A new approach to stage 3 macular holes

Short-Term Results of Ocriplasmin Versus Prompt Vitrectomy for Macular Hole. Which Performs Better?

In this retrospective study, we compared the anatomical and functional changes in patients with vitreomacular traction associated with macular holes between the following groups: (1) Patients who were treated with a single intravitreal injection of ocriplasmin (the OCRIALONE group); (2) those who failed the ocriplasmin treatment and underwent vitrectomy one month later (the OCRIVIT group); and (3) patients who directly underwent par plana vitrectomy (VITREALONE group). A total of 38 patients, 19 in the OCRIALONE group + OCRIVIT group (seven and 12 patients, respectively) and 19 in the VITREALONE group with focal vitreomacular adhesion associated with macular holes were evaluated with spectral domain optical coherence tomography. Functional examinations included best-corrected visual acuity (BCVA) and microperimetry analysis. Visual function changes were compared between the OCRIALONE group + OCRIVIT group and VITREALONE group up to three months. Furthermore, a subgroup analysis compared the OCRIVIT group and the VITREALONE group. BCVA values and the mean retinal sensitivity showed statistically significant improvement in all groups (p < 0.001). Specifically, the retinal sensitivity values at the end of the follow-up were significantly higher in the OCRIALONE group + OCRIVIT group than in the VITREALONE group. These functional findings were also confirmed when the statistical analysis was conducted between the OCRIVIT group and the VITREALONE group. Although the OCRIALONE group + OCRIVIT group exhibited faster retinal thinning than the VITREALONE group (p = 0.006), the analysis of the OCRIVIT group versus the VITREALONE group did not show any statistically significant difference. The better functional results and similar anatomical findings suggest that ocriplasmin can be used as a first-line treatment, and that prompt pars plana vitrectomy as primary surgery does not provide better outcomes in comparison with pars plana vitrectomy after ocriplasmin injection.

Plasmin Enzyme-Assisted Vitrectomy in Pediatric Patients with Vitreoretinal Diseases

PURPOSE

To evaluate the efficacy and safety of using plasmin-assisted vitrectomy in pediatric patients with vitreoretinal diseases.

METHODS

We prospectively recruited children aged 16 years or younger who presented with vitreoretinopathies and underwent plasmin-assisted vitrectomy between 2012 and 2013. The main outcome measure was the induction of posterior vitreous detachment (PVD) using a suction power of 200 mm Hg or less during surgery.

RESULTS

Eleven eyes of 11 patients (mean age: 3.7 years; average follow-up duration: 14.1 months) were included. Of these 11 patients, there were 3 (27%) cases of stage 5 retinopathy of prematurity, 2 (18%) cases of persistent fetal vasculature, 2 (18%) cases of rhegmatogenous retinal detachment, 2 (18%) cases of idiopathic epiretinal membrane, 1 (9%) case of traumatic macular pucker, and 1 (9%) case of traumatic vitreous hemorrhage (9%). PVD was achieved in all cases (100%) during surgery using low suction after plasmin treatment (mean: 150 ± 39 mm Hg; range: 100-200). Overall, anatomical success was achieved in 8 eyes (73%). Visual acuity improved in all 5 (100%) patients for whom vision could be measured at 6 months after the operation. Cataracts were found in 4 eyes (36%), and a rise in transient intraocular pressure was observed in 1 eye (9%).

CONCLUSIONS

Plasmin-assisted vitrectomy offers an effective and less traumatic intervention for a variety of pediatric vitreoretinal diseases.

Novel plasminogen and hyaluronate sodium eye drop formulation for a patient with ligneous conjunctivitis

PURPOSE

The development, analysis, and first clinical use of a novel eye drop formulation of plasminogen and hyaluronate sodium for the treatment of a patient with ligneous conjunctivitis (LC) are described.

SUMMARY

LC is a chronic inflammatory disorder of the eye that can in rare cases lead to corneal involvement and subsequent blindness. Topically administered plasminogen is an effective treatment for LC; however, the lack of a specific and validated formulation of plasminogen for topical treatment can constitute a gap in the quality of care. A novel formulation of plasminogen and hyaluronate sodium for the treatment of LC was developed by combining commercially available products. Through a series of tests, including microbiological, viscosity, and pH analyses, the novel eye drop formulation was demonstrated to have constant activity (3.3 IU/mL or greater), to be microbiologically stable (i.e., sterile), and to be safe enough for daily administration. The first clinical application of the novel eye drop formulation was in the case of a nine-year-old girl with LC affecting both eyes. Initially, the girl's parents administered two drops every three hours to the left eye each day while the girl was awake. On examination after 30 days of daily use of the eye drop formulation, the patient was found to have a clear cornea and no membrane development on the conjunctiva; the formulation was subsequently administered in both eyes, with positive results.

CONCLUSION

A new formulation of plasminogen plus hyaluronate sodium was developed, tested, and used successfully in a girl with LC.

Ocriplasmin: who is the best candidate?

Enzymatic vitreolysis is currently the focus of attention around the world for treating vitreomacular traction and full-thickness macular hole. Induction of posterior vitreous detachment is an active area of developmental clinical and basic research. Despite exerting an incompletely elucidated physiological effect, ocriplasmin (also known as microplasmin) has been recognized to serve as a well-tolerated intravitreal injection for the treatment of vitreomacular traction and full-thickness macular hole. There are several unexplored areas of intervention where enzymatic vitreolysis could potentially be used (ie, diabetic macular edema). Recent promising studies have included combinations of enzymatic approaches and new synthetic molecules that induce complete posterior vitreous detachment as well as antiangiogenesis. Although no guidelines have been proposed for the use of ocriplasmin, this review attempts to aid physicians in answering the most important question, "Who is the best candidate?"

Induction of Posterior Vitreous Detachment in Pediatric Vitrectomy by Preoperative Intravitreal Injection of Tissue Plasminogen Activator

PURPOSE

To report the efficacy of intravitreal injection of tissue plasminogen activator (tPA) with or without autoserum in induction of posterior vitreous detachment (PVD) in pediatric vitrectomy.

METHODS

Retrospective, interventional case series of pediatric patients receiving intravitreal injection of tPA preoperatively to facilitate PVD in vitrectomy from January 2011 to December 2014 at the Changhua Christian Hospital, Taiwan. All patients received intravitreal injections of 25 µg of tPA 3 days before vitrectomy. For cases without preexisting vitreous hemorrhage, 0.1 mL of intravitreal autologous serum was co-administered. Main outcome measures included successful rate of posterior vitreous detachment in vitrectomy, visual outcome, and related ocular complications.

RESULTS

Four boys and 2 girls were included. Ages ranged from 39 weeks' postmenstrual age to 8 years. The indications for vitrectomy were traumatic macular hole (cases 1 and 2); premacular hemorrhage secondary to retinopathy of prematurity (case 3); abusive head trauma with premacular hemorrhage, subinternal limiting membrane hemorrhage, and macular hole (case 4); trauma with dense vitreous hemorrhage (case 5); and vitreous hemorrhage with unknown cause (case 6). Successful PVD was induced intraoperatively in all cases and the macular hole was closed successfully in 3 of 3 cases (cases 1, 2, and 4). No surgical complications were noted. Visual outcome improved in all 3 eyes with checkable preoperative visual acuity (cases 1, 2, and 6).

CONCLUSIONS

Intravitreal injection of tPA 3 days before vitrectomy may be a helpful adjunct to induce pediatric PVD.

Intravitreal autologous plasmin prepared by urokinase for vitreolysis: a pilot study

PURPOSE

To evaluate the effects of intravitreal autologous plasmin injection (IVAP) on vitreoretinal diseases and vitreolysis.

