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Biomedical subjects

M W Johnson

Publications and source records attributed to M W Johnson.

At least 73 records · Page 4Linked to original sources
PubMed1996

Thrombin in the management of full thickness macular holes.

PURPOSE: As thrombin is a known stimulator of retinal glial and pigment epithelial cells, we performed a pilot study to evaluate the use of thrombin as adjunctive mitogen therapy in vitreous surgery for full-thickness macular holes. METHODS: Macular hole surgery was performed on 25 eyes of 24 consecutive patients with stage II, III, or IV macular holes. After removal of the posterior hyaloid, peeling of epiretinal membranes, and fluid-air exchange, 0.05 mL or 0.1 mL of thrombin (100 units/ mL) was placed over the macular hole. After infusion of a gas tamponade, the patient's head was kept in a supine position for 1 hour, and then was kept in a prone position for approximately 2 weeks. RESULTS: Closure of the macular hole with one procedure was achieved in 80% of the eyes. Sixty-five percent of the eyes with a closed macular hole achieved a visual acuity of 20/40 or better. Postoperative inflammation was present in all eyes, and a small hypopyon developed in 28% of the eyes. CONCLUSION: Thrombin therapy failed to markedly increase the success rate of macular hole surgery.

Aged↗
PubMed1996

Selective use of veno-venous bypass in orthotopic liver transplantation.

The use of veno-venous bypass (VVB) during the anhepatic phase of orthotopic liver transplantation (OLT) remains controversial. We employ VVB on a selective basis: patients who tolerate intra-operative supra-hepatic IVC test cross-clamping undergo OLT without VVB while patients who, despite maximal volume resuscitation, develop hemodynamic instability during test cross-clamping, undergo OLT with VVB. The records of 150 adult orthotopic liver allograft recipients transplanted at the Massachusetts General Hospital from January 1984 to December 1994 were reviewed to identify any potential adverse affects on peri-operative, 6 months, 1 year outcomes in recipients foregoing VVB during liver transplantation. Thirty-eight patients (25%) underwent OLT without VVB with actuarial survivals of 78.4% and 69% at 6 months and 1 year. 112 patients (75%) underwent OLT with VVB with actuarial survivals at 6 months and 1 year of 73% and 72%. Demographic data, UNOS status, and diagnoses were similar in each group. There were no significant differences in intra-operative PRBC requirements; lengths of hospital stay; retransplantation rates; or 30 day, 6 months and 1 year survivals between these two groups. There was no significant difference in renal function as determined by preoperative, peak post-operative, discharge serum creatinine levels, or number of patients requiring HD between these two groups. There were two major complications (1.8%) possibly resulting from VVB. In conclusion, patients who tolerate IVC test cross-clamping can safely undergo orthotopic liver transplantation without veno-venous bypass. In our experience, there were no significant differences in peri-operative parameters, post-operative renal function, or short-term survival when compared to patients who, due to hemodynamic instability during IVC cross-clamping, underwent OLT with VVB. Given the potential complications associated with VVB, we feel that in those patients who tolerate intra-operative IVC cross-clamping, it is better to proceed without the use of VVB.

Actuarial Analysis↗
PubMed1995

Laser photocoagulation of the choroid through experimental subretinal hemorrhage.

OBJECTIVE: To study the differential abilities of diode infrared, krypton red, and argon blue-green laser energies to penetrate experimental subretinal hemorrhage and coagulate the underlying choroid. METHODS: Autologous, heparinized whole blood was injected beneath the neurosensory retina of pigmented rabbit eyes. After 30 to 60 minutes, confluent patches of moderate or severe diode, krypton, or argon laser burns were applied to adjacent healthy retina and continued into the region of the subretinal hematoma without varying the power setting or focal plane. Histopathologic evaluation of early lesions was performed in a masked fashion, and subretinal hemorrhage thickness was determined with computer-assisted image capture and analysis. RESULTS: Retina overlying treated subretinal hemorrhage showed no ophthalmoscopically visible signs of photocoagulation with diode energy, a faint gray reaction with krypton energy, and an intense white reaction with argon energy. Histopathologic analysis revealed photocoagulative inner choroidal damage beneath a mean (+/- SD) maximum blood thickness of 0.56 +/- 0.14 mm with severe diode burns, 0.42 +/- 0.09 mm with severe krypton burns, and 0.22 +/- 0.04 mm with severe argon burns. CONCLUSIONS: These data demonstrate that laser penetration of subretinal blood increases with longer wavelengths in vivo. Diode infrared laser energy is capable of penetrating subretinal blood to coagulate the choroid in the absence of ophthalmoscopically visible changes in the overlying retina.

