Safety assessment of silylates and surface-modified siloxysilicates.

The Cosmetic Ingredient Review (CIR) Expert Panel assessed the safety of silica silylate, silica dimethyl silylate, trimethylsiloxysilicate, and trifluoropropyldimethyl/trimethylsiloxysilicate as used in cosmetics. These silylates and surface-modified siloxysilicates function in cosmetics as antifoaming agents, anticaking agents, bulking agents, binders, skin-conditioning agents--emollient, skin-conditioning agents-occlusive, slip modifiers, suspension agents--nonsurfactant, and viscosity increasing agents--nonaqueous. The Expert Panel reviewed the available animal and clinical data as well as information from a previous CIR safety assessment of amorphous silica. The CIR Expert Panel concluded that silica silylate, silica dimethyl silylate, trimethylsiloxysilicate, and trifluoropropyldimethyl/trimethylsiloxysilicate are safe as used when formulated and delivered in the final product not to be irritating or sensitizing to the respiratory tract.

Evaluation of limbal and pars plana silicone oil removal in aphakic eyes.

PURPOSE: To compare limbal and pars plana silicone oil removal (SOR) in aphakic eyes and to evaluate the acute effect of silicone oil flow to the corneal endothelium. METHODS: Sixteen aphakic patients with silicone oil endotamponade requiring SOR were recruited for this prospective study and randomly scheduled for limbal or pars plana SOR. The central corneal thickness (CCT), visual acuity (VA) and intraocular pressure were measured preoperatively, on the first postoperative day and 4 months after surgery. Endothelial cell density (ECD) was measured preoperatively and at the end of follow-up. The in vitro study was performed on ten enucleated porcine eyes. Corneoscleral discs were prepared and fixed on artificial anterior chamber followed by 2.5-mm limbal incision and 5-ml silicone oil injection in six cases and 5 ml balanced salt solution (BSS) in four cases. RESULTS: The ECD decreased by 239.2 ± 86.7 (13.9%) and 86.7 ± 22.4 cells/mm(2) (5%) after limbal (n = 8) and pars plana SOR (n = 8), respectively (p < 0.001 for both). The difference between the groups was significant (p < 0.001). A significant increase in CCT and corresponding decrease in VA was noted on the first postoperative day using both procedures. At the end of follow-up, the CCT and VA were comparable to initial values. Postoperative hypotony (≤6 mmHg) was observed more frequently after limbal SOR. In the experiment, lamellar abrasions of corneal endothelium were observed after silicone oil injection, whereas no changes were observed after BSS injection. CONCLUSION: Limbal SOR causes more considerable damage to the corneal endothelium than the pars plana approach because of mechanical abrasion.

Emulsification and inverted hypopyon formation of oxane HD in the anterior chamber.

BACKGROUND: Oxane HD(R) is a "heavier-than-water" silicone oil which has a specific gravity of 1.02 g/cm(3). When dispersed into droplets, one expects them to sink. We report a case of emulsification of Oxane HD in an eye that unexpectedly manifested as an "inverted hypopyon". METHODS: The clinical findings of a 45-year-old man who underwent pars plana vitrectomy and Oxane HD endotamponade for a phakic inferior rhegmatogenous retinal detachment are described. RESULTS: A large silicone oil globule was noted to be floating in the anterior chamber on postoperative day 1. Emulsification of the globule and inverted hypopyon formation were subsequently observed at 2 months postoperatively. CONCLUSIONS: Emulsification and inverted hypopyon formation in the anterior chamber may occur with Oxane HD. One explanation might be that the Oxane HD has separated out into its constituent components of silicone and RMN3, which raises questions as to the basis for its claim to be a heavier-than-water tamponade.

Immunopathology of intraocular silicone oil: enucleated eyes.

AIMS: To characterise the distribution of silicone oil in ocular tissues in globes enucleated after complicated retinal detachment, and to document the distribution and nature of any associated inflammatory response. METHOD: 9 enucleated globes that had previously undergone retinal detachment surgery with silicone oil and 7 control globes that had undergone enucleation after retinal detachment surgery (n = 2) or ocular trauma (n = 5) were studied. Sections were histologically examined using light microscopy to document the distribution of silicone oil in ocular tissues. Immunohistochemical analysis was carried out using the ABC technique and a panel of monoclonal and polyclonal antibodies. Electron microscopy was undertaken to observe the penetration of silicone oil in the trabecular meshwork of the anterior chamber drainage angle. RESULTS: Silicone oil was distributed throughout the globes-notably in the iris, ciliary body, retina, trabecular meshwork and epiretinal membranes. Focal areas of intraretinal silicone were associated with disorganised retinal architecture, retinectomy sites or subretinal oil. The distribution of macrophages was closely related to the distribution of silicone oil. T and B lymphocytes were not associated with silicone oil unless additional pathology was also present-for example, cyclitic membrane or uveitis. One of the nine eyes had silicone oil present in the optic nerve. In the control globes, the inflammatory response was mediated primarily by macrophages and T lymphocytes, and was less marked than that observed in the silicone oil globes. CONCLUSION: This study shows that silicone oil may be sequestered in varied ocular tissues and is associated with localised inflammation mediated by macrophages.

