Effects of D-serine treatment on outer retinal function

The role of the N-Methyl-D-Aspartate Receptor (NMDAR) in the outer retina is unclear despite expression of the NMDAR-complex and its subunits in the outer retina. The flash-electroretinogram (fERG) offers a non-invasive measurement of the retinal field potentials of the outer retina that can serve to clarify NMDAR contribution to early retinal processing. The role of the NMDAR in retinal function was assessed using a genetic mouse model for NMDAR hypofunction (SR^-/-), where the absence of the enzyme serine racemase (SR) results in an 85% reduction of retinal D-serine. NMDAR hypo- and hyperfunction in the retina results in alterations in the components of the fERG. The fERG was examined after application of exogenous D-serine to the eye in order to determine whether pre- and post-topical delivery of D-serine would alter the fERG in SR^-/- mice and their littermate WT controls. Amplitude and implicit time of the low-frequency components, the a- and b-wave, were conducted. Reduced NMDAR function resulted in a statistically significantly delayed a-wave and reduced b-wave in SR^-/- animals. The effect of NMDAR deprivation was more prominent in male SR^-/- mice. A hyperfunction of the NMDAR, through exogenous topical delivery of 5 mM D-serine, in WT mice caused a significantly delayed a-wave implicit time and reduced b-wave amplitude. These changes were not observed in female WT mice. There were temporal delays in the a-wave and amplitude and a decrease in the b-wave amplitude and implicit time in both hypo- and NMDAR hyperfunctional male mice. These results suggest that NMDAR and D-serine are involved in the retinal field potentials of the outer retina that interact based on the animal's sex. This implicates the involvement of gonadal hormones and D-serine in retinal functional integrity.

Electrophysiological and SD-OCT findings in patients receiving chloroquine therapy in relation to cumulative dosage and duration of treatment

PURPOSE

Assessment of multifocal ERG (mfERG) changes in patients treated with chloroquine and their correlation with morphological abnormalities, detected by spectral-domain optical coherence tomography in relation to cumulative dosage.

METHODS

Data from 37 eyes of 20 patients were retrospectively collected, and one randomly selected eye per patient was considered for statistical analysis. Eyes were divided into three groups according to mfERG and visual acuity findings: normal, early and advanced maculopathy. Functional measures of the first three mfERG rings were compared with retinal thickness measures of the corresponding OCT ETDRS circles. Data on cumulative dose and duration of therapy were also evaluated.

RESULTS

The mean mfERG values progressively decreased according to the stage of the disease. In particular in the early maculopathy group, amplitudes were significantly reduced in all the three central rings. The mean ring ratio R1/R2 was abnormal only in the early maculopathy group. OCT thickness measures were significantly lower in all the three ETDRS circles in the advanced maculopathy group, and in the paracentral circle in the early maculopathy group. Considering all the eyes, there was a statistically significant correlation between functional and morphological values (p < 0.001). High chloroquine cumulative dosages were always associated with retinal toxic effects, whereas lower cumulative dosages generated different levels of toxicity.

CONCLUSIONS

This study shows a strong association between mfERG ring values and the corresponding OCT thickness measures; however, mfERG may enhance early detection of functional changes in patients treated with chloroquine, especially in ambiguous cases. At low chloroquine cumulative dosages, different subjects might have different susceptibilities to the drug.

Little effect of 0.01% atropine eye drops as used in myopia prevention on the pattern electroretinogram

PURPOSE

Daily administration of 0.01% atropine eye drops is a promising approach for myopia control. The mechanism of action is believed to involve the dopaminergic system of the retina, triggering an increased release of dopamine. Previous studies in psychiatric condition such as major depression suggest that pattern electroretinogram (PERG) amplitudes are modulated by changes in retinal dopamine. It is thus plausible that atropine eye drops could have an effect on PERG amplitudes. The present study was designed to test this, assessing the difference in amplitude between contrast levels and the ratio of amplitudes between check sizes as primary endpoints.

METHODS

We included 14 participants with no more than ± 2 diopters of ametropia and visual acuity of at least 1.0. One eye was chosen randomly in each participant for atropine application (14 days, one drop of 0.01% atropine solution once daily before bedtime). We recorded two sets of steady-state PERG recordings: one with different contrasts (25% and 98%) and one with different check sizes (0.8° and 17°). Near-point distance, near visual acuity, and pupil diameter were measured additionally.

RESULTS

The recordings to different contrasts did not show atropine-related changes of PERG amplitude. A small increase by 6% of the amplitude difference between contrast levels with atropine application was not significant (p = 0.08). Raw amplitudes in the check size condition increased with atropine by 17% (p < 0.01) and 10% (p < 0.03) for small and large checks, respectively, without a significant concomitant effect on the amplitude ratio. Pupil size was significantly affected (median increase 0.5 mm, p < 0.002). However, neither of the experimental conditions was associated with a significant correlation between pupil size and PERG effects.

CONCLUSION

The effects on PERG primary endpoints after the 14-day period of atropine administration were small, especially compared to effect sizes in major depression, and statistically insignificant. Effects on raw amplitude were inconsistent. The present results suggest that retinal processing as reflected by PERG does not sizably change following a treatment regimen with atropine that is typical for myopia control.

The neuro-ophthalmological effects related to long-term occupational exposure to organic solvents in painters

PURPOSE

Organic solvents are widely used in many industries, and usually, exposure occurs with mixtures of solvents. Organic solvent mixtures are known for their ability to affect tissues of high lipid content including the myelin sheath in the nervous system. The purpose of this work was to study the evidence that long-term (more than 10 years) exposure to organic solvent mixtures among painters can induce neuro-ophthalmological effects on the function of retinal ganglion cells and the optic tract.

METHODS

Twenty workers with long-term occupational exposure to mixed organic solvents were compared to 40 control subjects. The controls were matched for age, gender, and demographic characteristics but were not occupationally exposed to any known organic solvents, using the following comparators: visual evoked potential (VEP), electroretinogram (ERG), color vision (CV), and contrast sensitivity (CS) testing. Environmental monitoring was done in the work environment with consideration to the American Conference of Governmental Industrial Hygienists Threshold Limit Values (ACGIH-TLVs).

RESULTS

The exposed group had significantly longer latency and higher amplitude of VEP waves especially P100, higher Color Confusion Index (CCI), especially affecting the blue-yellow spectrum, and lower Log CS. There was no significant difference between exposed and nonexposed groups in full-field flash ERG response; however, in the pattern ERG, the exposed group had significantly longer latency of P50, which reflects changes in the retinal ganglion cell.

CONCLUSION

Long-term occupational exposure to mixed organic solvents appeared to affect the optic tract functions in the form of increasing latency of VEP response, affecting the quality of CV and decreasing CS. It also affects the retinal ganglion cell layer with increased latency of P50 of the pattern ERG response.