METHODS

In this interventional, prospective, case series pilot study, 8 eyes were assigned to IVAP. Plasminogen as centrifuged from the patients' plasma was converted to plasmin by adding urokinase. A total of 0.2 mL extracted plasmin was injected intravitreally. Posterior vitreous detachment (PVD) and potential injection-related complications at week 4 were the primary outcome measures. Secondary outcomes included changes in best-corrected visual acuity (VA) (logMAR) and central macular thickness (CMT).

RESULTS

Mean age of the patients was 54.35 years. Two patients had complete PVD and 3 patients had partial PVD. Four patients had decrease in CMT. The VA was not changed in 6 patients, improved in 1 patient, and decreased in 1 patient. No uveitis, endophthalmitis, or postinjection vitreous hemorrhage was observed.

CONCLUSIONS

This pilot study demonstrated the efficacy of urokinase-prepared IVAP injection on releasing vitreomacular traction and inducing vitreolysis.

Vitrectomy for idiopathic macular hole

BACKGROUND

A macular hole is an anatomic opening in the retina that develops at the fovea. Macular holes can be seen in highly myopic eyes or following ocular trauma, but the great majority are idiopathic. Pars plana vitrectomy was introduced to treat full-thickness macular holes, which if left untreated have a poor prognosis since spontaneous closure and visual recovery are rare.Vitrectomy is a surgical technique involving the removal of the vitreous body that fills the eye. The surgeon inserts thin cannulas into the eyes through scleral incisions to relieve traction exerted by the vitreous or epiretinal membranes to the central retina and to induce glial tissue to bridge and close the hole.

OBJECTIVES

The primary objective of this review was to examine the effects of vitrectomy for idiopathic macular hole on visual acuity. A secondary objective was to investigate anatomic effects on hole closure and other dimensions of visual function, as well as to report on adverse effects recorded in included studies.

SEARCH METHODS

We searched the Cochrane Eyes and Vision Group Trials Register (4 March 2015), the Cochrane Central Register of Controlled Trials (CENTRAL; 2015, Issue 2), Ovid MEDLINE, Ovid MEDLINE In-Process and Other Non-Indexed Citations, Ovid MEDLINE Daily, Ovid OLDMEDLINE (January 1946 to March 2015), EMBASE (January 1980 to March 2015), Latin American and Caribbean Health Sciences Literature Database (LILACS) (January 1982 to March 2015), the Web of Science Conference Proceedings Citation Index-Science (CPCI-S) (January 1980 to March 2015), the ISRCTN registry (www.isrctn.com/editAdvancedSearch), ClinicalTrials.gov (www.clinicaltrials.gov) and the World Health Organization (WHO) International Clinical Trials Registry Platform (ICTRP) (www.who.int/ictrp/search/en). We did not use any date or language restrictions in the electronic searches for trials. We last searched the electronic databases on 4 March 2015.

SELECTION CRITERIA

We included randomised controlled trials comparing vitrectomy (with or without internal limiting membrane peeling) to no treatment (that is observation) for macular holes.

DATA COLLECTION AND ANALYSIS

We used standard methodological procedures expected by Cochrane. Two review authors independently extracted the data. We estimated best corrected visual acuity and macular hole closure at 6 to 12 months of follow-up.

MAIN RESULTS

Three studies provided data on the comparison between vitrectomy and observation in eyes with macular hole and visual acuity less than 20/50. Two studies, conducted in the USA and published in 1996 and 1997, used a similar protocol and included participants with stage II macular hole (42 eyes randomised, 36 analysed, number of participants not reported) or participants with stage III/IV hole (129 eyes of 120 participants, 115 eyes in analyses). The third study, conducted in the UK and published in 2004, included 185 eyes of 174 participants with full-thickness macular hole (41 eyes with stage II holes and 74 eyes with stage III/IV holes in analyses). Studies were of good quality for randomisation and allocation concealment, whereas visual acuity measurement was unmasked.At 6 to 12 months, visual acuity was improved by about 1.5 Snellen lines (-0.16 logMAR, 95% confidence intervals -0.23 to -0.09 logMAR, 270 eyes, moderate-quality evidence). The chances of macular hole closure at 6 to 12 months were greatly increased using vitrectomy, yielding an odds ratio of 31.4 (95% confidence intervals 14.9 to 66.3, 265 eyes, high-quality evidence; raw sum data: 76% vitrectomy, 11% observation). Vitrectomy was beneficial both in smaller (stage II) and in larger (stage III/IV) macular holes.The largest study reported that cataract surgery was needed in about half of cases at two years after operation and that retinal detachment occurred in about 5% of operated eyes.

AUTHORS' CONCLUSIONS

Vitrectomy is effective in improving visual acuity, resulting in a moderate visual gain, and in achieving hole closure in people with macular hole. However, these results may not apply to modern surgery due to technological improvements in vitrectomy techniques.

Lens subluxation after plasmin and SF6 injections in rabbit eyes

Purpose

To investigate the rate of lens subluxation following plasmin and/or SF₆ injections in eyes, and whether a subsequent elevated level of vascular endothelial growth factor (VEGF) and vitreous tap would aggravate subluxation.

Methods

Four groups of rabbits were used. Group 1 received an intravitreal injection (IVI) of plasmin and SF₆ in the right eye; group 2 received an IVI of plasmin in the right eye; group 3 received an IVI of SF₆ in the right eye; and group 4 received an IVI of balanced salt solution in the right eye. After treatment, IVIs of VEGF were given and vitreous tap was performed three times, followed by clinical observation of lens subluxation and scanning electronic microscope evaluation of the zonular fibers.

Results

After IVIs of plasmin and SF₆, and VEGF and vitreous tap had been performed one to three times, lens subluxation was noted in 0%, 43%, 71%, 71%, and 86% of the eyes in group 1. After IVIs of plasmin, VEGF, and vitreous tap had been performed one to three times, lens subluxation was noted in 11%, 22%, 44%, 44%, and 67% of the eyes in group 2. The eyes in group 3 and 4 did not show signs of lens subluxation after VEGF IVIs and vitreous tap. Histology confirmed zonular fiber damage in the eyes treated with plasmin.

Conclusions

The incidence of lens subluxation increased following plasmin injections in the eyes, and this was aggravated by the subsequent high VEGF level in the eyes and vitreous tapping. Zonular fibers were disrupted following plasmin treatment. These effects should be kept in mind when using plasmin enzymes in patients with vitreoretinal abnormalities.

The International Vitreomacular Traction Study Group classification of vitreomacular adhesion, traction, and macular hole

OBJECTIVE

The International Vitreomacular Traction Study (IVTS) Group was convened to develop an optical coherence tomography (OCT)-based anatomic classification system for diseases of the vitreomacular interface (VMI).

DESIGN

The IVTS applied their clinical experience, after reviewing the relevant literature, to support the development of a strictly anatomic OCT-based classification system.

PARTICIPANTS

A panel of vitreoretinal disease experts was the foundation of the International Classification System.

METHODS

Before the meeting, panel participants were asked to review 11 articles and to complete 3 questionnaires. The articles were preselected based on searches for comprehensive reviews covering diseases of the VMI. Responses to questionnaires and the group's opinions on definitions specified in the literature were used to guide the discussion.

MAIN OUTCOME MEASURES

Optical coherence tomography-based anatomic definitions and classification of vitreomacular adhesion, vitreomacular traction (VMT), and macular hole.