A pilot study on the use of a perfluorohexyloctane/silicone oil solution as a heavier than water internal tamponade agent.

AIMS: To report a prospective two centred non-comparative interventional pilot study of a solution of perfluorohexyloctane and silicone oil (Densiron-68) as a heavier than water internal tamponade. METHODS: 42 consecutive patients were recruited. The indications include proliferative vitreoretinopathy, retinal detachments arising from inferior retinal breaks, and inability to posture. RESULTS: The success rate with one operation using Densiron was 81% and with further surgery 93%. At the end of the study all tamponade agents were removed in 90% of patients. Visual acuity improved from mean logMAR of 1.41 (SD 0.64) to 0.94 (SD 0.57), p = 0.001. There was little evidence of dispersion and excessive inflammation. CONCLUSION: This new tamponade agent is being compared to conventional silicone oil in a prospective international randomised trial.

Deposition of silicone oil droplets in the residual anterior lens capsule after vitrectomy and lensectomy in rabbits.

AIM: To examine the histology of preserved anterior lens capsule in vitrectomised and lensectomised rabbit eyes with and without silicone oil tamponade. METHODS: Forty adult Japanese albino rabbits received two port vitrectomy and lensectomy with or without silicone oil tamponade in one eye under both general and topical anaesthesia. Anterior lens capsule was preserved during operation. After healing intervals residual anterior capsule was histologically observed under light or electron microscopy. RESULTS: Immediately after operation, cuboidal lens epithelial cells were observed on the posterior surface of the preserved anterior capsule. During healing intervals in eyes with or without silicone oil tamponade, regenerated lens structure of Sommerring's ring and fibrous tissue formed in the peripheral and central areas of the residual capsule, respectively. Ultrastructural observation revealed the presence of many vacuoles amid matrix accumulation on the posterior capsular surface, suggesting the deposition of emulsified silicone oil droplets. CONCLUSION: Lens epithelial cells produce regenerated lenticular structure and fibrous tissue on the residual capsule following vitrectomy and lensectomy in rabbits. Silicone oil droplets formed by its emulsification deposit in extracellular matrix accumulated on the posterior surface of the anterior capsule. Emulsified silicone may potentially enhance opacification of residual anterior capsule following pars plana vitrectomy by silicone oil deposition and subsequent activation of lens epithelial cells.

Silicone oil-intraocular lens interaction: which lens to use?

AIM: To determine a suitable intraocular lens for implantation in patients at high risk of lens exposure to silicone oil in their lifetime. METHODS: PMMA, AcrySof, AR40, AQUA-Sense, and Raysoft lenses were examined. Each lens was immersed for 5 minute intervals in balanced salt solution (BSS), in stained silicone oil, and again in BSS before being photographed in air and in BSS. Percentage silicone oil coverage of the lens optic was determined. RESULTS: The mean percentage coating (MPC) for the lens biomaterials ranged from 5.2% to 21.5%. The Raysoft lens had significantly less oil coverage when statistically compared with the other lens types (p < 0.001). CONCLUSION: A Raysoft (Rayner) lens is a suitable lens for implantation in patients who are at risk of severe vitreoretinal disease.

[Toxic substances with silicone oil after intraocular injections]. / Toxische Substanzen im Silikonöl nach intraokularer Injektion.

In articles about the analysis of intraocular silicone oil, mostly the amount and toxicity of low-molecular-weight components (LMWC) have been investigated. This study was intended to analyze the components of silicone oil following a longer intraocular application. We analyzed silicone oil removed from human eyes with PVR a few months postoperatively. The fraction of LMWC was further investigated and we separated 16 different components belonging to hexachlorhexanes (HCH), polybiphenyls (PCB) and dichlor-diphenyl-trichlorethane (DDT). All these substances are said to have a toxic and cancerogenic effect as well as weakening the immune system. The concentration of these organic chloride components measured in intraocular injected silicone oil is about the same as fatty tissue but exceeds the concentration in human blood enormously. Possible damage to the retina by these toxic substances is another reason for early removal of silicone oil if the situation of the retina is stable.

