Risk factors for proliferative vitreoretinopathy

Retinal Oximetry Using Intravitreal Illumination

PURPOSE

To demonstrate spectroscopic retinal oximetry measurements on arteries and veins in swine using intravitreal illumination. Retinal arterial and venous saturations are measured for a range of inspired O2 levels after pars plana vitrectomy.

METHODS

Pars plana vitrectomy and intravitreal manipulations were performed on two female American Yorkshire domestic swine. Light from a scanning monochromator was coupled into a fiberoptic intraocular illuminator inserted into the vitreous. The retinal vessels were illuminated obliquely, minimizing vessel glints. Multispectral images of the retinal vasculature were obtained as the swine's arterial blood oxygen saturation was decreased from 100% to 67% in decrements of approximately 10%. Retinal vessel spectra were used to calculate oxygen saturation in selected arteries and veins. Arterial oxygen saturations were calibrated using blood gas analysis on blood drawn from a Swan-Ganz catheter placed in the femoral artery.

RESULTS

Oblique illumination of retinal vessels using an intravitreal fiberoptic illuminator provided a substantial reduction in the central vessel glint usually seen in fundus images, thus simplifying the analysis of spectral data. The vessel shadows were displaced from the vessel image simplifying the light paths in the eye. Using a full spectral analysis simplified by the light path reductions, we calculated retinal vessel saturations. The reduction of glint allowed for increased accuracy in measuring retinal vessel spectral optical density. Abnormally low retinal venous oxygen saturations were observed shortly after pars plana vitrectomy.

CONCLUSIONS

Retinal oximetry using intravitreal illumination has been demonstrated. As a research tool, intravitreal illumination addresses several difficulties encountered when performing retinal oximetry with transcorneal illumination.

All-trans retinoic acid remodels extracellular matrix and suppresses laminin-enhanced contractility of cultured human retinal pigment epithelial cells

All-trans retinoic acid (atRA) has been reported to inhibit the proliferation of retinal pigment epithelial (RPE) cells and used in treatment of proliferative vitreoretinopathy (PVR) in animal model. This study aimed at examining the effectiveness of atRA in inhibiting the extracellular matrix (ECM) biosynthesis by RPE cells and the RPE cell-mediated collagen gel contraction. Cultured RPE cells were treated with atRA and the expression of four ECM proteins (collagen types I, III, IV and laminin beta1) was profiled. The results indicated that atRA treatment up-regulated de novo synthesis of collagen type I, but decreased that of laminin beta1 in a dose-dependent manner. Moreover, the effect of atRA on RPE cell contraction was evaluated by measuring the area of collagen gel where RPE cells populated. Treatment with atRA significantly inhibited RPE cell-mediated collagen gel contraction. Addition of exogenous laminin nonapeptide into gels promoted RPE cell contraction, while atRA reversed the laminin-enhanced contractility. atRA treatment significantly suppressed the gene expression of integrin beta3 but not alphaV subunit, and effectively inhibited the tyrosine phosphorylation of integrin beta3 at residue 747 in RPE cells grown on laminin-coated dish, suggesting that atRA may suppress the RPE contractility through either inhibiting integrin beta3 expression or abrogating the integrin beta3-mediated signaling. In conclusion, atRA pharmacologically possesses a tissue-remodeling capacity and inhibits contractility of RPE cells. Therefore, atRA might be potentially a therapeutic agent for certain ocular disorders such as PVR.

Obestatin-mediated proliferation of human retinal pigment epithelial cells: regulatory mechanisms

In this work, we have evaluated the effect of the new discovered peptide obestatin on cell proliferation in primary cultures of human retinal epithelial cells (hRPE cells). The results showed that this peptide induced, in a dose-dependent manner, cell proliferation by MEK/ERK 1/2 phosphorylation. A sequential analysis of the obestatin transmembrane signaling pathway showed that the ERK 1/2 activity is partially blocked after preincubation of the cells with pertussis toxin (PTX), as well as by wortmannin (an inhibitor of PI3K), claphostin C (an inhibitor of PKC), and PP2 (which inhibits the non receptor tyrosine kinase Src). Upon administration of obestatin, the intracellular levels of phospho-PKCepsilon-, theta-, and micro-isoenzymes rise with different time courses, from which PKCepsilon might be responsible for ERK 1/2 response. Based on the experimental data, a signaling pathway involving the consecutive activation of Gi, PI3K, novel PKC (probably PKCepsilon), and Src for ERK 1/2 activation is proposed. These results incorporate a new mitogenic factor to the group of factors that regulate proliferation of hRPE cells.

