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Biomedical subjects

S X Stevens

Publications and source records attributed to S X Stevens.

11 recordsLinked to original sources
PubMed1999

Comparison of different biomaterials for glaucoma drainage devices.

OBJECTIVES: To compare the inflammatory reaction associated with the insertion of silicone and polypropylene endplates and endplates made of a new biocompatible polymer, Vivathane, in the rabbit subconjunctival space. METHODS: Similar-sized endplates made of 3 different biomaterials were sutured to the sclera in the superotemporal quadrant of the rabbit eye. Thirty eyes of 15 albino New Zealand rabbits were randomly assigned to the 3 groups. Conjunctival vascular hyperemia was graded in a masked fashion among groups. At the end of 3 weeks, the enucleated eyes were examined histologically and using scanning electron microscopy. RESULTS: Polypropylene and Vivathane were associated with significantly more inflammation in clinical observations and based on histological grading. Silicone was associated with the least amount of inflammation. Three polypropylene and 1 Vivathane plate were extruded between the second and third week. CONCLUSIONS: Silicone is the most inert of the 3 materials tested. Inflammation associated with biomaterials may contribute to the failure of the glaucoma drainage devices. CLINICAL RELEVANCE: Bleb inflammation may be related to the biomaterial being used as the endplate. Endplates should be handled carefully during surgery to avoid creating rough spots.

Animals↗
PubMed1999

The BioMask for treatment of corneal surface irregularities with excimer laser phototherapeutic keratectomy.

PURPOSE: To assess the characteristics of BioMask as a potential masking agent for use with the excimer laser. METHOD: We addressed ablation rate, smoothness, ease of use, dioptric shift, treatment of standardized irregular topography, and ability of BioMask to induce dioptric change in vivo. RESULTS: BioMask ablates at a rate of 0.28 microm per pulse. The BioMask conforms to the base curve of a contact lens in the excimer blank, eye bank eye, and rabbit eye with a r2 of 0.9982, 0.9844, 0.9858, respectively. We are readily able to create 20 diopters of flattening or steepening (r2 = 0.9944). Standardized irregular topography generation in the rabbit eye and then removal with BioMask was successful. The central corneal topography of the rabbit cornea showed predictable changes with various contact lens base curves with the BioMask (r2 = 0.875). CONCLUSIONS: BioMask has excellent potential as an ablatable mask material in the treatment of superficial corneal scars.

Animals↗
PubMed1998

Recurrent endophthalmitis after cataract surgery with a scleral-tunnel incision.

PURPOSE: To present a case of recurrent postoperative endophthalmitis with a scleral-tunnel abscess and adjacent microbial keratitis. METHODS: A 76-year-old woman with microbial keratitis and recurrent endophthalmitis after cataract surgery was referred to a tertiary care center for further management. The medical chart of the patient was reviewed. RESULTS: The patient was seen on the eighth postoperative day with endophthalmitis that responded to medical treatment. Initial vitreous cultures were negative. The endophthalmitis recurred after the medical treatment was discontinued. She subsequently developed microbial keratitis at 1 o'clock adjacent to the limbus. Cultures from the site of corneal abscess and vitreous grew coagulase-negative Staphylococcus. Gonioscopy revealed the presence of a scleral abscess, which responded to subconjunctival injection of vancomycin and an intense and prolonged course of topical antibiotics. CONCLUSION: A scleral abscess should be suspected in a patient with endophthalmitis or microbial keratitis or both after a scleral-tunnel incision for cataract surgery.

Administration, Topical↗
PubMed1998

Comparison of three computerized videokeratoscopy systems with keratometry.

