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Biomedical subjects

R Machemer

Publications and source records attributed to R Machemer.

At least 91 records · Page 5Linked to original sources
PubMed1985

Recurrent proliferations in macular pucker, diabetic retinopathy, and retrolental fibroplasialike disease after vitrectomy.

The clinical and ultrastructural details of recurrent epiretinal and transvitreal membranes from patients with macular pucker, diabetes mellitus, and a retrolental fibroplasialike disease are presented. The membranes were characterized ultrastructurally by the presence of reactive glia and moderate amounts of collagen in the extracellular matrix. Many of the cells in the recurrent membranes showed myofibroblastlike differentiation. Recurrence of transvitreal membranes in a previously vitrectomized eye may be explained by spontaneous detachment of contracting epiretinal membranes.

Adult↗
PubMed1985

The use of silicone oil following failed vitrectomy for retinal detachment with advanced proliferative vitreoretinopathy.

We have used silicone oil injection in a consecutive series of 44 patients with retinal detachment and advanced proliferative vitreoretinopathy, all of whom had previously failed to reattach with vitrectomy, membrane peeling, and scleral buckling. After a minimal follow-up period of six months, complete anatomic retinal reattachment posterior to the encircling scleral buckle was obtained in 64% of these eyes, and visual acuity of 5/200 or better was achieved in 57% of the anatomically successful cases. Silicone oil removal was performed in 69% of the anatomically and visually successful eyes without recurrent retinal detachment.

Adolescent↗
PubMed1985

Description and pathogenesis of late stages of retinopathy of prematurity.

The retinal and vitreous changes seen in retinopathy of prematurity (ROP) can be explained by proliferation and contraction of tissue originating in the shunt area. Avascular retina is stretchable, and therefore much of it stays attached, while vascular retina is nonstretchable and detaches. When the shunt area forms a circular ring, one of three distinct patterns of retinal detachment develops, according to whether the shunt area is anterior, equatorial, or posterior in location. The detachments of ROP are, typically, traction detachments.

Cell Division↗
PubMed1985

Long-term diabetic vitrectomy results. Report of 10 year follow-up.

Ten year follow-up examinations were obtained on 72 cases having pars plana vitrectomies for diabetic retinopathy complications from 1970 to 1973. Forty-two percent of the cases maintained 6/60 or better visual acuities through the tenth year. The visual results were quite stable, with 53% of the cases having the same or better visual acuities at ten years compared with six months. Neovascular glaucoma developed in 11 eyes, usually during the first six months, and open-angle glaucoma developed in 16 eyes, usually after the five-year follow-up examination. Both types of glaucoma occurred almost exclusively in aphakic eyes. Cataracts developed in 75% of retained clear lenses. The vitreous cavities remained clear in 67% of the eyes, and the maculas were attached in 65% of the eyes 10 years following vitrectomy. Fundus neovascularization did not recur.

Cataract Extraction↗
PubMed1984

The importance of fluid absorption, traction, intraocular currents, and chorioretinal scars in the therapy of rhegmatogenous retinal detachments. XLI Edward Jackson memorial lecture.

The combination of traction on the retina and of intraocular currents in the presence of a retinal hole is the cause of rhegmatogenous retinal detachment. The strong suction forces of the pigment epithelium and choroid counteract such a development. Chorioretinal scars serve as a seal against currents. Eliminating the effects of traction and of intraocular currents and making use of the absorption forces of the pigment epithelium and choroid are the primary aims in successfully treating rhegmatogenous retinal detachment. Direct closure of the retinal hole is not always necessary.

Adult↗
PubMed1984

Subretinal proliferation.

Subretinal proliferation is often present but less often identified as a component of proliferative vitreoretinopathy. Subretinal membranes form from retinal pigment epithelial cells and retinal glial cells that migrate into the subretinal space of eyes with long-standing retinal detachments. The membranes grow as sheets but break up into bands as the cells contract, with the stronger parts remaining intact.

