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Biomedical subjects

R Machemer

Publications and source records attributed to R Machemer.

At least 19 recordsLinked to original sources
PubMed1992

Retinal oxygenation and laser treatment in patients with diabetic retinopathy.

The oxygen tension in the preretinal vitreous cavity was measured in human patients undergoing vitreous operations for proliferative diabetic retinopathy. The oxygen tension was significantly higher (P = .004) over areas of retina that had been treated with panretinal photocoagulation than it was over untreated areas in the same retina. This confirmed previous results in animals that showed that panretinal photocoagulation increases the inner retinal oxygen tension. We concluded that panretinal photocoagulation improves the oxygen supply to the inner retina and thereby minimizes the influence of retinal ischemia in diabetic retinopathy.

Blood Pressure↗
PubMed1992

The lack of an effect of intraocular steroids on irradiated fibroblasts in experimental proliferative vitreoretinopathy.

Contraction of intraocular membranes is an important event in the development of proliferative vitreoretinopathy (PVR). When sufficient numbers of cells are present in the vitreous cavity, the retina usually detaches as a result of the contractive force generated by these cells. Steroids reduce the occurrence of retinal detachments in rabbit models of PVR by inhibiting the proliferation of injected fibroblasts. In this study, we used non-proliferative, irradiated cells to determine a possible effect of steroids on preretinal membrane contraction in PVR. We found no clinical difference between steroid treated eyes and sham-treated control eyes. Surgical reduction of the contractile tissue and medical therapy to prevent reproliferation are necessary in order to treat PVR effectively.

Animals↗
PubMed1992

Pigment epithelial repair.

We studied the repair of large, surgically induced retinal pigment epithelial defects in rabbit eyes for up to 28 days. Ophthalmoscopically, the pigment epithelium surrounding the defect became less pigmented and scattered pale foci appeared. The margin remained distinct for 28 days and the defect was subsequently covered by a variable lacework of pigmentation. Angiographically, the acute defect was hyperfluorescent and leaked heavily, but within 7 days fluorescein leakage had ceased. Histology, transmission and scanning electron microscopy, and autoradiography for the study of cells in division revealed that the pigment epithelium surrounding the defect became pleomorphic after 1 day, began to proliferate within 3 days, and covered the defect within 7 days. Subsequently, many cells became pigmented and some were fibrocyte-like. The cells within the healing defect appeared to have derived from the pigment epithelium. Our findings suggest that similar processes occur in large human defects such as pigment epithelial rips.

Animals↗
PubMed1992

Scleral buckling surgery for stage 4B retinopathy of prematurity.

Results of scleral buckling in 15 consecutive eyes of 13 infants with stage 4B retinopathy of prematurity (ROP) were reviewed. Ten of 15 retinas achieved macular reattachment with a single scleral buckling procedure. Four of 15 retinas unable to be attached by scleral buckling were reattached after the addition of a single vitreous operation. One of 15 retinas was unable to be reattached despite both a scleral buckling and a single vitreous procedure. Despite macular attachment in all except one eye, visual results were disappointing. Fix and follow visual acuity was present in 3 eyes, light perception in 11 eyes, and no light perception in 1 eye. Average follow-up was 10 months. Possible causes for poor visual outcomes despite retinal reattachment include retinal abnormalities as a result of detachment and amblyopia.

Female↗
PubMed1991

An updated classification of retinal detachment with proliferative vitreoretinopathy.

The Retinal Society classification on proliferative vitreoretinopathy of 1983 has been updated to accommodate major progress in understanding of this disease. There are three grades describing increasing severity of the disease. Posterior and anterior location of the proliferations have been emphasized. A more detailed description of posterior and anterior contractions has been made possible by adding contraction types such as focal, diffuse, subretinal, circumferential contraction, and anterior displacement. The extent of the abnormality has been detailed by using clock hours instead of quadrants.

Eye Diseases↗
PubMed1991

Experimental traction retinal detachment in the cat.

We developed a reproducible model of traction retinal detachment (TRD) in the cat eye by creating a serous retinal detachment and then injecting 2.5 x 10(5) kitten dermal fibroblasts into the vitreous cavity at the site of a retinal wound. Serous detachments were produced by exposing an area of retina to focused light after intravenous injection of rose bengal (a photosensitizing dye). TRD developed rapidly within the first 2 weeks after fibroblast injection, accompanied by the formation of vitreoretinal strands and, to a lesser degree, epiretinal and/or subretinal proliferation. Histopathology demonstrated fibroblasts within the vitreous or along the posterior hyaloid face. Focal deposits of fibroblasts were occasionally found on the inner surface of the retina and/or in the subretinal space. Fibroblast proliferation was confirmed by uptake of radiolabeled thymidine. Deposition of collagen was noted at as early as 3 days after fibroblast injection. Neovascularization was not observed. Control eyes that did not receive fibroblasts showed resolution of serous detachment without retinal traction. In all eyes, retinal degeneration and thinning were seen in the area of previous photodynamic treatment. In this model of TRD, anteroposterior traction (due to vitreous strands) predominates, as is observed in experimental posterior penetrating ocular injury induced by intravitreal blood injection, which also results in vitreous strand formation. Our model, however, enables clinical assessment of TRD in the cat without the media opacification produced by vitreous blood.

Animals↗
PubMed1979

Experimental double-perforating injury of the posterior segment in rabbit eyes: the natural history of intraocular proliferation.