PURPOSE: To compare the reproducibility of computerized videokeratoscopy systems by using normal eyes and calibrated objects. METHODS: We evaluated the reproducibility of three commercially available videokeratoscopes [EyeSys, TechnoMed C-Scan, and PAR Corneal Topography System (CTS)] with the manual keratometer (Bausch & Lomb) by using calibration spheres and 10 normal subjects (20 eyes). All videokeratoscopy and keratometer results were obtained by one investigator (R.M.). Each eye and calibration sphere were submitted to 10 serial examinations by using each system. The average K of all points within the central 3.0 mm of the topography systems (central 3.0 mm) was compared with the average K of the manual keratometer. RESULTS: All videokeratoscopy systems correlated well with each other and manual keratometry when accessing aspheric and spherocylinder calibration balls. EyeSys central keratometry clinical results had the strongest correlation with the average keratometry results at 35%, followed by PAR-CTS at 25% and C-Scan at 5%. Among the videokeratoscopy units, EyeSys and PAR-CTS had the strongest correlation at 65%. The correlation between the TechnoMed C-Scan and both the EyeSys and PAR-CTS systems was 25%. There was a statistically significant difference (p < 0.05) between the systems when analyzing the results obtained from clinical subjects. The average keratometry (K) difference of human eyes between videokeratoscopy systems is <0.35 diopters (D) (p < 0.05), which may be clinically significant. The average manual K reading (42.97 D) is statistically significantly flatter (p < 0.05) than each of the videokeratoscopy units (EyeSys = 43.49 D; PAR = 43.48 D; C-Scan = 43.83 D). Comparing the 10 measurements of each eye or calibration object in the same videokeratoscopy system verified that the devices give reproducible results. The average standard deviation (ASD) of the keratometer was 0.10 D. The ASD of the videokeratoscopy units was 0.05 D for the EyeSys, 0.29 D for the PAR-CTS, and 0.31 D for the C-Scan systems. CONCLUSION: Based on this study, we should not assume that the results of different topography systems can be interchanged in clinical studies.

Cornea↗
PubMed1997

The Tampa Trephine technique with cat corneal endothelium.

The Tampa Trephine (Martin Marietta Speciality Components, Largo, FL, U.S.A.) penetrating keratoplasty technique uses a 7.0-mm corneal donor button with six rectangular 1 x 2-mm tabs of Bowman's layer, 75 microns in thickness, which are inserted into the recipient stroma beneath Bowman's layer. We evaluated the safety of the Tampa Trephine tissue-trephination method on the cat corneal endothelium combining vital staining and scanning electron microscopy, comparing it with the standard Weck trephination technique. The Tampa Trephine tissue trephination produces a donor button with a 6.7-mm diameter central area of normal endothelium. Localized peripheral areas of cellular loss, endothelial and Descemet's tears, endothelial detachment, and folding along the border of the trephination were observed with the Tampa Trephine method, all located in an area of < or = 150 microns, adjacent to the edge of the button. Standard trephination induced a localized peripheral area of endothelial damage < 50 microns in extension from the donor edge. A theoretic maximal 8.4% peripheral endothelial cell loss is induced with the Tampa Trephine trephination method, compared with a 2.8% loss with the standard procedure. The peripheral location of the alterations after the Tampa Trephine does not hinder the viability of the corneal endothelium, as it has been clinically observed.

Animals↗
PubMed1996

Use of a mirror needle holder with transsclerally sutured posterior chamber intraocular lenses.

A mirror needle holder has been designed to facilitate the passage of a needle through the ciliary sulcus during transscleral fixation of posterior chamber (PC) intraocular lens (IOLs). Two human postmortem eyes were used to demonstrate the efficacy of this mirror used as the needle holder. This method was compared with the current method of passing sutures without view of the ciliary sulcus. The mirror needle holder demonstrated precise passage of the needle into the ciliary sulcus by direct visualization of the ciliary processes and sulcus. This method may avoid the complications associated with transsclerally sutured PC IOLs during penetrating keratoplasty and secondary IOL placement.

Ciliary Body↗
PubMed1992

A hemolysin-encoding plasmid contributes to bacterial virulence in experimental Enterococcus faecalis endophthalmitis.

Beta-hemolysin production is a variable trait of the Lancefield group D streptococcus, Enterococcus faecalis. The E. faecalis hemolysin is encoded by large transmissible plasmids. The variable nature of this putative virulence factor provided an ideal system for testing its contribution in experimental endophthalmitis. In this study, isogenic E. faecalis strains were compared to determine whether the presence of the hemolysin-encoding plasmid affected the severity of disease in a rabbit endophthalmitis model. Experimental infections (n = 6) with 10(1)-10(4) E. faecalis organisms harboring the hemolysin-encoding plasmid resulted in a 98% loss of retinal function (by electroretinography [ERG]) and white reflex by postoperative day 3. By contrast, infections of similar numbers of plasmid-free E. faecalis organisms (n = 5) resulted in retention of some retinal function (23% per ERG) with a red reflex demonstrated on postoperative day 3. Results of light microscopy, slit-lamp examination, ERG, and indirect ophthalmoscopy indicated that infections with hemolysin-encoding plasmid-containing E. faecalis resulted in a more aggressive endophthalmitis compared with the endophthalmitis caused by plasmid-free E. faecalis. This is the first endophthalmitis model to the authors' knowledge that specifically evaluates bacterial virulence using isogenic strains.

