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Biomedical subjects

M B Shields

Publications and source records attributed to M B Shields.

At least 55 records · Page 3Linked to original sources
PubMed1994

Noncontact transscleral Nd:YAG cyclophotocoagulation: a long-term follow-up of 500 patients.

Long-term experience with transscleral cyclophotocoagulation in 500 patients suggests that this operation is the cyclodestructive procedure of choice. It offers a reasonable surgical option in the high-risk glaucoma population, which includes patients with neovascular glaucoma, glaucomas with active uveitis, glaucomas in aphakia or pseudophakia, and other cases in which filtering surgery has failed or is felt to have a low chance for success. Satisfactory intraocular pressure reduction was achieved in 62% of the patients with one treatment session. After one or more repeated procedures in 21% of the study group, the final intraocular pressure was below baseline in 94%, with a mean final reduction of 24 mm Hg, which was judged to be adequate for 87% of the patients. However, visual loss remains a significant postoperative complication, with some degree of reduced vision occurring in 39% of the study population. Patients with neovascular glaucoma had the greatest percentage of visual loss at 46%, compared with 34% and 38% for patients with glaucomas in pseudophakia and aphakia, respectively. While it is hard to know how many of these cases of visual loss were a direct result of the cyclophotocoagulation, the procedure should be used with caution in eyes with a potential for good central vision. Further study is needed to determine the relative indications for transcleral cyclophotocoagulation and the various operations to increase aqueous outflow in the management of patients in the high-risk glaucoma population.

Adolescent↗
PubMed1994

Evaluation of a tapered, blunt, bipolar cautery tip for trabeculectomy.

A bipolar cautery instrument with a tapered, blunt tip has been developed for glaucoma filtering surgery. Evaluated in 30 consecutive trabeculectomy procedures, the instrument proved suitable for all aspects of the operation. The narrow, 23-gauge shaft and tapered, blunt tip allowed gentle, pin-point coagulation of individual bleeders, as well as cauterization of tracks of tissue in a continuous motion. The unit was effective for external cauterization of conjunctival and scleral vessels, as well as for internal cauterization of anterior uveal tissue.

Conjunctiva↗
PubMed1993

Clinical and histopathologic observations concerning hypotony after trabeculectomy with adjunctive mitomycin C.

Prolonged hypotony-induced maculopathy is a serious complication of trabeculectomy with adjunctive mitomycin C. We performed trabeculectomies with intraoperative mitomycin C on 59 eyes of 52 consecutive patients. Exposure time to mitomycin C was five minutes in the first seven patients, two of whom had prolonged hypotony-induced maculopathy. One of these required surgical revision of the filtering procedure. Light and electron microscopic study of the excised, avascular bleb disclosed an irregular epithelium and largely acellular subepithelium of loosely arranged connective tissue. In the remaining 52 eyes, the exposure time to mitomycin C was titrated between two and five minutes according to each patient's risk for failure of filtration from excessive fibrosis. Four additional cases of prolonged hypotony-induced maculopathy occurred among these 52 cases (7.7%), all of which were in the lower risk groups that received two- or three-minute exposure to mitomycin C. Four procedures failed, requiring further glaucoma surgery, and all of the patients were in the higher risk groups, receiving three- to five-minute exposures. Our titration of the exposure time to mitomycin C may have reduced, but did not eliminate, the risk fo prolonged hypotony-induced maculopathy, and further study is needed to establish the optimum protocol for the use of this drug as an adjunct to trabeculectomy.

Adolescent↗
PubMed1993

Effects of ocular carteolol and timolol on plasma high-density lipoprotein cholesterol level.