Animals↗
PubMed1995

A comparison of surface doses for two immobilizing systems.

To achieve accurate and reproducible treatments, many types of immobilizing systems have been used. Two of these systems: Alpha Cradle and VacFix, conform around the patient to improve day-to-day treatment repositioning. The Alpha Cradle system has been in clinical use for several years. The system involves two polyurethane chemicals which upon mixing in a latex bag will expand and harden around the patient. The second system (VacFix) uses a 0.15 mm thick plastic bag loosely filled with 1 mm polysterol spheres. The patient lays on the bag in the treatment position and the air is evacuated from the bag. This system retains its shape for the entire treatment and can be re-used. In some patient set-ups, it is possible that the beam is modified as it passes through these devices, causing a potential change in the target dose and an increase in the patient surface dose. CT scans of the Alpha Cradle and VacFix systems were performed and relative densities were calculated and compared to air. Material densities and surface dose data for a Cobalt-60 teletherapy unit and a dual photon linear accelerator are presented.

Cobalt Radioisotopes↗
PubMed1995

Vitrectomy for proliferative diabetic retinopathy with severe equatorial fibrovascular proliferation.

PURPOSE: We studied the surgical treatment and visual outcome in a consecutive series of eyes with an unusual syndrome of diabetic retinopathy and severe peripheral fibrovascular proliferation involving the equatorial and pre-equatorial fundus. METHODS: In a retrospective study of 276 eyes (245 patients) that underwent pars plana vitrectomy for diabetic retinopathy between November 1988 and February 1993, nine eyes of eight patients (3.3% of eyes and 3.3% of patients) had severe equatorial fibrovascular proliferation. The condition occurred primarily in previously unoperated-on eyes (except for panretinal photocoagulation) and resulted in peripheral traction or traction-rhegmatogenous retinal detachment (six eyes), severe vitreous hemorrhage (two eyes), and severe hypotony (one eye). Relief of traction from peripheral fibrovascular membranes was obtained with an encircling scleral buckle (nine eyes) and limited delamination and segmentation (five eyes) or relaxing retinectomy (two eyes). Lensectomy was required for adequate membrane dissection in three eyes. RESULTS: After follow-up of six to 52 months (mean, 20.4 months), the visual acuity was 20/200 or better in seven of nine eyes, with complete retinal attachment in seven of nine eyes and postequatorial attachment in all eyes (100%). Poor outcome resulted from a persistent response resembling Coats' disease in one eye and preexistent long-standing retinal detachment in one eye. CONCLUSIONS: Vitrectomy for severe equatorial fibrovascular proliferation differs from conventional approaches to diabetic retinopathy in that relief of retinal traction must be attained by scleral buckling and adequate dissection of peripheral fibrovascular tissue. In advanced cases, lensectomy and relaxing retinotomy may be required.

Adult↗
PubMed1995

Fluorescein labeling of tissue plasminogen activator for subretinal thrombolysis.

PURPOSE: To assess a technique that facilitated the use of tissue plasminogen activator in the dissolution and evacuation of subretinal blood. METHODS: Fluorescein dye was added to the tissue plasminogen activator solution before subretinal injection. RESULTS: Labeling tissue plasminogen activator solution with fluorescein made the solution easily visible, enhancing the ability of the surgeon to assess clot lavage, detect reflux into the vitreous cavity, and judge the extent of clot dissolution. CONCLUSIONS: Adding fluorescein dye to tissue plasminogen activator solution is simple and gives the surgeon added control of clot lysis.

Fibrinolytic Agents↗
PubMed1995

Acute posterior ophthalmomyiasis interna treated with photocoagulation.

PURPOSE/METHODS: We studied a patient with subretinal myiasis with pain and rapidly progressive visual loss and found that prompt photocoagulation resulted in marked visual improvement. A 16-year-old boy had subconjunctival hemorrhage and periocular pain associated with progressive visual loss of 6/200 over a four-day period. RESULTS/CONCLUSIONS: A live maggot found crawling in the subretinal space was promptly photocoagulated with an argon green laser. Within one month, the visual acuity improved to 20/50. Laser treatment of a subretinal larva does not generally induce marked inflammation and often results in good visual recovery.

Adolescent↗
PubMed1994

Reversal of resistance to Bacillus thuringiensis in Plutella xylostella.

