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Biomedical subjects

D F Williams

Publications and source records attributed to D F Williams.

At least 109 records · Page 6Linked to original sources
PubMed1990

Rebleeding in experimental traumatic hyphema treated with intraocular tissue plasminogen activator.

Tissue plasminogen activator has recently been shown to enhance the clearance of experimental nontraumatic hyphema in animals. However, hyphema in human eyes usually results from ocular trauma, and rebleeding is a serious complication. Hemorrhage is also a potential complication of fibrinolytic therapy. We assessed the incidence of rebleeding in an animal model of surgically induced traumatic hyphema after intracameral injection of tissue plasminogen activator (25 micrograms) or physiological saline. Eight eyes were each treated with tissue plasminogen activator or physiological saline at 10 minutes, 24 hours, 48 hours, or 72 hours after injury. Controls were 8 eyes with hyphema but no intracameral injection. No eyes treated with physiological saline (total, 32 eyes) or control eyes rebled. In contrast, the incidence of rebleeding from the injury site in eyes treated with tissue plasminogen activator was 88% (7/8) at 10 minutes, 75% (6/8) at 24 hours, 50% (4/8) at 48 hours, and 0% (0/8) at 72 hours after injury. Treatment of traumatic hyphema with tissue plasminogen activator prior to healing of damaged vascular endothelium may contribute to rebleeding.

Animals↗
PubMed1990

Clearance of experimental vitreous hemorrhage after panretinal cryotherapy is related to macrophage influx.

We investigated the effect of panretinal cryotherapy on blood clearance and on the inflammatory cellular response in rabbit eyes with experimental vitreous hemorrhage. Eyes treated with cryotherapy demonstrated less extensive vitreous opacity and more rapid clearance of blood than untreated eyes. The peak inflammatory cellular response measured by counts or radiolabeled cells in the optic nerve was 2.5 times greater in the cryotherapy-treated eyes. Panretinal cryotherapy may promote the clearance of vitreous hemorrhage by stimulating the influx of increased numbers of phagocytic inflammatory cells.

Animals↗
PubMed1990

A two-stage technique for intraoperative fluid-gas exchange following pars plana vitrectomy.

We describe herein a two-stage technique of intraoperative fluid-gas exchange following pars plana vitrectomy. The first stage is a complete fluid-air exchange using an air pump and intraocular linear suction. The air pump then maintains the intraocular pressure at the desired level during adjunctive procedures, such as laser endophotocoagulation. The second stage is an air-gas mixture exchange in which the desired gas, premixed in air to the desired final intraocular concentration, is manually flushed through the eye. This technique allows the attainment of an accurate concentration of intraocular gas if the air-gas mixture exchange is complete. In vitro and in vivo experiments in aphakic human eyes demonstrated that an effectively complete air-gas mixture exchange occurs with a 25-mL flush volume. This result compares favorably with the theoretical prediction derived from a "pharmacokinetic approximation" equation.

Body Fluids↗
PubMed1990

Retained intraocular foreign bodies and endophthalmitis.

Retained intraocular foreign bodies (IOFBs) are associated with endophthalmitis in approximately 7 to 13% of cases. The role of prompt surgical removal of the foreign body along with the use of intravitreal antibiotics in reducing this figure is uncertain. Retained IOFBs presenting to The Medical College of Wisconsin between July 1986 and June 1989 were reviewed. A total of 27 cases were evaluated and surgically treated. None of the 27 cases presented with or developed clinical signs of endophthalmitis, yet bacterial cultures of the removed intraocular material were positive in seven cases (foreign body in 5 cases, the aqueous fluid and the vitreous fluid in 1 case each). All eyes presenting within 24 hours of injury underwent immediate surgery (average, 4.5 hours after presentation). Of the seven eyes with positive intraocular cultures, all had pars plana vitrectomy removal of the IOFB and three of these eyes received intravitreal antibiotics at the time of surgery over concern of a high risk of infection. Two of these eyes eventually grew out the Bacillus sp. All eyes received subconjunctival antibiotics and postoperative topical and systemic antibiotics. Even after the positive cultures, no signs of clinical infection developed in any of the eyes. All seven eyes retained excellent visual acuity of 20/70 or better at an average of 10 months' follow-up. Follow-up ranged from 1 to 31 months. Prompt surgical intervention, the use of intravitreal antibiotics in high-risk-type injuries, and the possible use of vitrectomy surgery may reduce the incidence and severity of endophthalmitis.

Adolescent↗
PubMed1990

Fly pupae as attractant carriers for toxic baits for red imported fire ants (Hymenoptera: Formicidae).