Animals↗
PubMed1991

Intraocular safety of ciprofloxacin.

Retinal toxicity resulting from the treatment of exogenous bacterial endophthalmitis with multiple antibiotics has increased the importance of evaluating the efficacy of new potent antibiotics for monotherapy. The retinal and corneal toxicity of ciprofloxacin hydrochloride, which is rapidly bactericidal against gram-positive and gram-negative bacteria, was evaluated in the rabbit eye. Retinal toxicity was dose-dependent in phakic and aphakic rabbit eyes as determined with electroretinography, light microscopy, and transmission electron microscopy. An intravitreal dose of greater than 100 micrograms also resulted in dose-dependent acute corneal toxicity in aphakic vitrectomized rabbit eyes. Results of instillation of ciprofloxacin directly into the anterior chamber of phakic rabbit eyes confirmed dose-dependent corneal toxicity. No retinal or corneal damage was observed in aphakic or phakic rabbit eyes after administration of an intravitreal dose of 100 micrograms. Results of electroretinography and light microscopy alone are insufficient to evaluate the retinal toxicity of antibiotics. Ultrasonic pachymetry is the best method of detecting probable associated corneal toxicity.

Animals↗
PubMed1991

Corneal topography as a predictor of refractive change in the prospective evaluation of radial keratotomy (PERK) study.

The first operated eyes of 435 patients undergoing radial keratotomy in the Prospective Evaluation of Radial Keratotomy (PERK) study were evaluated by photokeratography to document the preoperative and postoperative corneal shape. We determined by regression analysis and analysis of variance that the corneal shape preoperatively improved the prediction of the corneal shape 6 months postoperatively in the 3-mm-clear-zone population. The reduction of myopia in all 435 eyes ranged from 1.25 to 9.75 diopters. We studied the effect of the preoperative corneal shape on this variability in the outcome of the surgery using rings 2 and 7 on photokeratography and corneal diameter. In the 3-mm-clear-zone group, eyes with flat prolate corneas had a greater reduction in myopia (4.65 D); those with steeper, more spherical corneas had less reduction in myopia (3.48 D). In addition, eyes with a 3-mm clear zone and flat central corneas alone (8.0 mm = 42.19 D) flattened approximately 0.75 D more than those with steep central corneas (7.0 mm = 48.21 D). In the 3.5-mm and 4.0-mm clear zone groups, the change in corneal curvature was not related to the preoperative curvature. A stepwise regression analysis of the 151 eyes in the 3.0-mm-clear-zone population demonstrated the following predictive equation for radial keratotomy; change in cycloplegic refraction = -14.55 + [-2.097 x average ring-2 radius] + [3.605 x average ring-7 radius] + [0.69 x horizontal corneal diameter] + [0.079 x age] + [-0.379 x spherical equivalent cycloplegic refraction]. There was a 1.17-D observed difference in the effect of radial keratotomy between those eyes with a steep/steep corneal topography (7.2% of the 3.0-mm-clear-zone population) and the flat/flat topography (29% of the 3.0-mm-clear-zone PERK population). A knowledge of corneal topography provides an additional tool for understanding the operative variability of radial keratotomy.

Cornea↗
PubMed1989

Accuracy and reproducibility of KeraScanner analysis in PERK corneal topography. PERK Study Group.

The measurement of the corneal radius of curvature centrally and in the corneal periphery is exceedingly difficult because of variables in photography and data acquisition. We present a technique of Automated image scanning of corneal photographs which provides a more accurate and reproducible analysis of the paracentral corneal contour. We analyzed the sources of error of corneal topography measurement. CorneaScope photographs of calibration balls were generated by each Prospective Evaluation of Radial Keratotomy (PERK) Surgical Center. The 90% confidence intervals for individual ring-radial positions on the 8.00 and 10.00 mm balls were 7.91 to 8.09 mm and 9.89 to 10.11 mm respectively. Our isopter method of analysis for clinical comparison averages all eight radii of curvature for each CorneaScopef ring. This isopter technique reduces the corresponding 90% confidence intervals to 7.96 to 8.03 and 9.95 to 10.06 mm. The measurement variability of a 10 mm calibration ball decreased in the following order: calibration ball positioning, scanner personnel, photograph movement between scans, and nonrepositioned scanning. Photographs of calibration balls demonstrate +/- 4 microns of measurement resolution and patient corneal photographs may be evaluated to +/- 40 microns. This automated scanning system provides consistent data when digitizing keratographs.

Biometry↗