RESULTS

Vitreomacular adhesion is defined as perifoveal vitreous separation with remaining vitreomacular attachment and unperturbed foveal morphologic features. It is an OCT finding that is almost always the result of normal vitreous aging, which may lead to pathologic conditions. Vitreomacular traction is characterized by anomalous posterior vitreous detachment accompanied by anatomic distortion of the fovea, which may include pseudocysts, macular schisis, cystoid macular edema, and subretinal fluid. Vitreomacular traction can be subclassified by the diameter of vitreous attachment to the macular surface as measured by OCT, with attachment of 1500 μm or less defined as focal and attachment of more than 1500 μm as broad. When associated with other macular disease, VMT is classified as concurrent. Full-thickness macular hole (FTMH) is defined as a foveal lesion with interruption of all retinal layers from the internal limiting membrane to the retinal pigment epithelium. Full-thickness macular hole is primary if caused by vitreous traction or secondary if directly the result of pathologic characteristics other than VMT. Full-thickness macular hole is subclassified by size of the hole as determined by OCT and the presence or absence of VMT.

CONCLUSIONS

This classification system will support systematic diagnosis and management by creating a clinically applicable system that is predictive of therapeutic outcomes and is useful for the execution and analysis of clinical studies.

Review and perspectives on pharmacological vitreolysis

The vitreous is involved in multiple diseases when an incomplete posterior vitreous detachment (PVD) occurs. An incomplete PVD can lead to several pathological conditions. Such visually threatening conditions are traditionally of exclusive surgical interest. In contrast, pharmacological vitreolysis is the effort to reduce or eliminate the pathogenetic role of the vitreous solely by means of drug delivery. Here we aim to review and summarize the evidence available to date about this challenging new approach.

Microplasmin (ocriplasmin) in pediatric vitreoretinal surgery: update and review

PURPOSE

To discuss the potential role of microplasmin (ocriplasmin) as a surgical adjunct to vitrectomy in pediatric vitreoretinopathies.

METHODS

Literature review of the laboratory and clinical evidence to date for the use of both autologous plasmin enzyme as an adjunct to vitrectomy and more recently recombinant microplasmin (ocriplasmin) as monotherapy for focal vitreomacular traction in adults.

RESULTS

Autologous plasmin enzyme is currently being used as a surgical adjunct to vitrectomy, with supporting Levels 2 and 3 published evidence in a range of pediatric vitreoretinopathies including Stage 5 retinopathy of prematurity and congenital X-linked retinoschisis. The availability of autologous plasmin enzyme is limited. In recent Phase 3 clinical trials, intravitreal ocriplasmin versus sham injection resulted in resolution of focal vitreomacular traction in 27% versus 10% (P < 0.001, n = 652).

CONCLUSION

Ocriplasmin may potentially be used as a surgical adjunct to vitrectomy in place of autologous plasmin enzyme. A Phase 2, randomized, placebo-controlled surgical trial is under way to assess this.

Vitreomacular adhesion and neovascular age-related macular degeneration

We explore the hypothesis that vitreomacular adhesion (VMA) and vitreomacular traction (VMT) play a role in the pathogenesis and clinical course of neovascular ("wet") age-related macular degeneration (AMD). Several biological theories are offered to explain this possible association, including direct tractional force, altered vitreous oxygenation, altered diffusion coefficients of intravitreal molecules, and alterations in the pharmacokinetics of intravitreal drugs. Release of VMT may improve the clinical course of neovascular AMD, and a few case series suggest that vitrectomy can lead to both a functional and anatomic improvement. A large, randomized, controlled clinical trial is underway, investigating pharmacologic release of VMA in eyes with neovascular AMD.

Idiopathic full-thickness macular holes and the vitreomacular interface: a high-resolution spectral-domain optical coherence tomography study

PURPOSE

To analyze the vitreomacular interface in idiopathic full-thickness macular holes (MHs) using spectral-domain optical coherence tomography.

DESIGN

Prospective cross-sectional case series.

METHODS

Ninety-one eyes of 86 consecutive patients with a MH were examined by spectral-domain optical coherence tomography. The vitreomacular interface was assessed and the presence or absence of an operculum was analyzed.

RESULTS

Fifty-two eyes had a stage 2 MH, 12 eyes a stage 3 MH, and 27 eyes a stage 4 MH. No posterior hyaloid membrane was detected in any eyes with a stage 4 MH. In 35 (54.7%) of the 64 eyes with an MH without a complete posterior vitreous detachment (PVD), we saw a perifoveal PVD with vitreofoveal adhesion and partial dehiscence of the raised inner retina with an outer retinal separation in the MHs. In 24 (37.5%) of the 64 eyes without a complete PVD, an operculum, which is a hyperreflective structure of the foveal retina, was in front of the MH. The posterior hyaloid membrane was separated completely but adhered to the optic disc. In 2 (3.1%) of the 64 eyes without a complete PVD, the posterior hyaloid membrane was separated from the macula without an operculum. In 3 (4.7%) of the 64 eyes without a complete PVD, vitreofoveal adhesion on both edges of the hole was connected to the taut posterior hyaloid membrane without an operculum.

CONCLUSIONS

The vitreomacular interface had 4 configurations in MHs without a complete PVD. Approximately 55% of cases with an open roof in the eyes without a complete PVD may be at risk for progression to operculum formation (loss of retinal tissue).

Ocriplasmin for vitreoretinal diseases

Fibronectin and laminin are clinically relevant plasmin receptors in the eye. Located at the vitreoretinal interface, they are cleaved by ocriplasmin (Microplasmin, ThromboGenics, Iselin, NJ), a novel ophthalmic medication. A series of clinical trials to study ocriplasmin for the treatment of vitreoretinal diseases such as vitreomacular traction, macular hole, and exudative age-related macular degeneration are underway. The results are promising and may impact patient care.

Emerging nonsurgical methods for the treatment of vitreomacular adhesion: a review

With the dissemination of optical coherence tomography over the past two decades, the role of persistent vitreomacular adhesion (VMA) in the development of numerous macular pathologies - including idiopathic macular hole, vitreomacular traction syndrome, cystoid and diabetic macular edema, neovascularization in diabetic retinopathy and retinal vein occlusion, exudative age-related macular degeneration, and myopic traction maculopathy - has been established. While invasive vitreoretinal procedures have long been utilized to address complications related to these disorders, such an approach is hampered by incomplete vitreoretinal separation and vitreous removal, surgical complications, and high costs. In light of such limitations, investigators have increasingly looked to nonsurgical means for the treatment of persistent pathologic VMA. Chief among these alternative measures is the intravitreal application of pharmacologic agents for the induction of vitreous liquefaction and/or vitreoretinal separation, an approach termed pharmacologic vitreolysis. This article aims to review the available evidence regarding the use of pharmacologic agents in the treatment of VMA-related pathology. In addition, a discussion of vitreous molecular organization and principles of physiologic posterior vitreous detachment is provided to allow for a consideration of vitreolytic agent mode of action and molecular targets.

Macular hole formation in fellow eyes with a perifoveal posterior vitreous detachment of patients with a unilateral macular hole

PURPOSE

To estimate the rate of macular hole formation in fellow eyes with a perifoveal posterior vitreous detachment (PVD) and early stage 1 intrafoveal lesions in patients with a unilateral idiopathic full-thickness macular hole (MH) using optical coherence tomography (OCT).

DESIGN

Retrospective observational case series.

METHODS

Fellow eyes of consecutive patients with a unilateral full-thickness MH were examined on OCT. A subset of fellow eyes with a perifoveal PVD had been followed to investigate the rates of macular hole formation in fellow eyes with early stage 1 intrafoveal lesions.

