Neuroprotective effects of a taurine-containing irrigation solution for vitrectomy.

BACKGROUND: During pars plana vitrectomy, the retina is exposed to several iatrogenic risk factors, including excitotoxicity. A taurine-containing irrigation solution for pars plana vitrectomy (PURI PROTECT) has been developed and is claimed to have neuroprotective properties. METHODS: Retinal ganglion cells (RGC-5) and retinal whole mounts were incubated in standard irrigation solution (SIS) and SIS supplemented with 3 mM taurine (SIS-taurine). Excitotoxicity was induced by the addition of 8, 10, and 12 mM or 250 µM glutamate. Cell viability and cell survival were assessed by the MTT test and Annexin-V/propidium iodide flow cytometry. Whole mounts were stained with the Live/Dead staining assay. Pars plana vitrectomy with SIS or SIS-taurine was performed in rabbits. Animals were followed-up by electroretinography. RESULTS: RGC-5 incubated in SIS-taurine showed a 4.3-fold (P < 0.0005) better overall cell viability and an up to 8.5-fold (P < 0.05) increased cell survival under excitotoxic conditions compared with that incubated in SIS. Whole mounts incubated in SIS-taurine showed a 1.7-fold (P < 0.0005) and 1.6-fold (P < 0.0005) better cell survival under excitotoxic and nonexcitotoxic conditions, respectively. In the immediate postoperative period, b-wave amplitudes were significantly better in animals operated with SIS-taurine compared with control (P < 0.01). CONCLUSION: A taurine-containing irrigation solution may protect retinal ganglion cells against excitotoxicity.

How do spontaneous pupillary oscillations in light relate to light intensity?

Characteristics of light-induced pupillary oscillations at constant light intensities have been investigated sparsely compared to sleepiness-related pupillary oscillations in darkness. This study presents the first controlled analysis of light-induced pupillary oscillations and their relationship to illumination. Pupillary oscillations of alert subjects were recorded by infrared video pupillography in different background lighting. Although showing obvious relationships of mean frequency and amplitude to light intensity, there were considerable inter- and intra-individual differences in the appearance of light-induced oscillations. As they looked rather similar to sleepiness waves, the question remains to identify light-induced oscillations in day light and to differentiate them from sleepiness-related oscillations.

The effects of triamcinolone crystals on retinal function in a model of isolated perfused vertebrate retina.

A good clinical experience of intravitreal triamcinolone acetonide (TA) has been reported in several studies, but there are growing indications that epiretinal crystals of TA exhibit retinal toxicity. To investigate the effects of TA on retinal function we used a model of an electrophysiological in vitro technique for testing retinal toxicity. Isolated bovine retinas were perfused with an oxygen saturated nutrient solution. The electroretinogram (ERG) was recorded as a transretinal potential using Ag/AgCl electrodes. After reaching stable ERG-amplitudes TA at the maximum solubility equilibrium (36 microg/ml) was either applied to the nutrient solution for 45 min or TA was administered epiretinally at concentrations (1 mg/ml, 4 mg/ml, 8 mg/ml, 20 mg/ml and 40 mg/ml) above the maximum solubility equilibrium to assure direct contact of the TA crystals with the isolated perfused retinas. After that the retinas were reperfused for 75 min with the standard nutrient solution. The percentage of a- and b-wave reduction directly after the application and at the washout was calculated. To assess the effects of TA at the level of the ganglion cell layer a Viability/Cytotoxicity Kit for mammalian cells was used. No changes of the ERG-amplitudes were detected during the exposure to 36 microg/ml TA for 45 min (b-wave: 9.6 microV+/-2.1 vs. 8 microV+/-2.1 (p=0.135); a-wave: -11 microV+/-2.7 vs. -10.6 microV+/-2.3 (p=0.889)) and at the washout (b-wave: 8 microV+/-2.1 vs. 8.3 microV+/-2.4 (p=0.18); a-wave: -10.6 microV+/-2.3 vs. -12 microV+/-2.6 (p=0.225)). At concentrations higher than 1mg/ml TA induced a decrease of the a- and b-wave in a concentration dependent manner. These changes were reversible for concentrations of TA up to 20mg/ml (b-wave: 9 microV+/-2.4 vs. 6.6 microV+/-2.5 (p=0.08); a-wave: -11.4 microV+/-2.0 vs. -11.2 microV+/-2.2 (p=0.37)), but irreversible at 40 mg/ml even at the end of the washout (b-wave: 9.8 microV+/-1.9 vs. 3 microV+/-1.7 (p=0.009); a-wave: -9.8 microV+/-2.1 vs. -2.6 microV+/-2.1 (p=0.001)). Histological examination of the preparations revealed a dramatic ganglion cell death, in which an application of 20mg/ml and 40 mg/ml TA led to a 60.53% (p=0.013) and 82.35% (p=0.002) ganglion cell death, respectively. The epiretinal application of 4 mg/ml TA and higher resulted in distinct effects on the ERG of the isolated perfused retinas. Ganglion cell death was induced at a concentration of 20mg/ml and higher. TA shows an asymmetric and partly high concentrated distribution after intravitreal application. Therefore, we consider concentrations of 4 mg/ml and higher might be toxic and should be avoided in clinical use.

