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PubMedDate not supplied

Corneal endothelial cell loss after multiple vitreoretinal procedures and the use of silicone oil.

BACKGROUND AND OBJECTIVE: Corneal decompensation and complications are a frequent cause of visual loss after vitreoretinal surgery. This paper presents data regarding endothelial cell loss in aphakic and pseudophakic silicone oil filled eyes when oil was retained for many months. This study updates our previous investigation on the subject. PATIENTS AND METHODS: The corneal endothelial cell count of 10 eyes of 10 consecutive patients who had undergone vitreoretinal surgery, including fluid-gas exchange and ultimately silicone oil placement, were obtained. The patients underwent an average of 2.7+/-0.9 vitreoretinal procedures before the final procedure which induced the placement of silicone oil in the vitreous cavity. All had inferior iridectomies. The endothelial cell density measurements were obtained an average of 1 year after silicone oil placement. In all eyes, the oil was felt necessary for long term tamponade and therefore was not removed. The cell density of the operated eye was compared to the fellow eye, none of which had undergone silicone oil placement. RESULTS: Both gas and retained silicone oil contribute to the loss of corneal endothelial cell density. The average endothelial cell loss in the 10 eyes with oil retained for an average of 10+/-12 months was 68.8 +/-31.4%, as compared to the fellow eye. The average cell loss was higher in the three eyes with silicone oil in the anterior chamber (range 44 to >95%). Pseudophakic eyes fared better, on average, than aphakic eyes (51.66+/-28% vs. 66.63+/-26.3%) with respect to cell loss. Five aphakic eyes and 1 pseudophakic eye developed corneal edema. CONCLUSIONS: Endothelial cell loss occurs after vitreoretinal surgery and is exacerbated by long term silicone oil retention. The corneal endothelial cell damage is probably cumulative from procedure to procedure. Endothelial cell loss may be pronounced in eyes without a physical barrier between the anterior segment and the vitreous cavity, and in eyes where oil migrates into anterior chamber.

Adult↗
PubMed2002

[The influence of silicone oil removal on intraocular pressure].

PURPOSE: The aim of this study was to evaluate the influence of silicone oil removal on intraocular pressure. MATERIAL AND METHOD: Our material consists of 98 patients (104 eyes), who underwent vitrectomy with silicone oil tamponade. Sixteen eyes in this group were aphakic before vitrectomy. The mean duration of silicone-oil tamponade was 8.8 months. We examined and compared intraocular pressure in all cases before vitrectomy, during tamponade and after silicone oil removal. RESULTS: The increased intraocular pressure (> 22 mmHg) was found in 27 eyes (seven of them were aphakic) during tamponade. We had to remove silicone oil due to glaucoma in 6 eyes (three of them were aphakic). In 9 eyes (four aphakic) the intraocular pressure was higher than 22 mmHg after silicone oil removal. Seven patients required additional topical medication and 2 patients were qualified for operation--trabeculectomy. Hypotony (< 10 mmHg) was observed in 11 eyes, and it coexisted with retinal redetachment in 4 cases. CONCLUSIONS: The increased intraocular pressure is a frequent complication of silicone oil tamponade, and it normalizes after silicone oil removal in most of these cases.

Adult↗
PubMed2001

Silicone sheeting decreases fibroblast activity and downregulates TGFbeta2 in hypertrophic scar model.

BACKGROUND: Fibroproliferative disorders, which include hypertrophic scars and keloids, represent deviations from the normal process of wound healing. The fibrogenic cytokines have been associated with excessive scarring. It has been proposed that placing silicone in contact with hypertrophic scars may prove to be an effective form of treatment. This may be a result of downregulating fibroblasts and/or decreasing the fibrogenic cytokines. An in vitro model to study wound contraction is a fibroblast populated collagen lattice (FPCL). This study used FPCL as a method to study the effect of silicone sheeting on hypertrophic scar fibroblasts. METHODS: Fibroblast cultures were obtained and collagen lattices were prepared. Silicone sheeting was placed over the collagen matrix versus Saran wrap used as a treatment control. The amount of gel contraction was measured every 24 hours for five days. The supernatant obtained from the culture medium following completion of the FPCL portion of the experiment was then used in an immunoassay for TGFbeta2. RESULTS: A statistically significant decrease in amount of FPCL contraction occurred between three of the four brands of silicone sheets used compared to untreated control or Saran wrap treated FPCL. The immunoassay for TGFbeta2 showed a statistically significant decrease with all four types of silicone sheeting. CONCLUSION: FPCLs populated with burn hypertrophic scar fibroblasts exposed to silicone sheeting have decreased contraction compared to an unexposed control and Saran wrap treated control. In addition, TGFbeta2 is downregulated in the silicone exposed group. It appears that silicone sheeting may act by downregulating fibroblasts and decreasing fibrogenic cytokines.

