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Biomedical subjects

M B Shields

Publications and source records attributed to M B Shields.

At least 19 recordsLinked to original sources
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↗
PubMed1979

Corneal edema in essential iris atrophy.

In a clinical study of the essential iris atrophies, corneal edema occurred in 49 of 90 patients, and a characteristic hammered-silver appearance of the posterior cornea was visible in 54 cases. Intraocular pressure in the eyes with corneal edema ranged from normal to extreme elevation with glaucomatous damage, and lowering the pressure relieved the corneal edema in many cases with penetrating keratoplasty being effective when other measures failed. Electron microscopy of two keratoplasty specimens revealed extremely few, distinctly abnormal cells lining a collagenous layer posterior to Descemet's membrane.

Adolescent↗
PubMed1978

The corneal endothelium and the spectrum of essential iris atrophy.

We found that the spectrum of essential iris atrophy (progressive essential iris atrophy, Chandler's syndrome, and the Cogan-Reese syndrome) began as a corneal endothelial degeneration, which, with ectopic endothelial membrane overgrowth over an open angle, followed by contraction of this membrane and further growth onto the iris, accounted for all aspects of the syndrome. The contractile membrane caused the synechiae, the glaucoma, the corectopia, the ectropion uveae, the occasional iris nodules, and the iris atrophy. Thus we found this disease to be primarily of the cornea, and only secondarily of the iris. The results of this study led us to propose a new designation for this spectrum: primary proliferative endothelial degeneration.

Adult↗
PubMed1978

The essential iris atrophies.

We studied 82 cases of essential iris atrophy. The findings support some traditional concepts of this complex spectrum of disorders, but conflict with others. Corneal abnormality appeared early and may be the primary disorder. A corneal endothelial disturbance was present in 55% of cases and corneal edema was present in 50%. Peripheral anterior synechiae occurred in all but one of the cases studied by gonioscopy. The pupil was distorted in 71% of the cases and was usually pulled in the direction of the most prominent synechia. The iris was stretched with stromal atrophy in 71%. Iris holes occurred in 33%. The degree of corneal and iris changes occurred as a spectrum of disorders. The prognosis for most patients with essential iris atrophy is slow progression with eventual involvement of vision because of corneal edema, secondary glaucoma, or both. Treatment of increased IOP was required in 77% of our cases, and 44% required surgical intervention.

Adolescent↗
PubMed1978

Effect of timolol therapy on outflow facility.

A 14-week course of timolol therapy in 38 eyes with open-angle glaucoma produced a statistically significant drop (6 mm Hg) in their mean intraocular pressure but had no effect on the mean coefficient of aqueous outflow. These data are compatible with those of Zimmerman et al. obtained after a single drop of treatment and suggest that timolol reduces intraocular pressure by inhibiting aqueous production.

Adult↗
PubMed1978

Thermal sclerostomy and posterior lip sclerectomy: a comparative study.

Eighty-two consecutive filtering procedures (47 thermal sclerostomies and 35 posterior lip sclerectomies), performed by senior staff and residents at the Duke University Eye Center between 1972-1976, were reviewed and compared. Operative and early postoperative complications were more common with the posterior lip sclerectomies. However, late postoperative complications were equal for the two groups, with cataracts occurring in approximately 30% of both categories. A final intraocular pressure of 20 mm Hg or less, with or without medication, was achieved in 66% of the thermal sclerostomies and 85.7% of the posterior lip sclerectomies. Residents did not perform as well as the senior staff when using thermal sclerostomy (60% vs. 70%, respectively), but performed equally well when using posterior lip sclerectomy (85.7% for both groups). In comparing black and white patients, the final intraocular pressures were the same in both groups.

Evaluation Studies as Topic↗
PubMed1977

An evaluation of anticoagulation in glaucoma therapy.

It has been suggested that glaucomatous field loss may progress on the basis of ischemia of the optic nerve head alone after the intraocular pressure has been controlled. Bishydroxycoumarin (Dicumarol) has been reported to be of benefit in such situations. A review of 551 consecutive glaucoma records did not support this theory. Apparent progression of field loss at intraocular pressures of 20 mm Hg or less was either due to artifacts in field testing or to a pressure that was still too high. A pilot study suggested that bishydroxycoumarin was of no benefit in these situations.

Adult↗
PubMed1977

The ultrastructure of human limbal collagen.

In human limbal tissue from four glaucomatous and four nonglaucomatous eyes, the average collagen fibril diameter in the inner and outer layers was 100.86 and 115.33 nm., respectively. In both layers the fibrils occupied an average of two thirds of the total area The possible implications of this observation in the trabeculectomy procedure are discussed.

Collagen↗
PubMed1977

Glaucoma in oculodermal melanocytosis.

Case reports of oculodermal melanocytosis (nevus of Ota) and ipsilateral glaucoma often have other ocular disorders which could account for the glaucoma. It has not been clearly shown that the oculodermal melanocytosis alone can cause secondary glaucoma. In the present case report, optic nerve head and visual field changes, suggestive of a long-standing unilateral elevation of intraocular pressure, occurred in an eye with oculodermal melanocytosis and no other apparent ocular disorder to account for the chronic glaucoma.

Adult↗
PubMed1976

Iris nodules in essential iris atrophy.

Seven cases are reported, believed to be the first in the literature, in which iris nodules are verified in the complete spectrum of essential iris atrophies. This feature appears late in the course of the disease as small yellow nodules that progressively increase in number and gradually become dark brown. The differential diagnosis of multiple iris nodules includes neurofibromatosis, melanomas, inflammatory nodules, and developmental anomalies such as iridocorneal dysgenesis.

Adult↗
PubMed1976

Urinary calculus during methazolamide therapy.

A 68-year-old white man with Paget's disease and open-angle glaucoma was treated with methazolamide, 50 to 100 mg three times daily. Ten months after the medication was initiated he developed ureteral colic and a calcium oxalate stone was surgically removed. Three months after the drug was reinstituted the patient passed three calcium phosphate stones. This suggested a casual relationship between methazolamide and stone formation, although renal calculi also complicate Paget's disease and acetazolamide had been administered briefly.

Acetazolamide↗