Outcomes in Autoimmune Retinopathy Patients Treated With Rituximab

PURPOSE

To evaluate clinical and ancillary testing, including adaptive optics, outcomes in autoimmune retinopathy (AIR) patients treated with rituximab.

DESIGN

Retrospective, interventional case series.

METHODS

patients: Sixteen AIR patients treated with rituximab.

OBSERVATION PROCEDURES

All patients were treated with a loading and maintenance dose schedule of intravenous rituximab. Visual acuity (VA), electroretinography (ERG), and spectral-domain optical coherence tomography (SDOCT) and visual field (VF) results were recorded. A subset of patients was also imaged using adaptive optics scanning laser ophthalmoscopy (AO-SLO).

MAIN OUTCOME MEASURES

Rates of VA change before vs after rituximab initiation were compared with mixed-model linear regression.

RESULTS

The rate of visual decline was significantly less after rituximab initiation compared with the rate of visual decline prior to rituximab initiation (P = .005). Seventy-seven percent of eyes had stable or improved VA 6 months after rituximab initiation. Amplitudes and implicit times on ERG, mean deviation on VF, central subfield mean thickness, and total macular volume did not decrease to a significant degree over the rituximab treatment period. Six eyes had serial AO-SLO imaging. Cone densities did not change significantly over the treatment period.

CONCLUSION

VA was stable or improved in a majority of AIR patients while they were being treated with rituximab. OCT and ERG parameters, as well as AO-SLO cone densities, were stable during treatment. Studies with additional patients and longer follow-up periods are needed to further explore the utility of rituximab in the management of AIR.

Preclinical Acute Ocular Safety Study of Combined Intravitreal Carboplatin and Etoposide Phosphate for Retinoblastoma

BACKGROUND AND OBJECTIVE

To describe the ocular toxicity of intravitreal carboplatin and etoposide phosphate (VP16P) in Dutch-Belted rabbits.

MATERIALS AND METHODS

Twenty-two adult male Dutch-Belted rabbits (Cohort 1) each received a single, bilateral intravitreal injection (0.05 mL). For Cohort 1, safety was assessed via electroretinograms (ERGs) and ocular examination. Of nine total groups in Cohort 1, the first five received the following single agents: Group 1: normal saline; Group 2: VP16P 75 µg; Group 3: VP16P 100 µg; Group 4: carboplatin 4 µg; and Group 5: carboplatin 8 µg. Groups 6 through 9 received the following combination of carboplatin/ VP16P, respectively: Group 6: 8 µg/75 µg, Group 7: 8 µg/50 µg, Group 8: 4 µg/50 µg, and Group 9: 2 µg/25 µg. Cohort 2 consisted of 15 Dutch-Belted rabbits in seven groups (Groups 10 through 16), each receiving a single, bilateral intravitreal injection. For Cohort 2, safety was assessed via histopathology.

RESULTS

Groups 2 through 8 demonstrated a statistically significant decrease (relative to Group 1) in at least one ERG waveform amplitude obtained 4 weeks postinjection (P < .05). Group 9 (carbo 2 µg/VP16P 25 µg) did not manifest ERG toxicity. Fundoscopic toxicity consisted of slight-to-moderate attenuation of vessels in rabbits receiving doses above carbo 4 µg/VP16P 50 µg. Histopathologic retinal toxicity (Cohort 2) was dose-dependent, ranging from full-thickness atrophy in rabbits receiving the highest dose to normal in rabbits receiving carbo 2 µg/VP16P 25 µg.

CONCLUSIONS

Combined carboplatin and VP16P may be compatible for intravitreal injection therapy, and a single dose of 2 µg/25 µg appears to be safe in a rabbit model. These agents may be a safer alternative to intravitreal melphalan (Alkeran; GlaxoSmithKline, Brentford, United Kingdom) for the treatment of vitreous seeds in retinoblastoma. [Ophthalmic Surg Lasers Imaging Retina. 2017;48:151-159.].

Constant luminance (cd·s/m2) versus constant retinal illuminance (Td·s) stimulation in flicker ERGs

Purpose

To compare the effect of variable pupil size on the flicker electroretinogram (ERG) between a stimulus having constant luminance and a stimulus having constant retinal illuminance (constant Troland) that compensates for pupil size.

Methods

Subjects (n = 18) were tested with 12 pairs of the stimuli. The stimulus pair consisted of the ISCEV standard constant luminance stimulus (3 cd·s/m² with a 30 cd/m² background) and a constant retinal illuminance stimulus (32 Td·s with a 320 Td background) selected to provide the same stimulus and background when the pupil diameter is 3.7 mm. Half the subjects were artificially dilated, and their response was measured before and during the dilation. The natural pupil group was used to assess intra- and inter-subject variability. The artificially dilated group was used to measure the flicker ERG’s dependence on pupil size.

Results

With natural pupils, intra-subject variability was lower with the constant Troland stimulus, while inter-subject variability was similar between stimuli. During pupil dilation, the constant Troland stimulus did not have a dependence on pupil size up to 6.3 mm and had slightly larger amplitudes with longer implicit times for fully dilated pupils. For the constant luminance stimulus, waveform amplitudes varied by 22% per mm change in pupil diameter, or by 48% over the 2.2 mm diameter range measured in dilated pupil size. There was no difference in inter-subject variability between constant Troland natural pupils and the same subjects with a constant luminance stimulus when dilated (i.e., the ISCEV standard condition).

Conclusions

These results suggest that a constant Troland flicker ERG test with natural pupils may be advantageous in clinical testing. Because of its insensitivity to pupil size, constant Troland stimuli should produce smaller reference ranges, which in turn should improve the sensitivity for detection of abnormalities and for monitoring changes. In addition, the test can be administered more efficiently as it does not require artificial dilation.

Clinical Trial registration number

This trial is registered at ClinicalTrials.gov (NCT02466607).

Acetagastrodin effects on retinal oscillatory potentials in patients during the early stages of diabetes

AIMS

To investigate the protective effect of acetagastrodin on visual electrophysiology in patients with early-stage diabetes.

METHODS

A prospective, randomized, controlled, double-blind trial was conducted. Subjects who were randomly assigned to either the treatment group or the control group were orally administered acetagastrodin or placebo, respectively, for 6 months. The quantity, mean amplitude and mean latency of oscillatory potentials (OPs) wavelets at baseline and 6 months were measured on electroretinogram (ERG), in all subjects.

RESULTS

A total of 92 right eyes in 92 patients with type 2 diabetes, who were diagnosed for the first time, were enrolled. Each group consisted of 46 cases (46 eyes). There was no significant difference in baseline characteristic between treatment and control groups at baseline, but quantity in treatment group was more than that in control group at 6 months (P = 0.001). The mean amplitude of OPs was reduced in the control group 6 months later compared with treatment group (P = 0.001). As to mean latency of OPs, statistical difference was also detectable between the treatment group and control group 6 months later (P < 0.001). No statistical differences were found in hemoglobin between both groups at 6 months (P > 0.05).