Cells, Cultured↗
PubMed1992

Effects and distribution of intravitreally or subretinally injected silicone oil identified in rabbit retina using osmium tetroxide method.

Silicone oil was injected into the eyes of 28 rabbits. Utilizing the specific affinity of osmium tetroxide for lipids, the pathological features and histochemical localization of silicone oil within the retina were studied. This osmium tetroxide technique makes it possible to identify the presence of silicone oil particles in the ocular tissues. It was demonstrated that in eyes with silicone oil injected into the vitreous cavity or subretinal space, silicone oil was detected in the inner retinal layer and in phagocytes in the vitreous cavity but not in the outer retinal layer, retinal pigment epithelium and choroid. In addition, prominent subretinal and epiretinal proliferation with abundant phagocytes containing silicone oil particles were noted in the eyes with subretinal injection of silicone oil through an artificial retinal break. This study suggests that when injected subretinally silicone oil induces excessive subretinal and epiretinal proliferation.

Animals↗
PubMed2003

Vitrectomy and silicone oil in the treatment of acute endophthalmitis. Preliminary results.

PURPOSE: To evaluate the role of pars plana vitrectomy (PPV) and silicone oil injection in the treatment strategy of severe endophthalmitis. PATIENTS AND METHODS: This study analyses a retrospective case series of 34 patients with signs and symptoms of severe endophthalmitis with visual acuity limited to light perception. All underwent PPV with intraocular injection of antibiotics (IOAB), together with topical and oral antibiotics. In 10 patients (group 1), this treatment alone was sufficient to control infection. In 10 other patients (group 2) with the same initial treatment, a new vitrectomy was needed: 8 because of retinal detachment, 2 because of persistent infection. In 2 patients (group 3), initially treated with PPV and IOAB, a second vitrectomy with IOAB and silicone oil tamponade was needed to stop infection. In 12 patients (group 4), with the worse prognosis related to the severity of infection and/or to associated retinal necrosis, PPV, IOAB and silicone oil tamponade were conducted at first surgery. Final anatomic status and visual acuity were assessed to compare the effectiveness of these different treatments. RESULTS: In 22 patients (group 1, 2 and 3) treated initially without silicone oil, 12 patients (55%) needed further surgery, either for persistent infection or retinal detachment. Twelve patients (group 4) treated at first with silicone oil had a rapid control of the infectious process and better anatomical results with this procedure only. Final visual acuity was also better in the silicone oil groups (group 3 and 4) than in the non silicone groups (group 1 and 2). CONCLUSION: These results suggest that silicone oil tamponade might be beneficial in the treatment strategy of severe endophthalmitis.

Acute Disease↗
PubMedDate not supplied

Silicone implants and systemic immunological disease: review of the literature and preliminary results.

Silicone has been utilized as an implant in reconstructive surgery. For years, silicone has been considered to be biologically inert and essentially harmless. Several studies and case reports show that female patients treated with silicone implants developed a systemic disease associated with immunological abnormalities. Removal of the silicone implants was associated with recovery and resolution of the immune abnormalities. Recently, specific antibodies to silicone have been isolated in children with silicone implants. Additionally, immunological abnormalities and high incidence of systemic progressive sclerosis in patients with silicone implants or injections further support the notion that silicone is not biologically inert, and can cause a syndrome of a systemic disease and immunological abnormalities. The specific mechanisms and duration of the latency period is not yet fully understood.

Adult↗
PubMed2004

[Pathological analysis of breast carcinoma after silicone gel injection].

OBJECTIVE: To explore the correlation between breast carcinoma and silicone gel injection for breast augmentation. METHODS: Four cases of breast cancer after silicone gel injection were studied by means of clinical pathological analysis. RESULTS: In the four women, breast lump of over 5 cm in diameter was found half year to 2 years after silicone injection. The tumor was misdiagnosed to inflammatory reaction of silicone gel injection. Definite diagnosis was made by histological examinations, which showed there was mucoid, light blue and well-distributed silicone gel among the nests of neoplasm cells. Lymph node metastasis of cancer cells was observed. CONCLUSIONS: Silicone gel injection to the breast may be a reason for evoking or accelerating breast cancer. Breast cancer that occurred after breast augmentation with silicone gel injection could be misdiagnosed. Final diagnosis depends on biopsy. Silicone gel injection for breast augmentation should be abandoned.

