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Biomedical subjects

R Machemer

Publications and source records attributed to R Machemer.

At least 109 records · Page 6Linked to original sources
PubMed1983

Closed vitrectomy for severe retrolental fibroplasia in the infant.

Fifteen infants between the ages of 5 months and 2 years suffering from severe retrolental fibroplasia with near total and total retinal detachment and retrolental scar tissue formation were operated upon with closed vitrectomy. The surgical technique and the problems related to the smallness of the eye and the changes caused by RLF are discussed in detail. Seven retinas were reattached completely and one retina partially reattached. Vision was definitely improved, although the visual acuity was probably low.

Cataract Extraction↗
PubMed1982

The clearance of intravitreal triamcinolone acetonide.

Since high corticosteroid levels are important in achieving inhibition of intraocular cellular proliferation, we studied the clearance of an intravitreally injected slowly dissolving corticosteroid in the rabbit eye. Triamcinolone acetonide (0.5 mg) disappeared rapidly in eyes that underwent a combined vitrectomy and lensectomy (average, 6.5 days) and more slowly in eyes that underwent vitrectomy only (average, 16.8 days) compared with unoperated normal rabbit eyes (average, 41 days). The ophthalmoscopic disappearance of the white crystals correlated well with a sensitive colorimetric test for clearance of the corticosteroid. Direct observation is therefore an accurate method of assessing the absorption of the corticosteroid. If used therapeutically, this study suggests that more frequent injections of triamcinolone acetonide would be necessary in eyes that underwent vitrectomy, compared with normal eyes.

Animals↗
PubMed1982

A new approach to treating retinal detachment with macular hole.

Six consecutive cases of retinal detachment with macular hole were treated successfully by vitrectomy, partial gas-fluid exchange, and prone positioning of the patient for 12 hours. Macular coagulation and macular buckling were not necessary. In five cases the retina remained flat during follow-up periods ranging from one to 16 months. In one case a small detachment recurred 13 months after surgery. A renewed partial gas-fluid exchange resolved the problem. This new technique simplifies the treatment of such cases and macular function is preserved rather than destroyed. We believe than many detachments with macular holes are caused by vitreous traction.

Aged↗
PubMed1982

A transmission and scanning electron microscopic study of surgically excised preretinal membrane proliferations in diabetes mellitus.

Thirty preretinal membranes excised from diabetic patients during pars plana vitrectomy were examined by transmission electron microscopy, scanning electron microscopy, or both. All the specimens were still correctly orientated after removal from the eyes. All the specimens contained collagen in varying amounts and most had blood vessels with a thickened basal lamina and adjacent pericytes. Fenestrated capillaries were identified in only four of the 21 membranes containing blood vessels. A wide variety of cell types were scattered within the membranes, including polymorphonuclear leukocytes, lymphocytes, plasma cells, macrophages (containing melanin and hemosiderin), glial cells, retinal pigment epithelium, and cells of uncertain derivation. Scanning electron microscopy showed the retinal side of the membranes to be smoother than the vitreal side and disclosed preretinal cells on the vitreal side of the membranes, either as individual stellate cells or as a monolayer of flattened cells with microvilli. Membranes stripped from the surface of the retina had a smooth, generally acellular surface on the retinal side.

Diabetic Retinopathy↗
PubMed1982

Experimental subretinal hemorrhage in rabbits.

In order to simulate the hemorrhagic detachment stage of disciform macular degeneration, we injected fresh autologous blood into the subretinal space of albino rabbits and studied these hemorrhages clinically with the ophthalmoscope and by light and electron microscopy. One hour after injection, retinal changes were minimal and limited to occasional photoreceptor edema. At one day, there was marked damage of the photoreceptor cells characterized by edema and disintegration of the photoreceptors and pyknosis of the outer nuclear layer. Some photoreceptors had been pulled off the retina by contraction or movement of the blood clot, or both. By seven days, the photoreceptor cells were almost absent. Subretinal hemorrhage in rabbits led to irreversible retinal destruction within 24 hours. We think that the mechanism of the destruction of the overlying retina consists of a combination of a diffusion barrier by the clot, mechanical damage to the outer segments by contraction of the clot, and iron toxicity.

Animals↗
PubMed1981

Steam-sterilizable fundus contact lenses.

We designed small, lightweight, steam-sterilizable contact lenses for use during vitreous surgery. One lens is freely floating, and another lens has an infusion handle.

Contact Lenses↗
PubMed1981

Membrane peeler cutter. Automated vitreous scissors and hooked needle.

A new instrument, the membrane peeler cutter (MPC), has a solenoid-activated right-angled microscissors (diameter, 0.9 mm) that can be used as a hooked needle as well. It has been successfully used in more than 50 vitrectomy procedures that were complicated by intraocular membrane formation at the preretinal level. It has also been helpful in the cutting of pupillary membranes.

Humans↗
PubMed1981

A bipolar coaxial microprobe for safe transvitreal diathermy.