CONCLUSIONS

Electrophysiological changes would go on worsening even hemoglobin was under control during the initial stage of diabetes. Acetagastrodin treatment may be an effective treatment to protect retinal neurons against such functional impairment during the early stages of diabetes.

Flat Electroretinography and Acute Visual Loss After Ocriplasmin Injection for Vitreomacular Adhesion Complicating Macular Schisis

A 53-year-old woman with macular and diffuse retinoschisis complicated by presumed vitreomacular traction underwent unilateral intravitreal ocriplasmin injection. Within hours after injection, she noted a loss of vision and the perception of "negative" images in the treated eye. Electrophysiologic testing revealed flat waveforms, and optical coherence tomography (OCT) showed initial decreased central macular thickness at day 1, followed by massive increased macular thickness with subfoveal neurosensory retinal detachment at 1 week. Her central macular thickness on OCT slowly returned to baseline during a period of 1 month until development of a macula-off rhegmatogenous retinal detachment at 6 months after injection. The authors believe this unique case of vitreomacular adhesion and macular schisis complicated by post-injection visual loss and electroretinography changes may offer further insight into this unusual complication.

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.

Vigabatrin can enhance electroretinographic responses in pigmented and albino rats

PURPOSE

To evaluate the effects of the antiepileptic medication vigabatrin (VGB) on the retina of pigmented rats.

METHODS

Scotopic and photopic electroretinograms were recorded from dark- and light-adapted Long-Evans (pigmented) and Sprague Dawley (albino) rats administered, daily, 52-55 injections of 250 mg·kg(-1)·day(-1) VGB or 25-26 injections of 500 mg·kg(-1)·day(-1) VGB, or a corresponding number of sham injections. Sensitivity and saturated amplitude of the rod photoresponse (S, Rm(P3)) and postreceptor response (1/σ, Vm) were derived, as were sensitivity and amplitude of the cone-mediated postreceptor response (1/σ(cone), Vm(cone)). The oscillatory potentials and responses to a series of flickering lights (6.25, 12.5, 25 and 50 Hz) were studied in the time and frequency domains. A subset of rats' eyes was harvested for Western blotting or histology.

RESULTS

Of the parameters derived from dark-adapted ERG responses, in both pigmented and albino rats, VGB repeatedly and reliably enhanced electroretinographic parameters; no significant ERG deficits were noted. No significant alterations were observed in ER/oxidative stress or in the Akt cell death/survival pathway. There were migrations of photoreceptor nuclei toward the RPE and outgrowths of bipolar cell dendrites into the outer nuclear layer in VGB-treated rats; these were never observed in sham-treated animals.

CONCLUSIONS

Although VGB is associated with retinal dysfunction in patients and VGB toxicity has been demonstrated by other laboratories in the albino rat, in our pigmented and albino rats, VGB did not induce deficits in, but rather enhanced, retinal function. Nonetheless, retinal neuronal dysplasia was observed.

Exendin-4 alleviates retinal vascular leakage by protecting the blood-retinal barrier and reducing retinal vascular permeability in diabetic Goto-Kakizaki rats

The breakdown of the inner endothelial blood-retinal barrier (BRB) and subsequent retinal vascular leakage are the main causes of vision loss due to diabetic retinopathy (DR). Exendin-4 (E4) is a long-acting agonist of the glucagon-like peptide 1 hormone receptor (GLP-1R) that is widely used in clinics and has shown a neuroprotective effect. Our previous studies demonstrated the protective effect of E4 in early experimental DR; however, the molecular and cellular mechanisms that mediate this protective effect are not fully known. The BRB plays a key role in DR. We speculated that E4 may exert its protective effects on the BRB. To test this hypothesis, E4 (0.1 μg/2 μL/eye) or vehicle were intravitreally injected into diabetic Goto-Kakizaki(GK) rats and control animals. The results revealed that E4 significantly inhibited the reductions in electroretinogram (ERG) amplitudes in the GK rats, particularly in the b-wave and oscillatory potentials (OPs). E4 upregulated retinal GLP-1R expression and downregulated the expressions of placental growth factor (PLGF) and vascular endothelial growth factor (VEGF) via the ERK and AKT/PKB pathways. Decreases in tight junction protein (i.e., claudin-5 and occludin) expression and increases in Evans blue permeation (EBP) were inhibited by E4. Similar results were also found in primary rat Müller cells in high glucose concentration cultures in vitro. We conclude that E4 may protect the BRB from diabetic insults by decreasing PLGF and ICAM-1 expression and maintaining the integrity of the BRB. Thus, E4 treatment may be an effective therapeutic approach for DR.

Chlorogenic acid supplementation improves multifocal electroretinography in patients with retinitis pigmentosa

To evaluate the effect of chlorogenic acid supplementation in patients with retinitis pigmentosa, we evaluated objective change in visual function with multifocal electroretinography, along with visual acuity, visual field, standard electroretinography, and contrast sensitivity. Eighteen patients diagnosed with retinitis pigmentosa were enrolled in this prospective, non-comparative, single-arm study. Multifocal electroretinography, best-corrected visual acuity in Early Treatment Diabetic Retinopathy Study letters, total point score on visual field examination with Humphrey Field Analyzer II, electroretinography, and contrast sensitivity were measured and repeated after 3 months supplementation with chlorogenic acid. The amplitude of ring 5 was significantly higher on multifocal electroretinography after 3 months of chlorogenic acid supplementation (7.2 ± 9.5 vs 8.3 ± 10.8 nV/deg(2), mean ± standard deviation, P = 0.022). There were no significant changes in the best-corrected visual acuity, total point score on Humphrey Field Analyzer, 30 Hz flicker amplitude on standard electroretinography, or contrast sensitivity. Chlorogenic acid may have a beneficial effect on the peripheral area at the margins of retinal degeneration, and should be considered as an anti-oxidant for the management of retinitis pigmentosa.

Effects of dopamine receptor blockade on the intensity-response function of ERG b- and d-waves in dark adapted eyes

The effects of dopamine receptor blockade by sulpiride (D2-class antagonist) and sulpiride plus SCH 23390 (D1-class antagonist) on the V - log I function of the ERG b- and d-waves were investigated in dark adapted frog eyes. We observed that sulpiride enhanced the amplitude of the suprathreshold b- and d-waves in the lower intensity range, where the responses were mediated by rods, but diminished it in the higher intensity range, where the responses were mediated by cones. A similar effect on the b-, but not d-wave amplitude was seen during the perfusion with sulpiride plus SCH 23390. The d-wave amplitude was enhanced over the whole intensity range with the exception of the highest intensities during the combined D1 and D2 receptor blockade. The results obtained indicate that the endogenous dopamine has an overall inhibitory action on the suprathreshold rod-mediated ON and OFF responses, while its action on the cone-mediated responses shows clear ON-OFF asymmetry. It is excitatory upon the ON responses, but inhibitory upon the OFF responses except for those in the highest intensity range. Participation of different types of dopamine receptors (predominantly D2 for the ON versus D1 for the OFF response) is probably responsible for this difference.