Adult↗
PubMed1991

Effect of silicone oil on ocular tissues.

The effect of silicone oil on ocular tissues was investigated histopathologically in rabbit eyes by injecting silicone oil into the anterior chamber or the vitreous cavity after vitrectomy. The eyes were enucleated 3, 6, 9, 12 or 18 months after the injection and various tissues were observed by light and electron microscopy. Silicone oil was first observed in the retrocorneal membrane at 18 months after the injection. In the trabecular meshwork silicone oil was seen for the first time at 12 months after injection. Migrating cells engulfing silicone oil attached to the internal limiting membrane of the retina 3 months after the injection. Twelve and 18 months after the injection, silicone oil passed through the internal limiting membrane and was engulfed by Müller cells. These results indicate that attention should be paid to the effects of silicone oil on ocular tissues when it remains in the eye for a long time since, after a certain period, cells of the trabecular meshwork and retina may engulf silicone oil.

Animals↗
PubMed1990

[Experimental studies of the so-called emulsification behavior of silicone oil: effect of viscosity].

The stability of intraocularly applied silicone oils plays an important role in their biocompatibility. The clinically used silicone oils are not a unique group of materials. There are important differences regarding viscosity and the amount of low molecular and ionic components. A sign of bioinstability of silicone oils is silicone oil emulsification. According to clinical experience and experimental studies, less viscous silicone oils seem to emulsify earlier then more viscous oils. Therefore, we investigated three highly purified polydimethylsiloxanes with defined physicochemical characteristics and viscosities of 1,000 cs, 5,000 cs and 10,000 cs for their in vitro stability. As detergents, we used fibrin, fibrinogen, gammaglobulins, acidic alpha-1-glycoprotein, very-low-density lipoprotein (VLDL), and serum. The oil with a viscosity of 1000 cs was the most unstable silicone oil whereas the oils of 5,000 cs and 10,000 cs reacted similarly. The most effective detergents were fibrin, fibrinogen and serum-causing emulsification for all silicone oils investigated whereas gamma-globulins, acidic alpha-1-glycoprotein and VLDL only emulsified the less viscous oil of 1,000 cs. Our results show the importance of viscosity for the stability of silicone oils and the effect of biologically potential detergents.

Drug Stability↗
PubMed1990

[The effect of silicone oil on the ocular tissues].

It has been pointed out that the silicone oil tamponade can result in complications such as corneal damage, elevation of intraocular pressure and retinal toxicity against. The effect of silicone oil on the ocular tissues was investigated histopathologically by injecting silicone oil into the anterior chamber of the eyes of rabbits. In addition, in order to study its effect on the retina, silicone oil was injected into the vitreous cavity after vitrectomy. The eyes were extracted 3, 6, 9, 12 and 18 months after injection and various tissues were observed by light and electron microscopy. Silicone oil particles were first observed in the retro-corneal membrane 18 months after injection. In the trabecular meshwork silicone oil particles were seen for the first time 12 months after injection. Migrating cells engulfing silicone oil particles were attached to the internal limiting membrane of the retina three months after injection. Twelve and 18 months after injection, silicone oil particles passed through the internal limiting membrane and were engulfed by Mueller cells.

Animals↗
PubMed1995

Silicone implants and the inhibition of cancer.

The safety of augmentation mammaplasty and its relationship to breast cancer has been a much debated topic. The authors previously showed a decreased incidence of breast cancer in rats who had received silicone implants 2 weeks before carcinogen stimulation. The present study was designed to determine (1) whether this protective effect is influenced by the location of the implant, and (2) whether tumor incidence could also be altered in spontaneous mammary tumor-forming animals, the C3H/OuJ mice. (1) A total of 110 rats received either a silicone implant or a sham operation in one of three locations: inframammary region, dorsum, or intraperitoneal cavity. Methylnitrosoured (MNU) injections occurred 14 days after implantation. Animals were examined weekly for tumor growth and were killed 250 days after MNU injection. Animals with silicone implants beneath the mammary gland had a statistically significant lower incidence of breast cancer formation (11.5 percent) compared with both dorsally implanted animals (45.8 percent) and sham controls (64 percent). (2) Sixty C3H/OuJ mice underwent implantation of either a silicone implant, free silicone gel, silicone sheet, or a sham operation. At 50 weeks of age, after weekly examinations, the animals were killed. The cancer incidence in mice with silicone implants was 17 percent compared with 50 percent found in sham controls. Exposure to a silicone prosthesis at an early age does not seem to increase tumor incidence and may even have a locally protective effect against breast cancer formation.

Age Factors↗
PubMed1993

[Ocular tissue after intravitreous silicone oil injection. Histologic and electron microscopy studies].

