Tamponade efficiency of perfluorohexyloctane and silicone oil solutions in a model eye chamber

Improved Outcomes with Heavy Silicone Oil in Complex Primary Retinal Detachment: A Large Multicenter Matched Cohort Study

PURPOSE

To establish whether Densiron 68, a heavier-than-water endotamponade agent, is an effective alternative to conventional light silicone oil in primary rhegmatogenous retinal detachment (RD) surgery for eyes with inferior breaks in the detached retina and severe proliferative vitreoretinopathy (PVR).

DESIGN

Cohort study of routinely collected data from the European Society of Retina Specialists and British and Eire Association of Vitreoretinal Surgeons vitreoretinal database between 2015 and 2022.

PARTICIPANTS

All consecutive eyes that underwent primary rhegmatogenous RD surgery using Densiron 68 or light silicone oil as an internal tamponade agent.

METHODS

To minimize confounding bias, we undertook 2:1 nearest-neighbor matching on inferior breaks, large inferior rhegmatogenous RDs, PVR, and, for visual analyses, baseline visual acuity (VA) between treatment groups. We fit regression models including prognostically relevant covariates, treatment-covariate interactions, and matching weights. We used g-computation with cluster-robust methods to estimate marginal effects. For nonlinear models, we calculated confidence intervals (CIs) using bias-corrected cluster bootstrapping with 9999 replications.

MAIN OUTCOME MEASURES

Presence of a fully attached retina and VA at least 2 months after oil removal.

RESULTS

Of 1061 eyes enrolled, 426 and 239 were included in our matched samples for anatomic and visual outcome analyses, respectively. The primary success rate was higher in the Densiron 68 group (113 of 142; 80%) compared with the light silicone oil group (180 of 284; 63%), with an adjusted odds ratio of 1.90 (95% CI, 1.63-2.23, P < 0.001). We also observed a significant improvement favoring Densiron 68 of -0.26 logarithm of the minimum angle of resolution (logMAR) in postoperative VA between the 2 groups (95% CI, -0.43 to -0.10, P = 0.002). The anatomic benefit of using Densiron 68 in eyes with inferior retinal breaks and large detachments was more pronounced among eyes with PVR grade C. We found no evidence of visual effect moderation by anatomic outcome or foveal attachment.

CONCLUSIONS

Densiron achieved higher anatomic success rates and improved visual outcomes compared with conventional light silicone oil in eyes with inferior retinal pathology and severe PVR.

FINANCIAL DISCLOSURE(S)

Proprietary or commercial disclosure may be found in the Footnotes and Disclosures at the end of this article.

Sustained-release drug delivery systems

The design and development of a sustained-release drug delivery system targeting the administration of active pharmaceutical ingredients (APIs) to the eye could overcome the limitations of topically administered eye drops. Understanding how to modify or design new materials with specific functional properties that promote the attachment and release of specific drugs over longer time periods, alongside understanding clinical needs, can lead to new strategic opportunities to improve treatment options. In this paper we discuss two approaches to the design or modification of materials to produce a sustained therapeutic effect. Firstly, we discuss how the synthesis of a peptide hydrogel from a naturally-derived antimicrobial material led to the design of a bandage contact lens which may be able to be used prophylactically to reduce post-surgery infection. Secondly, we discuss how silicone oil tamponade agents used to treat retinal detachments can have adjunctive behaviour to enhance the solubility of the anti-proliferative drug retinoic acid and produce a sustained release over several weeks. These studies are the result of close partnerships between clinical ophthalmologists, materials scientists, and chemists, and illustrate how these partnerships can lead to comprehensive understandings that have the potential to change patient outcomes.

Advances in Polysaccharide- and Synthetic Polymer-Based Vitreous Substitutes

The vitreous humour is a gel-like structure that composes the majority of each eye. It functions to provide passage of light, be a viscoelastic dampener, and hold the retina in place. Vitreous liquefaction causes retinal detachment and retinal tears requiring pars plana vitrectomy for vitreous substitution. An ideal vitreous substitute should display similar mechanical, chemical, and rheological properties to the natural vitreous. Currently used vitreous substitutes such as silicone oil, perfluorocarbon liquids, and gases cannot be used long-term due to adverse effects such as poor retention time, cytotoxicity, and cataract formation. Long-term, experimental vitreous substitutes composed of natural, modified and synthetic polymers are currently being studied. This review discusses current long- and short-term vitreous substitutes and the disadvantages of these that have highlighted the need for an ideal vitreous substitute. The review subsequently focuses specifically on currently used polysaccharide- and synthetic polymer-based vitreous substitutes, which may be modified or functionalised, or employed as the derivative, and discusses experimental vitreous substitutes in these classes. The advantages and challenges associated with the use of polymeric substitutes are discussed. Innovative approaches to vitreous substitution, namely a novel foldable capsular vitreous body, are presented, as well as future perspectives related to the advancement of this field.

Vitreous Substitutes from Bench to the Operating Room in a Translational Approach: Review and Future Endeavors in Vitreoretinal Surgery

Vitreous substitutes are indispensable tools in vitreoretinal surgery. The two crucial functions of these substitutes are their ability to displace intravitreal fluid from the retinal surface and to allow the retina to adhere to the retinal pigment epithelium. Today, vitreoretinal surgeons can choose among a plethora of vitreous tamponades, and the tamponade of choice might be difficult to determine in the ever-expanding range of possibilities for a favorable outcome. The currently available vitreous substitutes have disadvantages that need to be addressed to improve the surgical outcome achievable today. Herein, the fundamental physical and chemical proprieties of all vitreous substitutes are reported, and their use and clinical applications are described alongside some surgical techniques of intra-operative manipulation. The major upcoming developments in vitreous substitutes are extensively discussed, keeping a translational perspective throughout. Conclusions on future perspectives are derived through an in-depth analysis of what is lacking today in terms of desired outcomes and biomaterials technology.