Fifty-eight healthy, normolipidemic adult men participated in a prospective, masked, randomized crossover study designed to compare the effects of two topical nonselective beta-adrenergic antagonists, carteolol and timolol, on plasma high-density lipoprotein cholesterol levels. Two eight-week treatment periods were separated by an eight-week drug-free period. Carteolol 1.0% or timolol 0.5% was used, one drop twice daily, in both eyes without nasolacrimal occlusion. Fresh plasma was assayed for levels of total cholesterol, high-density lipoprotein cholesterol, low-density lipoprotein cholesterol, triglycerides, and apolipoproteins A-I and B-100. With indistinguishable effects on intraocular pressure, carteolol and timolol induced different (P = .013) decrements in high-density lipoprotein cholesterol levels. Carteolol treatment decreased high-density lipoprotein cholesterol levels by 3.3% (-0.04 mmol/l) and raised the ratio of total to high-density lipoprotein cholesterol levels by 4.0% (0.15 unit); timolol treatment decreased high-density lipoprotein cholesterol levels by 8.0% (-0.10 mmol/l) and raised the ratio of total to high-density lipoprotein cholesterol levels by 10.0% (0.37 unit). There was no differential drug effect on the other lipid variables measured. Ocular nonselective beta-adrenergic antagonist therapy can produce clinically relevant decrements in high-density lipoprotein cholesterol levels in healthy men.

Administration, Topical↗
PubMed1993

A comparison of two energy levels for noncontact transscleral neodymium-YAG cyclophotocoagulation.

In a prospective, clinical trial, 89 patients undergoing transscleral neodymium-YAG cyclophotocoagulation for intractable glaucoma were randomized to approximately 4 or 8 J of laser energy per application and followed up for an average of 1 year. The only statistically significant difference between the two groups was early anterior chamber reaction, which was more severe among those receiving 8 J. There was a trend toward better intraocular pressure control in the 8-J group, compared with the 4-J group, with 33 (75%) of 44 patients and 27 (60%) of 45 patients, respectively, requiring no further surgical intervention during the follow-up period. Among those patients not requiring further surgery, there was no significant difference in final visual acuities between the two groups. These findings suggest that within the range of 4 to 8 J, transscleral neodymium-YAG cyclophotocoagulation at the higher energy level may have some advantage with regard to intraocular pressure reduction without an increased risk of visual loss, compared with the same treatment at the lower energy level.

Adolescent↗
PubMed1993

Four-week safety and efficacy study of dorzolamide, a novel, active topical carbonic anhydrase inhibitor.

OBJECTIVE: To investigate the activity and local and systemic safety of the topical carbonic anhydrase inhibitor, dorzolamide hydrochloride. DESIGN: Four-week, double-masked, randomized, placebo-controlled, parallel, three-center study. SETTING: Referral centers. PATIENTS: Forty-eight patients with bilateral open angle glaucoma or ocular hypertension and intraocular pressure (IOP) greater than 22 mm Hg entered the study. Two of 28 patients receiving dorzolamide and two of 20 patients receiving placebo were withdrawn due to adverse experiences. INTERVENTION: Dorzolamide (2%) or placebo to each eye three times daily for 4 weeks. MAIN OUTCOME MEASURES: Diurnal IOP curves; ophthalmologic evaluations including corneal ultrasound pachymetry and endothelial cell count; and systemic evaluations including vital signs, blood chemistries, complete blood cell counts, urinalysis, electrocardiogram, and drug and carbonic anhydrase activity levels in red blood cells. RESULTS: Mean IOP at morning trough (8 AM) decreased from 27.1 mm Hg at baseline to 23.5 mm Hg on day 29 with dorzolamide (-13.3%) compared with a decrease from 27.1 mm Hg to 26.4 mm Hg with placebo (-2.3%). Peak activity occurred 2 hours after administration, with IOP decreasing from 26.8 mm Hg at baseline to 21.8 mm Hg on day 29 with dorzolamide (-18.4%) vs 26.1 mm Hg to 25.5 (-2.4%) with placebo. Mean corneal thickness was slightly increased for the dorzolamide-treated group compared with the placebo-treated group (0.009 mm vs 0.001 mm, respectively, P < .05) and changes in endothelial cell counts were similar (-24 cells/mm2 vs -27 cells/mm2, respectively, P > .25). Mean carbonic anhydrase isoenzyme II activity in red blood cells decreased to 21% of baseline in dorzolamide-treated patients. There were no clinically significant differences in ocular or laboratory parameters between the dorzolamide and placebo groups. CONCLUSIONS: Dorzolamide demonstrated significant IOP lowering activity over 4 weeks. It was well tolerated and there were no clinically significant changes in ocular or systemic safety parameters.