A microparticle/hydrogel combination drug-delivery system for sustained release of retinoids

PURPOSE

To design and develop a drug-delivery system containing a combination of poly(D,L-lactide-co-glycolide) (PLGA) microparticles and alginate hydrogel for sustained release of retinoids to treat retinal blinding diseases that result from an inadequate supply of retinol and generation of 11-cis-retinal.

METHODS

To study drug release in vivo, either the drug-loaded microparticle-hydrogel combination was injected subcutaneously or drug-loaded microparticles were injected intravitreally into Lrat(-/-) mice. Orally administered 9-cis-retinoids were used for comparison and drug concentrations in plasma were determined by HPLC. Electroretinography (ERG) and both chemical and histologic analyses were used to evaluate drug effects on visual function and morphology.

RESULTS

Lrat(-/-) mice demonstrated sustained drug release from the microparticle/hydrogel combination that lasted 4 weeks after subcutaneous injection. Drug concentrations in plasma of the control group treated with the same oral dose rose to higher levels for 6-7 hours but then dropped markedly by 24 hours. Significantly increased ERG responses and a markedly improved retinal pigmented epithelium (RPE)-rod outer segment (ROS) interface were observed after subcutaneous injection of the drug-loaded delivery combination. Intravitreal injection of just 2% of the systemic dose of drug-loaded microparticles provided comparable therapeutic efficacy.

CONCLUSIONS

Sustained release of therapeutic levels of 9-cis-retinoids was achieved in Lrat(-/-) mice by subcutaneous injection in a microparticle/hydrogel drug-delivery system. Both subcutaneous and intravitreal injections of drug-loaded microparticles into Lrat(-/-) mice improved visual function and retinal structure.

Anthocyanins from the seed coat of black soybean reduce retinal degeneration induced by N-methyl-N-nitrosourea

Anthocyanins are known to have antioxidant effects and thus may play an important role in preventing various degenerative diseases. In this study, we examined the effect of anthocyanins extracted from the seed coat of black soybean on an animal model of retinal degeneration (RD), a leading cause of photoreceptor cell death resulting in blindness. RD was induced in rats by an intraperitoneal injection of N-methyl-N-nitrosourea (MNU) (50mg/kg), a DNA-methylating agent that causes photoreceptor damage. Anthocyanins extracted from black soybean seed coat (50mg/kg) were daily administered, orally, for 1, 2, and 4 weeks after MNU injection. Electroretinographic (ERG) recordings and morphological analyses were performed. In control rats with MNU-induced retinal damage, the ERG recordings showed a gradual significant time-dependent reduction in both a- and b-wave amplitudes compared with those of normal animals. In the MNU-induced RD rats given anthocyanins for 4 weeks, ERG responses were significantly increased compared with untreated RD rats, more apparently in scotopic stimulation than in the photopic condition. However, in the MNU-injected rats given anthocyanins for 1 and 2 weeks, the increase in ERG responses was not significant. Morphologically, the outer nuclear layer, where photoreceptors reside, was well preserved in the anthocyanin-treated rat retinas throughout the experimental period. In addition, retinal injury, evaluated by immunolabeling with an antibody against glial fibrillary acidic protein, was markedly reduced in anthocyanin-treated retinas. These results demonstrate that anthocyanins extracted from black soybean seeds can protect retinal neurons from MNU-induced structural and functional damages, suggesting that anthocyanins from black soybean seed coat may be used as a useful supplement to modulate RD.

Processing of retinal signals in normal and HCN deficient mice

This study investigates the role of two different HCN channel isoforms in the light response of the outer retina. Taking advantage of HCN-deficient mice models and of in vitro (patch-clamp) and in vivo (ERG) recordings of retinal activity we show that HCN1 and HCN2 channels are expressed at distinct retinal sites and serve different functions. Specifically, HCN1 operate mainly at the level of the photoreceptor inner segment from where, together with other voltage sensitive channels, they control the time course of the response to bright light. Conversely, HCN2 channels are mainly expressed on the dendrites of bipolar cells and affect the response to dim lights. Single cell recordings in HCN1^−/− mice or during a pharmacological blockade of I_h show that, contrary to previous reports, I_kx alone is able to generate the fast initial transient in the rod bright flash response. Here we demonstrate that the relative contribution of I_h and I_kx to the rods' temporal tuning depends on the membrane potential. This is the first instance in which the light response of normal and HCN1- or HCN2-deficient mice is analyzed in single cells in retinal slice preparations and in integrated full field ERG responses from intact animals. This comparison reveals a high degree of correlation between single cell current clamp data and ERG measurements. A novel picture emerges showing that the temporal profile of the visual response to dim and bright luminance changes is separately determined by the coordinated gating of distinct voltage dependent conductances in photoreceptors and bipolar cells.

Therapeutic benefit of melatonin in experimental feline uveitis

Uveitis is a frequent ophthalmic disorder which constitutes one of the main causes of blindness in domestic cats. The aim of this report was to analyze the effect of melatonin on experimentally induced uveitis in cats. Bacterial lipopolysaccharide (LPS) was injected intravitreally into one eye from intact cats, while the contralateral eye was injected with vehicle. Melatonin was orally administered every 24 hr to a group of ten cats, from 24 hr before until 45 days after intravitreal injections. Eyes were evaluated by means of clinical evaluation, intraocular pressure (IOP), blood-ocular barrier integrity (via measurement of protein concentration and cell content in samples of aqueous humor [AH]), electroretinogram (ERG), and histological examination of the retinas. In LPS-treated eyes, several clinical signs were observed until day 45 postinjection. The treatment with melatonin significantly decreased clinical signs and prevented the reduction in IOP induced by LPS. In LPS-injected eyes, melatonin significantly preserved the blood-ocular barrier integrity, as shown by a decrease in the number of infiltrating cells and protein concentration in the AH. Mean amplitudes of scotopic ERG a- and b-waves were significantly reduced in eyes injected with LPS, whereas melatonin significantly prevented the effect of LPS. At 45 days after injection, LPS induced alterations in photoreceptors and at the middle portion of the retina, whereas melatonin preserved the retinal structure. These results indicate that melatonin prevented clinical, biochemical, functional, and histological alterations induced by LPS injection. Thus, melatonin might constitute a useful tool for the treatment of feline uveitis.