Adolescent↗
PubMed1984

Gas-mediated vitreous compression: an experimental alternative to mechanized vitrectomy.

We have developed a simple technique in rabbit and baboon eyes that utilizes intravitreally injected perfluoropropane gas, which expands slowly to efficiently compress and displace nearly completely the vitreous body. There is cataract formation after extended contact of the gas bubble with the lens. However, it is rapidly reversible by reducing the duration of lens contact (gas-fluid exchange) and by using young animals. No long-term alterations in intraocular pressure or retinal function were observed, as determined by electroretinography, during the 4-month test period. Gross examination and scanning electron microscopy revealed that the vitreous cavity, shortly after full expansion of the gas bubble, was practically free of collagen. The vitreous body had been detached from most of the retina and compressed into a collagenous strand between the optic nerve head and lens in the rabbit eyes, and there was also a dense collagen accumulation on the inferior retinal surface and anterior vitreous base in the rabbits and the baboon. Large areas of the retina and medullary wings were stripped of overlying collagen. By the end of 4 months, the compressed vitreous body had expanded to become an irregular structure that remained separated from the retina in areas of previous detachment. Mechanized vitrectomy is a difficult procedure often needed in experimental work. We believe that the vitreous compression and gas-fluid exchange technique is a valid alterative to a mechanical approach. We also believe that we have a model that simulates the human situation of posterior vitreous detachment and vitreous syneresis.

Animals↗
PubMed1984

Vitreous hemorrhage nontoxic to retina as a stimulator of glial and fibrous proliferation.

To test the belief that blood is toxic to the retina, we developed an experimental model of vitreous hemorrhage in rabbits by injecting various amounts of autologous, uncoagulated , whole blood into their vitreous cavities, with the vitreous humor either intact or previously compressed by an expanding perfluoropropane gas bubble. Blood in the eyes with compressed vitreous cleared in half the time required for the same volume injected into eyes with intact vitreous (75.6 days vs 39.2 days). Large volumes of intravitreal blood (0.25 to 0.50 ml) were never toxic to the retina by ganzfeld and bright-flash electroretinography throughout a four-month observation period. The results indicated that massive vitreous hemorrhage has a dense filtering effect that can extinguish the ganzfeld but not the bright-flash electroretinogram. Blood caused moderate hemoglobin staining of the retina, without significant iron staining (confirmed by X-ray microprobe analysis). Hemoglobin residues accumulated within cells of the inner retina, especially Müller's cells. Blood clot retraction after the injection of large volumes of fresh blood (1 ml) produced traction retinal detachment, hole formation, and subretinal accumulation of blood. This correlated with a complete and persistent extinction of the ganzfeld and bright-flash electroretinograms throughout the four-month observation period. A striking finding was that almost all eyes developed glial membranes on the peripheral retina. Fibrous membranes, causing local retinal contraction, were found over the medullary wings and optic disk in eyes with vitreous compression.

Animals↗
PubMed1984

Spontaneous reattachment of the retina despite proliferative vitreoretinopathy.

In six cases of spontaneous retinal reattachment despite severe proliferative vitreoretinopathy, the retina was initially attached after a buckling procedure or vitreous surgery for proliferative vitreoretinopathy. However, each retina suddenly detached several weeks later. Surprisingly, the retinas settled slowly during the following weeks without further treatment. One case was marked by repeated episodes of detachment and reattachment. In none of the cases could an open retinal break be detected. In certain cases of proliferative vitreoretinopathy in which no open break is apparent and the detachment appears to be tractional, an observation period of several weeks may allow the retina to reattach spontaneously without further surgery.

Adult↗
PubMed1984

Rubeosis iridis: preoperative iris fluorescein angiography and periocular steroids.