Eight laboratory-reared ant species were fed baits of house fly, Musca domestica L., pupae treated with hydramethylnon. Two fire ant species, Solenopsis invicta Buren and Solenopsis geminata (F.), and Pheidole morrissi (Forel) were killed; average percentage of mortality of the five other species was less than 20%. In contrast, all species that were fed the commercial fire ant bait containing hydramethylnon (Amdro) died or were adversely affected. In the field, applications of house fly pupae and eye gnat, Hippelates pusio Loew, pupae dipped in acetone solutions of fenoxycarb significantly reduced population indices of the red imported fire ant, S. invicta, compared with commercial formulations of fenoxycarb (Logic) and hydramethylnon (Amdro). Field observations showed that the pupae of either species can be carried or moved by one or two worker ants. The smooth, hard cuticle of the pupae make them easy to handle and apply with application equipment. The current cost of house fly pupae is considerably more than the cost of a granular carrier, pregel defatted corn grits. However, if mass-production methods reduce this price differential, fly pupae could become an effective and more species-specific fire ant bait carrier.

Animals↗
PubMed1990

Posterior segment manifestations of ocular trauma.

Nonpenetrating or blunt ocular trauma, orbital trauma and systemic trauma may cause a variety of posterior segment abnormalities. Blunt ocular trauma may cause damage to the retina (commotio retinae), retinal pigment epithelium (retinal pigment epithelial edema), choroid (choroidal rupture) and optic nerve (optic nerve evulsion) alone or in combination. Traumatic macular holes and retinal detachment or dialysis may also occur after blunt ocular trauma. Trauma to the orbital tissues adjacent to the globe can cause concussive forces with damage to multiple structures within the eye (chorioretinitis sclopetaria). Systemic trauma may result in diffuse retinopathy (Purtscher's retinopathy, shaken baby syndrome) or localized retinal abnormalities (whiplash retinopathy, fat embolism syndrome). Alterations in intravascular (Valsalva retinopathy) or intracranial pressure (Terson's syndrome) due to a variety of causes may result in preretinal or vitreous hemorrhage and associated visual loss. The purpose of this report is to review each of these entities of traumatic posterior segment abnormalities.

Choroid Diseases↗
PubMed1990

Intraocular foreign bodies in young people.

The authors examined 104 patients with penetrating ocular injuries and retained intraocular foreign bodies. Nineteen patients (18%), with 20 injured eyes, were aged 18 years or younger. Fifty percent of eyes in the young people (10/20) achieved a final visual acuity of 20/30 or better and 65% (13/20) achieved 20/100 or better. Young people were significantly more likely than adults to be injured as a result of a projectile weapon or explosion (P less than 0.001). They also had a greater incidence of an initial visual acuity worse than 5/200 (P less than 0.001), which was statistically associated with a greater incidence of hyphema (P = 0.002), retinal detachment (P = 0.022), and uveal prolapse (P = 0.082). Although the distribution of final visual acuity was not significantly different between young people and adults, the latter tended to have poorer visual outcome after adjusting for initial visual acuity (P = 0.01).

Adolescent↗
PubMed1990

Magnetic resonance imaging of juxtapapillary plaques in cadaver eyes.

Adequate treatment of juxtapapillary melanomas with episcleral plaque brachytherapy using lower energy radiation sources may be difficult because of uncertainties regarding the relationship of the plaque to the optic nerve and tumour base. We obtained magnetic resonance images of a dummy plaque placed in a juxtapapillary location in cadaver specimens. Although it is possible to place a plaque in close association with the optic nerve sheath, a tissue barrier exists which may prevent actual contact between the plaque and nerve. Posterior tilting of the plaque may also occur. Because of these uncertainties regarding plaque placement, juxtapapillary melanomas should be considered a distinct subgroup when evaluating the efficacy of radioactive plaque brachytherapy in the treatment of choroidal melanoma.

Brachytherapy↗
PubMed1990

Modulation of growth in retina-derived cells by extracellular matrices.

Intravitreal membranes from patients with proliferative vitreoretinopathy (PVR) consist partly of retinal glial (RG) and retinal pigment epithelial (RPE) cells surrounded by varying amounts of extracellular matrix (ECM). The contribution of the ECM to the growth of PVR membranes is unknown. This study was undertaken to determine if proliferation in cultured RPE and RG cells is affected by different substrates, including some ECM materials which have been identified in PVR membranes. Substrates tested included type I collagen, basement membrane Matrigel, and poly-D-lysine, as well as uncharacterized cell type-specific matrices deposited by cultured RPE and RG cells. Proliferation was quantified by 3H-thymidine incorporation and radioautography 24 hours after plating and by cell counts after 14 days in the presence of serum. Relative to uncoated culture plastic, growth of RPE cells was inhibited by Matrigel, enhanced by poly-D-lysine, and unaffected by type I collagen. In contrast, growth in RG cells was inhibited by type I collagen and unaffected by the other substrates. Analysis of the timing of DNA synthesis after plating suggested that the substrates which affected RPE growth did so by altering the fraction of cycling cells rather than the cell cycle time. For the cell-derived matrices, heterotypic matrix (matrix produced by the other retinal cell type) enhanced the growth of both RPE and RG. The results suggest that the ECM may modify the growth of cells contributing to PVR membranes. Of note is that the cell-derived matrices reciprocally stimulated growth of RG and RPE cells, cell types which may interact in PVR membranes.