Heavy silicone oil tamponade: a multicentre experience

OBJECTIVE

To report multicentred use of the heavy silicone oil Densiron 68 for anatomical reattachment following rhegmatogenous retinal detachment (RRD) repair and its associated complications.

METHODS AND ANALYSIS

Patients from seven vitreoretinal units within the UK that underwent RRD repair with Densiron 68 between January 2015 and December 2019 were identified. Primary outcome measures were primary and final reattachment rate, retained Densiron and failure rate. Secondary outcome measures were duration of tamponade, final visual acuity (VA) and complications of heavy silicone oil.

RESULTS

134 eyes of 134 patients were involved in the study. Primary surgical success was achieved in 48.5%, while a final reattachment rate of 73.4% was observed. The mean duration of Densiron 68 tamponade was 139.5 days. Mean final VA was 1.01 (range 0-2.9). 8 eyes (6.0%) required long-term topical steroids for anterior uveitis, whereas none of the eyes required long-term pressure-lowering treatment. Emulsification rate was 10.7% (6 eyes).

CONCLUSION

This is the largest real-world study on Densiron 68 in the UK. Densiron 68 facilitates tamponade of inferior retinal pathology and may be considered as an option for tamponade of inferior retinal pathologies.

Optical and Physical Properties of Silicone Oil Extracted from the Vitreous of Patients Who Underwent Vitrectomy for Retinal Detachment

Purpose: Silicone oil (SO) is a crucial tool in vitreoretinal surgery. SO has the tendency to emulsify depending on certain factors. In this work, detailed analyses have been conducted to understand changes that occurred to the physical, optical, and chemical characteristics of the oil after removal from the vitreous cavity. Methods: Five samples of SO were collected from patients who underwent vitrectomy for rhegmatogenous retinal detachment. The fourier-transform infrared (FTIR) spectroscopy, ultraviolet-visible spectrometer, and contact angle analysis were utilized to determine the changes in its chemical bondings, transmittance, absorbance, viscosity, buoyance, and specific gravity. Results: FTIR analysis showed significant changes in the chemical bonding that might be related to the age of the patient, lens status, the presence of retinal hemorrhages, and the exposure to laser after implantation of SO. In addition, contact angle analysis revealed that the viscosity might be affected by duration of implantation and the age of the patient. Moreover, transmittance and absorbance were largely affected by the exposure to laser retinopexy after implantation. Conclusion: This study showed that certain factors such as the age of the patient, the exposure to laser, lens status, and the presence of retinal hemorrhages may contribute to the emulsification process.

Transscleral Removal of Subretinal Strand without Vitrectomy: A Case Report

Recurrence of inferior retinal detachment, after vitreoretinal surgery and silicone oil tamponade, along with a subretinal strand, presents a challenge for surgeons. Vitrectomy and retinotomy are the usual treatment in such cases. Here, we present a new transscleral method for addressing this problem. A 13-year-old boy with recurrent retinal detachment after silicone oil tamponade underwent scleral buckling surgery and had a transscleral subretinal strand removed without retinotomy. The retina reattached, and silicone oil was removed 3 months later. The best-corrected visual acuity was 0.4 in decimal vision at 1 year after silicone oil removal. Scleral buckling surgery combined with subretinal strand removal may be used as an alternative to retinotomy, especially for patients with an inferior retinal detachment and local subretinal strand formation.

Current Situation and Challenges in Vitreous Substitutes

Vitreo-retinal disorders constitute a significant portion of treatable ocular diseases. These pathologies often require vitreo-retinal surgery and, as a consequence, the use of vitreous substitutes. Nowadays, the vitreous substitutes that are used in clinical practice are mainly divided into gases (air, SF₆ , C₂ F₆ , C₃ F₈ ) and liquids (perfluorocarbon liquids, silicone oils, and heavy silicone oils). There are specific advantages and drawbacks to each of these, which determine their clinical indications. However, developing the ideal biomaterial for vitreous substitution continues to be one of the most important challenges in ophthalmology, and a multidisciplinary approach is required. In this sense, recent research has focused on the development of biocompatible, biodegradable, and injectable hydrogels (natural, synthetic, and smart), which also act as medium and long-term internal tamponade agents. This comprehensive review aims to cover the main characteristics and indications for use of the extensive range of vitreous substitutes that are currently used in clinical practice, before going on to describe the hydrogels that have been developed recently and which have emerged as promising biomaterials for vitreous substitution.

Assessing bulk emulsification at the silicone oil - saline solution interface in a 3D model of the eye

PURPOSE

Emulsification of silicone oil (SiOil) in a vitrectomized eye was investigated using a 3D model of the vitreous cavity to test the hypothesis that oil droplet formation arises from the breakdown of the bulk SiOil-aqueous interface during eye saccadic movement.

METHODS

Round bottom flasks filled with SiOil and a saline phase modelled the vitrectomized SiOil-filled eye. A stepper motor imposed saccadic movements and the oil/aqueous interface was monitored with digital cameras. A range of SiOil viscosities, flask diameters, motion scenarios and levels of fill were studied. Estimates of velocity profiles in the fluid on the equatorial plane of a sphere subject to saccadic motion were obtained from an analytical solution to the Navier-Stokes equations.

RESULTS

Interfacial waves were observed at saccadic motions with higher acceleration, amplitude and frequency. Low interfacial tension between the two fluids, lower oil viscosity and smaller level of SiOil fill all promoted large deformations of the interface. No droplets were formed at the bulk SiOil-aqueous interface. However, formation and detachment of oil droplets were observed at the three-phase contact line under certain conditions.