Retinal disorders in northern Brazilian patients treated with chloroquine assessed by multifocal ERG

The effects of chloroquine intake on the retinal function in a Brazilian population of patients were assessed by multifocal electroretinography. Twenty-four randomly chosen eyes of patients treated with chloroquine for rheumatoid arthritis and systemic lupus erythematosus were examined using multifocal electroretinography (mfERG). Control measurements were acquired from 21 randomly chosen eyes of age-matched healthy subjects. None of the study participants had an inherited retinal disease or a Snellen visual acuity reduced to less than 20/40. In patients and control subjects, cumulative chloroquine dose, total daily dose, duration of treatment, retinal examination, visual field defects, visual acuity, and the mfERG were assessed. The average amplitudes and implicit times of the N1, P1, and P2 components of the mfERGs were measured in the central hexagon (R1) and in five rings (R2-R6). The values measured in patients and normal subjects were compared. The P1 amplitudes in R2 were significantly decreased in the patients. In addition, the amplitudes of N1 and N2 in R1 were significantly smaller in the patients. The implicit times of none of the components were significantly different between patients and controls. The response amplitude was not significantly correlated with cumulative dose and duration of intake. There was no correlation with retinal appearance, visual field, and visual acuity. In agreement with earlier data, the central mfERG amplitudes were decreased in chloroquine patients indicating functional alterations in the retina. These changes are also present in a Brazilian population suggesting that the effects of chloroquine are general and that genetic background and life circumstances probably have, if at all, only little effect.

Effects of red ginseng extract on visual sensitivity and ERG b-wave of bullfrog's eye

The purpose of the present study was to investigate the effect of red ginseng (Panax ginseng) extracts on the visual process in bullfrog's eye. The results obtained indicated that both dark-adapted and light-adapted ERG b-wave peak amplitude was increased with red ginseng treatment. Furthermore, the ERG sensitivity was elevated by 1.4 log units of light intensity. It was found that red ginseng acts as a retinal neural antagonist but not as a GABA receptor antagonist. Red ginseng improved the alcohol dehydrogenase activity and speeded up the delivery of 11 CIS-retinal from retinal pigment epithelium (RPE) to the outer disc of the photoreceptors which resulted in decreased regeneration time of rhodopsin. In the spectral scan, red ginseng treatment brings an increment in absorbance over the whole spectral range (300-800 nm) with maximum difference at around 500 nm. It is concluded that red ginseng may be used to improve visual process, and can potentially be used to treat certain ophthalmic diseases.

Antagonists of ionotropic gamma-aminobutyric acid receptors impair the NiCl2-mediated stimulation of the electroretinogram b-wave amplitude from the isolated superfused vertebrate retina

PURPOSE

NiCl(2) (15 microM) stimulates the electroretinogram (ERG) b-wave amplitude of vertebrate retina up to 1.5-fold through its blocking of E/R-type voltage-gated Ca(2+) channels. Assuming that such an increase is mediated by blocking the release of the inhibitory neurotransmitter gamma-aminobutyric acid (GABA) via ionotropic GABA receptors, we tested the effect of both GABA itself and GABA-receptor antagonists such as (-)bicuculline (1.51-fold increase) and (1,2,5,6-tetrahydropyridin-4-yl)methylphosphinic acid (TPMPA; 1.46-fold increase) on the b-wave amplitude.

METHODS

Recording of the transretinal potentials from the isolated bovine retina.

RESULTS

GABA (100 microM) reduced the b-wave amplitude only when NiCl(2) (15 microM) was applied first. Each antagonist applied on its own stimulated the b-wave amplitude only partially: subsequent NiCl(2) superfusion caused a small but additional increase, leading to a 1.69- and a 1.88-fold total increase of the amplitude by Ni(2+) plus (-)bicuculline or Ni(2+) plus TPMPA, respectively. Only the application of both antagonists in combination, before superfusing low NiCl(2) (15 microM), completely prevented subsequent stimulation by NiCl(2) with a similar 1.90-fold total increase of b-wave amplitude. Those retina segments that did not respond to NiCl(2) could not be stimulated by (-)bicuculline and vice versa.

CONCLUSION

The stimulatory effect of NiCl(2) on the ERG b-wave amplitude is mainly, but not only, mediated by a NiCl(2)-sensitive, Ca(v)2.3-triggered GABA release acting through ionotropic GABA-A and GABA-C receptors.

Safety and Pharmacokinetics of an Intravitreal Biodegradable Implant of Dexamethasone Acetate in Rabbit Eyes

The treatment of vitreoretinal diseases is limited and, nowadays, new drug delivery approaches have been reported in order to increase drug bioavailability. The objective of the current study was to determine the pharmacokinetic profile of a biodegradable dexamethasone acetate implant inserted into the vitreous of rabbits and to evaluate its potential signs of toxicity to the rabbits' eyes. The results showed that the intravitreous drug concentration remained within the therapeutic range along the 8-week period of evaluation. The system under study was not toxic to the normal rabbit retina, and no significant increase in intraocular pressure was observed.

Effects of Kallidinogenase on Ischemic Changes Induced by Repeated Intravitreal Injections of Endothelin-1 in Rabbit Retina

PURPOSE

Repeated intravitreal injections of endothelin-1 (ET-1) lead to alterations in the visually evoked potentials (VEPs) and loss of retinal ganglion cells (RGCs) in rabbits. The purpose of this study was to determine whether kallidinogenase can offset the alterations induced by ET-1.

METHODS

ET-1 (2.5 x 10(-7) M, 20 microL) was injected into the vitreous of the right eye of rabbits (ET-1-treated eyes, n = 30) twice a week for 4 weeks. The vehicle for ET-1 was injected into the left eye on the same schedule (vehicle treated eyes, n = 30). During this 4 weeks period, kallidinogenase (1.0 unit/kg/day, kallidinogenase-treated group) or saline (saline-injected control group) was continuously delivered intravenously by an implanted osmotic pump. VEPs were recorded before, and 2 weeks and 4 weeks after, the first ET-1 injection, and all rabbits were sacrificed at 4 weeks. The number of RGC cells was counted in hematoxylin- and eosin-stained retinal sections. In the analyses, the ET-1 induced alterations were normalized to the values in the vehicle treated control eyes, i.e., kallidinogenase (K) + ET-1/K+ vehicle or saline (S) +ET-1/S + vehicle. Retinal sections were also examined by immunohistochemistry with antibodies to single-stranded DNA (ssDNA) or to glial fibrillary acidic protein (GFAP). The effect of kallidinogenase on the ONH blood flow was determined by a hydrogen gas clearance flowmeter.

RESULTS

The significant prolongation of the relative VEP implicit times (ITs) 4 weeks after the ET-1 injection (P < 0.01, paired t test; post-ET-1 vs. pre-ET-1) was significantly decreased by kallidinogenase (P < 0.001, t test, K + ET-1/K+ vehicle vs. S +ET-1/S + vehicle). The relative number of RGCs was decreased in the saline-injected group, and this decrease was also decreased by kallidinogenase (P < 0.05, t test, K + ET-1/K+ vehicle vs. S +ET-1/S + vehicle). ssDNA staining showed fewer apoptotic cells in the retina of kallidinogenase-treated rabbits. Intravitreal injection of ET-1 also decreased the blood flow in the optic nerve head and increased the GFAP immunostaining and axonal degeneration. These changes were also counteracted by kallidinogenase.

