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

Photovoltaic, wireless wide-field epiretinal prosthesis to treat retinitis pigmentosa

PURPOSE

To develop and evaluate a photovoltaic, wireless wide-field epiretinal prosthesis for the treatment of retinitis pigmentosa.

METHODS

A mosaic array of thinned silicon-based photodiodes with integrated thin-film stimulation electrodes was fabricated with a flexible polyimide substrate film to form a film-based miniaturized electronic system with wireless optical power and signal transmission and integrated electrostimulation. Manufactured implants were characterized with respect to their optoelectronic performance and biocompatibility following DIN EN ISO 10993.

RESULTS

A 14 mm diameter prosthesis containing 1276 pixels with a maximum sensitivity at a near infrared wavelength of 905 nm and maximized stimulation current density 30-50 μm below the electrodes was developed for direct activation of retinal ganglion cells during epiretinal stimulation. Fabricated prostheses demonstrated mucosal tolerance and the preservation of both metabolic activity, proliferation and membrane integrity of human fibroblasts as well as the retinal functions of bovine retinas. Illumination of the prosthesis, which was placed epiretinally on an isolated perfused bovine retina, with infrared light resulted in electrophysiological recordings reminiscent of an a-wave (hyperpolarization) and b-wave (depolarization).

CONCLUSIONS

A photovoltaic, wireless wide-field epiretinal prosthesis for the treatment of retinitis pigmentosa using near infrared light for signal transmission was designed, manufactured and its biocompatibility and functionality demonstrated in vitro and ex vivo.

Diabetic macular edema: Safe and effective treatment with intravitreal triamcinolone acetonide (Taioftal)

Purpose

To suggest the safety and efficacy of preservative-free triamcinolone acetonide intravitreal injectable suspension (Taioftal) for the treatment of diabetic macular edema.

Methods

A prospective clinical study involved 49 patients (49 eyes), that were treated with Taioftal and followed-up for six months. Complete ophthalmic examination, including spectral domain optical coherence tomography, was performed at baseline, and at month 1, 3, 6 after the intravitreal injection. Accurate collection and analysis of best-corrected visual acuity (BCVA), central foveal thickness (CFT), intraocular pressure (IOP), and adverse events (AEs) were carried out in order to evaluate visual function and macular morphology before and after treatment

Results

Median BCVA value chosen as comparing statistics was significantly improved at every follow-up time points (gain of 6 letters at month 1, 12 at month 3 –improvement up to 24% at month 3 with stabilization until month 6) compared to baseline, as certified by Kruskal-Wallis rank sum test (P<0.05). Median CFT significantly waned at each follow-up times (decrease of about 65 μm at month 1, 155 at month 3 –reduction up to 28% at month 3 keeping good outcome until month 6) compared to baseline (P<0.05). IOP elevation, with no severe increases, was the most common among spotted AEs (median of 23 mmHg at month 1, 20 at month 3).

Conclusion

Intravitreal injection of preservative-free triamcinolone (Taioftal) is an effective, safe and inexpensive drug used to improve visual acuity and reduce central foveal thickness in eyes affected by diabetic macular edema during an average time of 6 months. Temporary, never severe, elevation of IOP is totally manageable with topical medications. No serious vision-threatening complications are related to the use of intravitreal triamcinolone injections.

Comparison of Different Cell Culture Media in the Model of the Isolated and Superfused Bovine Retina: Investigating the Limits of More Physiological Perfusion Solutions

PURPOSE

The isolated superfused retina is a standardized tool in ophthalmological research. However, stable electroretinogram (ERG) responses can only be obtained for around eight hours; therefore, limiting its use. The aim of this study was to evaluate the short-term potential of different cell culture media and to promote long-term testing based on the results obtained.

MATERIALS AND METHODS

For the experimental procedure bovine retinae were prepared and perfused with the standard Sickel solution and an ERG was performed. After recording stable a- or b-waves, different media (Dulbecco's Modified Eagle's Medium (DMEM), MACS, and Neurobasal) were superfused for 45 minutes. ERG recovery was monitored overall for 75 minutes. Analysis of the mRNA expression of Thy-1, GFAP, Bax/Bcl-2-ratio, Rhodopsin, and Opsin via qRT-PCR was performed directly after ERG recording on the same retina.

