Biomedical subjects

R Machemer

Publications and source records attributed to R Machemer.

At least 73 records · Page 4Linked to original sources

PubMed1987

Mechanical retinal fixation using tacks.

Since their introduction, retinal tacks have been increasingly used as an adjunct in the repair of complicated retinal detachments. Indications, results, and complications in a consecutive series of patients undergoing surgery for complicated retinal detachment are reported. Of the 47 patients with the potential for 6-month follow-up, 44 were available for evaluation. Overall complications were infrequent and usually controllable. At the 6-month follow-up interval, the macula was attached in 27 of the 44 patients (61%). Vision improved in 21 patients (48%). Between the intervals of 6 and 12 months, there was basic stability with two patients worsening in acuity, two patients improving, and 11 patients demonstrating no change. The use of retinal tacks appears to be a procedure with an acceptable complication rate which is helpful in repair of complex retinal detachments.

Humans↗

PubMed1987

Transvitreal cyanoacrylate retinopexy in the management of complicated retinal detachment.

Failures in vitreous surgery for complex vitreoretinal disorders are frequently due to an inability to keep preexisting or iatrogenic retinal breaks permanently closed. We have used transvitreally delivered cyanoacrylate tissue adhesive to seal retinal breaks in selected patients undergoing vitreous surgery for complicated retinal detachment. With a minimum follow-up period of 6 months, all but one retinal hole have remained closed and complete retinal reattachment posterior to the encircling buckle was achieved in 18 of 25 eyes (72%). In 10 of the 25 eyes (40%) the final visual acuity was 5/200 or better.

Adolescent↗

PubMed1987

Retinopathy of prematurity. Surgical technique.

Retinal detachment, as the end result of severe retinopathy of prematurity (ROP), continues to account for many cases of blindness. Vitreous surgery can result in retinal reattachment in a significant percentage of these patients. The authors report their current techniques, which are based on improved understanding of the pathoanatomy and experience with more than 100 cases of retinal detachment in ROP treated with vitreous surgery.

Humans↗

PubMed1986

Vitrectomy for advanced stages of retinopathy of prematurity.

We did a retrospective review of the consecutive vitrectomies for traction retinal detachment associated with retinopathy of prematurity performed at our institution. Fifty-eight eyes were operated on in 46 patients at less than 1 year of age, including 12 eyes with partial retinal detachments and 46 eyes with total retinal detachments. Only patients with at least six months follow-up were considered for success. Twenty-five eyes (43%) were anatomically reattached. Factors associated with good anatomic outcome included greater mean preoperative pupillary dilation, absence of posterior synechiae, deep anterior chamber, partial detachment or open-funnel total detachment configuration, and adequate posterior membrane removal. Of the 25 eyes with attached retinas, 11 had fixing and following visual acuities or better. Three eyes with attached retinas had no light perception and 11 eyes with attached retinas had light perception only. To maximize anatomic and functional results we emphasize the need to operate early, when the retinal funnel is still open.

Evaluation Studies as Topic↗

PubMed1986

Temperature-dependent light damage to the retina.

We examined the ability of hypothermic infusion fluid to reduce the risk of light damage to the retina from the intraocular fiberoptic probe during vitreous surgery. Following vitrectomy, we exposed the retina of rabbits to light from an intraocular fiberoptic probe during infusion of fluid at body temperature (39 C) and compared this with exposures during infusion of room temperature fluid (22 C). Retinal irradiance was 0.33 W/cm2. Damage was determined ophthalmoscopically and histologically. Cooling the infusion fluid from body to room temperature extended the damage threshold from approximately 25 to 60 minutes. A 35-minute exposure to body temperature fluid was compared with the same exposure during infusion of room temperature fluid. While retinal and retinal pigment epithelium damage was present after the body temperature exposure, no damage was detected after the room temperature exposure. Vitreoretinal surgeons should avoid warming intraocular infusion fluids to levels above room temperature.

Animals↗

PubMed1986

Relaxing retinotomies and retinectomies.

