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 as Drug Release Systems

Vitreous substitutes are traditionally used to stabilize the retina after vitrectomy. In recent years, various approaches have been developed for using the vitreous substitute not only as a tamponade but also as a drug release system to tackle ocular diseases. This review provides an overview of the requirements for vitreous substitutes and discusses the current clinically applied as well as novel polymer-based vitreous substitutes as drug delivery systems, including their release mechanisms, efficiencies, challenges, and future perspectives.

Classifications for Proliferative Vitreoretinopathy (PVR): An Analysis of Their Use in Publications over the Last 15 Years

Purpose. To evaluate the current and suitable use of current proliferative vitreoretinopathy (PVR) classifications in clinical publications related to treatment. Methods. A PubMed search was undertaken using the term "proliferative vitreoretinopathy therapy". Outcome parameters were the reported PVR classification and PVR grades. The way the classifications were used in comparison to the original description was analyzed. Classification errors were also included. It was also noted whether classifications were used for comparison before and after pharmacological or surgical treatment. Results. 138 papers were included. 35 of them (25.4%) presented no classification reference or did not use any one. 103 publications (74.6%) used a standardized classification. The updated Retina Society Classification, the first Retina Society Classification, and the Silicone Study Classification were cited in 56.3%, 33.9%, and 3.8% papers, respectively. Furthermore, 3 authors (2.9%) used modified-customized classifications and 4 (3.8%) classification errors were identified. When the updated Retina Society Classification was used, only 10.4% of authors used a full C grade description. Finally, only 2 authors reported PVR grade before and after treatment. Conclusions. Our findings suggest that current classifications are of limited value in clinical practice due to the inconsistent and limited use and that it may be of benefit to produce a revised classification.

[Heavy silicone oil (Densiron® 68) in proliferative vitreoretinopathy: 4 years of experience]

METHOD

Prospective observational study including 10 patients (age range: 27-74 years) with recurrent retinal detachment (RD) and proliferative vitreoretinopathy (PVR) and 2.8 mean unsatisfactory previous surgeries. Densiron® was injected in all patients, with surgical retinectomy being required in 70% of them. Minimum follow-up time was 12 months.

RESULTS

The mean length of time before Densiron® withdrawal was 4 months. Three patients (30%) presented with a new RD. The main complication detected was cataract development. No relationship was found between re-detachments and tamponade time, baseline disease or RD evolution time. Densiron® may be a good option in cases of recurrent RD in which previous treatment with scleral buckle, gas and/or 1,000/5,000 silicone oils has proven to be unsatisfactory.

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.

Densiron 68 as an intraocular tamponade for complex inferior retinal detachments

INTRODUCTION

Densiron(®) 68 is a high-density liquid used to tamponade inferior retinal detachments. We present a case series of 12 patients treated with Densiron as an intraocular tamponade agent.

METHODS

A retrospective analysis of 12 eyes in 12 patients was carried out. The primary endpoint was anatomic reattachment of the retina following removal of Densiron oil.

RESULTS

All patients had inferior detachments; 33% had associated proliferative vitreoretinopathy (PVR). Densiron was utilized as a primary agent in five patients (42%); the remaining patients had prior unsuccessful surgery for retinal reattachment, including pars plana vitrectomy, cryotherapy, laser, encirclement, gas (C3F8 or C2F6), or silicone oil. Eleven patients (91%) had successful reattachment of the retina at 3 months following removal of Densiron; one patient had extensive PVR, total retinal detachment, preretinal macula fibrosis, and chronic hypotony, and surgical intervention was unsuccessful. Six patients (50%) had raised intraocular pressure (IOP), resolving in the majority of cases following Densiron removal; two patients had long-term raised IOP requiring topical or surgical therapy. Of the six phakic patients, 50% developed significant cataract in the operated eye. Of those with successful retinal reattachment, visual outcome was variable, with 36% patients gaining two to four lines on Snellen, 27% remaining objectively the same, and 36% losing one to two lines.

CONCLUSION

The anatomic success rate is high (91%) in patients requiring Densiron tamponade for inferior retinal detachments with or without evidence of PVR either as a primary or secondary intervention. A common complication is raised IOP; however, this most often resolves following removal of the oil.

High-density silicone oil as an intraocular tamponade in complex retinal detachments

OBJECTIVE

To evaluate the efficacy and safety of high-density silicone oil (HDSO) as an internal retinal tamponade after vitrectomy for complicated retinal detachment.

DESIGN

Retrospective, non-randomized study.

PARTICIPANTS

Forty-one eyes of 41 patients who were 5-73 years of age.

METHODS

Medical records of patients with retinal detachment (RD) complicated with inferior proliferative vitreoretinopathy (PVR) requiring internal tamponade with HDSO were reviewed. Eyes with retinal vascular diseases and inflammatory diseases were excluded from the study. Follow-up examinations were scheduled at 1 week and 1, 3, 6, and 12 months after the initial surgery.

RESULTS

Median value of follow-up was 8 months (range, 3-40 months). Twenty-five patients had rhegmatogenous RD with significant PVR and the remaining patients had complicated RD secondary to trauma. Preoperative visual acuity was 2.55 ± 0.75 logMAR, which became 1.89 ± 0.91 at the last follow-up visit (p < 0.05). Complications included increased intraocular pressure (9.7%), hypotony (2.4%), cataract (57.1%), silicone oil in anterior chamber (17%), persistent total corneal edema (7.3%), band keratopathy (7.3%), and significant inflammation (2.4%). Intraretinal or subretinal fibrosis was found in 12 eyes (29.2%). HDSO removal was performed after a mean period of 5.7 months (range, 3-34 months) in 34 patients. The anatomical success was 87.8%.

CONCLUSIONS

The high anatomical success rate of 87.8% is a satisfactory result for these complicated RD cases. Subretinal proliferations and early emulsification limit the results. Further studies, with longer follow-ups and more patients, are needed to be conclusive.