The bovine vitreous-derived lipid factor (bVLF) is a powerful inhibitor of retinal pigmented epithelial (hRPE) cell proliferation

Human retinal pigmented epithelial cell (hRPE) proliferation plays a significant role in various proliferative diseases associated to the retina that leads to loss of vision, such as proliferative vitreoretinopathy. In the current study, the role of the bovine vitreous lipid factor (bVLF) in hRPE cell proliferation has been investigated. bVLF is a bioactive lipid isolated from the bovine vitreous body with strong Ca(2+)-mobilizing activity in fibroblast. In the first approach, the effects of bVLF on Ca(2+)-mobilizing activity were investigated in hRPE. The results showed that bVLF induced, in a dose-dependent manner, a Ca(2+) mobilization from PA-sensitive intracellular stores [non-Ins(1,4,5)P(3)-sensitive stores], in which extracellular Ca(2+) participated. The increase in intracellular Ca(2+) was associated with a dose-dependent inhibiting effect on cell proliferation. At a dose of 10 microg/mL, bVLF caused a 26% or a 44% inhibition in hRPE cell proliferation during the 3- or the 6-day culture periods, respectively. These effects appear to be specific in hRPE cells, since EFGR-T17 fibroblast cells treated with equivalent amounts of bVLF did not show any inhibiting effects. This inhibitory action was not associated to apoptotic/necrotic processes. Furthermore, bVLF inhibited EGF-, bFGF-, IGF-I-, PDGF-, HGF- and VEGF-induced proliferation of the hRPE cells. Moreover, this inhibitory response was also observed in FBS-induced hRPE cell proliferation. bVLF, at a concentration of 10 microg/mL, induced 16% inhibition of proliferation during a culture period of 3 days. This inhibitory action was greater during the 6-day culture period, exceeding 40%. With regard to this action, the results showed that bVLF has a potent inhibitory effect on ERK1/2 activation, and plays a key role in the control of hRPE cell proliferation. These observations contribute to the knowledge of inhibitory factors responsible for keeping antiproliferative environment that preserve the RPE-associated activities in normal states. It advances the interesting possibility that this factor or a factor with characteristics common to bVLF might be involved in the pathogenesis of abnormal proliferative eye processes.

Interaction between surgical procedure for repairing retinal detachment and clinical risk factors for proliferative vitreoretinopathy

PURPOSE

To asses risk factors of proliferative vitreoretinopathy (PVR) and a model for predicting it.

METHODS

Observational, case-control. 335 patients with non-complicated retinal detachment (RD) were included: 134 developed PVR (Cases); 201 patients did not (Controls). Risk factors for PVR were identified by multivariate analysis. Influence of variables was assayed according to the surgical approach. By logistic regression analysis a model to predict the risk of developing PVR and odds ratio (OR) values for each clinical factor were estimated.

RESULTS

Risk was higher in patients > 70 years and with intraocular pressure lower than 14 (OR: 3.84; CI 95%: 2.04-7.30) and in retinal breaks larger than "1 clock hour" (OR: 2.54; CI: 1.28-5.05), extended retinal detachments (OR: 4.01; CI: 1.98-8.10) and reinterventions (OR: 1.55; CI: 1.14-9.22). Scleral surgery also was a risk factor (OR: 3.89; CI: 2.12-7.14) and aphakia/pseudophakia when scleral surgery is performed (OR: 3.33; CI: 1.54-7.22). A model to predict PVR was proposed with these results.

CONCLUSIONS

Surgical approach modifies risk factors of PVR, and should be taken into account to improve the models for predicting it.