Animals↗
PubMed1989

The spatial resolution of protein adsorption on surfaces of heterogeneous metallic biomaterials.

This study was designed to examine the heterogeneity of the adsorption of proteins onto metallic materials. The materials studied included pure Ag, Au, and Ti and sintered Ag 10% Ti and Ag 10% Ta. The distribution of the protein adsorption was studied using I-125 labeled albumin detected by microautoradiography. The surface morphology of the specimens was examined in the scanning electron microscope prior to exposure to the protein solution. A heterogeneous distribution in albumin adsorption was observed over the Ag surface. Similar regions were observed over parts of the mixed metal specimens, but superimposed on this pattern were distinct regions of very low protein adsorption which appeared to correlate closely with the regions of Ti or Ta observed in the scanning electron microscope. A uniform distribution of adsorbed albumin was observed on the Au and Ti, with Au giving a much denser microautoradiograph than Ti. This work demonstrates that variations in the protein adsorption to heterogeneous materials can be observed on a microscopic scale.

Adsorption↗
PubMed1989

A model for biocompatibility and its evaluation.

Concepts of biocompatibility have changed radically in recent years. This paper describes these new concepts and the present knowledge of the components and mediators of biocompatibility and leads to the development of a model for the explanation and rationalization of these phenomena. Of particular importance is the question of the assessment or evaluation of biocompatibility. The paper concludes with comments on the need for a schedule of biocompatibility assessment procedures to take into account this new thinking.

Biocompatible Materials↗
PubMed1989

Results of vitrectomy for diabetic traction retinal detachments using the en bloc excision technique.

En bloc excision is a technique in which fibrovascular diabetic membranes and the posterior hyaloid are separated from the retina as a single unit. In a consecutive series of 69 eyes with diabetic traction retinal detachment treated with this technique, initial retinal reattachment was accomplished in 100% (69/69) of the eyes. With a minimum of 6 months' follow-up, the retina remained completely attached in 83% (57/69) of eyes, while the macula was attached in 88% (61/69) of eyes. Final visual acuity was 5/200 or better in 71% (49/69) of eyes. While current surgical techniques allow a high rate of anatomic success in the repair of diabetic traction retinal detachment, visual results remain limited by irreversible alterations in retinal function.

Adolescent↗
PubMed1989

Resolution of an apparent choroidal melanoma.

A 67-year-old white woman had a lesion that clinically, echographically, and angiographically appeared to be consistent with choroidal melanoma. At follow-up examination 2 months later, the lesion had clinically completely resolved. A limited choroidal hemorrhage simulating a choroidal melanoma is postulated.

Aged↗
PubMed1989

Long-term follow-up of acute multifocal posterior placoid pigment epitheliopathy.

Eleven patients with acute multifocal posterior placoid pigment epitheliopathy were followed up for 47 to 175 months (mean 106 months). Seven of 18 affected eyes (39%) developed progressive mild alterations in the retinal pigment epithelium. Seventeen eyes (94%) had a final visual acuity of 20/30 or better. One eye with progressive retinal pigment atrophy involving the fovea lost visual acuity from 20/25 to 20/60.

Adult↗
PubMed1988

Echographic verification of radioactive plaque position in the treatment of melanomas.

Visualization of the position of an episcleral plaque in relation to the underlying choroidal melanoma during the early radiation treatment period reconfirms accurate plaque location and may help assure optimal treatment. We used high-resolution B-scan echography to confirm the position of the episcleral plaque in 16 consecutive cases of choroidal melanoma. The technique is most useful for well-defined tumors as small as 3 mm in height whose anterior border does not extend beyond the ora serrata.

Brachytherapy↗
PubMed1988

Albumin adsorption on metal surfaces.

Studies of adsorption kinetics, desorption and adsorption isotherms concerning the interaction between albumin and a range of metal and metal oxides were undertaken in vitro. Three distinct types of behaviour concerning the adsorption of albumin on to metal surfaces were identified. Some metals adsorb considerably greater amounts of protein than might be expected from surface energy alone and it is suggested that electrostatic forces could be responsible for this phenomenon.

Adsorption↗