Improvement in efficacy of corticosteroid therapy in an animal model of proliferative vitreoretinopathy by pretreatment

Proliferative vitreoretinopathy: an update on the current and emerging treatment options

Proliferative vitreoretinopathy (PVR) remains the main cause of failure in retinal detachment (RD) surgery and a demanding challenge for vitreoretinal surgeons. Despite the large improvements in surgical techniques and a better understanding of PVR pathogenesis in the last years, satisfactory anatomical and visual outcomes have not been provided yet. For this reason, several different adjunctive pharmacological agents have been investigated in combination with surgery. In this review, we analyze the current and emerging adjunctive treatment options for the management of PVR and we discuss their possible clinical application and beneficial role in this subgroup of patients.

The Efficacy of Intravitreal Triamcinolone Acetonide on Macular Edema in Branch Retinal Vein Occlusion

PURPOSE

To evaluate the effectiveness of intravitreal triamcinolone acetonide as primary treatment of macular edema in branch retinal vein occlusion.

METHODS

Fifteen eyes of 15 patients with macular edema due to branch retinal vein occlusion (Group 1) who received 8 mg/0.2 ml of intravitreal triamcinolone injection as primary treatment were retrospectively evaluated. The control group (Group 2) consisted of 19 eyes of 19 patients who had received laser treatment for macular edema. The main outcome measures included best-corrected visual acuity, intraocular pressure, and macular edema map values of Heidelberg Retinal Tomograph II.

RESULTS

In Group 1, mean visual acuity improved significantly from a mean logMAR (logarithm of minimal angle of resolution) value of 0.98+/-0.19 at baseline to a maximum of 0.24+/-0.24 during a mean follow-up time of 6.3 months. In the control group, the mean baseline log-MAR visual acuity before laser treatment was 1.02+/-0.22, and it was 0.50+/-0.28 at 6-month examinations. Mean improvement in visual acuity at 1-, 3-, and 6-month examinations was significantly higher in Group 1 when compared with the control group (for each, p<0.001). The mean edema map value of Group 1 significantly decreased by 40% at 6-month examinations when compared with preinjection value (p<0.001). In Group 1, mean increase in intraocular pressure elevation was 19.8% at the 1-month, 26.9% at 3-month, and 5.7% at 6-month visits, but intraocular pressures were under control with topical antiglaucomatous medications.

CONCLUSIONS

Intravitreal triamcinolone acetonide injection may be a new and promising approach as initial therapy for macular edema due to branch retinal vein occlusion.

Histopathological and ophthalmoscopic evaluation of apocynin on experimental proliferative vitreoretinopathy in rabbit eyes

The aim of the current study was to evaluate the effect of apocynin (APO) on the development of proliferative vitreoretinopathy (PVR). New Zealand-type male rabbits were randomly grouped into three as follows: (1) Sham group rabbits which were applied intraperitoneal (i.p.) vehicle without PVR; (2) PVR group rabbits where PVR was created and an i.p. vehicle was administered for 21 successive days; (3) PVR + APO group rabbits where PVR was created and i.p. APO was administered for 21 successive days. Fundus examination was conducted with an indirect ophthalmoscope before starting the experiments and at each visit afterwards. At the end of the work, the rabbits were sacrificed under high-dose anesthesia and then eye tissues were taken for histopathological analyses. In the PVR + APO group, histopathologic and ophthalmoscopic examination revealed significant decrease in PVR formation. As the result, it has been observed that APO at least partially inhibits PVR formation.

The effect of a preoperative subconjuntival injection of dexamethasone on blood-retinal barrier breakdown following scleral buckling retinal detachment surgery: a prospective randomized placebo-controlled double blind clinical trial

Background

Blood–retinal barrier breakdown secondary to retinal detachment and retinal detachment repair is a factor in the pathogenesis of proliferative vitreoretinopathy (PVR). We wished to investigate whether an estimated 700 to 1000 ng/ml subretinal dexamethasone concentration at the time of surgery would decrease the blood–retinal barrier breakdown postoperatively.

Methods

Prospective, placebo-controlled, double blind clinical trial. In 34 patients with rhegmatogenous retinal detachment scheduled for conventional scleral buckling retinal detachment surgery, a subconjunctival injection of 0.5 ml dexamethasone diphosphate (10 mg) or 0.5 ml placebo was given 5–6 hours before surgery. Differences in laser flare photometry (KOWA) measurements taken 1, 3 and 6 weeks after randomisation between dexamethasone and placebo were analysed using mixed model ANOVA, while correcting for the preoperative flare measurement.

Results

Six patients did not complete the study, one because of recurrent detachment within 1 week, and five because they missed their postoperative laser flare visits. The use of dexamethasone resulted in a statistically significant decrease in laser flare measurements at the 1-week postoperative visit.

Conclusion

The use of a preoperative subconjunctival injection of dexamethasone decreased 1-week postoperative blood–retina barrier breakdown in patients undergoing conventional scleral buckling retinal detachment surgery. This steroid priming could be useful as a part of a peri-operative regime that would aim at decreasing the incidence of PVR.