RESULTS

None of the tested media had a negative effect on a-wave amplitudes, although b-wave amplitudes decreased (DMEM) or increased (MACS and Neurobasal) compared to the standard solution (Sickel) after 45 minutes of exposure. However, after 75 minutes of wash-out, no difference to the standard solution alone could be observed. Exposure to different media either had no effect or decreased the Opsin and Rhodopsin mRNA levels. Thy-1 expression was strongly diminished in DMEM and MACS (by 2-3-fold), whereas incubation in Neurobasal medium led to a slight increase compared to incubation with the standard solution. Furthermore, the Bax/Bcl-2 ratio indicated an anti-apoptotic effect (Bax/Bcl-2 = 0.16; p < 0.05) for Neurobasal.

CONCLUSION

Neurobasal medium displayed the best electrophysiological properties in the short-term and may be applicable for stable long-term escalation testing.

Low concentrations of ethanol but not of dimethyl sulfoxide (DMSO) impair reciprocal retinal signal transduction

BACKGROUND

The model of the isolated and superfused retina provides the opportunity to test drugs and toxins. Some chemicals have to be applied using low concentrations of organic solvents as carriers. Recently, E-/R-type (Cav2.3) and T-type (Cav3.2) voltage-gated Ca(2+) channels were identified as participating in reciprocal inhibitory retinal signaling. Their participation is apparent, when low concentrations of NiCl2 (15 μM) are applied during superfusion leading to an increase of the ERG b-wave amplitude, which is explained by a reduction of amacrine GABA-release onto bipolar neurons. During these investigations, differences were observed for the solvent carrier used.

METHODS

Recording of the transretinal receptor potentials from the isolated bovine retina.

RESULTS

The pretreatment of bovine retina with 0.01 % (v/v) dimethylsulfoxide did not impair the NiCl2-mediated increase of the b-wave amplitude, which was 1.31-fold ± 0.03 of initial value (n = 4). However, pretreatment of the retina with the same concentration of ethanol impaired reciprocal signaling (0.96-fold ± 0.05, n = 4). Further, the implicit time of the b-wave was increased, suggesting that ethanol itself but not DMSO may antagonize GABA-receptors.

CONCLUSION

Ethanol itself but not DMSO may block GABA receptors and cause an amplitude increase by itself, so that reciprocal signaling is impaired.

Investigating retinal toxicity of tempol in a model of isolated and perfused bovine retina

PURPOSE

Tempol (4-hydroxy-2,2,6,6-tetramethylpiperidinyl-1-oxyl) is a membrane-permeable superoxide dismutase and potentially neuroprotective substance. This study evaluates the retinal tolerance of 0.5 mM, 1 mM, 2 mM, and 5 mM tempol measured by the electroretinogram (ERG) of an isolated and perfused retina whole mount.

METHODS

For functionality testing, bovine retinas were prepared and perfused with an oxygen-saturated standard solution, and the ERG was recorded until stable b-wave amplitudes were reached. Tempol concentrations of 0.5 mM, 1 mM, 2 mM, and 5 mM were tested for 45 minutes. To investigate the effects on photoreceptor function, 1 mM aspartate was added to suppress the b-wave and obtain isolated a-waves. ERG amplitudes were monitored for 100 minutes.

RESULTS

While no toxic effects for concentrations of 0.5 mM and 1 mM tempol could be detected, concentrations of 2 mM tempol and higher caused statistically significant negative effects on the b-wave amplitude (-38 %, p = 0.02 for 2 mM; -54 %, p = 0.02 for 5 mM). The a-wave amplitude remained stable even at higher concentrations.

CONCLUSIONS

Although the photoreceptors seem to have a tolerance to high concentrations of tempol, higher intravitreal concentrations than 1 mM should be considered critical.

The retinal biocompatibility of dyes in the ex vivo model of the isolated superfused vertebrate retina

BACKGROUND

Peeling of the internal limiting membrane or epiretinal membranes is a successful principle in macular surgery to achieve a functional benefit. Different dyes are used to facilitate the identification of intraocular tissues. The aim of our work was to investigate the retinal tolerance to the different dyes and their solvent carriers to provide valuable data for surgeons in handling for an optimal intraoperative use.