CONCLUSIONS

The stresses generated at the liquid-liquid interface are not large enough to form droplets in the bulk region for conditions representative of these in the eye. Bulk emulsification of the SiOil, reported as the main formation mechanism by some workers, is not responsible for droplet formation in a vitrectomized SiOil-filled eye set-up. This result confirms recent finding on droplet formation driven by a surface emulsification mechanism.

Study of wetting of the animal retinas by Water and organic liquids and its Implications for ophthalmology

Interfacial properties of the animal retinas are reported. Wetting of the retina-retinal pigment epithelium-choroid-sclera tissues of cow, sheep, and pig eyes by water, silicone and castor oil was explored experimentally. Both water and silicone oils demonstrated complete wetting of the retina, regardless of the viscosity of the silicone oil, whereas the castor oil demonstrated a partial wetting regime. Similar wetting regimes were observed for sheep, cow and pig retinas. The intact surface of animal retina was found to be both hydrophilic and oleophilic. Wetting experiments with double sandwich oil/water layers were performed. Water demonstrated stronger affinity to the retina than silicone and castor oils, and eventually replaced the oils at the liquid/retina interface. We conclude that aqueous solutions continuously secreted in the living eye may displace silicone oil from the retinal surface and contribute to retinal re-detachment. Study of dynamics of wetting of the animal retina by water and organic oils is reported. The exponent describing the dynamics of spreading of the castor oil is lower than that predicted by the Tanner law. Castor oil may provide more effective tamponade than silicone oil.

In vitro and computational modelling of drug delivery across the outer blood-retinal barrier

The ability to produce rapid, cost-effective and human-relevant data has the potential to accelerate the development of new drug delivery systems. Intraocular drug delivery is an area undergoing rapid expansion, due to the increase in sight-threatening diseases linked to increasing age and lifestyle factors. The outer blood-retinal barrier (OBRB) is important in this area of drug delivery, as it separates the eye from the systemic blood flow. This study reports the development of complementary in vitro and in silico models to study drug transport from silicone oil across the OBRB. Monolayer cultures of a human retinal pigmented epithelium cell line, ARPE-19, were added to chambers and exposed to a controlled flow to simulate drug clearance across the OBRB. Movement of dextran molecules and release of ibuprofen from silicone oil in this model were measured. Corresponding simulations were developed using COMSOL Multiphysics computational fluid dynamics software and validated using independent in vitro datasets. Computational simulations were able to predict dextran movement and ibuprofen release, with all of the features of the experimental release profiles being observed in the simulated data. Simulated values for peak concentrations of permeated dextran and ibuprofen released from silicone oil were within 18% of the in vitro results. This model could be used as a predictive tool for drug transport across this important tissue.

A New, Heavier-Than-Water Silicone Oil: A Solution of Perfluorohexyloctane in Polydimethylsiloxane

Purpose

To prepare and explore new solutions of semifluorinated alkane in silicone oil, which have a specific gravity slightly higher than silicone oil and vitreous fluid (referred to in the following as heavier-than-water silicone oils (HWSs), and to investigate, in vitro, whether HWSs can be used to plug retina holes, while allowing dehydration of the subretinal space.

Methods

HWS solutions were prepared with silicone oil 5000 and perfluorohexyloctane (F6H8). The stability was investigated under different conditions. The viscosity was determined by means of a capillary viscometer. The surface and interface tension were measured using the ring method.

Results

HWSS are insoluble in an aqueous medium. Densiron®68 (HWS 1.06) is a transparent homogeneous liquid which is slightly heavier (1.06 g/cm3) than water and has a refractive index close to that of vitreous liquid. Densiron®68 (HWS 1.06) has a low viscosity (1480 mPas) and interface tension (40.82 mN/m), making it an effective tamponade in the surgical treatment of an inferior detached retina. In addition, the interfaces between Densiron®68 and other perfluorocarbon liquids are clearly visible. However, the interface layer between Densiron®68 and water is not clear. Finally, all HWSs are stable over the long term at ambient temperatures, as well as physically and thermally resistant.

Conclusions

Due to its physiochemical properties, Densiron®68 could meet the requirements for a heavier-than-water tamponade.

Heavy silicone oil and intraocular inflammation

In the past two decades, many advances have been made in vitrectomy instrumentation, surgical techniques, and the use of different tamponade agents. These agents serve close retinal breaks, confine eventual retinal redetachment, and prevent proliferative vitreoretinopathy (PVR). Long-acting gases and silicone oil are effective internal tamponade agents; however, because their specific gravity is lower than that of the vitreous fluid, they may provide adequate support for the superior retina but lack efficacy for the inferior retina, especially when the fill is subtotal. Thus, a specific role may exist for an internal tamponade agent with a higher specific gravity, such as heavy silicone oils (HSOs), Densiron 68, Oxane HD, HWS 45-300, HWS 46-3000, and HeavySil. Some clinical evidence seems to presume that heavy tamponades are more prone to intraocular inflammation than standard silicone if they remain in the eye for several months. In this review, we discuss the fundamental clinical and biochemical/molecular mechanisms involved in the inflammatory response after the use of heavy tamponade: toxicity due to impurities or instability of the agent, direct toxicity and immunogenicity, oil emulsification, and mechanical injury due to gravity. The physical and chemical properties of various HSOs and their efficacy and safety profiles are also described.