Intravitreal injection of therapeutic agents

BACKGROUND

Intravitreal injection (IVI) with administration of various pharmacological agents is a mainstay of treatment in ophthalmology for endopthalmitis, viral retinitis, age-related macular degeneration, cystoid macular edema, diabetic retinopathy, uveitis, vascular occlusions, and retinal detachment. The indications and therapeutic agents are reviewed in this study.

METHODS

A search of the English, German, and Spanish language MEDLINE database was conducted. A total of 654 references spanning the period through early 2008 were individually evaluated.

RESULTS

The advantage of the IVI technique is the ability to maximize intraocular levels of medications and to avoid the toxicities associated with systemic treatment. Intravitreal injection has been used to deliver several types of pharmacological agents into the vitreous cavity: antiinfective and antiinflammatory medications, immunomodulators, anticancer agents, gas, antivascular endothelial growth factor, and several others. The goal of this review is to provide a detailed description of the properties of numerous therapeutic agents that can be delivered through IVI, potential complications of the technique, and recommendations to avoid side effects.

CONCLUSION

The IVI technique is a valuable tool that can be tailored to the disease process of interest based on the pharmacological agent selected. This review provides the reader with a comprehensive summary of the IVI technique and its multitude of uses.

The effect of short-term exposure of triamcinolone acetonide on fibroblasts and retinal pigment epithelial cells

PURPOSE

We investigated the effects of short-term exposure to triamcinolone on cultured choroidal fibroblast (CFB) cells and retinal pigment epithelial (RPE) cells.

METHODS

To evaluate the effect of triamcinolone on cell proliferation, CFB and RPE cells were divided into three groups: a short-term exposure group; a longterm exposure group, and a non-treated control group. Cells in the short-term exposure group were briefly exposed (5, 15 or 30 mins) to triamcinolone (0.01 mg/ml, 1 mg/ml or mitomycin C (0.01 microg/ml, 1 microg/ml). Cells in the longterm exposure group were continuously incubated in culture medium containing the drug until assessment. The control group was cultured without drugs. Cell viability and the number of cells were assessed at day 5 after exposure. To investigate the direct toxicity of triamcinolone on confluent RPE cells, completely confluent cells were exposed to the drugs in the manner as described above. Cell viability was determined on days 0, 3 and 5 after treatment.

RESULTS

In the short-term exposure group, 1 mg/ml triamcinolone caused a significant reduction in the proliferation of CFB and RPE cells. The proliferation of CFBs decreased even with exposure to 0.01 mg/ml triamcinolone. In the longterm exposure group, triamcinolone and mitomycin C reduced the proliferation of both CFB and RPE cells. Even very short periods of exposure to triamcinolone caused a significant reduction in the viability of completely confluent RPE cells.

CONCLUSIONS

Even short periods of exposure to triamcinolone inhibited the proliferation of fibroblasts and RPE cells and were significantly toxic to completely confluent RPE cells.

Intravitreal triamcinolone acetonide: a change in a paradigm

BACKGROUND

Based on experimental studies and clinical observations by Robert Machemer, Gholam Peyman and others, the vitreous cavity has increasingly been used as a reservoir of drugs for the direct treatment of intraocular diseases.

METHODS AND RESULTS

The most widely injected drug so far has been triamcinolone acetonide for various intraocular neovascular and edematous diseases. Comparing the various diseases with respect to effect and side effects of the treatment, the best response in terms of gain in visual acuity has been achieved for intraretinal edematous diseases such as diffuse diabetic macular edema, branch retinal vein occlusion, central retinal vein occlusion, and pseudophakic cystoid macular edema. In eyes with various types of noninfectious uveitis including acute or chronic sympathetic ophthalmia and Adamantiadis-Behçet's disease, visual acuity increased and the degree of intraocular inflammation decreased. Some studies have suggested that intra- vitreal triamcinolone may be useful as an angiostatic agent in eyes with iris neovascularization and proliferative ischemic retinopathies. Intravitreal triamcinolone may possibly be helpful as adjunct therapy for exudative age-related macular degeneration, particularly in combination with photodynamic therapy. In eyes with chronic, therapy-resistant ocular hypotony, intravitreal triamcinolone can induce an increase in intraocular pressure and may stabilize the eye. The complications of intravitreal triamcinolone therapy include secondary ocular hypertension in about 40% of the eyes injected; medically uncontrollable high intraocular pressure leading to antiglaucomatous surgery in about 1-2% of the eyes; posterior subcapsular cataract and nuclear cataract leading to cataract surgery in about 15-20% in elderly patients within 1 year after injection; postoperative infectious endophthalmitis with a rate of about 1:1,000; noninfectious endophthalmitis, perhaps due to a reaction to the solvent agent, and pseudoendophthalmitis with triamcinolone acetonide crystals appearing in the anterior chamber. Intravitreal triamcinolone injection can be combined with other types of intraocular surgery including cataract surgery, particularly in eyes with iris neovascularization. Cataract surgery performed some months after the injection does not show a markedly elevated complication rate. The injection may be repeated, if vision redecreases. In nonvitrectomized eyes, the duration of the effect and side effects of a single intravitreal injection of triamcinolone is about 6-9 months for a dosage of about 20 mg, and about 2-4 months for a dosage of 4 mg. It has remained unclear so far, whether and how to remove the solvent agent. In the future, intravitreal triamcinolone may be combined with other antiangiogenic drugs for the treatment of exudative age-related macular degeneration or with neuroprotective drugs for treatment of diabetic retinopathy.

