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Biomedical subjects

M B Landers

Publications and source records attributed to M B Landers.

At least 19 recordsLinked to original sources
PubMed1995

Comparison of techniques for transscleral diode photocoagulation in the rabbit.

PURPOSE: To assess the optimum probe design and treatment parameters for transscleral diode laser retinopexy. METHODS: Transscleral diode photocoagulation was performed on the eyes of Dutch-belted rabbits using three different transscleral probes: a straight, 400-microns diameter probe; a prism-tipped 400-microns diameter probe; and a prism-tipped 900-microns diameter probe. RESULTS: Transscleral diode photocoagulation with all three probe types was an effective method of ablating the retina and creating chorioretinal adhesions. Both the burn diameter and the mean radiant output energy requirement increased as the burn duration and probe aperture diameter was increased. Explosive retinal holes were encountered in 12% of the burns created with the straight probe. The use of the prism-tipped probes significantly reduced the incidence of retinal holes to < 4% (P < 0.005). Histopathologically, all burns were grade III in intensity with severe choroidal injury. In many of the burns, there was histopathologic evidence of thermal injury to the inner sclera. The frequency of these inner scleral changes was reduced with a long burn duration (5 seconds). CONCLUSION: This study confirms that diode transscleral photocoagulation is a feasible method of thermal retinopexy. The use of the prism-tipped probes and long duration burns resulted in the fewest adverse reactions.

Animals↗
PubMed1994

Fibrinolytic-assisted removal of experimental subretinal hemorrhage within seven days reduces outer retinal degeneration.

PURPOSE: To better determine the surgical window for removing experimental subretinal hemorrhages in the cat model and to compare the histopathologic effect of such removal with the natural history of untreated subretinal hemorrhages. METHODS: Twenty-three large experimental subretinal hemorrhages were created with a neodymium:YAG laser focused through a performed retinal bleb in a cohort of cats. Fourteen subretinal hemorrhages were observed without treatment, six were removed at 7 days through a micropipette after injecting 10 micrograms/ml of human recombinant tissue plasminogen activator (rt-PA) into the subretinal space, and three were removed through an access retinotomy without the use of rt-PA. The tissues from these eyes were examined with light and electron microscopy 14 to 28 days after creation of the subretinal hemorrhages. RESULTS: Severe outer retinal degeneration was evident by day 14 in all of the untreated subretinal hemorrhages 3 disc diameters or greater in size. In contrast, the outer retinal architecture was better preserved in the eyes that underwent rt-PA-assisted removal of their subretinal hemorrhage that was 3 disc diameters or greater on day 7. In these eyes, mild abnormalities such as abnormally short and misaligned photoreceptor outer segments with vacuolization were present within the retina that was formerly located over the hemorrhage center. The eyes that underwent subretinal hemorrhage removal through an access retinotomy without rt-PA on day 7 had a low-lying retinal detachment and outer retinal degeneration. CONCLUSION: Removing experimental subretinal hemorrhages within 7 days of their occurrence with the assistance of rt-PA and an ultramicrosurgical approach may reduce outer retinal degeneration in the cat model.

Animals↗
PubMed1992

Intraocular fluid cultures after primary pars plana vitrectomy.

To determine what organisms enter the eye and remain in the eye after pars plana vitrectomy, vitreous cavity aspirates were cultured postoperatively. Two of 33 (6%) consecutive eyes undergoing primary pars plana vitrectomy had positive cultures. One sample grew a single colony of Staphylococcus epidermidis, the second grew two colonies of Acinetobacter lwoffi. Neither of these eyes developed endophthalmitis. This study demonstrates that bacteria enter the eye at a low rate during pars plana vitrectomy and that the eye on which a vitrectomy has been performed is capable of clearing a low inoculum of bacteria.

Acinetobacter↗
PubMed1992

Ultramicrosurgical removal of subretinal hemorrhage in cats.