Tamponade or filling effect: changes of forces in myopic eyes

Myopia is the most common ocular abnormality. Its high and growing prevalence has contributed to a recent surge in surgical interest in the disorder, since retinal detachment in eyes with high myopia differs from that in emmetropic eyes or eyes with low myopia. The myopic eye, because of its specific anatomy, poses special challenges that need to be overcome to ensure the appropriate use of vitreous substitutes. However, intraocular tamponades have shown great potential for revolutionizing retinal detachment surgery and vitreomacular surgery in general in myopic eyes. We provide an updated review of the clinical use of vitreous substitutes in the myopic eye, paying particular attention to analyzing the ideal function of endotamponade agents and comparing the effects of these agents on the physical and biological properties of the eye.

Vitreous substitutes: the present and the future

Vitreoretinal surgery has advanced in numerous directions during recent years. The removal of the vitreous body is one of the main characteristics of this surgical procedure. Several molecules have been tested in the past to fill the vitreous cavity and to mimic its functions. We here review the currently available vitreous substitutes, focusing on their molecular properties and functions, together with their adverse effects. Afterwards we describe the characteristics of the ideal vitreous substitute. The challenges facing every ophthalmology researcher are to reach a long-term intraocular permanence of vitreous substitute with total inertness of the molecule injected and the control of inflammatory reactions. We report new polymers with gelification characteristics and smart hydrogels representing the future of vitreoretinal surgery. Finally, we describe the current studies on vitreous regeneration and cell cultures to create new intraocular gels with optimal biocompatibility and rheological properties.

Supplemental scleral buckling for inferior retinal detachment in silicone oil-filled eyes

PURPOSE

To evaluate the efficiency of treating selected cases of inferior retinal detachment in silicone oil-filled eyes using a supplemental scleral buckling with external drainage of subretinal fluid, versus performing a second vitreoretinal surgery and silicone oil endotamponade.

METHODS

A prospective interventional pilot study that was performed on silicone oil-filled eyes with inferior retinal detachment. Twenty-three eyes of 23 consecutive patients were alternatively distributed between 2 groups: Group A included 12 eyes treated with supplemental scleral buckling with drainage of subretinal fluid and without the removal of silicone oil, and Group B included 11 eyes treated with silicone oil removal, vitreoretinal surgery, and reinjection of silicone oil. The preoperative data included indications and details of primary vitreoretinal surgery, cause of retinal redetachment, subretinal fluid, grade of proliferative vitreoretinopathy, lens status, and the duration between primary vitreoretinal surgery and reoperation. The postoperative examination included the best-corrected visual acuity, retina status, proliferative vitreoretinopathy, silicone oil, and any reported complication. Follow-up examinations were scheduled at Day 1, weekly for 1 month, and monthly thereafter till the end of the follow-up period which extended for at least 2 months after silicone oil removal.

RESULTS

The average number of detached clock hours per eye was 2.7 in Group A and 2.4 in Group B, caused by a mean of 1.58 ± 0.80 break per eye in Group A and 1.48 ± 0.66 break per eye in Group B. The mean interval between the primary vitreoretinal surgery and the scleral buckling procedure in Group A patients was 2.83 ± 1.22 months (range, 1-5 months), while in Group B, the mean interval between the primary and the secondary vitreoretinal surgeries was 3.00 ± 1.61 months (range, 1-6 months). The mean operative time was statistically significantly (P < 0.05) shorter in Group A (38.7 ± 11.2 minutes) than in Group B (65.3 ± 15.1 minutes). The mean follow-up duration was 15.00 ± 3.22 months in Group A and 14.18 ± 2.99 months in Group B. After silicone oil removal, the retina was attached in 10 of the 12 eyes (83.3%) and redetached in 2 eyes (16.7%) in Group A, while in Group B, the retina was attached in 9 of the 11 eyes (81.8%) and redetached in 2 eyes (18.2%) after silicone oil removal. The mean logarithm of the minimum angle of resolution best-corrected visual acuity has improved from 1.82 ± 0.72 to 1.36 ± 0.52 in Group A patients (P > 0.05) and from 1.93 ± 0.74 to 1.55 ± 0.63 in Group B patients (P > 0.05) at the end of the follow-up duration.

CONCLUSION

For selected cases of inferior retinal detachment in silicone oil-filled eyes, supplemental scleral buckling could be as effective as a second vitreoretinal surgery. Scleral buckling could offer a faster, less invasive, and better economic alternative to repeated vitreoretinal surgery for treatment of such cases.

Heavy silicone oil: a "novel" intraocular tamponade agent

Advances in vitreoretinal surgery have greatly increased the anatomical re-attachment rate in cases with proliferative vitreoretinopathy. Intraocular tamponade agents have been in use by vitreoretinal surgeons for nearly a century. The effectiveness of an internal agent relies on its ability to make contact with the internal surface of the vitreous cavity. In the short term, this is controlled by the agent's specific gravity and interfacial tensions. In the long term, the viscosity of the material is critical to maintaining its integrity and thus reducing dispersion. The commonly used tamponade agents such as perfluoropropane (C3F8), sulfur hexafluoride (SF6), and silicone oil are "lighter than water" hence, float upward in the aqueous. A consequence of this is that in the upright position the superior retina is very well supported, leaving the inferior retina less well so. More recently, there has been interest in the development of "heavier than water" long-term tamponade agents that sink in the eye. Heavy silicone oil is a transparent, homogenous solution of two substances used as a single tamponade agent with improved properties and a specific gravity greater than water. Densiron (one of the two available heavy silicone oil's) is a mixture of perfluorohexyloctane (F6H8, with a specific gravity of 1.35 g/ml and viscosity of 2.5 mPas), and conventional silicone oil (specific gravity of 0.97 g/ml and viscosity of 5700 mPas depending on the molecular weight). The specific gravity of Densiron is 1.06 g/ml and the viscosity is 1400 mPas, making it a novel heavier-than-water, long-term internal tamponade agent, which means that in the upright position it sinks and provides support for the inferior retina.