To study the risk of developing rubeosis iridis following vitrectomy, the use of preoperative iris fluorescein angiography was prospectively investigated on patients with diabetes mellitus, without any clinically detectable iris or angle neovascularization. With increasing severity of fluorescein leakage, the risk of iris neovascularization with or without glaucoma, six months after vitreous surgery, is significantly increased. It was also determined whether postoperative steroid therapy (periocular triamcinolone acetonide and topical prednisolone phosphate) reduces the risk of developing iris neovascularization after vitrectomy. Controlled and treated patient eyes did not differ significantly in the degree of rubeosis. However, neovascular glaucoma statistically occurred more frequently in the nonsteroid group.

Diabetic Retinopathy↗
PubMed1983

Postoperative emesis in vitreoretinal surgical patients.

We studied, prospectively, the incidence of emesis in 64 consecutive patients undergoing retinal and vitreous surgery performed either under local or general anesthesia. Of these patients 19% had at least one episode of emesis within 12 h after surgery. 30% of the patients who underwent general anesthesia had emesis, whereas only 4% of the patients with local anesthesia vomited. These results were statistically significant. Unless special attention is paid to minimize emesis, we recommend the use of local anesthesia, especially in patients with unstable metabolic disorders such as diabetes mellitus. Emesis and its potential ocular and systemic complications add to the postoperative malaise of general anesthesia.

Adult↗
PubMed1983

Macular pucker. I. Prognostic criteria.

Thirty-three eyes with symptomatic epimacular membranes were treated by vitreous surgery and membrane removal. Vision improved in 79%. Eyes with clinically transparent membranes, but without preoperative cystoid macular edema, were most likely to achieve good vision, while opaque membranes had worse vision. Because cystoid macular edema was the most common obstacle to improved vision, membranes should be removed before this process begins, or as soon as possible thereafter. Angiography should precede consideration of surgery. Even though large parts of the internal limiting lamina of the retina were often peeled with the membranes, excellent vision was possible.

Humans↗
PubMed1983

Macular pucker. II. Ultrastructure.

Twenty symptom-producing epimacular membranes removed during vitreous surgery were examined by light microscopy, scanning and transmission electron microscopy. These membranes contain cells of glial and pigment epithelial origin, but one also finds myofibroblasts and fibroblasts which cannot be identified morphologically as to their origin. The membranes can be classified into two types. Membranes in one group are composed of numerous alternating layers of collagen and cells and some internal limiting lamina. The second type of membrane is generally composed of a single layer of cells with large sheets of internal limiting lamina from the retinal surface and little if any collagen. Both types of membranes have cells on the retinal side of the removed internal limiting lamina, presumably derived from neurosensory retina.

Humans↗
PubMed1983

Intraocular diathermy coagulation.

Previously used transvitreal diathermy systems were found to be less than adequate. A new, safer 1.25 MHz medium frequency bipolar instrument is presented, which obviates most of the earlier drawbacks. Coagulation at the retinal surface can be obtained with as little as 0.15 J.

Diathermy↗
PubMed1983

Posterior internal ophthalmomyiasis. Identification of a surgically removed Cuterebra larva by scanning electron microscopy.

The clinical presentation of an 11-year-old boy with unilateral posterior internal ophthalmomyiasis is described. Ophthalmoscopy of the affected eye in this individual disclosed characteristic subretinal depigmented linear tracks and a larva within the vitreous. The intravitreal larva was retrieved successfully by pars plana vitrectomy and identified as the first instar of Cuterebra sp. (rodent botfly) by scanning electron microscopy. This was done by examining the external features of the larva by scanning electron microscopy and comparing them to scanning electron micrographs that were prepared on other first instar larvae of flies known to be implicated in internal ophthalmomyiasis. The study demonstrates the usefulness of scanning electron microscopy for taxonomic identification of fly larvae. Since even a small fragment of these organisms may contain characteristic features of external morphology, scanning electron microscopy may be useful in cases where the specimen is damaged or incomplete.

Child↗