Continued success of the most widely used biopesticide, Bacillus thuringiensis, is threatened by development of resistance in pests. Experiments with Plutella xylostella (diamondback moth), the first insect with field populations resistant to B. thuringiensis, revealed factors that promote reversal of resistance. In strains of P. xylostella with 25- to 2800-fold resistance to B. thuringiensis compared with unselected strains, reversal of resistance occurred when exposure to B. thuringiensis was stopped for many generations. Reversal of resistance was associated with restoration of binding of B. thuringiensis toxin CryIA(c) to brush-border membrane vesicles and with increased biotic fitness. Compared with susceptible colonies, revertant colonies had a higher proportion of extremely resistant individuals. Revertant colonies responded rapidly to reselection for resistance. Understanding reversal of resistance will help to design strategies for extending the usefulness of this environmentally benign insecticide.

Animals↗
PubMed1994

Idiopathic recurrent branch retinal arterial occlusion. Natural history and laboratory evaluation.

PURPOSE: To investigate the long-term visual and systemic prognosis of patients with idiopathic recurrent branch retinal artery occlusions, and to test recent hypotheses regarding possible causes of this syndrome. METHODS: The authors retrospectively reviewed the medical and photographic records of 16 eligible patients. Each of 15 living patients was interviewed by one of the authors, then underwent follow-up ophthalmic examination, formal visual field testing, and a battery of clinical laboratory tests. RESULTS: Over a mean follow-up of 9 years, only three eyes (9%) lost visual acuity from foveal ischemia, although nine eyes (28%) had central and/or extensive peripheral visual field loss at final examination. Ocular neovascular complications developed in eight eyes (25%). Eight patients (50%) had associated vestibuloauditory and/or transient sensorimotor symptoms, but serious permanent neurologic deficits or recurrent systemic thromboembolic events did not develop. Although most patients had one or more vaso-occlusive risk factors, extensive laboratory testing failed to define the etiology of the arterial occlusions. CONCLUSIONS: On long-term follow-up, the visual, neurologic, and systemic prognosis for most patients with idiopathic recurrent branch retinal arterial occlusions remains favorable. Although it is probable that such patients are etiologically heterogeneous, the authors theorize that many have mild or partial manifestations of the microangiopathic syndrome of encephalopathy, hearing loss, and retinal arteriolar occlusions.

Adult↗
PubMed1994

Recommendations for measurement of tray and wedge factors for high energy photons.

Transmission factors for beam modifers such as wedges and blocking trays in dosimetry calculations are very common, but various methods have been used in measuring these factors. A systematic study to measure these factors as a function of field size and point of measurement was carried out. The beam modifiers were a blocking tray and the standard wedges supplied with a cobalt-60 unit and a medical electron accelerator (6- and 18-MV x rays). Several points of measurement were selected, using several depths: dmax, TG-21 calibration depth, 10 cm (wedge angle defining depth, ICRU), 15 cm and in-air (miniphantom), and various field sizes. The results show a small field size dependence in these transmission factors with more dependence found in the point of measurement.

Air↗
PubMed1994

Cross-Resistance to Bacillus thuringiensis Toxin CryIF in the Diamondback Moth (Plutella xylostella).

Selection with Bacillus thuringiensis subsp. kurstaki, which contains CryIA and CryII toxins, caused a >200-fold cross-resistance to CryIF toxin from B. thuringiensis subsp. aizawai in the diamondback moth, Plutella xylostella. CryIE was not toxic, but CryIB was highly toxic to both selected and unselected larvae. The results show that extremely high levels of cross-resistance can be conferred across classes of CryI toxins of B. thuringiensis.

Journal Article↗
PubMed1993

Resistance to Toxins from Bacillus thuringiensis subsp. kurstaki Causes Minimal Cross-Resistance to B. thuringiensis subsp. aizawai in the Diamondback Moth (Lepidoptera: Plutellidae).

Repeated exposure in the field followed by laboratory selection produced 1,800- to >6,800-fold resistance to formulations of Bacillus thuringiensis subsp. kurstaki in larvae of the diamondback moth, Plutella xylostella. Four toxins from B. thuringiensis subsp. kurstaki [CryIA(a), CryIA(b), CryIA(c), and CryIIA] caused significantly less mortality in resistant larvae than in susceptible larvae. Resistance to B. thuringiensis subsp. kurstaki formulations and toxins did not affect the response to CryIC toxin from B. thuringiensis subsp. aizawai. Larvae resistant to B. thuringiensis subsp. kurstaki showed threefold cross-resistance to formulations of B. thuringiensis subsp. aizawai containing CryIC and CryIA toxins. This minimal cross-resistance may be caused by resistance to CryIA toxins shared by B. thuringiensis subsp. kurstaki and B. thuringiensis subsp. aizawai.