Vitreous substitutes: a comprehensive review

Vitreoretinal disorders constitute a significant portion of treatable ocular disease. Advances in vitreoretinal surgery have included the development and characterization of suitable substitutes for the vitreous. Air, balanced salt solutions, perfluorocarbons, expansile gases, and silicone oil serve integral roles in modern vitreoretinal surgery. Vitreous substitutes vary widely in their properties, serve different clinical functions, and present different shortcomings. Permanent vitreous replacement has been attempted with collagen, hyaluronic acid, hydroxypropylmethylcellulose, and natural hydrogel polymers. None, however, have proven to be clinically viable. A long-term vitreous substitute remains to be found, and recent research suggests promise in the area of synthetic polymers. Here we review the currently available vitreous substitutes, as well those in the experimental phase. We classify these compounds based on their functionality, composition, and properties. We also discuss the clinical use, advantages, and shortcomings of the various substitutes. In addition we define the ideal vitreous substitute and highlight the need for a permanent substitute with long-term viability and compatibility. Finally, we attempt to define the future role of biomaterials research and the various functions they may serve in the area of vitreous substitutes.

The impact of axial length on retinal tamponade for gas, silicone oil, and heavy silicone oil, using an in vitro model

Background

To investigate whether ocular axial length influences the tamponade efficacy of three commonly used agents: gas, silicone oil, and heavy silicone oil.

Methods

A series of filling experiments was conducted using 19-mm and 25-mm surface-modified spherical model eye chambers to mimic the vitreous cavity. For each agent, tamponade efficacy was assessed across a range of percentage fills, and comparison was made between the two model eye chambers. The behavior of each tamponade agent was quantified by measuring (1) the maximum height of the tamponade bubble, and calculating (2) the arc of retinal contact subtended by the tamponade bubble.

Results

Polynomial regression analysis found no statistically significant difference between the regression models for the different-sized model eye chambers for bubble height or arc of retinal contact subtended. This applied to all of the tamponade agents under investigation.

Conclusions

Across the range of cavity sizes under investigation, no significant difference in tamponade efficacy (as reflected by the measured dimensions of the tamponade bubble) was identified.

Conventional surgery for complicated retinal detachment in silicone oil-filled eyes

PURPOSE

To evaluate the anatomic and functional outcomes of conventional surgery in silicone oil (SO)-filled eyes with complicated retinal detachment (RD).

METHODS

The records of patients who underwent scleral buckling surgery for complex RD in SO-filled eyes were retrospectively reviewed. Conventional RD surgery involved a 2.5-mm encircling band, 6-mm silicone strip for the inferior quadrants or local sponge implant, subretinal fluid (SRF) drainage, and/or SO aspiration with a 27-G needle. Cryotherapy and/or laser photocoagulation was applied around the tears and 360° of the peripheral retina.

RESULTS

In all, 4 of the cases had retinal breaks in the lower quadrants, 1 of which had a macular hole; recurrence was due to proliferative vitreoretinopathy (PVR) in the 3 other cases. Three cases were treated with external SRF drainage, 3 cases with SO aspiration, and 1 case with both external drainage and SO aspiration. The retina was attached at the last follow-up visit in 6 (85.7%) of the 7 eyes. One of the cases required secondary vitreoretinal surgery for recurrent RD due to PVR and still had SO tamponade at last follow-up visit. Mean follow-up period was 17.28 ± 8.64 months. Mean logMAR visual acuity was 1.47 ± 0.47 preoperatively and 1.4 ± 0.97 postoperatively.

CONCLUSIONS

Inferior RD in eyes treated with silicone oil tamponade, with or without a retinal break, can be treated with scleral buckling surgery, external SRF drainage, and/or pars plana SO aspiration with satisfactory functional and anatomic outcomes in selected complicated RD cases.

A modular approach for the generation, storage, mixing, and detection of droplet libraries for high throughput screening

The desire to make microfluidic technology more accessible to the biological research community has led to the notion of "modular microfluidics", where users can build a fluidic system using a toolkit of building blocks. This paper applies a modular approach for performing droplet-based screening, including the four integral steps of library generation, storage, mixing, and optical interrogation. Commercially available cross-junctions are used for drop generation, flexible capillary tubing for storage, and tee-junctions for serial mixing. Optical interrogation of the drops is achieved using fiber-optic detection modules which can be incorporated inline at one or more points in the system. Modularity enables the user to hand-assemble systems for functional assays or applications. Three examples are shown: (1) a "mix and read" assay commonly used in high throughput screening (HTS); (2) generation of chemically distinct droplets using microfractionation in droplets (microFD); and (3) in situ encapsulation and culture of eukaryotes. Using components with IDs ranging from 150 microm to 1.5 mm, this approach can accommodate drop assays with volumes ranging from 2 nL to 2 microL, and storage densities ranging from 300 to 3000 drops per metre tubing. Generation rates are up to 200 drops per second and merging rates are up to 10 drops per second. The impact of length scale, carrier fluid viscosity, and flow rates on system performance is considered theoretically and illustratively using 2D CFD simulations. Due to its flexibility, the widespread availability of components, and some favorable material properties compared to PDMS, this approach can be a useful part of a researcher's toolkit for prototyping droplet-based assays.

Macular hole surgery with inner limiting membrane peeling, endodrainage, and heavy silicone oil tamponade

PURPOSE

To evaluate the anatomical and functional outcomes in macular hole (MH) patients who underwent vitrectomy with inner limiting membrane (ILM) peeling, endodrainage, and heavy silicone oil (HSO) endotamponade.