CONCLUSIONS

Despite an exponentially increasing number of mostly case-series studies, the intravitreal injection of triamcinolone may still be considered an experimental procedure until randomized studies have been presented.

Intravitreal triamcinolone acetonide for treatment of intraocular oedematous and neovascular diseases

Intravitreal triamcinolone acetonide (IVTA) has increasingly been applied as treatment for various intraocular neovascular and oedematous diseases. Comparing the various diseases with respect to effect and side-effects of the treatment, the best response in terms of gain in visual acuity (VA) has been achieved for intraretinal oedematous diseases such as diffuse diabetic macular oedema, branch retinal vein occlusion, central retinal vein occlusion and pseudophakic cystoid macular oedema. In eyes with various types of non-infectious uveitis, including acute or chronic sympathetic ophthalmia and Adamantiadis-Behcet's disease, VA increased and the degree of intraocular inflammation decreased. Some studies have suggested that intravitreal triamcinolone may be useful as angiostatic therapy in eyes with iris neovascularization and proliferative ischaemic retinopathies. Intravitreal triamcinolone may possibly be helpful as adjunct therapy for exudative age-related macular degeneration (AMD), particularly in combination with photodynamic therapy. In eyes with chronic, therapy-resistant ocular hypotony, intravitreal triamcinolone can induce an increase in intraocular pressure (IOP) and may stabilize the eye. The complications of intravitreal triamcinolone therapy include: secondary ocular hypertension in about 40% of the eyes injected; medically uncontrollable high IOP leading to antiglaucomatous surgery in about 1-2% of the eyes; posterior subcapsular cataract and nuclear cataract leading to cataract surgery in about 15-20% of elderly patients within 1 year of injection; postoperative infectious endophthalmitis occurring at a rate of about one per 1000; non-infectious endophthalmitis, perhaps due to a reaction to the solvent agent, and pseudo-endophthalmitis with triamcinolone acetonide crystals appearing in the anterior chamber. Intravitreal triamcinolone injection can be combined with other intraocular surgeries, including cataract surgery, particularly in eyes with iris neovascularization. Cataract surgery performed some months after the injection does not show a markedly elevated complication rate. The injection may be repeated if the resultant benefits decrease after the initial IVTA injection. In non-vitrectomized eyes, the duration of the effect and side-effects of a single intravitreal injection of triamcinolone is about 6-9 months for a dosage of about 20 mg, and about 2-4 months for a dosage of 4 mg. So far, it has remained unclear whether the solvent agent should be removed, and if so, how.

Intravitreal triamcinolone acetonide for treatment of intraocular proliferative, exudative, and neovascular diseases

Within the last three years, triamcinolone acetonide has increasingly been applied intravitreally as treatment option for various intraocular neovascular edematous and proliferative disorders. The best response in terms of gain in visual acuity after the intravitreal injection of triamcinolone acetonide was found in eyes with intraretinal edematous diseases such as diffuse diabetic macular edema, branch retinal vein occlusion, central retinal vein occlusion, and pseudophakic cystoid macular edema. Visual acuity increased and degree of intraocular inflammation decreased in eyes with various types of non-infectious uveitis including acute or chronic sympathetic ophthalmia and Adamantiadis-Behcet's disease. Intravitreal triamcinolone may be useful as angiostatic therapy in eyes with iris neovascularization and proliferative ischemic retinopathies. Possibly, intravitreal triamcinolone may be helpful as adjunct therapy for exudative age-related macular degeneration, possibly in combination with photodynamic therapy. In eyes with chronic, therapy resistant, ocular hypotony, intravitreal triamcinolone can induce an increase in intraocular pressure and may stabilize the eye. The complications of intravitreal triamcinolone therapy include secondary ocular hypertension in about 40% of the eyes injected, cataractogenesis, postoperative infectious and non-infectious endophthalmitis, and pseudo-endophthalmitis. Intravitreal triamcinolone injection can be combined with other intraocular surgeries including cataract surgery. Cataract surgery performed some months after the injection does not show a markedly elevated rate of complications. If vision increases and eventually decreases again after an intravitreal triamcinolone acetonide injection, the injection can be repeated. The duration of the effect of a single intravitreal injection of triamcinolone depended on the dosage given. Given in a dosage of about 20mg to non-vitrectomized eyes, the duration of the effect and of the side-effects was 6-9 months. Intravitreal triamcinolone acetonide may offer a possibility for adjunctive treatment of intraocular edematous and neovascular disorders. One has to take into account the side-effects and the lack of long-term follow-up observations.

INTRAVITREAL CONCENTRATION AND CLEARANCE OF TRIAMCINOLONE ACETONIDE IN NONVITRECTOMIZED HUMAN EYES

PURPOSE

To determine the intravitreal concentration and clearance of triamcinolone acetonide at various intervals after intravitreal injection into nonvitrectomized eyes.