Journal Article↗
PubMed1992

Morbidity and mortality in pups from pet stores and private sources: 968 cases (1987-1988).

Morbidity (greater than or equal to 1 disease condition) for pups sold from 3 pet stores from January 1987 through December 1988 ranged from 54 to 68%. In 1 store, morbidity was higher for store pups, compared with pups originating from private parties, for such disease conditions as "kennel cough," diarrhea, and several species of gastrointestinal parasites. In-store mortality ranged from 5 to 9.5% of pups arriving for sale.

Animals↗
PubMed1992

Tissue plasminogen activator thrombolysis during surgical evacuation of experimental subretinal hemorrhage.

To assess the role for intraoperative thrombolysis during surgical evacuation of massive subretinal hemorrhage, the authors studied the ability of tissue plasminogen activator (tPA) to facilitate removal of an experimental subretinal blood clot through a small drainage retinotomy. In rabbit eyes, a single subretinal injection of tissue plasminogen activator in concentrations of up to 250 micrograms/ml failed to produce significant (greater than 50%) clot dissolution during a 3-hour period. However, repetitive subretinal lavage and aspiration with tPA (50 micrograms/ml) resulted in progressive intraoperative clot dissolution in rabbits and allowed complete evacuation of blood through a small drainage retinotomy in 6 (100%) of 6 cat eyes. Repetitive vigorous subretinal irrigation with saline solution had no discernible effect on clot size in rabbit eyes. Histopathologic examination of cat eyes following tPA-assisted surgical evacuation of subretinal blood showed preservation of the outer retina in 2 eyes and severe atrophy of the outer retina in 4 eyes.

Animals↗
PubMed1992

Photon beam attenuation for a patient support assembly during arc therapy for a medical linear accelerator.

Arc therapy is one of the treatment techniques for small, centrally located deep-seated tumors. However, care must be taken to remove any components that would interfere with the beam as the gantry rotates around the patient. One such component that may interfere with the beam is the patient support assembly (PSA) or treatment table. Beam attenuation factors due to the presence of the couch side-rails and the centerspine bar of the PSA are presented for both 6 MV and 18 MV photon beams of a Clinac 1800 during a 360 degrees rotation. Dose perturbations arising from these obstructions are displayed using an Alderson Rando phantom. A method is described to calculate the start and stop angles for the largest unobstructed arc for a given field size (FS), centerspine bar to the isocenter height (H), centerspine bar width (W), and SAD. As an illustration, for an SAD of 100 cm and a W of 4 cm, the start and stop angles for arc therapy with a FS of 10 x 10 cm2 and an H of 12.7 cm would be 29 degrees and 331 degrees.

Humans↗
PubMed1992

Complete blood count indices in colorectal carcinoma.

Since carcinomas of the colon or rectum are associated with blood loss, we wondered if complete blood count data were suggestive of iron deficiency in cases of colorectal carcinoma. The mean corpuscular volume and especially the red blood cell distribution width are thought to be more sensitive to early iron deficiency than the hemoglobin value. These values were recorded from a series of 98 consecutive cases of colorectal carcinoma and compared with an age-matched control group consisting of patients with no history or clinical suspicion of malignant neoplasm. We found that the hemoglobin level, mean corpuscular volume, and red blood cell distribution width in patients with colorectal carcinoma do not generally show evidence of iron deficiency. The addition of the mean corpuscular volume and red blood cell distribution width to the hemoglobin value does not seem to increase the sensitivity of the complete blood count in the detection or clinical suspicion of colorectal carcinoma.

Blood Cell Count↗
PubMed1992

Pars plana vitrectomy and direct diathermy for complications of multiple retinal angiomas.

A 16-year-old female had multiple retinal capillary angiomas, complicated by marked retinal and optic disc neovascularization, preretinal membranes, and retinal detachment in her right eye. Pars plana lensectomy, vitrectomy, fluid/gas exchange, direct transvitreal diathermy of the angiomas, endolaser scatter photocoagulation, and scleral buckling resulted in retinal reattachment and regression of the neovascularization. Although additional surgery was necessary for recurrent tractional retinal detachment, long-term retinal reattachment and stable vision was achieved following obliteration of all angiomas.

Adolescent↗