DESIGN

A retrospective case series with 54 consecutive eyes from 53 patients with idiopathic stage 3 or 4 MHs.

METHODS

Surgery with infracyanine green-assisted ILM peeling and endodrainage was performed. Patients who were phakic underwent a simultaneous phacoemulsification. At the end of the operation, a HSO tamponade was used in all cases. The patient maintained a face-up position for 24 hours postoperatively. The HSO was removed two to three months after initial surgery. Optical coherence tomography was performed preoperatively and postoperatively to determine the MH stage and the anatomical closure rate.

RESULTS

The mean follow-up time was 6.6 months (range, 3.6 to 18.2 months). The overall median duration between the first symptoms and the surgery was four months (range, two to 37 months). The overall anatomical closure success rate after one surgery was 100%. The median preoperative visual acuity (VA) was 20/200 (range, 20/40 to 20/600) and increased to 20/50 (range, 20/20 to 20/300) postoperatively. The median increase in VA was five lines (mean, 4.8 lines; range, -3 to 12 lines). Of all 54 eyes, 30 (55 %) eyes had a final VA of 20/50 or better.

CONCLUSIONS

These findings indicate that surgery for MH with ILM peeling, endodrainage, and HSO endotamponade appears to induce a high incidence of anatomical closure with good visual outcome.

A new heavy internal tamponade in vitreoretinal surgery: an in vitro study

AimTo study the solubility of perfluorohexyloctane (F6H8) in silicone oil (polydimethylsiloxane (PDMS) 1000) and to measure the viscosity and the specific gravity of the mixture obtained (heavy silicone oil or HSO tamponade) to define the ideal ratio of these components.MethodsThe solubility diagram of the mixture was obtained with the turbidimetric method, indicating the miscibility of F6H8 and silicone oil 1000 at all the useful temperatures. The viscosity was measured in steady shear conditions by using a controlled stress rheometer (Haake RS150) and a double cone/plate (DC 60/4) system, both at 25 and 37 degrees C for different volume per cent compositions of the mixture. The specific gravity was measured at 37 degrees C using a digital densimeter.ResultsA mixture of F6H8 30 v% and PDMS 70 v% was found to be transparent and stable at all the useful temperatures. By combining these proportions of the two substances, a resultant density of 1.06 g/cm(3) was obtained. The viscosity of the 30% F6H8 mixture was 203 mPa.s at 25 degrees C and 163 mPa.s at 37 degrees C respectively.ConclusionsThe ideal F6H8 and silicone oil mixture can be obtained combining 30% of F6H8 with 70% of silicone oil 1000. This mixture seems to have rheological properties useful for its use as an alternative intraocular heavy tamponade.Eye (2008) 22, 1082-1088; doi:10.1038/eye.2008.144; published online 6 June 2008.

[New developments in retinal detachment surgery]

The initial surgery is one of the most important factors influencing the anatomic and functional outcome of retinal detachment surgery. With the continual modifications in vitrectomy techniques, the strategy in primary vitrectomy surgery is also changing. Recent developments are the use of 25- and 23-gauge trocar systems and new surgical techniques without the use of perfluorcarbons or gas or silicone oil tamponade. In addition, heavy silicone oils are now entering routine clinical use, especially for proliferative vitreoretinopathy (PVR) redetachments of the lower fundus periphery. Regarding adjunct pharmacologic therapy, daunorubicin and 5-fluorouracil/low molecular weight heparin have been found to improve the results of patients with PVR or at risk for PVR.

Semifluorinated alkanes--primitive surfactants of fascinating properties

Semifluorinated alkanes (SFAs) are diblock molecules, in which two mutually immiscible moieties, namely the hydrocarbon segment and the perfluorinated segment are bound covalently. The presence of two opposing segments within one molecule makes semifluorinated alkanes a very interesting class of compounds, which show a particular behavior both in bulk and at interfaces. Their highly asymmetric structure, arising from the incompatibility of the both constituent parts, results in surface activity of these molecules (so-called primitive surfactants) when dissolved in organic solvents, and allows for the Langmuir monolayer formation if spread at the air/water interface, despite of the absence of any polar group. Since 1984 (when SFAs have been characterized for the first time by Rabolt et al. [Rabolt JF, Russell TP, Twieg RJ. Macromolecules 1984;17:2786]), semifluorinated alkanes have been subjected to many studies. The present article reviews the results obtained so far and covers the aspects of their synthesis, properties in bulk (solutions and solid state) and applications. Special emphasis is put on the Langmuir monolayer properties and self-organization of SFAs on solid substrates.

Heavy tamponade 1: a review of indications, use, and complications

BACKGROUND

Heavier than water intraocular tamponades have several theoretical advantages over conventional tamponades, especially in the treatment of complicated retinal detachments and proliferative viteroretinopathy of the lower fundus periphery. However, initial clinical series of various heavy tamponades have reported significant complication rates. Therefore, heavy tamponades have not found widespread acceptance. Three recently developed heavy silicone oil tamponades, Oxane HD, Densiron 68, and HWS 46-3000, are much better tolerated and presently seem to enter routine clinical practice.

MATERIALS AND METHODS

Literature review of 21 publications on the clinical application of 9 different heavy tamponades (fluorosilicone, C10F18, F6H8, OL62HV, Oxane HD, O62, F6H8-silicone oil mixture, Densiron 68, and HWS 46-3000).

RESULTS

The first generation (fluorinated silicone and perfluorocarbon liquids) and second generation (partially fluorinated alkanes) of heavy tamponades were associated with relatively high complication rates, for example, tamponade emulsification, intraocular inflammation, and rise in intraocular pressure. The complication spectrum of the new generation of heavy silicone oils (Oxane HD, Densiron 68, and HWS 46-3000) seems to be comparable to conventional silicone oil tamponades while providing better support for the inferior retina and the posterior pole.