METHODS

Six participants were administered 4 mg (0.1 cc) of triamcinolone acetonide ophthalmic suspension. All six eyes underwent therapeutic pars plana vitrectomy with membranectomy at various post injection intervals ranging from 1.25 to 5 months from the intravitreal injection. Undiluted specimens of vitreous overlying the macula and of aqueous humor were submitted for analysis. Vitreous and aqueous humor concentrations of triamcinolone were measured by high performance liquid chromatography.

RESULTS

Four eyes demonstrated detectable intravitreal concentrations of triamcinolone acetonide between 1.25 and 2.75 months after a single injection. Two eyes had an undetectable level of triamcinolone in both the vitreous and aqueous at 3 and 5 months post single injection.

CONCLUSIONS

The intravitreal concentration of triamcinolone acetonide is detectable up to 2.75 months post a single 4 mg injection in nonvitrectomized eyes. A reinjection interval of 3 months may be needed to achieve sustained measurable levels of triamcinolone in nonvitrectomized patients.

Synthesis, pharmacokinetics, efficacy, and rat retinal toxicity of a novel mitomycin C-triamcinolone acetonide conjugate

A novel conjugate of mitomycin C (MMC) and triamcinolone acetonide (TA) was synthesized using glutaric acid as a linker molecule. To determine the rate of hydrolysis, the conjugate was dissolved in aqueous solution and the rate of appearance of free MMC and TA was determined by high-performance liquid chromatography analysis. Antiproliferative activity of the MMC-TA conjugate and parent compounds was assessed using an NIH 3T3 fibroblast cell line. Cell growth was quantified using the MTT assay. Kinetic analysis of the hydrolysis rate demonstrated that the conjugate had a half-life of 23.6 h in aqueous solutions. The antiproliferative activities of the MMC-TA conjugate and MMC were both concentration dependent, with similar IC(50) values of 2.4 and 1.7 microM, respectively. However, individual responses at concentrations above 3 microM showed that the conjugate was less active than MMC alone. TA alone showed only limited inhibition of cell growth. Studies evaluating intravitreal injection of the conjugate demonstrate that this agent produced no measurable toxicity. Our data provide evidence that the MMC-TA conjugate could be used as a slow-release drug delivery system. This could in turn be used to modulate a posttreatment wound healing process or to treat various proliferative diseases.

Regression of neovascular iris vessels by intravitreal injection of crystalline cortisone

PURPOSE

To report the clinical outcome of patients who received an intravitreal injection of crystalline triamcinolone acetonide as treatment of neovascular glaucoma.

PATIENTS AND METHODS

The study included 14 eyes of 14 patients with secondary neovascular glaucoma attributable to proliferative diabetic retinopathy (n = 9) or ischemic central retinal vein occlusion (n = 5). All patients received an intravitreal injection of 20 mg of crystalline triamcinolone acetonide as the only procedure (n = 4) or in combination with additional procedures, such as goniosynechiolysis (n = 1), phacoemulsification and intraocular lens implantation (n = 2), or transscleral peripheral retinal cryocoagulation (n = 7). Mean follow-up time was 3.10 +/- 2.40 months (median, 3.5 months; range, 0.50-5.7 months). A goniosynechiolysis was carried out in those patients in whom the anterior chamber was circumferentially closed.

RESULTS

After surgery, including the first days after surgery, the patients were nearly pain-free. Intraocular pressure was significantly (P < 0.01) reduced from 33.4 +/- 14.5 mm Hg before surgery to 20.7 +/- 8.2 mm Hg at the end of the follow-up period. Postoperative visual acuity (mean, 0.09 +/- 0.07; median, 0.10; range, finger counting to 0.25) was slightly but not significantly (P = 0.31) better than the preoperative values. Degree of rubeosis iridis decreased significantly (P = 0.02) from 2.6 +/- 1.3 relative units to 1.3 +/- 1.2 relative units. When considering only the four patients for whom the intraocular cortisone injection was the only procedure performed, mean intraocular pressure decreased from 26.5 +/- 12.1 mm Hg to 21.75 +/- 11.3 mm Hg.

CONCLUSIONS

Intravitreal injection of crystalline cortisone with most of the vehicle removed may be a potentially useful additional tool in the treatment of neovascular glaucoma.

Intravitreal injection of crystalline cortisone as adjunctive treatment of proliferative diabetic retinopathy

PURPOSE

To report the clinical outcome and complications of intravitreal injections of crystalline cortisone in patients undergoing pars plana vitrectomy for treatment of proliferative diabetic retinopathy.

METHODS

The prospective, interventional case series study included 29 consecutive patients (29 eyes) who underwent pars plana vitrectomy for treatment of complicated proliferative diabetic retinopathy associated with central retinal traction detachment. All patients received an intravitreal injection of 15 to 20 mg of crystalline triamcinolone acetonide at the end of surgery, and were operated on by the same surgeon. Mean follow-up time was 1.4 +/- 1.1 months (median, 1 month; range, 0.30 to 4.9 months).