Administration, Topical↗
PubMed1992

The influence of exposure duration in transscleral Nd:YAG laser cyclophotocoagulation.

Transscleral cyclophotocoagulation was performed in human autopsy eyes by using three Nd:YAG lasers with different durations of exposure: a pulsed, contact laser with a duration of 0.75 millisecond and a range of one to ten pulses per burst (GLase 106, Sunrise Technologies, Fremont, California); a pulsed, noncontact laser with a duration of 20 milliseconds (Microruptor 2, Lasag Medical Lasers, Thun, Switzerland); and a continuous-wave, contact laser with durations of 700 and 2,000 milliseconds (Microruptor 3, Lasag Medical Lasers, Thun, Switzerland). Tissue responses were observed with a high-magnification videographic recording technique to analyze the immediate, real-time laser effects, and by light microscopy to characterize the laser-induced lesions further. Videographically, both pulsed lasers were noted to cause mild whitening of the pigment epithelium with frequent vaporization and explosive tissue disintegration. Histologically, the 0.75-millisecond pulse typically produced the most marked epithelial disruption, referred to as an explosive-like lesion, whereas the 20-millisecond pulse more often caused moderate tissue disruption with elevation of the epithelial layers in a blister-like lesion. In contrast, the continuous-wave laser was observed videographically to produce prominent tissue whitening and puckering, seen histologically as convolution of the epithelium and coagulation of stroma, which was called a shrinkage-like lesion. Our study suggests that exposure duration influences in vitro tissue response to transscleral Nd:YAG cyclophotocoagulation, although in vivo studies and clinical trials are needed to determine which tissue response is optimum for clinical use.

Ciliary Body↗
PubMed1992

Peripheral visual field testing in glaucoma by automated kinetic perimetry with the Humphrey Field Analyzer.

A Humphrey automated perimeter was used to measure the central 24 degrees of vision with static threshold targets and the peripheral field with two automatic kinetic stimuli in 100 eyes of 100 patients with glaucoma or a suspicion of glaucoma and to compare the additional information gained with the peripheral tests. The peripheral visual field supported the diagnosis made with central field testing in approximately one third of the eyes and added additional diagnostic information in another fourth of the cases. In 4% of patients a normal central field was associated with a glaucomatous peripheral defect. Virtually all peripheral defects were in the nasal quadrant, and the more sensitive isopter uncovered the vast majority of the defects.

Automation↗
PubMed1992

Inflammatory effects of continuous-wave neodymium: yttrium aluminum garnet laser cyclophotocoagulation.

The uveal inflammatory response was studied in 31 rabbits treated unilaterally with neodymium: yttrium aluminum garnet (Nd:YAG) cyclophotocoagulation. Fifteen applications of 3.5-J energy were delivered to the dorsal and ventral perilimbal sclera using a contact continuous-wave system. On days 1, 3, 8, and 15, the inflammatory effects were assessed. Peak levels of aqueous humor protein (11 +/- 3 mg/ml), prostaglandin E2 (8.9 +/- 3.0 ng/ml), leukocytes (205 +/- 113/microliters), and iris-ciliary body myeloperoxidase activity (6.32 +/- 1.4 U/mg protein) occurred on day 3 and rapidly decreased between days 7 and 15. Vitreal protein levels also peaked at day 3 but remained elevated through day 15 (3.8 +/- 1.3 mg/ml). By contrast, aqueous erythrocytes were most numerous (22,614 +/- 10,517/microliters) on day 8. Levels of leukotriene B4 remained low in all eyes at all intervals. Correlative histologic changes were ciliary coagulation necrosis, severe vascular congestion, and a predominantly mononuclear inflammatory cell infiltrate. These data suggest that Nd:YAG cyclophotocoagulation in rabbits induces a relatively mild inflammatory response that is associated with significant vascular compromise. Although these observations may not be analogous to the situation in the human eye, they may provide a model with which to compare the relative effects of different treatment parameters to help establish the optimum protocol.

Animals↗
PubMed1992

Inhibition of human subconjunctival fibroblast proliferation by immunotoxin.