CONCLUSION

The recently developed heavy silicone oil tamponades are safe and effective tools for the use of complicated retinal detachments of the inferior fundus.

Heavy tamponade 2 Densiron 68 in routine clinical practice: anatomical and functional outcomes of a consecutive case series

PURPOSE

To evaluate the safety and efficacy of Densiron 68 in the clinical management of complex vitreoretinal cases with inferior retinal pathology.

METHODS

We present a prospective interventional non-comparative case series of 122 eyes of 121 consecutive patients. The primary end point was anatomical re-attachment of the retina, defined as retinal re-attachment in the absence of any tamponade agent. The secondary end point was to record the visual function and surgical complications. Inclusion criteria were proliferative vitreoretinopathy, posterior or inferior retinal breaks, and the patient's inability to posture.

RESULTS

Patients were 59.9 years (+/- 19.6), (m/f= 72:49), (R/L=65:57). Seventy-seven (63.1%) had previous unsuccessful retinal surgery and 45 had Densiron 68 at first procedure. The extent of the detachments was 2.21 quadrants (+/- 1.07) with macular involvement in 66 cases (54%). Eighty-seven (71.3%) patients achieved retinal re-attachment with one retinal operation and ultimately no tamponade, 102 (83.6%) achieved retinal re-attachment with more than one operation and ultimately no tamponade, and 112 (91.3%) patients achieved flat retina with tamponade in situ. Visual acuity rose from 1.38 LogMar (+/- 0.87) to 1.06 (+/- 0.83) (P=0.007). Densiron was removed after 135 days (+/- 73.2; range 35-405).

CONCLUSION

No tamponade agent can provide simultaneous support for the superior as well as the inferior retina; therefore, a tamponade agent that 'sinks' is a welcome new tool at the surgeon's disposal. The sequential use of heavy silicone oil followed by conventional silicone oil may be an acceptable management strategy in recurrent detachment.

Anatomical and Functional Results of Endotamponade with Heavy Silicone Oil – Densiron® 68 – in Complicated Retinal Detachment

BACKGROUND

High-density silicone oils are newly developed long-term tamponade agents for the treatment of complicated retinal detachment in the inferior retina. Previous studies describe satisfying anatomical and functional results. In this study we examined the largest cohort so far for a 9-month follow-up and performed a comparison to conventional silicone oil.

METHODS

Our study documents results and adverse effects after vitreoretinal surgery and endotamponade with Densiron 68 in 99 cases of complicated retinal detachment. A 9-month follow-up was performed. Data of 21 patients with intraocular conventional silicone oil tamponade in complicated retinal detachment were retrospectively analyzed and served as control.

RESULTS

Anatomical success was achieved in 78 of 89 eyes (87.6%) with completed follow-up; visual acuity did not change significantly (from mean preoperative logMAR 1.88 to postoperative logMAR 1.96 (p = 0.9). Compared to control a higher anatomical success but a similar number of adverse effects were observed with heavy silicone oil in vitreous. Nevertheless, patients who received Densiron 68 twice due to redetachment showed a significantly higher rate of intraocular inflammation with the tamponade agent in situ.

CONCLUSION

Our results support the hypothesis of Densiron 68 as potent tamponade agent for complicated retinal detachment in the inferior retinal segments especially in eyes where a previous operation failed.

A NEW HEAVY SILICONE OIL (HWS 46-3000) USED AS A PROLONGED INTERNAL TAMPONADE AGENT IN COMPLICATED VITREORETINAL SURGERY

PURPOSE

To report the results of a prospective pilot study using a new heavy agent, HWS 46-3000, as long-term endotamponade in complicated retinal detachment.

METHODS

Thirty-two consecutive patients were enrolled in the study. Indications for enrollment included retinal detachment with proliferative vitreoretinopathy arising from inferior or posterior tears. The patients underwent pars plana vitrectomy, membrane peeling, and HWS 46-3000 filling. Follow-up examinations were scheduled at 1 day to 7 days and 1 month to 3 months after initial surgery and 7 days and 1 month to 6 months after endotamponade removal.

RESULTS

At baseline examination, mean best-corrected Snellen visual acuity was 2.44 logarithm of the minimal angle of resolution (logMAR). HWS 46-3000 was removed after 45 days to 96 days. Initial retinal reattachment was achieved in all eyes. HWS 46-3000 endotamponade was associated with a success rate of 84.6% with a single surgery and an overall success rate of 100% at 6 months with the second operation and conventional silicone oil endotamponade. At 6 months, mean best-corrected visual acuity was +1.09 logMAR (P < 0.0001). Complications were posterior subcapsular cataract formation (100%), membrane formation (3 eyes, 9%), and increased intraocular pressure (1 eye). Emulsification and intraocular inflammation were not observed.

CONCLUSION

HWS 46-3000 was well tolerated, effective in the inferior quadrants with a low incidence of membrane development. The main complication was the high rate of tamponade-related cataract formation.

Nuclear magnetic resonance analysis of emulsified silicone oil RMN-3 (Oxane HD)

BACKGROUND

Oxane HD is a mixture of 5700 cs silicone oil and RMN-3 (a partly fluorinated olefin), which has a specific gravity greater than water, thereby enabling endotamponade of inferior retinal breaks. Droplets of emulsified oil were found in the anterior chamber of two patients with complex retinal detachments who had been treated with Oxane HD. Samples removed from these two eyes were analysed in order to investigate the nature of the emulsified substance.