RESULTS

Of 176 patients with a unilateral full-thickness MH, 42 fellow eyes (42 patients) with a perifoveal PVD were identified. During follow-up, a foveolar detachment was seen in 16 eyes, and 4 eyes had a foveal pseudocyst alone. In the 16 eyes with a foveolar detachment, 9 eyes had concurrent inner foveal splits. Within another 2 years of follow-up, OCT showed that 5 of 16 fellow eyes (31%) with a foveolar detachment developed a second full-thickness MH and 5 of 9 fellow eyes with a foveolar detachment and inner foveal splits developed a second full-thickness MH. Two of 4 eyes with a foveal pseudocyst alone developed vitreofoveal separation without hole formation. The remaining 2 eyes with a foveal pseudocyst alone remained stable at the last follow-up visit.

CONCLUSIONS

Fellow eyes with a foveolar detachment and a perifoveal PVD may be at high risk, and fellow eyes with a foveolar detachment and inner foveal splits might be at higher risk for progression to macular hole formation.

Intravitreal injection of autologous plasmin enzyme for macular edema associated with branch retinal vein occlusion

PURPOSE

To investigate the effects of an intravitreal injection of autologous plasmin enzyme for macular edema associated with a branch retinal vein occlusion (BRVO).

DESIGN

Prospective, interventional case studies.

METHODS

Twenty-six eyes of 26 patients (14 men and 12 women) with macular edema resulting from a BRVO were studied. None of the eyes had a posterior vitreous detachment (PVD). The average age at the onset of BRVO was 58.7 ± 6.6 years. The interval between onset of the macular edema and injection of autologous plasmin enzyme was 4.2 months. One international unit of autologous plasmin enzyme in 0.1 mL was injected into each vitreous. The presence of a PVD was evaluated 1 week after the injection, and the visual acuity and macular thickness were measured before and 1 week and 1, 3, 6, and 12 months after the autologous plasmin enzyme injection.

RESULTS

After the autologous plasmin enzyme injection, a total PVD was observed in 23 eyes and no PVD was observed in 3 eyes. The visual acuity gradually recovered after the injection, improved by 2 lines or more in 23 eyes, and remained unchanged in the 3 eyes. The retinal thickness also recovered gradually at 1, 3, 6, and 12 months. The mean retinal thickness was reduced from 602.12 to 253.62 μm at 12 months after surgery. It was reduced significantly after 1, 3, 6, and 12 months (P < .0001).

CONCLUSIONS

Intravitreal autologous plasmin enzyme may lead to an improvement of visual acuity and a reduction of macula edema in eyes with BRVO.

Intravitreal injection of microplasmin for treatment of vitreomacular adhesion: results of a prospective, randomized, sham-controlled phase II trial (the MIVI-IIT trial)

PURPOSE

Vitreomacular adhesion causing vitreomacular traction is a common indication for vitrectomy. It may be avoided by using enzymatic vitreolysis. The MIVI-IIT (traction) study evaluated the ability of a single or repeated injection of microplasmin to release vitreomacular traction.

METHODS

This randomized, double-masked, Phase II trial with control sham injection enrolled 60 patients. Patients in each of the 4 cohorts were randomized (4:1) to active treatment or sham injection. In the first 3 cohorts, increasing doses of microplasmin (75, 125, and 175 microg) were administered. In the fourth cohort, an initial injection of 125 microg microplasmin or sham was administered followed 1 month later by an injection of 125 microg microplasmin if no release of adhesion occurred. A third dose was injected 4 weeks later if there was still no release of adhesion.

RESULTS

Within 28 days of sham, 75, 125, and 175 microg microplasmin administration, nonsurgical resolution of vitreomacular adhesion was observed in 8, 25, 44, and 27% of the patients, respectively. When the 125 microg dose was repeated up to 3 times, adhesion release was observed in 58% of patients 28 days after the final injection.

CONCLUSION

These results provide support for the potential of microplasmin as a nonsurgical treatment for vitreomacular adhesion.

Efficacy of plasmin, microplasmin, and streptokinase-plasmin complex for the in vitro degradation of fibronectin and laminin- implications for vitreoretinal surgery

PURPOSE

Plasmin enzyme generates vitreoretinal separation by degradation of laminin and fibronectin in the vitreoretinal interface. It can be activated from plasminogen by urokinase, tissue plasminogen activator, or by formation of a 1:1 complex with streptokinase. The latter is then converted into a streptokinase-plasmin-complex (SK-P), which displays fibrinolytic activity and can generate free plasmin by proteolysis of plasminogen. We compared the efficacy of SK-P, SK-P activated plasmin, urokinase activated plasmin (UK-P), and microplasmin, a truncated form of plasmin, in cleaving laminin and fibronectin.

METHODS

Streptokinase (SK) was added to human plasminogen in molar ratios between 1:100 and 2:1, generating SK-P at ratios > 1:1, and mixtures of SK-P and free plasmin (SK-P/plasmin) at lower ratios. SK-PL, SK-P/plasmin, UK-P, and microplasmin were added to laminin and fibronectin, incubated at 37 degrees C for 30 min-22 hr and processed for SDS-PAGE.

RESULTS

Proteolysis using SK-activated plasminogen increased when the SK/plasminogen ratio was decreased, generating increasing amounts of free plasmin. Microplasmin and urokinase-activated plasmin displayed similar proteolysis of both laminin and fibronectin as SK/plasminogen at ratios of 1:10 or lower.

CONCLUSION

The mode of plasminogen activation influences the efficacy of proteolysis for laminin and fibronectin and should be considered when plasmin is used in vitreoretinal surgery.

Vitreoretinal disease in the coming decade

PURPOSE OF REVIEW

The field of vitreoretinal disease and surgery has seen tremendous growth and innovation in recent years. In view of the latest advances, the present article highlights some of the current trends in vitreoretinal research that promise to be revolutionary in the coming decade.

RECENT FINDINGS

Pharmacologic vitreolysis may greatly impact the current approach to treatment of various vitreoretinopathies. New methods of drug delivery to the posterior segment either via nanoparticles or sustained-release intravitreal implants may supplant repetitive intravitreal injections. Gene therapy may become more common as the genetic basis of inherited retinal diseases is further elucidated. Stem-cell transplantation and the implantation of artificial retinal prostheses offer promise for long-term sight restoration.

SUMMARY

Based on recent advances in ongoing vitreoretinal research, the spectrum of treatable retinal disease is likely to expand significantly in the coming decade, with enormous public health impact, as well as significant changes in the practice patterns of retina specialists worldwide.

Differential vitreous dye diffusion following microplasmin or plasmin pre-treatment

PURPOSE

Plasmin and microplasmin are related enzymes that differ mainly in size. The differential effect of plasmin and microplasmin on vitreous structure, protein degradation, and dye diffusion through porcine vitreous was evaluated.

METHODS

The enzymatic effect was examined using a number of approaches on fresh porcine eyes: (1) structural integrity of vitreous after a 2-hr incubation using the electron microscope (EM); (2) effect on soluble proteins within the vitreous using gel electrophoresis after incubation at various time points over a 24-hr period; (3) fluorescein dye diffusion within the vitreous cavity measured over a 1-hr period following a 2-hr incubation. The chosen enzymatic activities for plasmin 0.5 IU and microplasmin 125 microg were within the clinical range, and were chosen for equipotence. A saline control was also used in all experiments.

RESULTS

Significant structural changes were seen with both microplasmin and plasmin when examined by EM. Gel electrophoresis showed that microplasmin and plasmin digested the same proteins, mainly molecular weights above 50 kDa. The enzymatic effect was noticeable earlier in microplasmin-treated eyes and was more significant by the end of the incubation period. Differential fluorescein diffusion rates were seen between normal saline, plasmin, and microplasmin within the vitreous cavity. The greatest diffusion rate was seen with microplasmin and was statistically significantly higher than plasmin.