RESULTS

At the end of the follow-up period, the retina was attached in 26 of the 29 patients (89.7%). In three of the 29 patients (10.3%), a retinal redetachment had occurred. None of the patients developed iris neovascularization, and the iris neovascularization, present preoperatively in 12 patients, slightly to markedly regressed in all 12 patients. Preoperative and postoperative intraocular pressure values (P =.72) and blood glucose measurements did not vary significantly. A pseudohypopyon consisting of cortisone crystals in the inferior anterior chamber angle was detected in one patient and resolved spontaneously within 4 days.

CONCLUSIONS

The present clinical study suggests that intravitreal injection of crystalline cortisone with most of the vehicle removed seems to be well tolerated by eyes undergoing pars plana vitrectomy for treatment of complicated diabetic proliferative retinopathy. In view of the antiphlogistic and antiproliferative effect of cortisone, future randomized clinical trials may be indicated to investigate further the role of intravitreal injection of crystalline cortisone in the treatment of proliferative diabetic retinopathy.

Dexamethasone concentration in the subretinal fluid after a subconjunctival injection, a peribulbar injection, or an oral dose

PURPOSE

To determine dexamethasone concentrations in the subretinal fluid of patients after a peribulbar injection, a subconjunctival injection, or an oral dose of dexamethasone and to compare the results with those of previous similar studies of dexamethasone concentrations in the vitreous.

DESIGN

Prospective, nonrandomized, comparative trial.

PARTICIPANTS

One hundred forty-eight patients with a rhegmatogenous retinal detachment.

METHODS

Fifty patients received a peribulbar injection of 5 mg dexamethasone disodium phosphate, 49 received a subconjunctival injection of 2.5 mg dexamethasone disodium phosphate, and 49 received an oral dose of 7. 5 mg dexamethasone at various time intervals before surgery. At the time of surgery, a subretinal fluid sample was taken from each patient.

MAIN OUTCOME MEASURES

The dexamethasone concentration in the subretinal fluid measured by radioimmunoassay.

RESULTS

The estimated maximum dexamethasone concentrations in the subretinal fluid after the peribulbar injection, the subconjunctival injection, and the oral dose were, respectively, 82.2 ng/ml (standard error, 17. 6), 359 ng/ml (standard error, 80.2), and 12.3 ng/ml (standard error, 1.61). Corrected for dose, the maximum dexamethasone concentrations after subconjunctival injection and peribulbar injection were, respectively, 120 (95% confidence interval, 54/180) and 13 (95% confidence interval, 6.8/20) times greater than after oral administration.

CONCLUSIONS

A subconjunctival injection of dexamethasone disodium phosphate is more effective in delivering dexamethasone into the subretinal fluid of patients with a rhegmatogenous retinal detachment compared with peribulbar injection or oral administration. The subretinal dexamethasone concentrations were higher than concentrations measured in the vitreous in previous studies with a similar setup after all three delivery methods.

Intravitreal injection of crystalline cortisone as adjunctive treatment of proliferative vitreoretinopathy

AIM

To report on clinical outcome and complications of intravitreal injection of crystalline cortisone in patients undergoing pars plana vitrectomy for treatment of proliferative vitreoretinopathy.

METHODS

The study included all 16 patients who underwent pars plana vitrectomy for treatment of proliferative vitreoretinopathy, who received an intravitreal injection of 10-20 mg crystalline triamcinolone acetonide at the end of surgery, and who were operated on by the same surgeon. Most of the vehicle of the solution containing the cortisone crystals was removed before performing the injection. Mean follow up time was 1.64 (SD 2.15) months (median 1. 23 months; range 0.20-9.20 months). The study group was compared with a control group which consisted of 144 patients undergoing pars plana vitrectomy for proliferative vitreoretinopathy performed by the same surgeon.

RESULTS

In the study group compared with the control group, intraocular inflammation, as estimated clinically by slit lamp biomicroscopy, was lower, appearance of the fundus upon ophthalmoscopy in the first postoperative week was clearer, and postoperative pain in the first two postoperative days was reduced. Intraocular pressure measured at the end of the first postoperative week did not vary significantly between the groups. A pseudohypopyon consisting of cortisone crystals in the inferior anterior chamber angle was detected in one patient. Postoperative infectious endophthalmitis was not encountered.

CONCLUSIONS

This pilot study suggests that intravitreal injection of crystalline cortisone with most of the vehicle removed is not toxic to intraocular structures, reduces postoperative intraocular inflammation, and may be a potentially useful additional tool in the treatment of proliferative vitreoretinopathy.

Proliferative vitreoretinopathy: an overview

Proliferative vitreoretinopathy (PVR) is still the most common cause of failure of surgery for rhegmatogenous retinal detachment, despite the substantial effort that has been devoted to better understanding and managing this condition during the past 25 years. Basic research has indicated that PVR represents scarring, the end stage of the wound-healing process that occurs after retinal detachment surgery. Medical treatment has been directed toward preventing inflammation, the first phase of the wound healing process, and inhibiting cell proliferation, the second phase. The 1983 Retina Society classification was modified in 1989 by the Silicone Study Group, whose classification differentiates between posterior and anterior forms of PVR and recognizes three patterns of proliferation: diffuse, focal, and subretinal. The anterior form has a worse prognosis than the posterior form, and its treatment requires more complex surgical procedures. In this review, risk factors and pathobiology of PVR are discussed, and management of PVR of various degrees of severity are considered.