The intraocular tolerance of silicone oil is still a matter of ongoing controversy. To evaluate a possible migration of silicone oil into eye tissues we examined various tissues from eyes that were injected with silicone oil for a period of 6 months to 3.5 years. The histological and ultrastructural characteristics of these tissues are reported (cornea, 4 cases; iris, 3 cases; retina, 8 cases; retinal pigment epithelium and optic nerve, 1 case). In the iris and in corneas showing a perforating injury light microscopy revealed vacuoles presumably lying in the cytoplasm of macrophages. Using immunohistochemistry and electron microscopy, macrophages could also be found in the retina of eyes that had been filled with silicone oil for longer than 6 months. Using energy dispersive X-ray analysis, vacuoles could be identified as storage sites of the silicone oil. This observation demonstrates that a long-term silicone oil tamponade may cause a migration of silicone oil into the retina and other ocular tissues. In order to prevent this complication, removal of silicone oil should be performed as early as possible.

Choroid↗
PubMed1996

[Recurrent vitreoretinal membranes in intravitreal silicon oil tamponade. Morphologic and immunohistochemical studies].

During intraocular silicon oil tamponade, recurrent vitreoretinal membranes can become clinically relevant and may need surgical excision. We investigated 40 PVR and 10 diabetic membranes which had formed during intraocular tamponade with highly purified silicone oil (5000 cs). The membranes were investigated by light and electron microscopy with respect to silicone oil-specific alterations. The participating cells were differentiated immunohistochemically. Mechanisms of intercellular growth regulation were analyzed by the use of antibodies against cell adhesion molecules and growth factor receptors (PDGFr-B). Most of the membranes showed typical signs of the underlying disease process. However, seven PVR and four diabetic membranes had specific interstitial and intracellular vacuoles which were considered to be silicone oil droplets. The phagocytosing cells were macrophages, partially embedded within vitreous residues. T-lymphocytes can be drawn to the area of macrophage activity by the expression of ICAM-1 and LFA-1. The residual parts of the membranes are typical vitreoretinal membranes. The receptors for PDGF, fibronectin and laminin were negative, but the receptors for collagen and vitronectin were positive within these membranes. The silicone oil-specific macrophage reaction might be supported by emulsified silicone oil droplets, which might get phagocytosed at a certain size. The secondary inflammatory reactions can further enhance silicone oil emulsification and start a vicious circle. Nevertheless, the underlying disease process seems to be much more important in stimulating recurrent membrane formation than silicone oil-specific cell reactions.

Cell Division↗
PubMed1996

[Changes in ocular refraction after tamponade with silicone oil].

In order to study refractive changes caused by a intravitreal silicone oil injection we retrospectively analyzed 25 eyes after vitreoretinal surgery combined with silicone oil tamponade. In all cases the postoperative visual acuity was 0.1 or better. Mean difference in refraction after silicone oil tamponade in phakic eyes was +5.07 Dsph (+2.0 to +8.0 Dsph). Mean refractive change in the aphakic silicone oil filled eyes was - 6.63 Dsph (-4.0 to -9.0 Dsph). Silicone oil extraction induced a greater refractive change (myopic shift, mean -5.57 Dsph) than silicone oil injection. After silicone oil extraction from the aphakic eyes refractive changes (shift towards hypermetropia, mean +5.86 Dsph) were less manifest than after silicone oil injection. The disparity could be explained by eye elongation after cerclage performed during primary vitreoretinal surgery.

Humans↗
PubMed1997

Explantation of silicone breast implants.

Silicone gel-filled breast implants have been employed clinically for decades for aesthetic augmentation or postmastectomy reconstruction. Most patients and surgeons attest to the efficacy and safety of these devices. However, more recently in the medical literature and popular media, silicone gel-filled breast implants have been claimed to incite an array of clinical sequelae such as capsular formation, granulomatous disease, arthritis, arthralgia, fibromyalgia, autoimmune collagen vascular disease, human adjuvant disease, siliconosis, silicone-related disease, and silicone implant-associated syndrome. During a recent 24-month period, 25 referred patients underwent explantation of bilateral silicone gel-filled prostheses at the University of South Alabama. Patient-reported symptoms and signs included mastodynia, arthralgia, fibromyalgia, xerophthalmia, xerostomia, hypesthesia, and amblyopia. Clinical examination and mammography were reliable in diagnosing implant rupture, but only re-exploration reliably detected implant leakage. Most patients underwent concurrent replacement with saline-filled devices. Histopathologic analyses of all tissue samples revealed chronic inflammation. Subjective improvement of patient-reported symptoms and signs occurred over the course of months postoperatively. There was no mortality associated with explantation, with or without replacement, but an overall morbidity incidence of 20 per cent (5 of 25) was observed. Predicated upon review of the available scientific literature and analysis of this modest number of patients, the following perspectives are germane. 1) A small cohort of patients of status postimplantation of silicone gel-filled devices will manifest chronic morbidity. Identifying such patients prospectively remains problematic. 2) Whether or not silicone gel incites adverse systemic phenomena is unproven, although it has been implicated. 3) Symptomatic patients with silicone gel-filled implants in place should be considered for removal, with full knowledge of the morbidity associated with revisional procedures. 4) Patients currently undergoing breast augmentation or reconstruction employing prosthetics are perhaps best served by insertion of saline-filled devices. 5) Patient-physician dialogue regarding the risk-benefit analysis of prosthetic implantation is imperative. Patients consenting to such procedures must be willing to assume risks.