Safety profile of a taurine containing irrigation solution (AcriProTect) in pars plana vitrectomy.

PURPOSE: To evaluate the clinical safety of a taurine containing irrigation solution (AcriProTect) before its routine application in pars plana vitrectomy (PPV). METHODS: Twenty-five patients who underwent PPV were included in this prospective interventional clinical study. Standard irrigation solution containing the addendum 3 mmol/L taurine was used during PPV. Postoperative follow-up visits included a standard eye examination, corneal thickness measurements, endothelial cell counts, determination of the foveal thickness by optical coherence tomography (OCT), and an electrophysiologic examination. For statistical analysis Wilcoxon test was used. RESULTS: Significant improvement of visual acuity (VA) was observed at the 3- and 6-month controls (P = 0.024; P = 0.002 for 3 and 6 months, respectively). Endothelial cell counts and corneal thickness at 3 and 6 months were not significantly different from preoperative values (P = 0.204; P = 0.126 for endothelial cell count and P = 0.475; P = 0.095 for corneal thickness at 3 and 6 months, respectively). Both scotopic and photopic Ganzfeld electroretinography and electro-oculography did not show significant changes during the follow-up. No increase in complication rate was detected. CONCLUSIONS: The investigation demonstrates a good biocompatibility of taurine-containing irrigation solution developed for vitrectomy in humans concomitant with habitually observed good functional outcome.

Systematic evaluation of ICG and trypan blue related effects on ARPE-19 cells in vitro.

The aim of our study was a systematic analysis of the impact of variable parameters on indocyanine green (ICG) and trypan blue (TB) related cytotoxicity on human RPE cells. ARPE-19 cells were incubated with ICG (5.0-0.025mg/ml), with ICG-free solutions of corresponding osmolarities or with TB (1.5-0.0375mg/ml). Incubation lasted 1-20min with or without endolight illumination for 1min or 5min. Cell viability and morphology were examined after 6h, 24h and 72h to detect acute and delayed effects. In the absence of endolight, ICG cytotoxicity depends on osmolarity and exposure time. In the presence of endolight, cytotoxic effects are influenced by dye concentration. TB cytotoxicity depends on dye concentration and exposure time, but not on illumination. All observed cytotoxic effects were mainly acute. Both ICG and TB can be cytotoxic depending on concentration and exposure time. ICG related cytotoxic effects are additionally determined by osmolarity and phototoxicity. However, concentrations (<1mg/ml) and incubation times (<5min) as used in clinical practice would appear to be well tolerated.

Primary silicone oil tamponade in the management of severe intraocular foreign body injuries: an 8-year follow-up.

PURPOSE: To evaluate the long-term outcome of pars plana vitrectomy and primary silicone oil tamponade in patients with severe intraocular foreign body (IOFB) injuries and high risk of proliferative vitreoretinopathy (PVR). METHODS: This retrospective consecutive study included 23 patients with severe IOFB injuries who had extensive lacerations including sclera, choroid, and retina, and were complicated by predictive factors for elevated proliferative activity and an unfavorable outcome. All patients underwent pars plana vitrectomy, removal of the IOFB, and primary silicone oil tamponade and were followed up for a mean 8.9 years. Main functional outcome was assessed as final best-corrected visual acuity. Anatomic success was defined as permanent retinal attachment. RESULTS: PVR occurred in 70% of all eyes and required 16 revisions. Silicone oil was removed in 78% of the eyes after a mean tamponade duration of 9.1 months. Complete retinal attachment was achieved in 83% of the eyes. Three eyes developed a persisting hypotony that was stabilized under permanent silicone oil. Functional stabilization was observed in the third year resulting in a final visual acuity of 20/630. Useful vision of better than 20/400 could be preserved in 55% of the patients. Only one eye underwent a late enucleation after 6.8 years. CONCLUSIONS: Primary silicone oil stabilizes the retina during the critical period of active PVR and may limit the visual loss in selected high-risk eyes in the long term.