Risk factors for proliferative vitreoretinopathy

Proliferative vitreoretinopathy (PVR) is one of the major causes of failure in retinal detachment surgery. To prevent PVR, it is necessary to determine factors predisposing its development. In primary PVR, large retinal tears, long duration of retinal detachment, vitreous hemorrhages, aphakia and choroidal detachment were demonstrated as clinical risk factors for PVR. In postoperative PVR, it was revealed that large breaks, pre- and postoperative choroidal detachment, minor intra- or postoperative hemorrhages, signs of uveitis, extensive retinal detachment, vitrectomy, cryopexy, air injection and preoperative PVR were risk factors for PVR by multivariate analysis. Almost all risk factors for PVR are associated with intravitreal dispersion of retinal pigment epithelial (RPE) cells or breakdown of the blood-ocular barrier which are prerequisite to development of PVR.

An intravitreal device providing sustained release of cyclosporine and dexamethasone

PURPOSE

A device that releases cyclosporine and dexamethasone into the eye for extended periods of time might be beneficial in diseases such as proliferative vitreoretinopathy and uveitis. In this study we examine the pharmacokinetics and toxicity of cyclosporine and dexamethasone combined in an intravitreal sustained-release device and the toxicity of a similar device containing only dexamethasone in rabbits.

METHODS

Rabbits were divided into three groups for (1) evaluation of the drug tissue levels and device release kinetics following implantation of a device containing 100 micrograms of cyclosporine labeled with 2 microCi of 3H-cyclosporine and 2 mg of dexamethasone; (2) evaluation of the toxicity of this intravitreal device; and (3) evaluation of the toxicity of a similar device containing 2 mg of dexamethasone only. Cyclosporine was measured using a scintillation counter and dexamethasone was measured by high pressure liquid chromatography (HPLC). Toxicity was evaluated by electroretinography, clinical examination, and light microscopy.

RESULTS

Vitreous concentrations of cyclosporine (+/- standard deviation) averaged 0.06 (+/- 0.02) microgram/ml over 10 weeks. The average dexamethasone concentration over the 10 week period was 2.9 (+/- 0.9) micrograms/ml. Devices containing cyclosporine and dexamethasone released each drug at rates similar to devices containing cyclosporine or dexamethasone alone. Devices containing both cyclosporine and dexamethasone caused reversible depressions in the b-wave amplitude of photopic and scotopic electroretinograms (ERG's). There was no evidence of toxicity associated with the devices containing dexamethasone only. There was no drug-related toxicity evident on clinical or histopathologic examination of eyes with devices containing the combination of cyclosporine and dexamethasone or dexamethasone alone.

CONCLUSIONS

We conclude that the device maintains potentially therapeutic levels of both cyclosporine and dexamethasone in the vitreous. Reversible electroretinographic abnormalities are attributable to cyclosporine. A sustained-release device containing cyclosporine and dexamethasone may be useful for reducing inflammation in diseases such as proliferative vitreoretinopathy and uveitis.

Fibroblast growth-promoting activity in proliferative vitreoretinopathy: antagonism by acetylsalicylic acid

Proliferative vitreoretinopathy is a severe reactive process which leads to the formation of cellular membranes on the surface of the retina and in the vitreous. We determined the fibroblast growth-promoting activity of intraocular fluid from patients suffering from proliferative vitreoretinopathy, retinal detachment or cataract and further evaluated the effect of acetylsalicylic acid on growth-stimulated fibroblasts. The results demonstrated a significant enhancement of growth-promoting activity of intraocular fluid in proliferative vitreoretinopathy as compared to that of control samples. We showed that the augmented growth-promoting activity of intraocular fluid in proliferative vitreoretinopathy was significantly antagonized by inhibition of cyclooxygenase with acetylsalicylic acid (ID50 approximately 5 microM). In contrast, no significant effect was seen in corresponding control experiments. The findings suggest that metabolites of the cyclooxygenase pathway are involved in the regulation of enhanced intraocular fluid-induced fibroblast proliferation in proliferative vitreoretinopathy and that acetylsalicylic acid might be useful as an antiproliferative agent in intraocular fibrogenesis.

The treatment of vitreoretinal scar tissue

Methods of treating vitreoretinal scarring have been transformed by the introduction and development of closed intraocular microsurgery. Controlled access to the posterior segment of the eye, under excellent conditions for intraoperative viewing, have increased our understanding of the pathophysiology of epiretinal membranes. The ready ability to harvest tissue specimens for histopathological and immunochemical study, enabled by this type of surgery, has provided the stimulus for much basic research into the nature of fibrocellular (and fibrovascular) proliferative disease. Treatment of retinal conditions characterised by the proliferation of fibrocellular membranes has been improved, but the most important future advances are likely to be made in the fields of molecular biology and pharmacology.