CONCLUSION

Microplasmin and plasmin have a similar enzymatic effect on vitreous. However, an equipotent amount of microplasmin appears to have a more extended effect on vitreous gel. This may, in part, be related to its smaller size allowing it to diffuse more readily through the vitreous matrix.

A placebo-controlled trial of microplasmin intravitreous injection to facilitate posterior vitreous detachment before vitrectomy

PURPOSE

To evaluate the safety and efficacy of a preoperative intravitreous injection of microplasmin in patients scheduled for vitreous surgery.

DESIGN

Phase 2, multicenter, placebo-controlled, double-masked, parallel-group, dose-ranging clinical trial.

PARTICIPANTS

One hundred twenty-five patients scheduled for pars plana vitrectomy (PPV), primarily for treatment of either vitreomacular traction or macular hole.

INTERVENTION

A single intravitreous injection of either microplasmin at 1 of 3 doses (25 microg, 75 microg, or 125 microg in 100 microl) or placebo injection administered 7 days before PPV.

MAIN OUTCOME MEASURES

Presence or absence of posterior vitreous detachment (PVD) at the time of PPV, progression of PVD, and resolution of vitreomacular interface abnormality precluding the need for PPV.

RESULTS

Rates of total PVD at the time of surgery were 10%, 14%, 18%, and 31% in the placebo group (n = 30), 25-microg (n = 29), 75-microg (n = 33), and 125-microg microplasmin groups (n = 32), respectively. The secondary end point resolution of vitreomacular interface abnormality precluding the need for vitrectomy at the 35-day time point was observed at rates of 3%, 10%, 15%, and 31% in the placebo, and the 25-microg, the 75-microg, and the 125-microg microplasmin groups, respectively. At the 180-day time point, the equivalent rates were 3%, 7%, 15%, and 28%, respectively.

CONCLUSIONS

Microplasmin injection at a dose of 125 microg led to a greater likelihood of induction and progression of PVD than placebo injection. Patients receiving microplasmin were significantly more likely not to require vitrectomy surgery. More definitive evaluation in phase 3 clinical trials therefore is warranted.

FINANCIAL DISCLOSURE(S)

Proprietary or commercial disclosure may be found after the references.

Microplasmin intravitreal administration in patients with vitreomacular traction scheduled for vitrectomy: the MIVI I trial

PURPOSE

To evaluate the safety and preliminary efficacy of 4 doses and several exposure times of intravitreal microplasmin given before pars plana vitrectomy for vitreomacular traction maculopathy.

DESIGN

A multicenter, prospective, uncontrolled, dose-escalation, phase I/II clinical trial.

PARTICIPANTS

Sixty patients enrolled into 6 successive cohorts.

INTERVENTION

A single intravitreal injection of microplasmin at 1 of 4 doses (25, 50, 75, or 125 microg in 100 microl) administered either 1 to 2 hours, 24 hours, or 7 days before planned pars plana vitrectomy.

MAIN OUTCOME MEASURES

For safety, a complete ophthalmologic examination, fundus photography, fluorescein angiography, Humphrey visual fields, and electrophysiology; for efficacy, posterior vitreous detachment (PVD) induction as assessed by B-scan ultrasound and ease of PVD induction at the time of vitrectomy.

RESULTS

The use of microplasmin led to a progressively higher incidence of PVD induction on ultrasonography with increasing time exposure. A PVD before surgery was observed with 25 microg microplasmin in 0, 2, and 5 patients with increasing exposures (2 hours, 24 hours, 7 days). With increasing dose, a PVD before surgery was observed by ultrasound as follows: 25 microg, 0; 50 microg, 1; 75 microg, 2; 125 microg, 3. However, at surgery, with a 125-microg dose, these patients had a discontinuous layer of vitreous present on the retinal surface resulting from the induction of an anomalous PVD in the form of vitreoschisis. One retinal detachment developed shortly after administration of microplasmin. Two developed after surgery. There were no other safety concerns.

CONCLUSIONS

Results from this initial clinical trial evaluating intravitreal microplasmin show the drug to be well tolerated and capable of inducing a pharmacologic PVD in some patients. These results warrant evaluation of microplasmin in larger, controlled trials.

Combined pars plana lensectomy/vitrectomy for idiopathic macular hole repair without postoperative prone positioning

Purpose

The aim of this study is to determine the anatomic and visual outcomes following combined pars plana lensectomy/vitrectomy (CPPLV) as a primary procedure for idiopathic macular hole (MH) without post-operative prone positioning (PPP).

Materials and Methods

A retrospective chart review of 42 patients (47 eyes) with MH who underwent CPPLV was performed. No PPP was performed; however, patients were instructed to avoid the supine position during the first postoperative week. The main outcome measures included MH closure rate, best corrected post-operative Snellen visual acuity (BCVA), and procedure complications.

Results

Anatomical closure was achieved in 44 eyes (93.6%). The average BCVA in these eyes improved from 20/203 at baseline to 20/91 post-operatively, with 28 (63.6%) having 20/40 or better. Twenty-eight (59.6%) of the 47 eyes had a BCVA of 20/40 or better post-operatively and 35 (74.5%) eyes improved by at least 2 Snellen lines. Post-operative retinal detachment (RD) was observed in 4 eyes (8.5%) and late reopening of the hole in 4 (9.1%).

Discussion

The anatomical and visual outcomes and the RD rate of CPPLV with sulcus intraocular lens implantation without PPP are comparable to those of traditional MH surgery techniques. The main advantages include sparing the patient the inconvenience of PPP and eliminating the need for additional post-vitrectomy cataract extraction procedure.

Enzymatic vitreous disruption

Enzymatic vitreous disruption refers to cleaving the vitreoretinal junction by enzymatic means, thereby inducing posterior vitreous detachment (PVD) and liquefaction of the vitreous gel. Several enzymes have been proposed in this respect, including chondroitinase, hyaluronidase, dispase, and plasmin. In an experimental setting, chondroitinase induced PVD and was helpful in removing epiretinal membranes but no further data have been reported yet. Hyaluronidase liquefies the vitreous as demonstrated in a phase III trial in diabetic patients with vitreous haemorrhage. Dispase induces PVD but also causes inner retinal damage and is now used as an animal model of proliferative vitreoretinopathy. Plasmin has the capability of both PVD induction and liquefaction. However, plasmin is highly unstable and not available for clinical use. Microplasmin (ThromboGenics Ltd, Dublin, Ireland) is a truncated form of human plasmin sharing the same catalytic activity like plasmin. Recombinant microplasmin is under clinical investigation in patients with vitreomacular traction. This review article reports on the current knowledge of enzymatic vitreous disruption and discusses details of the enzyme candidates in basic and clinical research terms.

Plasmin-assisted vitrectomy for management of proliferative membrane in proliferative diabetic retinopathy: a pilot study

PURPOSE

To demonstrate the feasibility of autologous plasmin for treatment of proliferative diabetic retinopathy.

METHODS

The study examined prospectively six patients with bilateral proliferative diabetic retinopathy. Comparisons of the surgical time and the incidence of retinal tears were made between the eyes treated with autologous plasmin and their respective opposite eyes, which were treated without plasmin.

RESULTS

All eyes treated with autologous plasmin required significantly less surgical time (68 versus 89 minutes, P = 0.04, paired t-test). In the plasmin group, no additional surgical procedures for removing the proliferative membrane were needed, including membrane delamination or segmentation. Moreover, with plasmin pretreatment, there were no retinal tears, which was in contrast to the control group, where three eyes with retinal tears were observed. There was no significant difference found between the two groups for final visual outcomes.