Subretinal hemorrhages are associated with progressive degeneration of the outer retina and a corresponding poor visual prognosis. Mixed results have been reported in previous attempts to remove such subretinal hemorrhages. We developed an ultramicrosurgical system that used the control of a stereotactic micromanipulator to direct a micropipette tip through a small retinotomy into the subretinal space in three cat eyes. Low-dose recombinant tissue plasminogen activator was then introduced into the subretinal space around the subretinal hemorrhage via a controlled microinfusion system. The recombinant tissue plasminogen activator solution facilitated clot lysis and subsequent removal through the micropipette. Light- and electron-microscopic analysis of histopathologic specimens disclosed good preservation of retinal architecture in the three cat eyes in which experimental subretinal hemorrhages were removed. This was in contrast to the retinal degeneration observed in similar but untreated experimental subretinal hemorrhages.

Animals↗
PubMed1992

Treatment of retinopathy of prematurity with argon laser photocoagulation.

Fifteen eyes of nine infants were treated for retinopathy of prematurity by confluent photocoagulation of the avascular retina using an argon laser indirect ophthalmoscope. All treated eyes presented at or beyond threshold of stage 3 retinopathy of prematurity with "plus" disease. Three treated eyes had retinopathy of prematurity in zone I. Early complete regression of extraretinal proliferation was seen in 13 eyes. At 6 month's [corrected] minimum follow-up, 11 (73%) of the treated eyes demonstrated a favorable outcome, while four eyes (27%) progressed to an unfavorable outcome. No intraocular hemorrhages occurred during any laser treatment.

Cryosurgery↗
PubMed1992

Antifibrotic and uveitogenic properties of gamma interferon in the rabbit eye.

The feasibility of gamma (gamma)-interferon injection for the treatment of ocular fibrotic conditions was studied in rabbits using recombinant rabbit gamma-interferon and the cell-injection model of tractional detachment. A toxicity study revealed that intravitreal injection of greater than 10(4) units gamma-interferon consistently produced panuveitis. For tractional detachment, 250,000 rabbit dermal fibroblasts were injected intravitreally into 20 eyes; 1 day later, 5 of these eyes received intravitreal injections of 10(4) units gamma-interferon, another 5 were given 10(6) units, and the remaining 10 received balanced salt solution. Slit-lamp examination and fundus photography were performed at regular intervals for 21 days and were graded by a masked observer. The eyes were then enucleated and processed for histology. Doses of 10(4) units gamma-interferon significantly reduced the severity of detachments, but injections of 10(6) units induced panuveitis.

Animals↗
PubMed1992

Comparison of photocoagulation with the argon, krypton, and diode laser indirect ophthalmoscopes in rabbit eyes.

PURPOSE: The purpose of this study is to compare photocoagulation with the argon green, krypton red, and diode infrared laser indirect ophthalmoscopes in an experimental setting. METHODS: Photocoagulation was performed with each of the laser indirect ophthalmoscopes in a grid pattern within one sector of the same eye of 14 Dutch-belted rabbits. Treatment was performed either with or without scleral depression. Measurements of the retinal burn diameters were performed after hemisecting the globes, and the burns were examined with light microscopy. RESULTS: Variation in burn intensity and diameter (10% to 28%) was common with all 3 laser indirect ophthalmoscopes. Five times more output energy was required to make equivalent burns with the diode laser indirect ophthalmoscope than with the argon or krypton laser indirect ophthalmoscopes. Choriovitreal hemorrhages only occurred during scleral depression. Histopathologically, the argon green laser indirect ophthalmoscope burns spared the choroid and inner sclera, while the intense krypton and diode burns had full-thickness choroidal involvement and even thermal injury to the inner sclera. Scleral depression reduced the mean energy required to create equivalent burns with all three laser indirect ophthalmoscopes. There was a 10% to 40% reduction in the mean retinal burn diameter with scleral depression (argon green, P < 0.0005; krypton red, P < 0.0005; and diode, P < 0.025). CONCLUSION: Photocoagulation with the argon green, krypton red, or diode infrared laser indirect ophthalmoscopes is a safe and effective method of retinal ablation. Decreasing the posterior nodal distance of the eye with scleral depression will produce a smaller spot on the retina with the laser indirect ophthalmoscope.

Animals↗
PubMed1992

An experimental model of ectropion uveae and iris neovascularization in the cat.