METHODS

Samples were dissolved in CDCl3 and, if necessary, dried using magnesium sulphate. Nuclear magnetic resonance (NMR) was used to compare these samples with the unused commercial product.

RESULTS

NMR analysis of the samples removed from the anterior segment of both eyes were mainly silicone oil with only trace amounts of RMN-3. Samples taken from different areas of an unused syringe of Oxane HD demonstrated varying concentrations of the RMN-3 compound within the silicone oil.

CONCLUSION

First, the mixture of RMN-3 and silicone oil is not homogenous either in vitro or in vivo. Second, emulsified oil found in the anterior chamber is composed almost entirely of silicone oil, containing only trace amounts of RMN-3.

An experimental study on the effect of encircling band procedure on silicone oil emulsification

AIM

Silicone oil is a useful tamponading material used in complex vitroretinal surgery. However, the use of silicone oil is associated with emulsification which can lead to vision threatening complications. The authors developed an experimental model to study the effect of encircling band on silicone oil emulsification.

METHODS

Two identical artificial eye chambers were constructed with circumferential indentations placed at the sphere's equator (mimicking an encircling band indentation), and filled with varying amounts of Silicone Oil 1000 centistrokes (Adato, Bausch and Lomb, UK) and balanced salt solution. The chambers were then placed on a horizontal rotating shaker, mimicking physiological saccadic eye movements, which spun the chambers at 100 Hz for 5 days at 37 degrees C. Emulsification was then quantified by dark field microscopy, digital photography, and manual counting by a masked observer.

RESULTS

The mean (standard deviation (SD)) values of silicone emulsification bubbles were as follows: in the 90% silicone oil filled chamber with no encircling band, 139.1 (SD 313.4); in the 90% silicone oil filled chamber with encircling band, 10.9 (SD 22.2) (p<0.0001); in the 75% silicone oil filled chamber with no encircling band, 103.6 (SD 272.6); in the 75% silicone oil filled chamber with encircling band, 18.5 (SD 32), (p = 0.001).

CONCLUSIONS

The emulsification of silicone oil results from friction between the silicone oil and aqueous liquids. The results from this study suggest silicone oil emulsification is reduced by (1) more complete silicone oil fill and (2) indentation from an encircling band. The authors hypothesise that both these measures resulted in reduced emulsification by reducing silicone oil/aqueous movement and resulting shearing forces.

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.

Combined use of perfluorohexyloctane and silicone oil as intraocular tamponade: an in vitro study

BACKGROUND

Double filling (DF) with perfluorohexyloctane (F6H8) and silicone oil (SIL) has been recently proposed and tested clinically as a means to improve the tamponade properties of single components. This in vitro study investigated (1) the kinetics of the mixing process of F6H8 with SIL (1,000 mPa s) and (2) the contact and emulsification behaviour of DF as compared with pure liquids, with the aim of assessing the tamponade efficiency and its evolution with time.

METHODS

(1) The velocity of the mixing process for F6H8+SIL was estimated by monitoring the position of the interphase in a rectangular cell kept at constant temperature. (2) The surface contact and the tendency to emulsification of DF and of SIL and F6H8 were visually examined by using a Perspex eye model.

RESULTS

(1) The mixing process for F6H8+SIL is slow. In the absence of stirring, equilibrium is reached no earlier than 1 month at 37 degrees C. (2) F6H8 was found to show close contact with the eye model and dispersion into droplets; SIL showed poor contact with the cell surface and no dispersion; DF exhibited poor contact with the superior cell surface and little evidence of dispersion.

CONCLUSIONS

F6H8 dissolves slowly in SIL and equilibrium is only reached after 1 month. The final ratio of the DF phases differs from the initial ratio. An initial F6H8/SIL ratio of 70%:30% vol results in 25% vol of pure F6H8 (density, 1.33 g/cm(3)) and 75% vol of a solution containing F6H8, viz. 60% vol F6H8 in SIL (density 1.17 g/cm(3)). Because of its density and contact properties, the investigated DF has a tamponade effectiveness better than that of SIL on the inferior retina. Compared with using F6H8 alone, DF reduces emulsification.

A pilot study on the use of silicone oil–RMN3 as heavier-than-water endotamponade agent

AIMS

This work was conducted to report an interventional non-comparative pilot study using Oxane HD, a mixture of ultra-purified silicone oil and RMN3, a partially fluorinated olefin, as heavier-than-water internal tamponade.

METHODS

Twenty-eight consecutive patients were recruited for this study. Indications included recurrent retinal detachment (RD) with proliferative vitreoretinopathy (PVR) (stage > or =C2) arising from inferior or posterior tears, recurrences after vitreoretinal surgery, penetrating trauma and combined rhegmatogenous and choroidal detachment. The patients underwent a pars plana vitrectomy, membrane peeling, and Oxane HD was used as long-term internal tamponade.

RESULTS

Oxane was removed after 88 days (range 45-96 days) and exchanged with BSS in five eyes, long-acting gas in 14 eyes and with silicone oil in nine eyes. Retinal reattachment was achieved in 15 eyes. The overall anatomical success rate obtained using Oxane HD was 53.5%. In 15 patients with previous marked scleral buckling, the success rate was 26%: in nine patients recurrent RD occurred in the inferior sector, in five patients new tears were detected in the lower sectors; membrane formation was observed in 15 eyes. In 13 patients without marked scleral indent, the success rate was 84.6%. There was no evidence of dispersion and excessive inflammation.

CONCLUSION

Oxane HD may be a useful tool in complicated RD with large inferior breaks, inferior PVR or combined rhegmatogenous, and choroidal detachment without marked scleral buckling, which put the eye profile out of shape, led to a higher failure rate and reduced the tamponading effectiveness of Oxane HD.