The ability to target proliferating cells is important for agents used to modulate wound healing by decreasing the growth of fibroblasts. Proliferating cells are known to express increased numbers of transferrin receptors and have increased receptor turnover. 454A12 Mab-rRA, an immunotoxin containing anti-human transferrin receptor monoclonal antibody conjugated to recombinant ricin A chain, was shown to inhibit the proliferation of human subconjunctival fibroblasts in vitro. A dose-related reduction of cell counts was observed in proliferating cells. More than 90% inhibition was achieved with an immunotoxin concentration of 10 ng/ml per 20,000 cells plated. In contrast, confluent fibroblasts were markedly less sensitive to the immunotoxin at equivalent concentrations. Comparative experiments demonstrated that 5-fluorouracil has less specificity for proliferating cells, with significant death of confluent fibroblasts at high drug concentrations.

Antibodies, Monoclonal↗
PubMed1991

Transscleral Nd:YAG laser cyclophotocoagulation with a contact lens.

Transscleral Nd:YAG laser cyclophotocoagulation was performed on 100 consecutive patients. A contact lens designed specifically for this operation was used, and the results were compared to those of a previously reported series of 100 patients in which the same procedure was performed without the lens. The lens provided intraoperative advantages of eyelid separation, compression and blanching of the conjunctiva at the treatment site, and precise measurements for placement of the laser applications. Early postoperative advantages were reduced conjunctival burns and less hyperemia. However, the long-term results were comparable between the two series, with the exception of a higher incidence of phthisis when the lens was used. The thinning and blanching of the conjunctiva may increase the percentage of laser energy reaching the ciliary processes, which suggests a need for reduced energy levels when using the lens.

Adult↗
PubMed1991

In vitro videographic comparison of argon and Nd:YAG laser iridotomy.

We used an in vitro technique with high-magnification video recording to evaluate from the posterior side of the iris the immediate sequence of events during argon and Nd:YAG laser peripheral iridotomy. The observed effects differed strikingly. The argon laser caused a gradual mounding up of iris pigment epithelium with each successive energy application before final penetration. This effect was reduced but not eliminated with higher power levels. The Nd:YAG laser caused complete disruption and dispersal of the pigment epithelium with a single pulse of energy. Additionally, a multiple focal point configuration of the Nd:YAG laser was observed to produce a significantly larger iridotomy than a single focal point configuration for comparable energy settings. These observations may in part explain the observed clinical advantage of the Nd:YAG laser over the argon laser for creation of a patent iridotomy.

Humans↗
PubMed1991

A comparison of total and partial tenonectomy with trabeculectomy.

We compared the results of two methods of tenonectomy at the time of trabeculectomy. Of 49 eyes, 23 were randomly assigned to a partial tenonectomy and 26 to a total tenonectomy. There was no statistically significant difference in the success rate between the two surgical groups using an upper limit of intraocular pressure of either 18 or 21 mm Hg as the criterion for success. There was no difference in the need for postoperative medications or further surgical intervention between the two groups. Although certain advantages exist with each technique, these findings suggest that equivalent results can be anticipated with either a total or partial tenonectomy.

Female↗
PubMed1991

Correlation between intraocular pressure control and progressive glaucomatous damage in primary open-angle glaucoma.

Fifty-five patients with primary open-angle glaucoma and early glaucomatous damage who had medical therapy and laser trabeculoplasty were followed up for four to 11 years or until progressive glaucomatous damage was documented. Factors associated with the stability or progression of glaucoma were evaluated. Eyes with mean intraocular pressure higher than 21 mm Hg during the follow-up period uniformly had progressive glaucomatous changes. Conversely, eyes with mean intraocular pressure less than 17 mm Hg remained stable, and approximately half of the eyes with mean intraocular pressure between 17 and 21 mm Hg had progressive glaucomatous changes. Patients who remained stable were slightly younger than those with progressive glaucomatous changes (P less than .05), but initial optic nerve head appearance, initial visual field findings, number of medicines used, medical history, and patient gender or race were not statistically associated with stability or progression of the glaucoma. These findings reinforce the importance of intraocular pressure control in primary open-angle glaucoma and the need to identify other markers that help determine the proper level of intraocular pressure for individual patients.

Adult↗