Macrophages in proliferative vitreoretinopathy and proliferative diabetic retinopathy: differentiation of subpopulations

Macrophages have long been known to play a major role in the pathogenesis of proliferative vitreoretinal disorders. Using the monoclonal antibodies EBM11 (pan macrophage), 27E10 (early inflammatory stage marker), and RM3/1 (healing phase marker), different subpopulations of macrophages were differentiated in surgically removed membranes from patients with macular pucker (n = 6), proliferative vitreoretinopathy (PVR) following rhegmatogenous retinal detachment (n = 11), traumatic PVR (n = 19), and proliferative diabetic retinopathy (PDR) (n = 11). Macrophages were predominantly found in traumatic PVR and PDR. Some healing phase (RM3/1) macrophages were detected in all disease entities. Inflammatory stage macrophages (positive staining for 27E10) could not be detected in PVR following rhegmatogenous retinal detachment and idiopathic macular pucker. In traumatic PVR inflammatory stage macrophages were associated with a short history of disease whereas in PDR all types of macrophages could be detected regardless of clinical history and duration of the disease.

Corticosteroids and daunomycin in the prevention of experimental proliferative vitreoretinopathy induced by macrophages

An experimental model of proliferative vitreoretinopathy (PVR) induced by macrophages simulates a special form of wound healing process in the eye and mimics the development of PVR from its initial stage. We used this model for the evaluation of drug efficacy in the prevention of PVR. One mg triamcinolone acetonide (TA), 10 micrograms daunomycin-liposome (DL), 5 micrograms free daunomycin (FD) and 0.1 ml saline or empty liposomes (as controls) were injected into the vitreous in four groups of animals (30 or 40 rabbit eyes each) after macrophage injection. Retinal detachment developed in 77.5% of the control eyes on day 28, compared to 13.3% of the TA-treated eyes (P < 0.01), to 33.3% of the eyes treated with DL (P < 0.01), and 50% of the FD-treated eyes (P < 0.05). TA cleared up from the vitreous within 35-63 days (average 45.5 days). The half-time of FD clearance was 145.5 min. Although DL declined rapidly during the first 2 days, there was an average of 0.64 microgram/ml daunomycin in the vitreous on day 14. Transmission electron microscopy showed that FD at a dosage of over 5 micrograms or DL over 20 micrograms was toxic to the retina and that up to 4 mg TA was nontoxic. These results suggest that steroids such as TA, given at the inflammatory stage, can effectively and safely prevent the development of PVR, and that encapsulation in liposomes of cytotoxic agents such as daunomycin can enhance drug efficacy and reduce toxicity. The time course of initiation and development of PVR is important in the selection of particular drugs.

The lack of an effect of intraocular steroids on irradiated fibroblasts in experimental proliferative vitreoretinopathy

Contraction of intraocular membranes is an important event in the development of proliferative vitreoretinopathy (PVR). When sufficient numbers of cells are present in the vitreous cavity, the retina usually detaches as a result of the contractive force generated by these cells. Steroids reduce the occurrence of retinal detachments in rabbit models of PVR by inhibiting the proliferation of injected fibroblasts. In this study, we used non-proliferative, irradiated cells to determine a possible effect of steroids on preretinal membrane contraction in PVR. We found no clinical difference between steroid treated eyes and sham-treated control eyes. Surgical reduction of the contractile tissue and medical therapy to prevent reproliferation are necessary in order to treat PVR effectively.

Daunorubicin treatment in a refined experimental model of proliferative vitreoretinopathy

A condition similar to proliferative vitreoretinopathy (PVR) in man can be produced by injecting 25,000 homologous dermal fibroblasts into rabbit eyes following gas compression of the vitreous. Daunorubicin (15 nmol) was effective in preventing retinal detachment in this model when injected simultaneously with the fibroblasts or in two doses (10 nmol followed by 5 nmol 4 h later) on the 3rd day after fibroblast injection. A single dose of 15 nmol on the 3rd day was not effective in preventing retinal detachment. These results suggest that daunorubicin may be clinically useful in preventing PVR when given by injection both at the time of vitrectomy as well as later, when protein exudation and pigment clumps in the vitreous cavity herald the onset of PVR.

Proliferative vitreoretinopathy--is it anything more than wound healing at the wrong place?

Proliferative vitreoretinopathy (PVR) is a reactive process of the ocular tissue after perforating trauma, retinal detachment, and surgical manipulations. Although several studies, most of them experimental, have focused on the detection of specific etiologic factors in the development of PVR, there is compelling evidence that PVR is nothing more than a physiologic tissue repair process with undesirable consequences for the retina. Important features of PVR involving the role of platelets, mononuclear phagocytes, and fibroblasts parallel the chain of events observed in tissue repair elsewhere in the body. Numerous experimental models for PVR, originally designed to find specific stimuli for the generation of intraocular traction membrane formation, have shown that the process of PVR is the common pathway of the eye's reaction to vitreoretinal trauma of any kind. Accordingly, vitreoretinal surgeons could learn a lot from the work of other disciplines, e.g. surgery and dermatology, on wound healing, and the factors known to modify wound healing elsewhere in the body should be taken into consideration. The well-established impairment of tissue repair processes caused by medical treatment with corticosteroids and cytotoxic agents suggests a combined medical approach to PVR as an adjunct to surgical treatment, using refined methods of application and dosage. Steroids and cytotoxic drugs will influence the course of PVR by suppressing macrophage recruitment and the initial inflammatory reaction as well as the proliferative phase of wound healing with traction retinal detachment, respectively.