The retinal tolerance to bevacizumab in co-application with a recombinant tissue plasminogen activator.

AIM: To investigate the retinal toxicity of bevacizumab in co-application with a commercially available recombinant tissue plasminogen activator (rt-PA), and to facilitate a new therapeutic concept in the treatment of massive subretinal haemorrhage caused by neovascular age-related macular degeneration (AMD). METHODS: Isolated bovine retinas were perfused with an oxygen-preincubated nutrient solution. The electroretinogram (ERG) was recorded as a transretinal potential using Ag/AgCl electrodes. Bevacizumab (0.25 mg/ml) and rt-PA (20 microg/ml) were added to the nutrient solution for 45 min. Thereafter, the retina was reperfused for 60 min with normal nutrient solution. Similarly, the effects of rt-PA (20 microg/ml, 60 microg/ml and 200 mug/ml) on the a- and b-wave amplitudes were investigated. The percentages of a- and b-wave reduction during application and at washout were calculated. RESULTS: During application of bevacizumab (0.25 mg/ml) in co-application with 20 microg/ml (rt-PA), the ERG amplitudes remained stable. The concentrations of rt-PA alone (20 microg/ml and 60 microg/ml) did not induce significant reduction of the b-wave amplitude. In addition, 20 microg/ml rt-PA did not alter the a-wave amplitude. However, 60 microg/ml rt-PA caused a slight but significant reduction of the a-wave amplitude. A full recovery was detected for both concentrations during the washout. At the highest tested concentration of 200 microg/ml rt-PA, a significant reduction of the a- and b-wave amplitudes was provoked during the exposure. The reduction of ERG amplitudes remained irreversible during the washout. CONCLUSION: The present study suggests that a subretinal injection of 20 microg/ml rt-PA in co-application with bevacizumab (0.25 mg/ml) for the treatment of massive subretinal haemorrhage seems possible. This is a safety study. Therefore, we did not test the clinical effectiveness of this combined treatment.

Effects of the protein tyrosine kinase inhibitor genistein and taurine on retinal function in isolated superfused retina.

BACKGROUND: Genistein has the potential to act as an intraocular antiangiogenic agent. Its therapeutical use, however, is limited by toxic side effects on the retina. This study was designed to evaluate the simultaneous use of taurine as a neuroprotective drug. METHODS: Bovine retinas were isolated and perfused with an oxygen-preincubated nutrient solution. The electroretinogram (ERG) was recorded as a transretinal electrical potential using Ag/AgCl electrodes. At stable ERG amplitudes, genistein at concentrations of 11, 37, and 150 microM was added to the nutrient solution for 45 min, in the absence or presence of taurine (3 mM). Thereafter, the retina was reperfused with the nutrient solution for another 100 min. The percentage of b-wave reduction during genistein and genistein/taurine application was calculated. RESULTS: The b-wave amplitude was reduced by a smaller amount during the application of genistein (11 and 37 microM) in the presence of taurine compared with genistein alone. For both, genistein/taurine and genistein alone the b-wave recovered completely during the wash-out of the drugs. However, during the application of the highest tested concentration of genistein (150 microM), taurine did not protect completely, leading to an irreversible b-wave reduction. CONCLUSIONS: The adjuvant use of taurine reduces the genistein-induced retinal toxicity to a certain degree. However, the protective effect of taurine is limited and there is only a narrow therapeutic index for a combined intravitreal administration of genistein in coapplication with taurine to inhibit pathological ocular neovascularization.

Sutureless amniotic membrane fixation using fibrin glue for ocular surface reconstruction in a rabbit model.

