PubMed Health⌕ Search

Biomedical subjects

H W Thompson

Publications and source records attributed to H W Thompson.

11 recordsLinked to original sources
PubMed1992

Vancomycin-enriched corneal storage medium.

Antibiotics in a corneal preservation solution probably have little effect during storage at 4 C, but are effective as the tissue is warmed. The tissue acts as a sponge, soaking up the antibiotic from the solution and releasing it into the eye, where the bactericidal effect is achieved. Currently, high concentrations of gentamicin (relative to the minimal inhibitory concentration) are used in the preserving solution for this purpose. Presumably, proportionately high concentrations of any proposed new antibiotic added to supplement the bactericidal effect of gentamicin, such as the vancomycin used in this study, would be required. However, neither the ability of donor tissue to tolerate high concentrations of vancomycin nor the stability of vancomycin at neutral pH in appropriate storage media has been documented. We evaluated the addition of vancomycin (100 micrograms/ml) to two corneal storage media that contained gentamicin in terms of stability of the antibiotic in solution and the effect on the endothelial cells of donor tissue stored for two weeks at 4 C. Vancomycin was stable in solution at neutral pH (7.2) during the five-month period of the study; the concentration exceeded 90 micrograms/ml for the first five weeks. The endothelial cells from donor tissue stored in the vancomycin-enriched media showed no notable differences from those stored in the same media without vancomycin in terms of cell shape, cell borders, cell swelling, and apical holes. The stability of vancomycin in storage and the absence of endothelial toxicity in vitro support the potential use of this antibiotic as a supplement to gentamicin for the prevention of endophthalmitis in patients receiving corneal transplants.

Aged↗
PubMed1992

Molecular and cellular responses of the corneal epithelium to wound healing.

The corneal epithelium responds rapidly to injury, repairing defects with a layer of cells that covers the denuded corneal surface and prevents infection and loss of vision. After a wound, reorganization of the remaining epithelial cells occurs over several hours, resulting in the formation of a migratory leading edge. However, expression of genes such as c-fos occurs within minutes of wounding. This early expression may be important for directing epithelial reorganization and the later mitotic burst. Our results show that receptors for epidermal growth factor are upregulated in the migratory cell population. Proliferation through a mitotic burst was observed in cells surrounding the original wound margin after 36 hours. The interaction between gene expression and cell surface receptors for growth factors and cell proliferation suggests that wound healing occurs in a complex, but tightly controlled process in the corneal epithelium.

Animals↗
PubMed1992

Effect of growth factors on collagen lattice contraction by human keratocytes.

A three-dimensional gel contraction model was used to evaluate interactions between human keratocytes and different kinds of collagen in the presence or absence of various growth factors. Bovine collagen type I or human placental copolymerized collagen type I/III was used to create the lattices. Normal keratocytes from neonatal, aged, and insulin-dependent diabetic donors, as well as abnormal keratocytes from a donor with macular corneal dystrophy, were cultured. Growth factors included epidermal growth factor (EGF), basic fibroblastic growth factor (FGF), insulin-like growth factor (IGF-I), and platelet-derived growth factor homodimer beta beta (PDGF). Gel area and optical transmittance were determined from computerized measurements. Dose-response experiments (0.01-100 ng/ml) demonstrated that PDGF at 10 ng/ml (P less than 0.005) and EGF at 1 and 10 ng/ml (P less than 0.0001) were the most effective in promoting gel contraction, compared to IGF-I and FGF. Comparison of cell strains revealed different dose-response profiles. Cells from insulin-dependent diabetics and cells from a donor with macular dystrophy contracted lattices more rapidly than cells from normal neonates (P less than 0.0001). Lattices of copolymerized human collagen type III/I demonstrated significantly reduced contraction rates (P less than 0.0001) and increased optical transmittance, compared to bovine collagen type I lattices. Ultrastructural studies revealed that keratocytes extend processes to form a network within the collagen lattice. Specialized intercellular junctional complexes were observed by transmission electron microscopy. This model provides a useful in vitro corneal stroma-equivalent for the study of keratocyte, extracellular matrix, and growth factor interactions.

Adolescent↗
PubMed1992

EGF cell surface receptor quantitation on ocular cells by an immunocytochemical flow cytometry technique.

A method is presented for the rapid flow cytometric determination of epidermal growth factor (EGF) receptor densities on the surface of cultured ocular cells. The technique uses a biotinylated monoclonal antibody directed against the EGF receptor in conjunction with a streptavidin-bound fluorochrome and requires the specific fluorescence per cell to be measured as a function of ligand and receptor concentration. Because the measurement is noninvasive and restricted to cell surface-bound material, the cells can be kept in a physiologic environment, even at the moment of assay. Calculated receptor densities ranged from 5142/cell (infant human corneal endothelium) to 35,678/cell (infant human keratocytes) to greater than 5 x 10(5)/cell for an A431 control cell line. Species and donor age differences were noted, as was transient receptor downregulation after EGF administration. Flow cytometry represents a valuable time saving procedure for large scale applications while providing the same level of sensitivity as standard radioimmunoassays. This technique is applicable to quantitation of other growth factor cell surface receptors and could greatly expand the use of flow cytometry in the research laboratory.

Animals↗
PubMed1991

Optisol corneal storage medium.