A reproducible model of double perforating injury of the posterior segment of the rabbit eye was developed. Immediately after injury, a viterous condensation was visible between wounds. The scleral exit wound was sealed by fibroblastic proliferation of probable episcleral origin by the fourth day and the entrance similarly by the seventh day. Cellular proliferations originating in the wounds crossed the vitreous cavity following the vitreous injury tract or condensed vitreous to the disc or to the vitreous base. The earliest intraocular proliferations, composed of spindle-shaped, fibroblast-like cells, were seen at day 4. Occasional pigment epithelia were present in and on these proliferations. Other proliferations occurred directly on the retinal surface adjacent to the wounds. The transvitreous proliferations employed the vitreous as a scaffold, while the surface proliferations used the retinal surface for contact guidance.

Animals↗
PubMed1979

Vitrectomy for injury: the effect on intraocular proliferation following perforation of the posterior segment of the rabbit eye.

Perforating injuries were produced in the posterior segments of rabbit eyes. A control group had no surgery; a second group underwent closed vitrectomy immediately after injury; and a third group had closed vitrectomy delayed two weeks following injury. The eyes were then observed for four weeks. Transvitreal proliferation, which was found in each of the control eyes, was effectively prevented in the eyes that underwent immediate vitrectomy. Established transvitreal proliferation was removed and its recurrence prevented by delayed vitrectomy. These results establish the principle that vitreous acts as a scaffold for proliferation. Removal of the vitreous eliminates the structures along which proliferation can occur and thus effectively prevents transvitreal proliferation. Early removal of vitreous in severely injured eyes with vitreous damage is recommended.

Animals↗
PubMed1979

Pars plana surgical approach for various anterior segment problems.

Various anterior segment problems can be approached through the pars plana and treated with instrumentation that has been developed for vitreous surgery. Two cases of aphakic bullous keratopathy due to vitreous touch and three cases of subluxated lenses were successfully treated. Of two cases of advanced, persistent hyperplastic primary vitreous, one showed a successful result.

Aged↗
PubMed1979

The lens and pars plana vitrectomy for diabetic retinopathy complications.

Major cataracts developed in 28 of 168 eyes during the six months after pars plana vitrectomy for complications of diabetic retinopathy. In only ten of these cases did the cataract influence the visual results. The visual acuities of the phakic and aphakic eyes six months after vitrectomy were almost identical. Rubeosis iridis occurred in 23% of the phakic eyes and 45% of the aphakic eyes, with the difference being related to the loss in the aphakic eyes of a protective barrier lens quality. However, this same barrier quality increased the incidence of postoperative opaque vitreous hemorrhage from 8% of the aphakic eyes to 21% of the phakic eyes. Corneal epithelial edema at surgery occurred in 55% of those eyes that had lens removal combined with vitrectomy, but in only 36% of those that retained their lenses, and the difference was caused by the increase in operative time and procedure.

Adult↗
PubMed1979

Choroidal folds.

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Choroid↗
PubMed1979

Streaks (schlieren) as a sign of rhegmatogenous detachment in vitreous surgery.

Schlieren or streaks can be observed as light passes through incompletely mixed fluids having different refractive indices. During vitreous surgery, the vitreous humor is replaced by an aqueous solution whose density and refractive index differ from those of subretinal fluid. The observation of schlieren during vitrectomy therefore suggests the presence of subretinal fluid and a retinal hole. After observing this sign, a careful search should be made for the retinal break if it has not been previously diagnosed.

Body Fluids↗
PubMed1979

Treatment of intraocular proliferations with intravitreal steroids.

Autotransplantation of 250,000 tissue cultured fibroblasts from rabbit rump skin into the vitreous cavity results in intravitreal strand formation and traction retinal detachment (27 of 47 eyes, 57%). A single intravitreal injection of 1 mg of dexamethasone alcohol inhibits fibroblast growth as judged by the significantly reduced number of retinal detachments (11 of 46 eyes, 24%).

Animals↗
PubMed1979

[Cutting of the retina: a means of therapy for retinal reattachment (author's transl)].

In a case of retinal incarceration after injury of the eye, the retina was mobilized by cutting it free and creating a 240 degree dialysis. The retina could be reattached with the help of intraocular gas techniques developed for the treatment of giant retinal tears. This case demonstrates that actual cutting of the retina can result in successful reattachment of the retina.

Humans↗
PubMed1978

An improved method for practice vitrectomy.

Practice is essential for acquiring the skills necessary for the delicate technique of pars plana vitrectomy. An improved animal model is presented for the beginning surgeon and the assistant to learn basic as well as advanced vitrectomy techniques. A stepwise scheme progressing from simple vitrectomy in the phakic rabbit eye to complicated situations is introduced. Fluorescein staining helps in visualization of the normal vitreous. Double perforating injuries are created to simulate complicated vitreoretinal problems. Methods for learning manipulations with two instruments in the eye are described.

Animals↗
PubMed1978

Pars plana approach for pupillary membranes.

Pars plana surgery was performed, using a vitreous infusion suction cutter, for the treatment of after-cataracts, traumatic pupillary membranes, inflammatory pupillary membranes, and varoius pupillary membranes combined with other posterior segment problems. Surgical complications were minimal. A permanent pupillary opening was achieved in all but one case. Visual success was dependent on the underlying disease. One should not operate during active phases of uveitis.

Aged↗