Relaxing retinotomies and retinectomies are helpful surgical techniques in the treatment of severe cases of retinal detachment with incarcerated retinas, retinal shrinkage caused by proliferative vitreoretinopathy, proliferative vasculopathies, or injury after failure of membrane removal and scleral buckling to reattach the retina. They should be considered as a last resort. The retina is reattached with an intraocular tamponade and then treated with transvitreal laser or cryotherapy. Temporary retinal tacking at the posterior retinal edge before intraocular tamponade is helpful. The retina was attached in 18 of 45 eyes with at least six months of follow-up. Visual acuity was counting fingers or better in 11 eyes and 5/200 or better in three.

Adult↗

PubMed1986

The use of retinal tacks in the repair of complicated retinal detachments.

Retinal tacks that can be easily placed and removed allow precise intraocular control of retinal fixation in the repair of complicated retinal detachments. We used this technique in 41 consecutive cases of complicated retinal detachment. In 37 cases follow-up was six months or more. We achieved reattachment of the posterior pole, including the macula, in 22 patients after six months or more of follow-up. Postoperative visual acuities were 1/200 or better in 15 patients and 5/200 or better in six.

Humans↗

PubMed1986

Panretinal photocoagulation and retinal oxygenation in normal and diabetic cats.

We measured preretinal oxygen tension over laser-treated and intact retina in normal and diabetic cats. The oxygen tension was significantly higher over the area given panretinal photocoagulation than over the intact retina when the cats breathed 100% oxygen and the same trend was seen when the cats breathed 21% oxygen. There was no difference in preretinal oxygen tension between the normal and diabetic retinas. Light and electron microscopy showed laser damage to the mitochondria-rich photoreceptors in the outer retina as well as the retinal pigment epithelium. The inner retina showed no photocoagulation damage. Because panretinal photocoagulation destroys parts of the outer retina, thus reducing its oxygen consumption and allowing oxygen to diffuse from the choroid into the inner retina, it improves the oxygen supply to the inner retina.

Animals↗

PubMed1986

Experimental and clinical observations of the intraocular toxicity of commercial corticosteroid preparations.

We tested the vehicles of six different commercially available depot corticosteroids (Celestone Soluspan, Depo-Medrol, Decadron, Decadron L. A., Aristocort, and Kenalog) for possible toxicity when injected intravitreally. When tested on rabbit eyes, the Celestone Soluspan and the Depo-Medrol vehicles caused remarkable retinal degeneration with preretinal membrane formation or cataracts in their standard concentrations. Three other vehicles (Decadron and Decadron L. A.) caused localized retinal degeneration in twice the standard concentration. Thus, toxic effects can be caused by preservatives or inadequate osmolarity of the vehicles alone. The development of proliferative vitreoretinopathy in some cases of injections of intraocular depot corticosteroid can be explained by retinal necrosis and repair processes caused by these vehicles.

Adrenal Cortex Hormones↗

PubMed1986

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 6 months, complete anatomic retinal reattachment posterior to the encircling scleral buckle was obtained in 64% of these eyes. Ambulatory visual acuity (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. Because of the frequent and severe complications associated with the use of silicone oil, we recommend that silicone-oil injection be considered only when conventional vitreoretinal techniques have failed to achieve retinal reattachment.

Eye Diseases↗

PubMed1986

A refined experimental model for proliferative vitreoretinopathy.

Animal models of proliferative vitreoretinopathy (PVR) in which the intact vitreous is injected with large numbers of tissue cultured fibroblasts do not accurately represent the disease as it is found in humans. A refined model of PVR is presented, in which the vitreous is compressed and partially detached using intravitreally injected perfluorpropane, followed by injection of 25,000 homologous fibroblasts. Proliferation occurred on the retinal surface, causing retinal detachments with the same frequency as models using greater numbers of cells.

Animals↗

PubMed1986

Ultrasonic examination of the silicone-filled eye: theoretical and practical considerations.

As the use of silicone oil in the treatment of complex retinal detachment becomes more frequent, an accurate assessment of ocular structures in these eyes by ultrasonic imaging is increasingly important. Because of the ultrasonic properties of silicone oil, the interpretation of ultrasound images of the silicone-filled eye is difficult. We have developed a mathematical model of ultrasound propagation in the eye. Using a computer simulation with graphic output, we have been able to make calculations concerning the interpretation and limitations of ultrasound examination in patients with intraocular silicone oil.