Expression of PDGF and their receptors in human retinal pigment epithelial cells and fibroblasts: regulation by TGF-beta

Platelet derived growth factors (PDGF) are known to be associated with vitreoretinal disorders such as proliferative vitreoretinopathy (PVR). We have studied the expression of PDGF and their receptors in human retinal pigment epithelial cells (HRPE) and choroid fibroblasts (HCHF), and the regulation of PDGF and its receptors by various cytokines and growth factors. RT-PCR analyses showed enhanced expression of PDGF-A and PDGF-B mRNA in HRPE treated with TGF-beta, but not with other cytokines. A minimal increase was observed in PDGF-A mRNA in TGF-beta treated HCHF cells. PDGF-R alpha mRNA, which was expressed prominently in HCHF and at very low levels in HRPE, was not affected by any of the agents. PDGF-R beta was not detectable in either HRPE or HCHF. HRPE secreted PDGF-AA and AB constitutively, and this secretion was significantly enhanced by TGF-beta. In contrast, HCHF cultures did not secrete detectable levels of any of the three isoforms of PDGF (AA, AB, BB). All three human recombinant PDGF isoforms enhanced HCHF cell proliferation significantly, while only a minimal increase was observed in HRPE. PDGF isoforms also induced HCHF cell elongation and promoted migration of HCHF in an in vitro wound assay. The results presented in this study demonstrate that TGF-beta activated RPE cells produce PDGF that may act on fibroblasts and other mesenchyme derived cells which express PDGF receptors. These studies indicate that the promotion of the proliferation and migration of mesenchymal cells by RPE cell derived PDGF may facilitate the formation of fibrovascular tissues associated with PVR.

Endothelin-1 distribution and basolateral secretion in the retinal pigment epithelium

Endothelins are a family of conserved vasoactive peptides that are widely expressed in different biological systems including the eye. In the cell culture model of retinal pigment epithelium, ARPE-19, the synthesis and secretion of endothelin-1 (ET-1) is regulated by cholinergics and TNF-alpha. In the present study we investigated the expression of ET-1 in RPE in situ, in rat and human eyes. Additionally, we have employed the human retinal pigment epithelial (ARPE-19) cells to delineate the apical and basolateral ET-1 expression and secretion by confocal microscopy and radioimmunoassay, respectively. Our results suggest a possible conservation of ET-1 expression predominantly in the mammalian RPE underlining its importance at this site. Additionally, our results suggest that constitutive ET-1 secretion is predominantly towards the basolateral side in cultured RPE possibly allowing ET-1 to activate its receptors located in the choroidal blood vessels and regulate retinal and choroidal blood flow.

Prevalence and risk factors for proliferative vitreoretinopathy in eyes with rhegmatogenous retinal detachment but no previous vitreoretinal surgery

PURPOSE

To determine the prevalence of and risk factors for proliferatative vitreoretinopathy (PVR) in eyes with rhegmatogenous retinal detachment but no previous vitreoretinal surgery.

DESIGN

Observational case series.

METHODS

Prospective study.

SETTING

A private vitreoretinal clinic in Caracas, Venezuela.

STUDY POPULATION

119 eyes of 119 patients who presented with rhegmatogenous retinal detachment but no previous vitreoretinal surgery between 1995 and 1998.

OBSERVATION PROCEDURES

Data from detailed preoperative and postoperative examinations of each eye were recorded prospectively and entered into an electronic database.

MAIN OUTCOME MEASURES

Prevalence of PVR of any type and severe PVR, preoperative risk factors for PVR of any type and severe PVR, effect of PVR and retinal detachment duration on initial and final visual acuity, and surgical complexity.

RESULTS

The prevalence of PVR of any type was 52.9% and of severe PVR was 26.9%. The mean retinal detachment duration (+/-SD) was 58.4 (+/-129.1) days, and the mean time from initial examination to surgical treatment (+/-SD) was 24.3 (81.2) days. By univariable analysis, long retinal detachment duration, poor initial visual acuity, and large retinal detachment extent were significantly associated with PVR prevalence and severity. The presence of vitreous hemorrhage was significantly associated with PVR prevalence, and cataract was significantly associated with PVR severity. By multivariable analysis, long retinal detachment duration and large retinal detachment extent were simultaneous risk factors for PVR prevalence, while long retinal detachment, large retinal detachment extent, and poor initial visual acuity were simultaneous risk factors for PVR severity. Eyes with longer retinal detachment duration, PVR of any type, and severe PVR had worse initial and final visual acuities than eyes with shorter retinal detachment duration or those without PVR, respectively. Eyes with PVR had more complex surgery than those without PVR.