PURPOSE: Amniotic membrane transplantation has become an important treatment option for corneal surface reconstruction. However, suture fixation of the transplant has various disadvantages like corneal irritation, scarring, graft loss due to membrane shrinkage, and the need for subsequent suture removal. Replacement of sutures by bioadhesives might be an advantageous alternative. This controlled study was designed to evaluate a new sutureless technique for amniotic membrane fixation onto the corneal surface by using fibrin glue. METHODS: Standardized disks of cryopreserved amniotic membranes were transplanted onto the deepithelialized cornea of 12 rabbits using either conventional suture fixation or a new fibrin glue technique. The rabbits were followed-up with slit-lamp examination and fluorescein staining until epithelialization was completed. Consecutively, the rabbits were killed and the eyes processed for histology and immunohistochemistry for cytokeratin-3. RESULTS: All membranes of both groups stayed in place throughout the follow-up time and showed a progressive graft epithelialization that was completed after 12 days. Whereas suture-fixated membranes showed progressive tissue shrinkage, fibrin-glued sheets remained unaltered. In the bioadhesive group, histology revealed a smooth fibrin layer in the graft-host interface and a continuous, stratified layer of cytokeratin-3 expressing corneal epithelial cells on the membrane surface. In contrast, suture-fixated membranes showed contracted and prominent membrane edges with epithelial ingrowth into the submembrane interface. CONCLUSION: Our results demonstrate the general feasibility of reproducible and reliable sutureless amniotic membrane fixation onto the corneal surface in rabbits. Stable adherence is maintained until epithelialization is completed. The sutureless technique gives sufficient manipulation time for the sheet before the final cross-linking process is completed. Furthermore, several advantageous characteristics could be demonstrated as increased biocompatibility, better epithelialization pattern and the lack of membrane shrinkage.

Experimental implantation and long-term testing of an intraocular vision aid in rabbits.

OBJECTIVE: To develop an intraocular vision aid to provide artificial vision in severely traumatized eyes, where neuroretinal function could be preserved but irreversible anterior segment opacification resulted in blindness. METHODS: The basis of an intraocular vision aid is in principle a telemetric circuit to bridge the opaque cornea and to allow for artificial light stimulation of the retina. The visual prosthesis comprises an external high-dynamic range complementary metal oxide semiconductor camera and digital signal processing unit and an intraocular miniaturized light-emitting diode array to project the image onto the retina. For in vivo testing of long-term function and biocompatibility, silicone-encapsulated active photodiodes were implanted in 13 pigmented rabbits and were followed up for up to 21 months. RESULTS: Lens extraction and stable fixation of the device in the ciliary sulcus were successful in all cases. For up to 21 months inductive energy transmission and wireless stimulation of the implants could be maintained. Electrophysiologic data and histology demonstrated a good tissue biocompatibility in the long-term follow-up. CONCLUSION: The results demonstrate the general feasibility and biocompatibility to implant and fixate an intraocular light-emitting diode prosthesis. Inductive energy transmission to the intraocular device and wireless light stimulation are assured in the long term but depend on meticulous water-impermeable encapsulation of the delicate microelectronic components. Clinical Relevance An intraocular vision aid compound system with a high-resolution light-emitting diode matrix might be a future treatment option to restore vision in blind eyes with severe anterior segment disorders.

Decorin modulates wound healing in experimental glaucoma filtration surgery: a pilot study.

PURPOSE: To analyze the effect of perioperative decorin in an experimental setting of glaucoma filtration surgery. METHODS: Glaucoma filtration surgery, similar to that performed in clinical practice, was performed on 35 chinchilla rabbits (ChBB:CH). The animals received a unilateral subconjunctival injection of decorin (40-100 microg) or the vehicle alone before surgery and at different time intervals thereafter. Antifibrotic efficacy was established by clinical response and histologic examination. The animals were killed on day 14, and the eyes processed for histology. RESULTS: Both the vehicle and the decorin solution were well tolerated. No adverse effects such as inflammation or blurring of the optical media were observed. Conjunctival scarification occurred within 1 week in the control groups but was suppressed in the experimental groups. The intraocular pressure correlated with the fibrotic process and reached normal levels within 7 days after surgery in control animals, but remained significantly (P <0.001) reduced in the experimental groups. Histologic examination of the surgical area 14 days after surgery disclosed massive fibrosis in the control animals, but little deposition of extracellular matrix in the experimental groups. CONCLUSIONS: The data of this pilot study suggest that perioperative subconjunctival decorin applications significantly affect conjunctival scarring and surgical outcome of glaucoma filtration treatments in rabbits.