentrations, are 4.72 X 10(-7) CM2/S at 2MG/CM3 and 4.

Ultrastructure of the human aortic valve.

The human aortic valve is examined histologically by light, transmission electron and scanning electron microscopy. The observations show that the valve leaflets are multi-laminated structures, whose laminae do not have very distinct boundaries. Through the whole thickness of the leaflets, the load-bearing collagenous fibers are preferentially oriented in the transverse direction.

Mechanical and histological study of aortic valve tissue from a patient with Marfan's disease.

A comparison between a normal and a Marfan's disease aortic valve has been attempted in terms of their tissue stress-strain characteristics and their histology. The diseased valve tissue was found to be more compliant by an order of magnitude than the normal valve, which is related to the disorientation of its collagen fibers, and the proliferation of mucopolysaccharides.

Growth of cultured calf aortic smooth muscle cells on cardiovascular prosthetic materials.

The growth of cultured calf aortic smooth muscle cells on cardiovascular biomaterials was investigated, using native and oxidized polyacrylonitrile (orlon) fabrics, dacron velour, and Parylene-C coated polypropylene microfabric as substrates. By light microscopic evaluation, surface cell coverage was most complete on microfabric, followed by native orlon, dacron velour, and oxidized orlon. Native orlon supported the greatest total cell growth, as determined by chemically extractable protein, followed by oxidized orlon, dacron velour, and the microfabric.