CONCLUSIONS

PVR occurred very frequently in this population and was associated with more complex surgery and worse visual outcomes than among eyes without PVR. We have identified preventable risk factors associated with PVR that suggest a specific and significant need for better access to ophthalmologic care and patient education in this group of patients.

Pars plana vitrectomy assisted by triamcinolone acetonide for refractory uveitis: a case series study

AIM

To examine the outcome of a triamcinolone acetonide (TA) assisted pars plana vitrectomy (PPV) for refractory uveitis.

METHODS

Six patients suffering from proliferative vitreoretinopathy (PVR) with refractory uveitis underwent a TA assisted PPV. The patients consisted of one with Vogt-Koyanagi-Harada disease, one with acute retinal necrosis, one with Behçet's disease, and three with sarcoidosis. TA was inoculated into the vitreous cavity to visualise the vitreous. In four of six patients, 4 mg of TA were intentionally left in the vitreous cavity to reduce the degree of postoperative inflammation.

RESULTS

The vitreous body was clearly seen using TA during surgery, which greatly helped us to perform a posterior hyaloid resection safely and thoroughly. As we previously observed in other disease, TA allowed us to visualise the transparent vitreous and thus was helpful in removing the vitreous cortex from the retina completely in uveitis. One patient (Behçet's disease, in whom TA was intentionally left) showed an elevated intraocular pressure (IOP) transiently after surgery which was controllable by topical eye drops. The remaining TA diminished day by day and had almost completely disappeared within a month from operation.

CONCLUSION

TA improved the visibility of the hyaloid and the safety of the surgical procedures and no serious complications were observed after TA assisted PPV in uveitis. Although the long term effects are still unknown, this method appears to be potentially useful as an improved treatment for PVR associated with refractory uveitis.

The cell cycle distribution of cultured human retinal pigmented epithelial cells under exposure of anti-proliferative drugs

It has been well documented that RPE cells play an important role in the formation of proliferative vitreoretinopathy (PVR). We studied the effects of four most widely used anti-proliferative drugs, i.e., 5-fluorouracil (5-FU), daunomycin (DM), mitomycin C (MMC) and dexamethasone (DEX) in an in vitro model system (cultured human RPE). The cells treated with indicated concentrations of drugs for 48 h were harvested for DNA content analysis. In addition, a time course study with constant dosage of drugs was performed. The results revealed that, after incubation for 48 h, an increased percentage (31.1%) of S phase cells was noted with exposure to MMC (10 ng/ml). It was confirmed by 5-bromodeoxyuridine (BrdU) incorporation test that this increase does not result from higher transition rate from G1 to S phase. The cells of G2/M phase markedly increased from 13.8% to 29.7% with 10 ng/ml DM. We also demonstrated that 5-FU and MMC treatment led to cell accumulation at S phase and DM treatment resulted in cell accumulation at G2/M phase, These findings were compatible with their pharmacological mechanisms. Development of an in vitro model using cultured human RPE to study the effects of various anti-proliferative drugs on cell cycle can provide a rapid, safe and inexpensive method for selection of drugs used for management of PVR.

A comparative study of effects of antiproliferative drugs on human retinal pigment epithelial cells in vitro

The effects of various antiproliferative drugs have been tested in numerous cell types in vitro, but a comparison of effects of these drugs on cultured human retinal pigment epithelium (RPE) has not been reported. We studied the effects of four most widely used antiproliferative drugs (5-FU, daunomycin, mitomycin and dexamethasone) in a new in vitro model system (cultured human RPE). Various concentrations and exposure periods were tested in four human RPE cell lines. 5-FU showed a dose-dependant growth inhibition, with an ID50 of 5.35 +/- 2.38 x 10(-7) M after 4 days culture. A decrease of cell number occurred relatively later, the slope of the dose-response curve was less steep than that of others. Mitomycin C showed an immediate and strong growth inhibition and cytotoxic effects, with an ID50 of 3.73 +/- 0.71 X 10(-9) M. RPE cultured with daunomycin showed an abrupt decrease of cell number from 10(-9) M to 10(-8) M, the ID50 value was 1.07 +/- 0.23 x 10(-8) M. Dexamethasone showed a biphasic effect; it stimulated cell growth at 10(-7) to 10-6 M and inhibited cell growth at 10(-4) M or higher, with an ID50 of 6.05 +/- 1.61 x 10(-3) M. The advantages and disadvantages of these drugs and the prospective clinical application of these drugs for management of proliferative vitreoretinopathy (PVR) were discussed. Development of an in vitro model using cultured human RPE to study the effects of various antiproliferative drugs can provide a rapid, safe and inexpensive method for selection of drugs used for management of proliferative vitreoretinopathy.