Neovascularization of the iris (NVI) is one of the most frequently studied intraocular vascular proliferations in animal models. Ectropion uveae has not been a consistent finding in these studies. In this study, a surgical model of ectropion uveae and iris neovascularization was developed that involved lensectomy, vitrectomy, bipolar cautery and transection of all three principal branch veins in the cat eye. Twelve of 14 eyes that received this procedure developed postoperative retinal detachments with a clinical picture of hemorrhagic retinopathy. These eyes progressed to a clinical picture of NVI within 1-7 wk. Eight eyes developed ectropion uveae for as much as 300 degrees. At the light microscopic level, a fibrovascular membrane was apparent on the anterior iris stroma in 9 of 14 eyes and further involved the angle in six eyes.

Animals↗
PubMed1991

A new inexpensive pump for vitreoretinal surgery.

An inexpensive and reliable fluid-gas exchange system has been developed for vitreous surgery. The system relies on a fish-tank air pump and was compared with the Grieshaber Air System in several laboratory and operating room situations. No significant differences were found between the two systems. Details of the Davis Ocular Air Pump are provided along with a cost analysis.

Drainage↗
PubMed1991

Fibrin directs early retinal damage after experimental subretinal hemorrhage.

Subretinal blood within the macula may cause visual loss in a number of macular diseases. The clinical and histopathologic effects of experimental subretinal hemorrhage were evaluated in the cat. Subretinal hemorrhages were produced by creating a focal neurosensory retinal detachment with micropipette techniques, then inserting a needle tip transsclerally to allow choroidal blood to fill the bleb. Experimental lesions were examined clinically and with light and electron microscopy during a 14-day postoperative period. Initial observations included clot organization with retraction of fibrin strands. In six of nine clots more than 1 hour old, fibrin was associated with tearing of sheets of photoreceptor inner and outer segments. Later degeneration progressed to involve all retinal layers overlying the densest areas of fibrin in the clots. Hemorrhages into subretinal blebs containing tissue plasminogen activator did not form fibrin strands or cause photoreceptor tearing. These findings highlight the potential for improved retinal survival if organized subretinal clot can be eliminated soon after formation.

Animals↗
PubMed1991

Evaluation of a commercial recombinant tissue-type plasminogen activator preparation in the subretinal space of the cat.

To explore the feasibility of using human recombinant tissue-type plasminogen activator in the management of subretinal hemorrhage, we examined the toxic effects of a commercial preparation of human recombinant tissue-type plasminogen activator in the subretinal space of the holangiotic retina of the cat. Various concentrations of human recombinant tissue-type plasminogen activator and controls were infused into the subretinal space with a glass micropipette (40- to 60-microns tip) to form a retinal bleb. Concentrations from 2.5 mg/L to 200 mg/L were well tolerated without ultrastructural toxic effects, while 1000 mg/L of human recombinant tissue-type plasminogen activator caused severe, irreversible toxic effects to the photoreceptor-retinal pigment epithelium complex. This toxic effect appeared to be due to the carrier vehicle rather than the human recombinant tissue-type plasminogen activator protein itself. Our results demonstrate that commercially prepared human recombinant tissue-type plasminogen activator can be safely used in the subretinal space of the cat with the range necessary for fibrinolysis.

Animals↗
PubMed1990

Reproducible estimation of retinal vessel width by computerized microdensitometry.

An objective method for reliably estimating the width of retinal vessels is presented. A computerized microdensitometer scans film negatives of fundus photographs and reconstructs black and white images of the fundus on a visual display terminal. After this initial scan, a desired region of a retinal vessel is selected with moveable cursors, and a cross-sectional density profile through the vessel is plotted. Vessel width is determined by the half-height width of the profile of the minimum (least transmitting) and average background film densities. Measurement sites can be accurately reproduced on different negatives by landmark mapping. A series of ten fundus photographs were taken of three healthy human eyes, and the width of the superior temporal vein was measured in two places on alle negatives. The coefficient of variation of the six sets ranged from 1.2 and 3.4% with an average of 2.2%.

Analysis of Variance↗