CONCLUSION

These results indicate that kallidinogenase can counter the effects of ET-1 and should be considered for the treatment of ischemic retinal and optic nerve disorders related to abnormal ET-1 production.

Retinal Toxicity of Intraocular Vancomycin and Ceftazidime in Vitrectomized Rabbit Eyes

The purpose of this study was to evaluate the retinal toxicity of vancomycin and ceftazidime combined into an infusion solution that was intraoculary given after or during vitrectomy. Forty albino rabbits were divided into 4 groups of 10 each. Vitrectomized right eyes of groups 1, 2, and 3 were given recommended doses of vancomycin and ceftazidime alone or combined, while right eyes in the fourth group were vitrectomized using an infusion solution to which was added ceftazidime and vancomycin combination. Toxicity was tested with electroretinography (ERG) and light microscopy. ERG and light microscopy did not show any toxicity signs associated with vancomycin or ceftazidime alone or with combined therapy. Vancomycin and/or ceftazidime can reliably and effectively be used combined in an infusion solution at recommended doses after and during vitrectomy. This treatment modality does not have any toxic effects to retinal structures and is an alternative method to separate injections of the two antimicrobial agents.

The dihydropyridine isradipine inhibits the murine but not the bovine A-wave response of the electroretinogram

PURPOSE

In order to record light-evoked responses from photoreceptor cells and the higher neuronal retinal network, the isolated vertebrate retina represents a sensitive tool for basic research of retinal function and for testing the toxicity of ocular therapeutics. In the past, this in vitro technique was optimized for frog and bovine retina; it should be transferred now to the isolated murine retina because the model could allow for functional testing of genes involved in retinal signalling using wild-type and gene-inactivated mice. Thus, alterations in the electroretinogram (ERG) may reveal differences in retinal information processing because of the inactivation of a specific gene.

METHODS

We used a superfused vertebrate retina assay to test bovine and murine retina.

RESULTS

In order to evaluate the sensitivity of the ERG recording technique from the isolated murine retina, we first determined the light intensity response and the stability of the a-wave amplitude during ERG recording, which did not differ between the species. However, testing the dihydropyridine sensitivity of the a-wave, we found that the murine a-wave was highly sensitive towards racemic isradipine (8-25 nM) but the bovine retina a-wave was not. A similar species-dependent difference was observed for mibefradil (10 muM).

CONCLUSION

Murine and bovine retina differ with respect to transretinal signalling. At the level of photoreceptor cells, the ERG/a-wave is modulated by isradipine-sensitive voltage-gated Ca(2+) channels, which trigger feedback signalling to photoreceptors.

Low-level human equivalent gestational lead exposure produces supernormal scotopic electroretinograms, increased retinal neurogenesis, and decreased retinal dopamine utilization in rats

BACKGROUND

Postnatal lead exposure in children and animals produces alterations in the visual system primarily characterized by decreases in the rod-mediated (scotopic) electroretinogram (ERG) amplitude (subnormality). In contrast, low-level gestational Pb exposure (GLE) increases the amplitude of scotopic ERGs in children (supernormality).

OBJECTIVES

The goal of this study was to establish a rat model of human equivalent GLE and to determine dose-response effects on scotopic ERGs and on retinal morphology, biochemistry, and dopamine metabolism in adult offspring.

METHODS

We exposed female Long-Evans hooded rats to water containing 0, 27 (low), 55 (moderate), or 109 (high) ppm of Pb beginning 2 weeks before mating, throughout gestation, and until postnatal day (PND) 10. We measured maternal and litter indices, blood Pb concentrations (BPb), retinal Pb concentrations, zinc concentrations, and body weights. On PND90, we performed the retinal experiments.

RESULTS

Peak BPb concentrations were < 1, 12, 24, and 46 microg/dL in control, low-, moderate- and high-level GLE groups, respectively, at PNDs 0-10. ERG supernormality and an increased rod photoreceptor and rod bipolar cell neurogenesis occurred with low- and moderate-level GLE. In contrast, high-level GLE produced ERG subnormality, rod cell loss, and decreased retinal Zn levels. GLE produced dose-dependent decreases in dopamine and its utilization.

CONCLUSIONS

Low- and moderate-level GLE produced persistent scotopic ERG supernormality due to an increased neurogenesis of cells in the rod signaling pathway and/or decreased dopamine utilization, whereas high-level GLE produced rod-selective toxicity characterized by ERG subnormality. The ERG is a differential and noninvasive biomarker of GLE. The inverted U-shaped dose-response curves reveal the sensitivity and vulnerability of the developing retina to GLE.

[Chloroquine/hydroxychloroquine: variability of retinotoxic cumulative doses]

OBJECTIVE

The critical dose of chloroquine/hydroxychloroquine leading to a maculopathy or generalised retinopathy remains undetermined. In the literature, 100 g is considered the dose at which regular vision checks should be performed. Generally, chloroquine is said to be more toxic than hydroxychloroquine. A young patient presenting with toxic maculopathy after 57 g of hydroxychloroquine and a daily dosage of 2 mg/kg body weight prompted us to retrospectively look at our patients examined in this respect over about 1 year.

METHODS

The data of patients who were examined because of chloroquine/hydroxychloroquine intake or a respective maculopathy/retinopathy were retrospectively analysed. The time period was January 2005 until March 2006. Retinal damage was defined by fundus changes and alteration of the multifocal electroretinogram (ERG).

RESULTS

Twenty-one patients--18 women and three men--were examined. The mean age was 51 years (range 6-71). Five of the nine chloroquine-treated patients developed a maculopathy, and one of them developed an additional generalised retinopathy. Of the patients treated by hydroxychloroquine, three of 12 suffered from a maculopathy and one from an additional generalised retinopathy. The cumulative doses leading to retinal damage ranged from 170 g to 1650 g for chloroquine and from 57 g to 1190 g for hydroxychloroquine. The highest cumulative doses without leading to signs of retinopathy were 790 g for chloroquine and 1200 g for hydroxychloroquine.

CONCLUSIONS

There is a high variability of cumulative doses of chloroquine/hydroxychloroquine that lead to a toxic retinopathy. Therefore, early and regular ophthalmologic examinations are recommended. Electrophysiological testing should be performed once a year, corresponding to about 60 g of base with one tablet a day. For electrophysiology, the multifocal ERG has turned out to be the most important test in this regard. However, visual acuity and funduscopy should be performed more frequently.

Safety of intravitreally administered recombinant erythropoietin (an AOS thesis)

PURPOSE

This study investigated the safety and potential retinal toxicity of intravitreally administered erythropoietin (EPO) in a rodent animal model.

METHODS

Forty-two healthy Sprague-Dawley rats were divided into one of 7 groups (N = 6 per group): control, sham injection, vehicle injection, and EPO injections of 50 ng (5 U), 100 ng (10 U), 250 ng (25 U), and 625 ng (62.5 U). Only the right eye was treated in each animal. Standard full-field dark- and light-adapted electroretinography (ERG) was obtained at 1 day prior to injection and then on postinjection days 3, 7, 14, and 21. Intraocular pressure (IOP) was measured at the conclusion of each ERG recording. Animals were sacrificed and the eyes underwent histologic examination with light microscopy and hematoxylin-eosin staining.