METHODS

Using the ex vivo model of the isolated superfused vertebrate retina technique, the effects of the dyes were tested on human and bovine retinal function. The retinas were perfused with an oxygen preequilibrated standard solution. The electroretinogram (ERG) was recorded using Ag/AgCl electrodes. After recording stable ERG amplitudes, the dyes brilliant blue G, indocyanine green, trypan blue, patent blue, triamcinolone and their solvent carriers were investigated.

RESULTS

Reductions of the ERG amplitudes were found for each tested dye. The effects after application of the dyes were dependent on time and concentration of the applied dyes, which were different for each dye.

CONCLUSION

In part, the ERG has shown strong effects already after a short period of dye application. Surgeons who rely on the intraocular use of the dyes should keep in mind our findings, and the use of some dyes should be limited to selected cases. The well-considered use of the dyes by the surgeons could lead to a better functional outcome and avoid a possible harmful outcome of the surgery after mishandling.

The safety profile of alkylphosphocholines in the model of the isolated perfused vertebrate retina

BACKGROUND

Alkylphosphocholines (APCs) are synthetic phospholipid derivatives, and have been demonstrated to inhibit ocular cell proliferation in vitro and in vivo. Currently, they are applied clinically for their antitumoral and antiparasitic properties, but have not yet been implemented for clinical use in proliferative ophthalmic disorders. The purpose of this study was to assess the safety of APC in the ex vivo model of the isolated perfused vertebrate retina.

METHODS

Bovine retina preparations were perfused with an oxygen pre-equilibrated standard solution. The electroretinogram (ERG) was recorded using Ag/AgCl-electrodes. After recording stable b-wave amplitudes, an APC was applied at the following concentrations to the nutrient solution: 0.25 microM, 2.5 microM and 25 microM. To investigate the effects of APC on photoreceptor function, a test series at the same concentrations was performed to evaluate the effects of APC on the a-wave amplitude. Aspartate at a concentration of 1 mM was added to the nutrient solution to obtain stable a-wave amplitudes. Thereafter, APC was applied at the same concentrations to the nutrient solution. The recovery of the ERG amplitudes was followed up for 75 minutes.

RESULTS

No reduction of the a- and b-wave amplitude was found at the end of the exposure time with APC added in each test series. No differences were found between the ERG amplitudes before and after application of APC at the end of the washout.

CONCLUSIONS

In the ex vivo model of the isolated perfused vertebrate retina, APC has proved to be a safe compound in the concentrations applied. Thus, APCs should further be considered as promising candidates for future clinical applications in ophthalmology.

Effect of intravitreal triamcinolone acetonide in the treatment of experimental Staphylococcus epidermidis endophthalmitis

PURPOSE

To investigate the effect of intravitreal injection of triamcinolone acetonide (TA) in the treatment of experimental Staphylococcus epidermidis endophthalmitis.

MATERIALS AND METHODS

Experimental endophthalmitis induced in one eye of 38 rabbits by intravitreal injection of Staphylococcus epidermidis. The infected rabbits were randomly divided into three groups. The rabbits in group 1 (n = 15) received intravitreal injection of 1 mg vancomycin hydrochloride. Group 2 eyes (n = 15) received intravitreal TA (4 mg) plus vancomycin hydrochloride (1 mg). Group 3 eyes (8 eyes) received normal saline. Clinical examination in each group was performed two, seven, and 15 days after inoculation of the bacteria. The eyes were enucleated for histopathologic evaluation on the 15th day. Clinical and histological scoring systems were used to evaluate clinical and histological severity of the intraocular infection.

RESULTS

The mean clinical scores of three study groups at the 7th day were 5.8 +/- 2.3, 3.3 +/- 1.5, and 9.5 +/- 2.1, respectively. The mean of this value at 15th day were 6.2 +/- 2.6, 3.9 +/- 2.1, and 10 +/- 2.2, respectively. At the 7th and 15th day, the mean clinical score of group 2 was significantly lower when compared with the other two groups. Mean histopathologic scores of group 1, group 2, and group 3 were 11 +/- 2.7, 7.9 +/- 2.9, and 14.0 +/- 3.1, respectively. Histopathologic studies revealed less tissue destruction for eyes treated with TA. There was a significant positive correlation between the severity of clinical signs and pathologic damage in all three experiment groups; however, it was weakest in the IVTA treated group.

CONCLUSION

A standard clinical dose of intravitreal TA attenuates the clinical signs and tissue destruction in a rabbit model of Staphylococcus epidermidis endophthalmitis.