Optisol is an investigational, intermediate-term corneal storage medium containing chondroitin sulfate and dextran to enhance corneal dehydration during storage. We used scanning electron microscopy to grade endothelial cell morphologic characteristics in terms of cell shape, cell borders, cell swelling, and apical holes in pairs of corneas stored in Optisol and Dexsol. Optisolstored corneas showed significantly fewer morphologic changes after 14 days at 4 degrees C than did Dexsol-stored corneas. No significant differences were seen after 1 to 4 days at 26 degrees C. Temperature-reversal analysis showed no significant change in corneal thickness with warming after 2-week storage at 4 degrees C in either medium, although Optisol-stored corneas were significantly thinner than those stored in Dexsol at all times. The results of scanning electron microscopy suggest that preservation at refrigerator temperature for 2 weeks in Optisol is superior to preservation in Dexsol. Both media may be useful in preserving endothelial structure for limited periods at room temperature, which could provide a measure of safety in shipping or storage where refrigeration is unreliable.

Adult↗
PubMed1991

Suppression of ocular herpes recurrences by a thymidine kinase inhibitor in squirrel monkeys.

5'-Ethynylthymidine, an inhibitor of viral thymidine kinase (TK), was given intraperitoneally to squirrel monkeys previously infected by the ocular route with Rodanus strain herpes simplex virus. Spontaneous ocular recurrences were reduced during therapy, compared to saline-treated controls. This is the first in vivo demonstration that a viral TK inhibitor can reduce recurrences of HSV-1. Similar benefit would be expected for HSV-2 and perhaps VZV (varicella zoster virus).

Animals↗
PubMed1991

Flow cytometry measurements of the DNA content of corneal epithelial cells during wound healing.

This study presents the first application of flow cytometry (FCM) techniques to the assessment of cell cycle dynamics in the corneal epithelium after experimental wounding. Anterior keratectomies 6 mm in diameter were created in the central corneas of albino rabbits. The authors sampled the epithelial tissue obtained outside the wound at 12-hr intervals until wound closure at 72 hr. Regenerated epithelium from the surface of the wounded area was collected at 78 hr. The percentages of nuclei in the G0/G1 (growth), S (DNA synthesis), and G2/M (tetraploid/mitosis) phases were determined by FCM. An increase in the percentage of nuclei in the G2/M phase at 36 hr was seen, compared with cell populations in samples from unwounded control corneas. The authors found an increase in mitotic activity in the corneal epithelium during the period of cell migration before wound closure.

Animals↗
PubMed1989

Tobramycin iontophoresis into corneas infected with drug-resistant Pseudomonas aeruginosa.

Iontophoretic application of tobramycin was used to deliver drug to the cornea of rabbit eyes infected with a tobramycin-resistant strain of Pseudomonas aeruginosa (MIC = 31.25 micrograms/ml). Corneas infected with P. aeruginosa 27853/pMG6 were treated 22 hours after infection with tobramycin delivered by either iontophoresis, mock iontophoresis (eye cup without current), or application of fortified topical drops. Corneal iontophoresis of tobramycin at 25 mg/ml caused more than a three log reduction in bacteria; yielding a significantly lower number of bacteria compared to untreated controls and all other treatments (P less than or equal to 0.0001). Corneal iontophoresis of tobramycin at 10 mg/ml showed a one log reduction in the number of bacteria per cornea, yielding a significantly lower number of bacteria compared to untreated controls (P less than or equal to 0.0001), corneas treated with nine topical applications of 1.36% tobramycin drops (P less than or equal to 0.0001), and corneas treated with mock iontophoresis (P less than or equal to 0.02). These results suggest that iontophoresis is a powerful ocular delivery system for tobramycin and may be suitable for use with other chemotherapeutic agents.

Administration, Topical↗
PubMed1988

Accuracy and precision of the Tono-Pen in measuring intraocular pressure after keratoplasty and epikeratophakia and in scarred corneas.

Intraocular pressure measurements with the Goldmann and Schiotz tonometers are unreliable when the cornea is irregular due to disease or surgery. The Tono-Pen (Oculab, Glendale, Calif) is an electronic applanation tonometer based on the same principle as the MacKay-Marg tonometer. We measured intraocular pressure in 37 eyes with irregular corneas, in 50 eyes that had recently undergone penetrating keratoplasty, in 16 eyes that had undergone epikeratophakia, and in 12 eyes with normal corneas with both the MacKay-Marg and Tono-Pen tonometers. The same two instruments were used, and the sequence of measurement was randomized. Analysis of variance demonstrated no significant difference between measurements obtained with the two tonometers in any of the groups. The data suggest that the Tono-Pen is as accurate as the MacKay-Marg tonometer in those situations where the Goldmann tonometer is inaccurate.

Cicatrix↗
PubMed1988

Collagen shield drug delivery: therapeutic concentrations of tobramycin in the rabbit cornea and aqueous humor.

Collagen shields made of porcine collagen were placed in a solution containing tobramycin sulfate (40 or 200 mg/ml) for five minutes, then applied to rabbit eyes. One, four, or eight hours after application, the corneas, aqueous humor samples, and shields were assayed for antibiotic. At all intervals, the concentration of antibiotic in the corneas and aqueous humor samples exceeded the mean inhibitory concentration for tobramycin, as determined for most strains of Pseudomonas. Shields immersed in 200 mg/ml tobramycin produced significantly higher concentrations of antibiotic in the cornea at one hour than subconjunctival injections of tobramycin (20 mg) (P = .0001). Shields immersed in 40 mg/ml tobramycin produced higher, although not significantly higher, concentrations of antibiotic in the cornea at one hour than subconjunctival injections of tobramycin (20 mg) (P = .318). Shields immersed in commercially available tobramycin drops or injectable tobramycin solution (40 mg/ml) caused no epithelial damage visible by slitlamp examination. Collagen shields containing antibiotics can serve as a vehicle for drug delivery and may prove superior to current methods for preoperative and postoperative antibiotic prophylaxis and the initial treatment of bacterial keratitis.

Animals↗