RESULTS

Rod peak, scotopic, and photopic responses (amplitude and latency) were not statistically different in the animals receiving 50 to 100 ng EPO. In the 250-ng group, the photopic b-wave amplitude at day 21 was elevated (P <.05), whereas in the 625-ng group, the scotopic OP3 latency ratio was higher at baseline (P <.05). No significant histologic abnormalities were noted except for one animal (625-ng group) with qualitative differences in retinal layer thickness and cellular density.

CONCLUSIONS

Intravitreal administration of EPO (at doses up to 625 ng) does not cause adverse effects on retinal function as assessed by ERG. Moreover, single intravitreal dosing does not appear to elicit retinal neovascularization. Further investigation is warranted to assess fully the potential of this neuroprotective cytokine as a treatment for glaucoma.

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.

Test of the paired-flash electroretinographic method in mice lacking b-waves

Previous studies of rod photoreceptors in vivo have employed a paired-flash electroretinographic (ERG) technique to determine rod response properties. To test whether absence versus presence of the ERG b-wave affects the photoreceptor response derived by the paired-flash method, we examined paired-flash-derived responses obtained from nob mice, a mutant strain with a defect in signal transduction between photoreceptors and ON bipolar cells that causes a lack of the b-wave. Normal littermates of the nob mice served as controls. The normalized amplitude-intensity relation of the derived response determined in nob mice at the near-peak time of 86 ms was similar to that determined for the controls. The full time course of the derived rod response was obtained for test flash strengths ranging from 0.11 to 17.38 scotopic cd s m(-2) (sc cd s m(-2)). Time-course data obtained from nob and control mice exhibited significant but generally modest differences. With saturating test flash strengths, half-recovery times for the derived response of nob versus control mice differed by approximately 60 ms or less about the combined (nob and control) average respective values. Time course data also were obtained before versus after intravitreal injection of L-2-amino-4-phosphonobutyrate (APB) (which blocks transmission from photoreceptors to depolarizing bipolar cells) and of cis 2,3-piperidine dicarboxylic acid (PDA) (which blocks transmission to OFF bipolar cells, and to horizontal, amacrine and ganglion cells). Neither APB nor PDA substantially affected derived responses obtained from nob or control mice. The results provide quantitative information on the effect of b-wave removal on the paired-flash-derived response in mouse. They argue against a substantial skewing effect of the b-wave on the paired-flash-derived response obtained in normal mice and are consistent with the notion that, to good approximation, this derived response represents the isolated flash response of the photoreceptors in both nob and normal mice.

Electronegative electroretinogram associated with topiramate toxicity and vitelliform maculopathy

Topiramate is known to cause ocular side effects such as refractive changes and angle closure. We describe a patient with an electronegative electroretinogram (ERG) which may have been related to topiramate use. Electronegative ERG's have been associated with other drugs in humans as well as topiramate use in rabbits. However, this would be the first suggestion of causality in humans.

Retinal safety of a new fluoroquinolone, pradofloxacin, in cats: assessment with electroretinography

PURPOSE

To investigate the safety of a new fluoroquinolone, pradofloxacin, on the cat retina using electroretinogram.

METHODS

Ganzfeld ERGs were recorded in 40 cats treated orally for 23 days in 4 groups: CTRL (n = 9): placebo-vehicle; PRADO30 (n = 10): pradofloxacin 30 mg/kg/day; PRADO50 (n = 14): pradofloxacin 50 mg/kg/day; and ENRO30 (n = 7): enrofloxacin at toxic doses of 30 mg/kg/day. ERG was performed before treatment and once weekly during the treatment period. An extended ISCEV protocol with addition of 8 steps of increasing luminance in dark adapted condition was carried out to assess: V (max) (saturated scotopic b-wave amplitude) and k (luminance inducing V (max)/2). OCT and retinal histological changes were also investigated.

RESULTS

Pradofloxacin showed no effects in respect to rod b-wave, V (max), k and maximum scotopic a-wave (P > 0.05). Oscillatory potentials, cone ERG and flicker were also unaltered (P > 0.05). Rod b-wave was undetectable after treatment in ENRO30 group, V (max) was reduced to 10.5% of the baseline (P < 0.05), accompanied by an increase of k by 1 log cd s/m(2) (P < 0.05). Oscillatory potentials, cone b-wave amplitude and 30 Hz flicker amplitude were reduced to 8.3%, 58.9% and 37.4% of the baseline, respectively (P < 0.05). Effects were also seen in OCT and retinal histology starting within one week after the start of treatment and thereafter remaining stable.

CONCLUSION

Pradofloxacin at 6 and 10 times the recommended doses was shown to have no retinal toxic effects in cats, neither on rod or cone function with ERG.

[Impact of ozone therapy on the electrophysiological parameters of the retina in patients operated on for its rhegmatogenous detachment]

The impact of ozone therapy on changes in the data of maximum combined electroretinography (ERG), macular ERG (MERG), and rhythmic ERG (RERG) at 12, 32, and 40 Hz was studied in the rehabilitative period in patients operated on for rhegmatogenous retinal detachment. The integral and local glial indices K(g) and K(c) were calculated. Studies were conducted before, within 1 week and 1 and 2 months after a course of therapy. With ozone therapy, ERG and RERG depended on the specific features of changes available in the fundus of the eye before surgery. In the early rehabilitative period after surgery (circlage with subretinal fluid removal), ozone therapy normalized the glial indices, by decreasing the supernormal activity of Muller's glial cells and drastically increasing their reduced activity. The maximum effect was revealed for the function of phororeceptors (except for the eyes showing pronounced myopic dystrophic changes in the fundus). There were increases in MERG, ERG b-wave, and low-frequency RERG by 12 Hz, i.e. improved functions of the macular region and distal neurons of the retinal rod cell system. A latent period was established for the manifestation of a positive effect of ozonwe therapy on the functional of neurons of the internal retinal nuclear layer, as evidenced by RERG changes. Ozone therapy positively affect retinal electrogenesis in cases of total retinal detachment accompanied by a pronounced reduction in the glial index Kg before surgery. The therapy was found to have a positive impact on the functional activity of the retina of pair eyes, by developing within a one-moth latent period.