CONCLUSION

Autologous plasmin may be beneficial in the surgical management of proliferative diabetic retinopathy.

Plasmin enzyme-assisted vitreoretinal surgery in congenital X-linked retinoschisis: surgical techniques based on a new classification system

PURPOSE

To review the surgical outcome of autologous plasmin enzyme-assisted vitreoretinal surgery in managing complications associated with congenital X-linked retinoschisis (CXLRS).

METHODS

Medical records of 20 patients (22 eyes) with CXLRS complications, treated with autologous plasmin enzyme-assisted vitreoretinal surgery, were reviewed. Surgical techniques were adapted according to a new CXLRS classification.

RESULTS

Median age of the cohort was 3.5 years. Indications for surgical intervention included 8 eyes with schisis involving or threatening the macula, 7 eyes with rhegmatogenous retinal detachment, 4 eyes with tractional retinal detachment, 1 eye with vitreous and intraschisis hemorrhage, 1 eye with obstruction of the macula by an overhanging bullous schisis cavity, and 1 eye with macular pucker. Ninety-one percent (20/22) of eyes had retinal attachment postoperatively after an average of 1.3 procedures per eye. Of the eyes in which visual acuity was measured, 53% (8/15) improved, 33% (5/15) had no change, and 13% (2/15) lost vision.

CONCLUSION

Plasmin enzyme-assisted vitreoretinal surgery is a safe and effective method for managing the complications associated with CXLRS. Most patients had improved or stable postoperative visions.

Pediatric traumatic macular hole: results of autologous plasmin enzyme-assisted vitrectomy

PURPOSE

To review our experience with plasmin-assisted vitrectomy surgery for the treatment of pediatric macular holes.

DESIGN

Retrospective, interventional case series.

METHODS

Thirteen pediatric patients aged one to 15 years with a traumatic macular hole underwent surgical repair. All patients underwent surgery between February 1997 and March 2005 with autologous plasmin enzyme-assisted vitrectomy. After induction of posterior vitreous detachment (PVD), vitrectomy with membrane peeling and gas or silicone oil injection were performed followed by prone positioning for seven days. Main outcome measures included anatomic closure rate, visual outcome, and ocular complications.

RESULTS

The macular hole was closed successfully in 12 (92%) of 13 cases. Of the 12 patients for whom vision could be measured, 11 patients (92%) had visual acuity improvement of 2 or more lines and six patients (50%) achieved vision of 20/50 or better; all of the patients achieved vision better than 20/200. The visual improvement was statistically significant (P = .005, Wilcoxon signed-rank test). Surgical complications included cataract formation in one patient and retinal detachment in one patient.

CONCLUSIONS

Autologous plasmin enzyme may be a helpful adjunct when performing vitrectomy for traumatic macular holes.

Enzymatic vitreolysis with recombinant microplasminogen and tissue plasminogen activator

PURPOSE

To generate microplasmin (microPlm) using recombinant microplasminogen (microPlg) and recombinant tissue plasminogen activator (rt-PA) before intravitreous injection and to investigate the efficacy of microPlm in inducing posterior vitreous detachment (PVD).

METHODS

Forty-eight female or male New Zealand white rabbits were randomized into three groups. Recombinant human microPlg was incubated with rt-PA with a 200:1 molar ratio at 37 degrees C for 40 min. The right eyes of groups 1, 2, and 3, were injected with 0.5, 1.0, and 1.5 U microPlm in 0.1 ml respectively, and 0.1 ml balanced salt solution (BSS) was injected into the left eye as controls. Scanning electron microscopy (SEM), gross specimen examination, B-ultrasonography and optical coherence tomography (OCT) were performed to detect vitreoretinal interface.

RESULTS

Over eighty percent of recombinant human microPlg could be activated to active microPlm by rt-PA after 40 min incubation. Complete PVD was found at vitreous posterior pole of microPlm-treated eyes without morphological change of retina. Complete PVD of 25, 75, and 87.5% rabbit eyes was induced by 0.5, 1.0 and 1.5 U recombinant microPlm respectively on day 1. The remnants of vitreous cortex at the posterior pole were dependent on the concentration of microPlm. Among the four approaches for detecting PVD, SEM, gross specimen examination, and B-ultrasonography were more effective methods than OCT.

CONCLUSION

Intravitreous injection of 1.5 U microPlm can effectively induce complete PVD in rabbit eyes on day 1 without morphological change of retina.

Time course of posterior vitreous detachment in the second eye

PURPOSE OF REVIEW

Posterior vitreous detachment is the principal predisposing event for the development of retinal breaks and rhegmatogenous retinal detachments. Patients with unilateral posterior vitreous detachment are potentially at risk of developing the complications associated with posterior vitreous detachment in the fellow eye. Thus, to identify when posterior vitreous detachment develops in the fellow eye after it develops in the first eye is important for managing patients with unilateral posterior vitreous detachment.

RECENT FINDINGS

The main theme in the literature is research regarding the mechanism of the development of posterior vitreous detachment. Various pharmacologic vitreolysis agents can induce posterior vitreous detachment. Changes in the enzymatic activities in the vitreous and vitreoretinal interface tend to promote vitreous separation from the inner retinal surface with aging. Clinical studies have shown a significant increase in the occurrence of posterior vitreous detachment with aging, and the interval between the development of posterior vitreous detachment in the first eye and in the second eye is short.

SUMMARY

Posterior vitreous detachment is one of the most important age-related changes in human eyes, and age-related changes develop equally in both normal eyes; thus, posterior vitreous detachment may develop in the second eye within a few years of developing in the first eye.

Pharmacologic vitreolysis with microplasmin increases vitreous diffusion coefficients

BACKGROUND

Pharmacologic vitreolysis is a new approach to improve vitreo-retinal surgery and ultimately to liquefy and detach the vitreous from the retina to eliminate the contribution of the vitreous to retinopathy. The mechanism of action of the agents being developed for pharmacologic vitreolysis remains unclear. The effect of microplasmin on vitreous diffusion coefficients was investigated using the non-invasive technique of dynamic light scattering (DLS).

METHODS

Vitreous diffusion coefficients in 18 intact porcine eyes were measured in vitro with dynamic light scattering (DLS). DLS was performed on all specimens at 37 degrees C 30 min after injections of human recombinant microplasmin at doses ranging from 0.125 to 0.8 mg, with 20-nm tracer nanospheres.

RESULTS

DLS findings in untreated porcine vitreous were similar to the previously described findings in bovine and human vitreous. Microplasmin increased porcine vitreous diffusion coefficients in a dose-dependent manner (correlation coefficient, r=0.93), with an 85% increase after a 30-min exposure to the maximum dose.

CONCLUSIONS

Pharmacologic vitreolysis with human recombinant microplasmin increases vitreous diffusion coefficients in vitro. The results of these studies have implications for the dosing, route of administration, duration of action and methods of determining efficacy in future studies of pharmacologic vitreolysis to enhance vitreo-retinal surgery, as well as the design of clinical trials to induce prophylactic posterior vitreous detachment.

Efficacy of plasmin enzymes and chondroitinase ABC in creating posterior vitreous separation in the pig: a masked, placebo-controlled in vivo study

BACKGROUND

Induction of posterior vitreous detachment (PVD) during vitrectomy helps to prevent proliferative complications, but can be traumatic to the retina, particularly in young patients. Adjunct enzymes have been proposed to facilitate PVD. We investigated the efficacy of enzymes in creating PVD as an adjunct to vitrectomy in the pig.