Autoimmune responsiveness to retinal IRBP, S-antigen and opsin in proliferative vitreoretinopathy

Proliferative vitreoretinopathy (PVR) was induced in rabbits by intravitreal injection of homologous fibroblasts. During the 8 weeks after injection the immune responsiveness to three purified retinal autoantigens was studied. From 2 weeks after injection, animals that developed serious forms of PVR exhibited definite mitotic responses of their lymphocytes to stimulation by the retinal antigens. These responses could consistently be demonstrated for S-antigen and interphotoreceptor retinoid-binding protein (IRBP) during the subsequent period of examination. Marked responses were also noted to opsin, however, their occurrence was more variable. In mild forms of PVR or in controls the responses were weak or absent. This showed that the elevated cellular reactivities were induced by the development of PVR and not by some other experimental factor. Humoral immune responses to the three antigens were absent (as assayed by ELISA). The control groups did not exhibit any elevated immune responsiveness. There appears to be accumulating evidence that inflammation may play a role in the development of PVR. The present results indicate that cellular autoimmune responses to photoreceptor antigens are a secondary phenomenon in PVR, nevertheless, they may be an important factor in the subsequent development of severe PVR. This autosensitization may consequently be taken into consideration in the treatment of complicated human PVR.

Evaluation of radiation therapy for experimental proliferative vitreoretinopathy in rabbits

We evaluated effects of radiation therapy on experimental proliferative vitreoretinopathy (PVR) induced in rabbits by double gas compression of the vitreous followed by homologous dermal-skin fibroblast injection. Electrons were irradiated in two rabbit groups. Group A animals (20 eyes) received 1000 cGy of irradiation immediately after cell injection; group B rabbits (9 eyes), which showed pucker formation 7 days after cell injection, were irradiated on that day at the same dose as was given to group A rabbit. Control animals (14 eyes) were not irradiated. The incidences of traction retinal detachment on day 28 were: control, 86%; group A, 10%; and group B, 22%. There were statistically significant differences between control and group A values and between control and group B values. No significant difference was found between group A and group B. Irradiation of 1000 cGy did not alter the histological picture of experimental PVR. The results showed that radiation suppressed the development of PVR when applied not only immediately after cell injection but also during pucker stages.

Management of anterior and posterior proliferative vitreoretinopathy. XLV. Edward Jackson memorial lecture

Proliferative vitreoretinopathy is a composite of anterior and posterior proliferation producing multidirectional tractional forces and resultant complex management problems. In a series of 98 consecutive cases of nondiabetic, nontraumatic proliferative vitreoretinopathy, anterior proliferation caused retinal detachment in 58 patients. Relaxation of circumferential traction created by anterior proliferation in the vitreous base and its contiguous surfaces is achieved by multiple radial incisions in the vitreous base and associated anterior retina is eliminated by incision of the displaced anterior and posterior hyaloid surfaces. The subsequent release of posterior traction and determination of residual traction by sequential fluid-air exchange before final tamponade with longer acting gas or silicone oil is described. Total retinal reattachment was achieved in 23 of 33 eyes (70%) with only posterior proliferation compared to 27 of 47 eyes (57%) with significant anterior proliferation. Retinal attachment posterior to the scleral buckle was achieved in 27 of 33 eyes (82%) and 37 of 47 eyes (79%), respectively. Although the success rate was less in eyes with anterior proliferation, the retinal reattachment rates in the two groups approached comparability as experience and understanding of the clinical significance increased.

Inflammation and the formation of epiretinal membranes

In this review of the literature evidence is provided from clinical, histological and experimental sources that inflammatory processes play a central role in the pathogenesis of contractile epiretinal membranes and proliferative vitreoretinopathy.

Immunochemical studies of epiretinal membranes using APAAP complexes: evidence for macrophage involvement in traumatic proliferative vitreoretinopathy

Proliferative vitreoretinopathy is characterized by cellular proliferations in the periretinal space resulting in traction retinal detachment. Numerous cellular elements and connective tissue components have been identified by morphologic criteria as well as immunochemical techniques. In this study, we used the recently introduced APAAP (alkaline phosphatase - anti-alkaline phosphatase) immunostaining procedure to identify macrophages, T-lymphocytes, the structural proteins fibronectin, vimentin, and cytokeratin, and a proliferating cell antigen, in eleven human epiretinal membranes obtained during vitreoretinal surgery. Our results confirm that the pathologic processes in PVR are not immunologically mediated, but reveal the features of physiologic wound healing and scar formation. Posttraumatic PVR seems to be characterized by a severe initial inflammatory reaction as evidenced by the presence of numerous macrophages, whereas idiopathic PVR, as a complication of retinal detachment, may be caused by different mechanisms in the early pathogenesis.