Adult↗
PubMed2005

Si-C linked organic monolayers on crystalline silicon surfaces as alternative gate insulators.

Herein, the influence of silicon surface modification via Si-C(n)H(2n+1) (n=10,12,16,22) monolayer-based devices on p-type 100 and n-type 100 silicon is studied by forming MIS (metal-insulator-semiconductor) diodes using a mercury probe. From current density-voltage (J-V) and capacitance-voltage (C-V) measurements, the relevant parameters describing the electrical behavior of these diodes are derived, such as the diode ideality factor, the effective barrier height, the flatband voltage, the barrier height, the monolayer dielectric constant, the tunneling attenuation factor, and the fixed charge density (Nf). It is shown that the J-V behavior of our MIS structures could be precisely tuned via the monolayer thickness. The use of n-type silicon resulted in lower diode ideality factors as compared to p-type silicon. A similar flatband voltage, independent of monolayer thickness, was found, indicating similar properties for all silicon-monolayer interfaces. An exception was the C10-based monolayer device on p-type silicon. Furthermore, low values of N(f) were found for monolayers on p-type silicon (approximately 6 x 10(11) cm(-2)). These results suggest that Si--C linked monolayers on flat silicon may be a viable material for future electronic devices.

Journal Article↗
PubMed2004

A high-speed silicon optical modulator based on a metal-oxide-semiconductor capacitor.

Silicon has long been the optimal material for electronics, but it is only relatively recently that it has been considered as a material option for photonics. One of the key limitations for using silicon as a photonic material has been the relatively low speed of silicon optical modulators compared to those fabricated from III-V semiconductor compounds and/or electro-optic materials such as lithium niobate. To date, the fastest silicon-waveguide-based optical modulator that has been demonstrated experimentally has a modulation frequency of only approximately 20 MHz (refs 10, 11), although it has been predicted theoretically that a approximately 1-GHz modulation frequency might be achievable in some device structures. Here we describe an approach based on a metal-oxide-semiconductor (MOS) capacitor structure embedded in a silicon waveguide that can produce high-speed optical phase modulation: we demonstrate an all-silicon optical modulator with a modulation bandwidth exceeding 1 GHz. As this technology is compatible with conventional complementary MOS (CMOS) processing, monolithic integration of the silicon modulator with advanced electronics on a single silicon substrate becomes possible.

Journal Article↗
PubMed2005

Strong quantum-confined Stark effect in germanium quantum-well structures on silicon.

Silicon is the dominant semiconductor for electronics, but there is now a growing need to integrate such components with optoelectronics for telecommunications and computer interconnections. Silicon-based optical modulators have recently been successfully demonstrated; but because the light modulation mechanisms in silicon are relatively weak, long (for example, several millimetres) devices or sophisticated high-quality-factor resonators have been necessary. Thin quantum-well structures made from III-V semiconductors such as GaAs, InP and their alloys exhibit the much stronger quantum-confined Stark effect (QCSE) mechanism, which allows modulator structures with only micrometres of optical path length. Such III-V materials are unfortunately difficult to integrate with silicon electronic devices. Germanium is routinely integrated with silicon in electronics, but previous silicon-germanium structures have also not shown strong modulation effects. Here we report the discovery of the QCSE, at room temperature, in thin germanium quantum-well structures grown on silicon. The QCSE here has strengths comparable to that in III-V materials. Its clarity and strength are particularly surprising because germanium is an indirect gap semiconductor; such semiconductors often display much weaker optical effects than direct gap materials (such as the III-V materials typically used for optoelectronics). This discovery is very promising for small, high-speed, low-power optical output devices fully compatible with silicon electronics manufacture.

Journal Article↗