Biomedical subjects
Publications and source records attributed to R Machemer.
We developed an automated diaphragm control to achieve constant good exposure during televised microsurgery by using a commercially available diaphragm control for a movie camera and modifying slightly the television camera.
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.
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%).
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.
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.
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.
Proliferative neovascular retinopathies may be caused by the release of a hypothetical vasoproliferative factor, but mechanical factors seem to self-perpetuate the disease as well. Contraction of proliferative tissue causes vitreous detachment and traction on the retina. Congestion of vascular fronds by traction further stimulates vascularization. Traction on vessels results in hemorrhages. Surgical removal of all intravitreal scaffolds by vitrectomy seems to eliminate the development of this vicious cycle. Results of vitreous surgery seem to indicate that the hypothesis of scaffold removal is valid.
We exposed the maculas of owl monkey eyes to light from an intraocular fiber optic light source similar to that used for human pars plana vitrectomy. Retinal irradiance was calculated at 0.22 W/cm2. Eyes were exposed for time intervals ranging from 30 minutes to five minutes and were observed after light treatment by fundus photography and fluorescein angiography. Tissue was obtained for light and electron microscopy by animal killing at one hour, 24 hours, one week, and four weeks. Fundus lesions were seen ophthalmoscopically as early as five hours following 30 minutes of light exposure. Significant damage to the photoreceptor layer and less damage to the pigment epithelium was present by light and electron microscopy as early as one hour after 30 minutes of light exposure. By one month complete loss of photoreceptors with Müller cell junctions between inner retina and flattened abnormal retinal pigment epithelium cells was observed. Fluorescein angiography revealed significant staining of the pigment epithelium and outer retina 24 hours after 30 minutes of light exposure. No leakage from retinal vessels occurred. At one month following light treatment, transmission of choroidal fluorescein through window defects in the pigment epithelium was present with no retinal staining. The threshold for ophthalmoscopically visible fundus lesions in this study was 15 minutes of light exposure. Ten minutes of light treatment was the threshold for microscopic changes. Short light exposures damaged the outer retina and spared the pigment epithelium. Removing a substantial amount of the infrared light from our light source did not protect the retina from damage. Removal of light between 400 and 500 nm is probably more helpful in protecting the retina. Intermittent light exposure of the retina seemed as harmful as uninterrupted illumination for the same cumulative period of time. We speculate that the retinal damage caused by intraocular fiber optic light has primarily a photic mechanism. Damage to the retinal pigment epithelium may be secondary to outer retinal damage. The present levels of intraocular light used for human pars plana vitrectomy are probably safe in most instances. Lengthy preretinal membrane stripping procedures during vitrectomy, however, may pose a threat of light damage to the retina. This damage must be appreciated as continued efforts are made to produce brighter sources of intraocular light for human pars plana vitrectomy.
Biopsy specimens from vitreous and preretinal membranes, obtained during vitreous surgery from 39 human eyes suffering from massive periretinal proliferation, were examined electron-microscopically. Analysis of the cellular membranes demonstrated mostly cells with epithelial characteristics: polarization of the cells, basal lamina formation, specialized cellular junctions, and microvilli formation. These epithelioid cells contained prominent rough endoplasmic reticulum, glycogen deposits, a multitude of cytoplasmic filaments, some resembling myofilaments, and nonmembrane bound, sometimes wedge-shaped pigment granules. Macrophages were interspersed in the membranes. There was a striking similarity of these findings to those of an experimental model of retinal detachment in owl monkeys, We concluded that most likely the described cells derived from cells of pigment epithelial origin.
To increase the versatility of a ceiling-mounted microsurgical unit, we instructed an instrument company to redesign an existant unit according to our requirements. The modified instrument has improved microscope supporting arms capable of supporting an inserted X-Y translation stage. The unit houses diathermy, cautery, fiberoptic light source, and suction devices. Most of these devices can be exchanged for other to adapt to individual requirements. Mirror image design increases versatility. Floor-mounted outlets avoid a multitude of cables. A double color television system for automatic recording of surgery has been installed.
Based on the improved understanding of massive periretinal proliferation (MPP) as a proliferative membrane-forming disease, a new therapeutic approach is presented with the technique of pars plana vitreous surgery. Not only vitreous membranes but also preretinal membranes are removed. Forty-seven consecutive patients who suffered from severe massive periretinal proliferation were operated on with this technique and followed for six months or more. Seventeen patients (36%) had an attached retina. Twelve patients had a major visual improvement. The major postoperative complication was phthisis bulbi, found in ten eyes (21%).
The general characteristics, preoperative findings, and operative procedures of 56 consecutive eyes having pars plana vitrectomies for complications of diabetic retinopathy are presented in this paper. Of the 34 eyes available for follow-up examinations five years after surgery, 50% had ambulating vision and 15% had 20/40 or better visual acuities. The vitreous cavities were clear in 59% and the maculae attached in 50% of the 34 eyes.
Evaluation of 200 consecutive pars plana vitrectomies shows delayed corneal epithelial healing after intentional scraping and formation of a posterior subcapsular cataract, presumably due to exposure to inadequate infusion fluids. Posterior retinal holes occur frequently, whereas entrance site complications have been reduced to an acceptable minimum. Temporary rise in intraocular pressure is common.
Massive periretinal proliferation (MPP), a serious complication of retinal detachment, is caused by proliferation and fibrous metaplasia of cells mostly deriving from retinal pigment epithelium and retinal glial cells. Contracting fibrous membranes in the vitreous, and on and also under the retina, cause the intraocular changes of MPP. Early signs such as increased 'tobacco dust', pigmented and unpigmented clumps in the vitreous, and subtle preretinal and even retroretinal membranes are usually overlooked. The late signs such as starfolds, irregular retinal folds, circumferential folds, and funnel-shaped detachments are well known. The pathogenesis of the clinically visible signs is described, and a 4-stage classification of the disease is given.
In 6 patients with macular puckers (3 spontaneous puckers and 3 puckers after retinal detachment procedures), the epiretinal tissue was surgically removed by pars plana vitrectomy and membrane peeling. 5 patients had visual improvement initially, 3 permanently. Cataract and retinal detachment were observed as complications. No recurrence of the macular pucker occured.
Six eyes, four obtained at autopsy and two enucleated for neovascular glaucoma, were studied histopathologically between one week and 3 1/2 years after pars plana vitrectomy (some combined with lensectomy) for proliferative diabetic retinopathy. Fibrovascular proliferation at the sclerotomy site was minimal. Lensectomy through the pars plana proved to be quite complete. A cyclitic membrane was found in eyes with postoperative rubeosis irides. Excision of the vitreous from the posterior part of the vitreous cavity was quite complete except for remnants of stalks and membranes on the retinal surface.
A cryoprobe with a large elliptical freezing surface, used in retinal surgery and cyclocryotherapy, reduced the number of applications and the treatment time.
An automatic timer, built into an electric cryounit, was useful when repeated applications were necessary during cryotherapy.