METHODS

Five groups of 8 pigs received a masked intravitreal injection of chondroitinase (1 IU), human (0.4 or 1.3 activity units [AU]) or porcine plasmin (0.18 AU or 0.47 AU) into one eye, and osmolarity adjusted control into the other. After incubation, a core vitrectomy was performed on each eye at low suction, without vitreous peeling. The occurrence of spontaneous PVD and its extent were graded. Eyes were investigated using scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Vitreous remnants on the retina were quantified in SEM. Data were analyzed using McNemar's test for paired observations and Wilcoxon paired signed rank test.

RESULTS

Spontaneous PVD occurred more frequently in human plasmin-treated eyes (p<0.025) and all plasmin eyes (p<0.025) than in placebo controls. The extent of PVD appeared larger in human plasmin (p<0.025) and all plasmin-treated eyes (p<0.025). In plasmin-treated eyes, SEM morphometry showed a significant reduction in the vitreous-covered retina areas. Chondroitinase failed to produce an effect.

CONCLUSIONS

Plasmin may prove a useful adjunct to conventional vitrectomy.

Use of autologous plasmin during vitrectomy for diabetic maculopathy

PURPOSE

To evaluate the efficacy of autologous plasmin enzyme as an adjunct to vitrectomy in diabetic macular edema.

METHODS

Plasmin derived from autologous blood was injected intravitreally into seven eyes 15 min before vitreous surgery. The development and progression of a posterior vitreous detachment (PVD) was followed, and the time required for vitreous removal was measured. Both pre- and postoperative visual acuities and optical coherence tomography (OCT)-determined macular thickness were measured.

RESULTS

In the seven eyes in which plasmin was used, a PVD developed approximately 5 min after the injection and was confirmed to extend to the far periphery. In all cases, the removal of the vitreous was completed in a shorter time and no complications were observed. A restoration of the shape of the macula was observed in all cases. The visual acuity improved by two or more lines in four eyes, and remained unchanged in the remaining three eyes.

CONCLUSIONS

Autologous plasmin alone will create a full PVD, and eliminates the need for a mechanical creation of a PVD. Thus, plasmin is a safe and effective adjunct to vitreous surgery for the treatment of diabetic maculopathy.

Production of recombinant human microplasminogen and pilot study in inducing posterior vitreous detachment

PURPOSE

To realize the high production of recombinant human microplasminogen (r-mPlg) with Pichia pastoris and demonstrate the efficacy of r-mPlg in inducing posterior vitreous detachment (PVD).

METHODS

Recombinant plasmid pAO815-3mPlg was constructed and transformed into SMD1168 cells. Positive recombinant clones were selected with MD plate and cultured in BMG medium, then induced in BMM medium. A protein band corresponding to mPlg with molecular mass of 29 kDa was revealed in SDS-PAGE and confirmed by Western blot. Anion-exchange chromatography and plasminogen activity assay kit were used to obtain purified r-mPlg with biological activity. Twenty eyes of freshly slaughtered pigs were divided into 4 groups, 5 eyes in each group. Group 1 served as normal control. Intravitreal injection of 0.1 ml BSS, 1000 IU/0.1 ml recombinant streptokinase (r-SK) and 1000 IU/0.1 ml r-SK plus 3 U/0.1 ml r-mPlg was done respectively to groups 2, 3, and 4. After incubation at 37 degrees C for 60 min, all eyes were processed for light microscopy, scanning electron microscopy (SEM), and transmission electron microscopy (TEM).

RESULTS

r-mPlg, which has potential fibrinolytic activity, was successfully obtained with yield of 30 mg/L and purity of 97%. PVD was demonstrated by SEM in group 4 but not in other three groups. The retina and the inner limiting membrane (ILM) were well preserved in all eyes.

CONCLUSION

r-mPlg, which has potential fibrinolytic activity, can be produced through Pichia pastoris expression system. Three U of r-mPlg combined with 1000 IU r-SK was effective in producing PVD without damaging the retina.

Efficacy of autologous plasmin for idiopathic macular hole surgery

PURPOSE

To determine whether a single intravitreal injection of autologous plasmin or a combination of plasmin and intraocular gas without peeling the internal limiting membrane (ILM) will close idiopathic macular holes.

METHODS

Eight eyes of seven patients with an idiopathic macular hole were studied. The degree of posterior vitreous detachment (PVD), vitreal liquefaction, closure of the macular hole, visual acuity, and complications following intravitreal plasmin or plasmin with gas were investigated. The removed ILM was examined by electron microscopy.

RESULTS

A PVD was created in seven out of eight eyes exposed to plasmin or plasmin with gas, however, the macular hole was not closed by either. Closure occurred in two eyes using conventional vitrectomy after the plasmin with gas injection, but peeling the ILM was required in the remaining six eyes. Vitreal fibers and glial cells were not observed on the vitreal surface of the extracted ILM.

CONCLUSIONS

A PVD was created safely and reliably although closure of the macular hole did not occur with either plasmin or with plasmin and gas injection. However, vitreous surgery became easier, and it required a shorter time to close the macular hole with intravitreal plasmin.

Safety profile of the intravitreal streptokinase-plasmin complex as an adjunct to vitrectomy in the rabbit

BACKGROUND

The generation of an atraumatic posterior vitreous detachment (PVD), a common goal in vitreoretinal surgery, is a challenge, particularly in children and young trauma patients. Plasmin has been proposed as an adjunct to vitrectomy to enzymatically generate a PVD. Low doses of streptokinase-activated plasmin were tested in human pilot studies. This dose-escalation study assesses the safety range of intravitreal human streptokinase-plasmin in rabbits.

METHODS

Plasminogen was isolated from human plasma by affinity chromatography, followed by activation with streptokinase (1:1), to generate the streptokinase-plasmin complex. Enzyme doses from 0.1-7 activity units (AU, in 0.1 ml) were injected into the mid-vitreous of 35 eyes; six control eyes were injected with balanced salt solution (BSS, 0.1 ml). Thirty minutes after injection, a two-port vitrectomy was performed. Fundus and slit lamp examinations were performed on days 1 and 7. On days 2 and 7, bright flash electroretinography was performed and compared with preoperative recordings. Some animals receiving higher doses of streptokinase-plasmin (1-7 AU) were followed clinically and with electroretinography for up to 9 months.

RESULTS

A mild-to-moderate inflammatory response was seen in both control and plasmin-treated eyes on day 1, but had disappeared completely by day 7 in most eyes. In the 7 AU group, inflammation was stronger and more protracted. Two of three eyes from this group developed wrinkling of the medullary rays; one of them showed discoloration and traction at the medullary rays in the late follow-up. Electroretinograms (ERGs) of vitrectomized control eyes showed the following changes from preoperative values: 48 h, a-wave -11.10% [no significant (n.s.)], b-wave -14.62% (P=0.046); 7 days, a-wave +9.18% (n.s.), b wave +11.69% (n.s.). For the enzyme-treated eyes: 48 h: a-wave -20.43% (P<0.001), b-wave -9.57% (p<0.001); 7 days: a wave -14.21% (P<0.001), b-wave +2.48% (P<0.001). There was no evidence of dose-dependent ERG changes in enzyme-treated eyes at doses up to 5 AU. Groups of up to 3 AU were investigated by light and transmission electron microscopy, without evidence of toxicity.

CONCLUSION

Streptokinase-plasmin doses up to 3 AU were found to be safe when injected into rabbit eyes followed by vitrectomy.