Computers↗

PubMed1986

Glio-vascular architecture in the rabbit retina.

Differences between the rabbit and human retinal circulation, and the use of the rabbit eye in a model of experimental retinal neovascularization, necessitates a complete description of the normal vascular structure in the rabbit and its relationship to adjacent tissue, particularly the glia. The gliovascular relationships in the rabbit were studied by scanning and transmission electron microscopy. Utilizing gas compression of the vitreous to clear the wings of overlying vitreous, the authors were able to make detailed observations of retinal surface by scanning electron microscopy. Glial sheaths surrounding a large number of medium size and smaller vessels were observed. The glial sheaths contained cells which were ultrastructurally similar to Müller cells. No isolated glial tufts were observed in avascular areas. Finally, small, smooth-surfaced cells were found adjacent to many vessels. The exact nature and function of these cells remains unknown.

Animals↗

PubMed1985

The three-port microcannular system for closed vitrectomy.

Microcannulas used during vitreous surgery protect the entry site, avoid vitreous base damage, and allow easy exchange of 20- and 19-gauge (0.9- and 1-mm) instruments. The use of three cannulas of equal size permits interchangeability of all instruments. A locking mechanism allows attachment and exchange of various infusion lines (balanced salt solution, gas, and oil). Temporary plugging of the cannula is possible. Selection of 1 mm as a standard diameter for all cannulas make multiple-function instruments feasible.

Catheterization↗

PubMed1985

Results of conventional vitreous surgery for proliferative vitreoretinopathy.

During a five-year period (1978 through 1982), we used conventional vitreous surgery techniques to treat patients who had recurrent retinal detachment as the result of proliferative vitreoretinopathy. At a six-month follow-up, 24 (33%) of 72 patients achieved total retinal reattachment; 14 patients regained ambulatory vision (5/200 or better) after one operation. Only 12 patients were reoperated on; four achieved retinal reattachment. Anatomic success correlated with a lesser grade of proliferative vitreoretinopathy and an absence of detectable retinal breaks. Creation of iatrogenic retinal tears and broad scleral buckling and an extended interval between the initial detachment and vitreous surgery did not improve the prognosis.

Eye Diseases↗

PubMed1985

The effect of triamcinolone acetonide on a refined experimental model of proliferative vitreoretinopathy.

Animal models of proliferative vitreoretinopathy in which the intact vitreous body is injected with large numbers of fibroblasts do not resemble the human situation. Using a refined rabbit model of proliferative vitreoretinopathy in which the vitreous is compressed and partially detached from the retinal surface and small amounts of tissue-cultured homologous fibroblasts (25,000) are scattered over the vascularized part of the retina, we reevaluated the effect of intravitreally injected triamcinolone acetonide. We found that 2 mg of the corticosteroid reduced the incidence of retinal detachments from 90% to 56%. The effect was less than in previous models with intact vitreous. Large doses of the corticosteroid had no additional effect on the reduction of retinal detachments, indicating an optimal dosage of 2 mg. The effect of the corticosteroid on neovascularization was considerable; with 8 mg it could almost be prevented (reduction from 74% to 8%).

Animals↗

PubMed1985

Retinal tacks.

An improved retinal tack and applicator can be used to fix the retina to the wall of the eye mechanically. The system consists of a small (1 X 2.7 mm) stainless steel tack with a blade-like tip and a forked applicator that can grasp the tack securely from any position. Two eyes with complex detachments with fixed rolled retinas could not have been repaired without the help of retinal tacks. The advantages of the retinal tack system over other methods include ease of handling, insertion, and removal.

Adult↗

PubMed1985

Subretinal strands: ultrastructural features.

This report describes the histologic and ultrastructural features of 13 subretinal strands removed during vitreous surgery for retinal detachment with proliferative vitreoretinopathy. On the surface of the subretinal strands, retinal pigment epithelial cells were found that maintained their cellular characteristics. Inside the strand were modified pigment epithelial cells, fibroblasts, fibrocytes, myofibroblasts, macrophages, basal lamina material, fibrin, and often large amounts of collagen. In some strands, the basal lamina material was similar to the types found in Drusen and in the inner layer of bruch's membrane. Glial cells were rarely found in these strands.

Basement Membrane↗