We present a new 22-gauge transvitreal bipolar diathermy microprobe. With the use of the coaxial principle, the current flows only at the probe's end surfaces. Because of its small size and end-on coagulation effect, and when used in conjunction with a low-frequency diathermy unit, the probe can be used safely on vessels lying directly on the retinal surface and close to the optic nerve head. We report three cases to demonstrate the usefulness of this instrument.

Adolescent↗
PubMed1981

Human massive periretinal proliferation. In vitro characteristics of cellular components.

The sources of cellular constituents of fibrous and cellophane membranes formed in massive periretinal proliferation have been unclear. We successfully obtained cellular outgrowths from abnormal vitreous specimens collected at surgery for massive periretinal proliferation in 13 patients, using standard culture techniques. By phase-contrast and ultrastructural morphological criteria, we identified four major cellular constituents: (1) macrophages present in all specimens: (2) pigmented epithelioid cells, present in a majority of specimens; (3) glial-like cells, present in a majority of specimens; and (4) fibroblastic cells, present in all specimens but much more prominent in grossly fibrous tissues. Our findings confirm published reports of pigmented epithelioid cells and glial-like cells in fixed surgical specimens and advance our understanding of the heterogeneity of pathologic cells active in producing this serious complication of retinal reattachment surgery.

Adolescent↗
PubMed1981

Histopathologic evaluation of adhesive properties of early lesions in diathermy and cryopexy.

We examined the histopathologic appearance of both cryopexy and diathermy lesions, ten to 60 minutes after application in the rabbit retina. Both lesions showed immediate subretinal fluid accumulation. Thus we would not substantiate the speculation that a diathermy lesion might have greater immediate adhesive strength than a cryotherapy lesion. This explains the clinical experience that retina tends to slip with either modality when trying to treat giant retinal tears.

Animals↗
PubMed1981

The lack of toxicity of intravitreally administered triamcinolone acetonide.

We gave one eye of each 21 rabbits an intravitreal injection of 1 mg of triamcinolone acetonide; the other eye received an injection of an equal volume of saline solution as a control. Results of slit-lamp examinations, ophthalmoscopy, intraocular pressure, electroretinography, and light electron microscopy all remained normal throughout the three-month course of the experiment, demonstrating the lack of ocular toxicity of triamcinolone acetonide in the rabbit.

Animals↗
PubMed1981

Glucocorticosteroid inhibition of intraocular proliferation after injury.

Perforating injuries were produced in the posterior segment of rabbit eyes. We studied the inhibitory effect of a slowly water-soluble corticosteroid, dexamethasone alcohol, on fibroblast growth. The treated group received a single intravitreal injection of 1 mg of the corticosteroid. The eyes were observed for four weeks. Transvitreal proliferation was significantly decreased and wound healing was delayed as compared to a control group. Inhibition of intraocular proliferation by high doses of intravitreally injected corticosteroid may be useful in the treatment of eyes with penetrating and perforating injuries.

Animals↗
PubMed1981

Diamond-coated all-purpose foreign-body forceps.

A new foreign-body forceps with diamond-coated jaws can grasp and hold intraocular foreign bodies of any shape and composition. A self-closing mechanism holds the material once grasped.

Eye Foreign Bodies↗
PubMed1981

Simulation of massive periretinal proliferation by autotransplantation of retinal pigment epithelial cells in rabbits.

We compared the clinical pattern, the histologic findings, and the electron microscopic appearance of lesions produced by the autotransplantation into rabbit vitreous of freshly harvested and tissue-cultured (250,000) retinal pigment epithelial cells. Both harvested and cultured cells formed intravitreal strands, traction detachments, and retinal puckers, resembling the most prominent features of massive periretinal proliferation in humans. Strands produced by both types of retinal pigment epithelial cells contained cells resembling myofibroblasts which may explain the contractability of the strand. The clinical, histologic, and electron microscopic observations were similar to those found in eyes injected with tissue-cultured skin fibroblasts.

Animals↗
PubMed1981

Retinotomy.

Retinotomy, performed during vitreous surgery, can be helpful in complicated cases of retinal detachment. The incisions are made with right-angled scissors in the peripheral retina. I have used this technique successfully in the treatment of a 21-year-old man who had a large retinal break with a shrunken edge, a 13-year-old boy with severe myopia and taut subretinal strands, and a 20-year-old man with an incarcerated retina.

Adolescent↗
PubMed1981

Retinal neovascularization after intravitreal fibroblast injection.

We have developed a new model of retinal neovascularization in the rabbit. After intravitreal autotransplantation of 250,000 tissue-cultured skin fibroblasts, we observed strand formation in the midvitreous cavity. These strands grew toward the vascularized part of the retina and attached to it. Once the attachment was established, retinal neovascularization began with growth of vessels along the fibrous strand. After three months, this retinal neovascularization regressed. The presence of immature capillaries was confirmed by electron microscopic examination. Of 43 eyes, 31 (72%) developed neovascularization.

Animals↗