Anomalous posterior vitreous detachment: a unifying concept in vitreo-retinal disease

Posterior vitreous detachment (PVD) is the consequence of changes in the macromolecular structure of gel vitreous that result in liquefaction, concurrent with alterations in the extracellular matrix at the vitro-retinal interface that allow the posterior vitreous cortex to detach from the internal limiting lamina of the retina. Gel liquefaction that exceeds the degree of vitro-retinal dehiscence results in anomalous PVD (APVD). APVD varies in its clinical manifestations depending upon where in the fundus vitreo-retinal adhesion is strongest. At the periphery, APVD results in retinal tears and detachments. In the macula, APVD causes vitreo-macular traction syndrome, results in vitreoeschisis with macular pucker or macular holes, or contributes to some cases of diabetic macular edema. At the optic disc and retina, APVD causes vitreo-papillary traction and promotes retinal and optic disc neovascularization. Unifying the spectrum of vitreo-retinal diseases into the conceptual frame-work of APVD underscores that to more effectively treat, and ultimately prevent, these disorders it is necessary to replicate the two components of an innocuous PVD, i.e., gel liquefaction and vitreo-retinal dehiscence. Pharmacologic vitreolysis is designed to mitigate against APVD by chemically breaking down vitreous macromolecules and weakening vitro-retinal adhesion to safely detach the posterior vitreous cortex. This would not only facilitate surgery, but if performed early in the natural history of disease, it should prevent progressive disease.

Intrasurgical plasmin enzyme in diabetic macular edema

PURPOSE

To evaluate in a prospective study the efficacy of intrasurgical autologous plasmin enzyme (APE) in producing posterior vitreous detachment.

DESIGN

Consecutive, interventional case series.

METHODS

A group of 12 eyes of 11 patients with diabetic macular edema secondary to posterior vitreous cortex contraction was considered. A quantity of 0.1- to 0.2-ml containing 0.8 to 1.2 IU of APE prepared by our Coagulation Service was injected into the vitreous body 25 minutes before surgery. The efficacy of the APE was subjectively evaluated. A control group of 10 eyes with the same clinical characteristics underwent the same surgery without APE injection. Complete eye examinations, including optical coherence tomography, were performed on all patients before surgery and during the 1-year follow-up period.

RESULTS

During surgery in the APE-treated group, the posterior vitreous cortex was judged adherent in three cases, partially detached in six cases, and totally detached in three cases. In two cases a complete collapse of the vitreous body was observed. During surgery in the non-APE-treated group, the posterior vitreous cortex was judged still adherent in nine of 10 eyes and partially detached in 1 eye. Comparing the postoperative results between the APE-treated group and the non-APE-treated group, we found no significant differences in final postoperative retinal thickness (P = .2552), whereas we found a significant difference in final visual acuity (P = .0121).

CONCLUSIONS

Autologous plasmin enzyme was useful in inducing a pharmacologic posterior vitreous detachment and in facilitating surgery. It did not seem to interfere with the final retinal thickness, and it ameliorates the final visual acuity.

The role of recombinant lysine-plasminogen and recombinant urokinase and sulfur hexafluoride combination in inducing posterior vitreous detachment

PURPOSE

To determine the optimal method of generating plasmin in vitreous using recombinant lysine-plasminogen and recombinant urokinase and to determine its efficacy in inducing posterior vitreous detachment when combined with sulfur hexafluoride.

METHODS

Plasmin concentration of the rabbit vitreous after separate and combined intravitreal administrations of recombinant lysine-plasminogen and recombinant urokinase was tested in 78 rabbits to determine the optimal method of administration. The safety and efficacy of these agents and sulfur hexafluoride in inducing complete posterior vitreous detachment (total separation of the vitreous apart from vitreous base) were also evaluated.

RESULTS

The highest plasmin concentration in vitreous was measured 10 minutes after injection. Intravitreal administration of recombinant lysine-plasminogen and recombinant urokinase did not cause any toxicity findings up to concentrations of 100 microg and 200 IU, respectively, on funduscopy, electroretinography, and histopathologic studies. When combined with sulfur hexafluoride injection, separate intravitreal administrations of 75 microg/0.1 mL of recombinant lysine-plasminogen and 15 IU/0.1 mL of recombinant urokinase induced complete posterior vitreous detachment in 75% of the eyes compared with 13% in eyes that received sulfur hexafluoride injection combined with balanced salt solution, recombinant lysine-plasminogen, or recombinant urokinase.

CONCLUSIONS

Plasmin was effectively generated in the vitreous after separate intravitreal administrations of recombinant lysine-plasminogen and recombinant urokinase. When combined with intravitreal gas injection, this method of plasmin production induced complete posterior vitreous detachment in 75% of the eyes.

Ultrastructure of internal limiting membrane removed during plasmin-assisted vitrectomy from eyes with diabetic macular edema

PURPOSE

To study the effect of autologous plasmin enzyme (APE) on the adhesion of the vitreous cortex to the internal limiting membrane (ILM) in eyes with diabetic macular edema.

DESIGN

Nonrandomized, comparative, interventional case series.

PARTICIPANTS

Ten eyes of 10 patients with diabetic macular edema without a posterior vitreous detachment (PVD), which were treated with APE as an adjunct to conventional pars plana vitrectomy, and 10 eyes of 9 patients without a PVD, which underwent pars plana vitrectomy without APE, were studied.

METHODS

In the APE group, 0.4 IU of APE was injected into the midvitreous cavity in 9 eyes, and 0.8 IU of APE in 1 eye. Thirty minutes after plasmin injection, the eyes underwent pars plana vitrectomy with ILM peeling. All eyes in the control group had conventional vitreous surgery with ILM peeling. The removed ILMs were investigated for the presence of vitreous and for ultrastructural differences by transmission and scanning electron microscopy.

MAIN OUTCOME MEASURES

The status of the vitreous and induction of a PVD during surgery, and the presence of vitreous and ultrastructural differences of the removed ILM by transmission and scanning electron microscopy.

RESULTS

In APE-treated eyes, the degree of liquefaction of the vitreous was graded as high in 4 eyes. Spontaneous PVD occurred in 2 eyes, whereas core vitrectomy with a maximum vacuum of 100 mmHg induced a PVD in 2 additional eyes. In the control group, 8 eyes required suction with a maximum of 200 mmHg to induce the PVD. Scanning electron micrography of the removed ILM in the APE-treated eyes showed a smooth surface on the vitreous side in 8 eyes and only sparse collagen fibers in 2 eyes. Conversely, in the control group, dense vitreous fibers were found in 4 eyes, sparse collagen fibrils in 3 eyes, and a smooth retinal surface in 3 eyes.

CONCLUSIONS

These findings indicate that APE helps separate the vitreous hyaloid from the ILM surface and may be a useful adjunct to conventional vitreous surgery for diabetic macular edema.

Long-term Effect of Plasmin on the Vitreolysis in Rabbit Eyes

The aim was to investigate the proteolytic activity of plasmin and its long-term complications. Plasmin was injected into the vitreous cavity of rabbits' eyes. Slit lamp biomicroscopy and electroretinography were performed. Rabbits were serially sacrificed at four months, and globes fixated and prepared for light and transmission electron microscopy. In both the plasmin-injected and control eyes, electroretinography showed a transient decrease in the amplitude, but this recovered to the baseline level in a week. Under the light microscope, the plasmin-treated eyes had a smooth retinal surface, implying separation of the vitreous cortex from the retina. In the control eyes, the collagen fibers remained on the retinal surface. By transmission electron microscopy, the plasmin-treated eyes showed a vitreous-free retinal surface, but no vitreoretinal separation was observed in the control eyes. Plasmin induces a cleavage between the vitreous and the internal limiting membrane, with no long-term complications, so may be a useful pharmacologic adjunct to vitrectomy.