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Biomedical subjects

R Machemer

Publications and source records attributed to R Machemer.

At least 127 records · Page 7Linked to original sources
PubMed1981

Vascular casts of experimental retinal neovascularization.

Autotransplantation of skin fibroblasts into the vitreous cavity of the rabbit eye resulted in the formation of fibrous strands that rapidly vascularized. To study this neovascularization, we injected methylmethacrylate monomer via the common carotid artery and made plastic casts between three days and three months after transplantation. Budding of new vessels into the fibrous tissue from retinal veins was observed as soon as three days after transplantation. The new vessels grew rapidly into the fibrous tissue matrix and an increasing number of anastomoses developed during the observation period. Neovascular fans developed at the proximal end of the proliferating fibrous tissue two to four weeks after injection. As the strands contracted, changes in blood flow resulted in aneurysmal dilatations and glomerular formations.

Animals↗
PubMed1981

Vitrectomy for proliferative diabetic retinopathy associated with vitreous hemorrhage.

This paper describes experience gained with 663 eyes of patients with diabetic vitreous hemorrhage treated by closed vitrectomy with a follow-up period of six months. Hemorrhages were nearly always associated with proliferative retinopathy (97%) and were thought to be caused always by ruptured proliferative vessels. Membrane removal was performed in 42% of all cases but in 60% when the retina was detached. The most common surgical complication was creation of retinal holes; more common when the posterior retina was detached (32%) than when it was attached (18%). The lens was removed in 73% of the cases. Eighty-two percent of the retained clear lenses remained clear at the six months follow-up period. Therefore, clear lenses should not be removed. Visual improvement could be achieved in 59% of the cases where the posterior retina was attached but only in 25% where it was detached resulting in an overall major visual improvement in 46% of the cases. If one adds to this group the cases that retained reasonable vision of 20/200 or better, the overall success rate was 51%. Posterior retinal detachment and rubeosis of the iris were the main factors for a bad prognosis. Forty-two percent of all eyes had at least some degree of rubeosis iridis. Most of the preoperative rubeotic eyes had rubeosis postoperatively (71%). Twenty-three percent of all eyes ended up with neovascular glaucoma.

Diabetic Retinopathy↗
PubMed1981

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

We examined the histopathologic appearance of both cryopexy and diathermy lesions, 10-60 min after application in the rabbit retina. Both lesions showed immediate subretinal exudation. Thus, we could 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.

Adhesiveness↗
PubMed1981

Further characterization of epiretinal membranes in human massive periretinal proliferation.

Periretinal membranes obtained at vitrectomy from three patients with massive periretinal proliferation were examined by immunofluorescence and electron microscopy. Immunofluorescent staining on fresh frozen sections showed positive stain with glial fibrillary acidic protein and a weaker stain with antibodies to actin, PBM-1 and laminin. Staining was negative for antibodies to actin, PBM-1 and laminin. Staining was negative for antibodies of collagen types I, III and IV. Electron microscopy revealed abundant glial cells arranged in a tubulo-acinar configuration with junctional complexes, apical microvillous processes and 9-10 nm cytoplasmic filaments.

Antibodies↗
PubMed1980

Support and air supply tube for vitreous surgery.

A metallic tube is attached to the operating table or wrist rest, acts as a support for the assistant's hand, and provides free air flow during vitreous surgery while the patient is under local anesthesia.

Humans↗
PubMed1980

Intravitreal autotransplantation of fibroblasts.

Tissue cultured skin fibroblasts autotransplanted into the vitreous cavity of rabbit eyes formed intravitreal strands that grew toward the medullary ray and optic nerve head and caused preretinal puckers and traction detachment. After four weeks, 32 of 51 eyes (63%) developed these changes. Light and electron microscopy revealed initial cell death. Remaining cells aligned themselves quickly into strands and began to multiply as shown by tritiated thymidine methyl incorporation. The appearance of cells that resemble myofibroblasts may explain the contractability of the strand. Because the effect of intraocular proliferation can be quantitated by the number of puckers and retinal detachments developing, this model may be useful for the study of therapeutic means to reduce intraocular proliferation.

Animals↗
PubMed1980

Inhibition of intraocular proliferations with intravitreal corticosteroids.

Autotransplantation of one fourth million tissue cultured fibroblasts from rabbit rump skin into the vitreous cavity resulted in intravitreal strand formation and traction retinal detachment (27 of 47 eyes, 57%). A single intravitreal injection of 1 mg of dexamethasone alcohol inhibited fibroblast growth as judged by the significantly reduced number of retinal detachments (11 of 46 eyes, 24%). Retinal neovascularization that was observed when fibrous strands came into contact with vascularized retina (nine of 47 eyes, 19%) was also inhibited after corticosteroid application (two of 46 eyes, 4%).

Animals↗
PubMed1980

Surgical approaches to subretinal strands.

I successfully removed subretinal strands or membranes surgically in three patients with retinal detachments. Two approaches were used: (1) by cutting through the sclera with vitreous scissors (external approach), or (2) by cutting holes through the retina (internal approach). In two cases of retinal detachment, massive periretinal proliferation occurred, one of which was successfully managed with the external approach. In the other case, recurrence of massive periretinal proliferation caused the retina to detach again. In a third case a nonrhegmatogenous retinal detachment caused by a subretinal membrane was managed successfully with the internal approach.

Adolescent↗
PubMed1980

Treatment of intraocular proliferation with intravitreal injection of triamcinolone acetonide.

We studied the inhibitory effect of triamcinolone acetonide on experimental intraocular proliferation. Autotransplantation of fibroblasts from rabbit rump skin into the vitreous cavity resulted in intravitreal strand formation and traction retinal detachment in 36 of 43 eyes (84%) over a period of three months. A single intravitreal injection of 1 mg of triamcinolone acetonide inhibited fibroblast growth and significantly reduced the number of retinal detachments in 15 of 44 eyes (34%). Retinal neovascularization caused by fibrous strands coming into contact with vacularized retina was also reduced by triamcinolone acetonide (31 of 43 control eyes [72%] vs eight of 44 treated eyes [18%]). Intravitreal corticosteroid therapy may be an important adjunct to the therapy of perforating injuries and massive periretinal proliferation.

Animals↗
PubMed1980

Cataract extraction in cases of cataract with vitreous abnormality.

Since good visibility of the deeper structures of the eye is a prerequisite for vitreous surgery, a lentectomy is often performed in combination with vitreous surgery even when the lens is only slightly cataractous. Clear lenses may have to be removed when complete intraocular gas tamponade is utilized (treatment of giant tears 180 degrees and larger). A pars plana approach is recommended, and the lens is removed with the vitrectomy instruments as long as the nucleus is not too hard. Otherwise, phacoemulsifying instruments are needed. The techniques are described. The worst complication of posterior lentectomy is loss of lens material into the vitreous cavity.

Cataract↗
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↗