Proliferative vitreoretinopathy: risk factors and pathobiology

Proliferative vitreoretinopathy (PVR) is still a major cause of failure of retinal detachment surgery. Despite a dramatic increase in our pathobiologic knowledge of PVR during the last 10 years, little of this information has been used to modify the surgical management of the disease, and, thus, the anatomic and functional results are still unsatisfactory. Collaborative research involving clinicians and basic researchers must be encouraged. PVR must be considered a multifactorial disease caused by interaction of several cells and intra- and extraocular factors. Therefore, therapeutic options based on the inhibition of one factor or phenomenon may be regarded with scepticism. To prevent PVR, it is necessary to determine the factors involved in its development, and because of its relatively small prevalence, large, prospective, multicenter studies seem necessary. In addition, clinical research must not be underestimated. PVR affects both sides of the retina and the retina itself, a point to which little attention has been paid and that is critical for surgical results. Therefore, a new classification that provides information about clinical relevance, such as the evolutionary stages of the disease (biologic activity) and the degree of surgical difficulty (location of the fibrotic process), seems necessary.

The effect of partial vitrectomy on blood-ocular barrier function in the rabbit

PURPOSE

To compare ocular vascular permeability in the rabbit after vitrectomy as assessed by contrast-enhanced magnetic imaging (CE-MRI) and measurements of aqueous and vitreous humor protein concentration.

METHODS

Partial vitrectomies were performed, irrigating with BSS or BSS PLUS. Post-operative vascular leakage was determined by CE-MRI following intravenous administration of gadolinium diethylenetriaminepentaacetic acid (Gd-DTPA). Aqueous and vitreous protein concentrations were quantified by standard biochemical assay. ERG evaluations were performed on postoperative days 1, 3, and 7.

RESULTS

Using BSS as irrigant, breakdown of the inner blood-retinal barrier (BRB) occurred in 4/7 eyes on post-operative day 1. The rate of Gd-DTPA leakage was significantly greater on postoperative day 1 than that in unoperated, control eyes, but declined approximately 50% by day 3. At both time points, outer BRB breakdown was restricted to the sclerotomy wounds. No BRB leakage was detectable in control eyes. Blood-aqueous barrier (BAB) leakage was bilateral on day 1. Significantly greater Gd-DTPA leakage occurred in the operated eye than in the nonsurgical contralateral eye. On day 3, approximately 40% bilateral reduction in leakage indicated resolution of BAB leakage. Notably, Gd-DTPA leakage of the BAB and BRB was significantly reduced in the BSS PLUS treated group. In contrast to MRI assessments, protein concentrations of the aqueous and vitreous in the surgical eye showed no detectable differences between BSS and BSS PLUS. Concurrent with the transient loss of ocular barrier function, ERG responses also declined. However, by day 7 greater than 90% recovery was noted in BSS PLUS treated animals but not in the BSS treatment group.

CONCLUSIONS

CE-MRI is capable of detecting subtle changes in vascular permeability following ocular surgery. Advantages of using BSS PLUS compared to BSS as the irrigating solution can be detected using this technique. BSS PLUS's protection of barrier function is consistent with a rapid recovery in retinal function not observed in BSS treated eyes.

Biomaterials used in the posterior segment of the eye

The treatment of posterior segment eye disease and related conditions has improved greatly in recent years with the advent of new therapies, materials and devices. Vitreoretinal conditions, however, remain significant causes of blindness in the developed world. Biomaterials play a major role in the treatment of many of these disorders and the success rate of vitreoretinal surgery, especially in the repair of retinal detachment and related conditions, would increase with the introduction of new and improved materials. This review, which focuses on disorders that feature retinal detachment, briefly describes the anatomy of the eye and the nature and treatment of posterior segment eye disorders. The roles, required properties and suitability of the materials used in vitreoretinal surgery as scleral buckles, tamponade agents or drug delivery devices, are reviewed. Experimental approaches are discussed, along with the methods used for their evaluation, and future directions for biomaterial research in the posterior segment of the eye are considered.