Egress route of emulsified 20 centistokes silicone oil from anterior chamber of rabbit.

Silicone oil is used in recent clinical practice, however, it may cause adverse reactions in the eyes. When the high viscosity silicone oil is contaminated with low molecular weight silicone oil, the contamination may cause ocular toxicity or elevation of the intraocular pressure. To obtain information on the distribution of this preparation, emulsified 20 centistokes silicone oil was injected into the anterior chamber of rabbit eyes. The silicone oil droplets were visualized by light and electron microscopy by using oil soluble phthalocyanine blue. This copper containing dye remains in the tissue after removal of the silicone oil by organic solvents. Two and 4 weeks after an injection, the silicone emulsion was observed as numerous small vacuoles with blue precipitate at the margin of vacuoles within elongated trabecular endothelial cells, fibroblasts along the route of uveoscleral outflow and cells of the iris. Three hours after the injection, only a few vacuoles were present in these cells. These results demonstrated that the emulsified silicone oil leaves the anterior chamber through the conventional and unconventional routes. Phagocytosis by the trabecular endothelial cells and fibroblasts along the uveoscleral route caused an accumulation of the emulsified silicone oil in these cells. With chronic exposure to emulsified silicone oil, changes in the trabecular meshwork may lead to a reduction in the outflow of aqueous humor and cause glaucoma.

Evaluation of the blood-aqueous barrier after vitreous replacement with perfluoropropane gas and liquid silicone.

Fluorophotometric measurements of blood-aqueous barrier permeability after intravitreal injection of perfluoropropane gas in rabbit eyes revealed fluorescein leakage immediately after injection; 3 days later, recovery of barrier integrity had begun to occur and 7 days and 14 days after gas injection, when the gas bubble was still in the eye, anterior chamber fluorescein concentrations were normal. Similarly, in eyes undergoing vitrectomy and injection of silicone liquid or vitrectomy only, anterior chamber fluorescein levels were elevated 3 days and 1 week after surgery. Nevertheless, normal barrier integrity was reestablished in both the silicone-filled eyes and the vitrectomized eyes after 1 week. Since there was no difference between the group injected with silicone and the group that underwent vitrectomy only with respect to anterior chamber fluorescein concentration at any of the times studied, it is concluded that the temporary disruption of the blood-aqueous barrier is associated with the surgical procedure rather than the presence of silicone liquid in the vitreous cavity.

Serum silicon levels in recipients of an electrohydraulic ventricular assist system.

This study was designed to determine the permeation rate of silicon oil from the authors' electrohydraulic ventricular assist system (EHVAS), and to evaluate influences on organ function. The permeation rate through the diaphragm of the EHVAS was determined by in vitro experiments. Influences on organ function were evaluated in three goats with EHVAS by monitoring blood chemical parameters and serum silicon levels (S-Si). The permeation rate from the EHVAS was about 0.2 ml/month, calculated from the data obtained in the in vitro experiments. S-Si levels did not increase during chronic animal implantation, and renal and hepatic function were not affected. The permeation rate through the diaphragm must, however, be taken into consideration.

[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.

Pressure probe study of the water relations of Phycomyces blakesleeanus sporangiophores.

The physical characteristics which govern the water relations of the giant-celled sporangiophore of Phycomyces blakesleeanus were measured with the pressure probe technique and with nanoliter osmometry. These properties are important because they govern water uptake associated with cell growth and because they may influence expansion of the sporangiophore wall. Turgor pressure ranged from 1.1 to 6.6 bars (mean = 4.1 bars), and was the same for stage I and stage IV sporangiophores. Sporangiophore osmotic pressure averaged 11.5 bars. From the difference between cell osmotic pressure and turgor pressure, the average water potential of the sporangiophore was calculated to be about -7.4 bars. When sporangiophores were submerged under water, turgor remained nearly constant. We propose that the low cell turgor pressure is due to solutes in the cell wall solution, i.e., between the cuticle and the plasma membrane. Membrane hydraulic conductivity averaged 4.6 x 10(-6) cm s-1 bar-1, and was significantly greater in stage I sporangiophores than in stage IV sporangiophores. Contrary to previous reports, the sporangiophore is separated from the supporting mycelium by septa which prevent bulk volume flow between the two regions. The presence of a wall compartment between the cuticle and the plasma membrane results in anomalous osmosis during pressure clamp measurements. This behavior arises because of changes in solute concentration as water moves into or out of the wall compartment surrounding the sporangiophore. Theoretical analysis shows how the equations governing transient water flow are altered by the characteristics of the cell wall compartment.