Pharmacologically defined components of the normal porcine multifocal ERG

Multifocal electroretinograms (mfERG) from isoflurane anesthetized pigs were recorded and sequential application of TTX, NMDA, APB and PDA were used to identify contributions to the mfERG from inner retinal neurons, ON-pathway, OFF-pathway and photoreceptors. The cellular origins of the first-order kernel (K1) and the first slice of the second-order kernel (K2.1) porcine mfERG are contributed from both inner and outer retina. For the K1 waveform, the n1 involved responses of cone photoreceptors and OFF-bipolar cells. The leading edge of p1 is dominated by ON-bipolar cell depolarization. The rear edge of p1, n2 and p2 are dominated by ON-bipolar activities and shaped by the activities of OFF-bipolar cells and retinal cells with NMDAr and voltage-gated sodium channels other than ganglion cells. The p3 is mainly inner retinal activities. For the K2.1 waveform, the p1 and n1 are the summation of activities of ON-, OFF-bipolar cells and retinal cells rich in NMDAr and voltage-gated sodium channels other than ganglion cells. The p2 seems to be related to the ganglion cells. Better understanding of the cellular origins of the normal porcine mfERG will be useful for comparing and defining the functional changes that may occur in diseased retinas.

Polylactic acid for visualizing the vitreous body during vitrectomy

PURPOSE

To investigate the possibility of using polylactic acid (PLA) as a surgical adjuvant for visualizing the vitreous body during vitrectomy.

METHODS

After a core vitrectomy, 1 mL of PLA suspension was injected into the rabbit vitreous in two groups: group A, 2.5% PLA (n = 5), and group B, 1% PLA (n = 9). Vehicle injection instead of PLA was used as a control (group C, n = 5). The clinical signs and electroretinogram (ERG) were evaluated for 28 days, and histologic findings were evaluated on day 28. Next, intraocular pressure (IOP) after intracameral injection of a PLA suspension was evaluated in the rabbits (n = 6). Last, the visualization of the vitreous body by PLA suspension was evaluated during vitrectomy in monkey eyes (n = 4).

RESULTS

The white granules of PLA disappeared from the vitreous cavity in 10 eyes within 3 weeks; however, a small amount of PLA remained in four eyes for 4 weeks. Mild inflammation of the anterior chamber was observed in one eye in group B and 1 eye in group C. No cataract or retinal hemorrhage was found in any eyes. The amplitude of ERG on each time point did not differ between the groups. IOP remained within normal range except for the initial spike. Retinal structure was well preserved histologically. During vitrectomy in monkey eyes, the vitreous body was well visualized, and the posterior vitreous separation was performed easily and safely.

CONCLUSIONS

PLA can be a new surgical adjuvant to visualize the vitreous body during vitrectomy.

Carotenoids and antioxidants in age-related maculopathy italian study: multifocal electroretinogram modifications after 1 year

OBJECTIVE

To evaluate the influence of short-term carotenoid and antioxidant supplementation on retinal function in nonadvanced age-related macular degeneration (AMD).

DESIGN

Randomized controlled trial.

PARTICIPANTS

Twenty-seven patients with nonadvanced AMD and visual acuity > or =0.2 logarithm of the minimum angle of resolution were enrolled and randomly divided into 2 age-similar groups: 15 patients had oral supplementation of vitamin C (180 mg), vitamin E (30 mg), zinc (22.5 mg), copper (1 mg), lutein (10 mg), zeaxanthin (1 mg), and astaxanthin (4 mg) (AZYR SIFI, Catania, Italy) daily for 12 months (treated AMD [T-AMD] group; mean age, 69.4+/-4.31 years; 15 eyes); 12 patients had no dietary supplementation during the same period (nontreated AMD [NT-AMD] group; mean age, 69.7+/-6.23 years; 12 eyes). At baseline, they were compared with 15 age-similar healthy controls.

METHODS

Multifocal electroretinograms in response to 61 M-stimuli presented to the central 20 degrees of the visual field were assessed in pretreatment (baseline) conditions and, in nonadvanced AMD patients, after 6 and 12 months.

MAIN OUTCOME MEASURES

Multifocal electroretinogram response amplitude densities (RAD, nanovolt/deg(2)) of the N1-P1 component of first-order binary kernels measured from 5 retinal eccentricity areas between the fovea and midperiphery: 0 degrees to 2.5 degrees (R1), 2.5 degrees to 5 degrees (R2), 5 degrees to 10 degrees (R3), 10 degrees to 15 degrees (R4), and 15 degrees to 20 degrees (R5).

RESULTS

At baseline, we observed highly significant reductions of N1-P1 RADs of R1 and R2 in T-AMD and NT-AMD patients when compared with healthy controls (1-way analysis of variance P<0.01). N1-P1 RADs of R3-R5 observed in T-AMD and NT-AMD were not significantly different (P>0.05) from controls. No significant differences (P>0.05) were observed in N1-P1 RADs of R1-R5 between T-AMD and NT-AMD at baseline. After 6 and 12 months of treatment, T-AMD eyes showed highly significant increases in N1-P1 RADs of R1 and R2 (P<0.01), whereas no significant (P>0.05) change was observed in N1-P1 RADs of R3-R5. No significant (P>0.05) changes were found in N1-P1 RADs of R1-R5 in NT-AMD eyes.

CONCLUSIONS

In nonadvanced AMD eyes, a selective dysfunction in the central retina (0 degrees -5 degrees ) can be improved by the supplementation with carotenoids and antioxidants. No functional changes are present in the more peripheral (5 degrees -20 degrees ) retinal areas.

Safety monitoring in bevacizumab (Avastin) treatment: retinal function assessed by psychophysical (visual fields, colour vision) and electrophysiological (ERG/EOG) tests in two subgroups of patients

BACKGROUND

Bevacizumab (Avastin) has been used as off-label treatment for the specific inhibition of the vascular endothelial growth factor (VEGF). Although only intravenous administration of the drug is approved in combination therapy of colorectal carcinoma, promising short-term results have been reported about its intravitreal administration. However, VEGF is also known to exhibit neurotrophic capabilities. Therefore, blockage of all VEGF isoforms by bevacizumab could induce toxic effects. Missing randomized controlled studies and unclear long-term risks require further evaluation.

METHODS

Intensified monitoring of bevacizumab treatment was performed in consecutive patients. In ten patients, the functional field score was calculated after obtaining Goldmann visual fields at baseline and 1 year after injection. The other subgroup was examined by means of EOG, ERG and colour testing at baseline and 4 months following treatment. Naka-Rushton plots were calculated to enable statements about retinal function. Lanthony desaturated D15 test was used for repeated colour testing.

RESULTS

Baseline parameters already disclosed predominant cone dysfunction. Drug-related effects caused a significant improvement of visual acuity. There was no sign of clinically relevant retinal toxicity following the bevacizumab injection. No progression of visual field defects was seen within the follow-up of 1 year. Performance in EOG testing was affected by restricted fixation stability, but no parameter indicated deterioration within the 4-month-period.

CONCLUSIONS

Short-term results underline that intraocular bevacizumab injection promises to be not only a cost-effective, but safe treatment option. Assessed functional parameters as error scores (e.g., Lanthony) corresponded to the impaired retinal function which was presumed to be disease-related. Further long-term results have to confirm the good tolerability in repeated treatment.

RETINAL TOXICITY OF INTRAVITREAL KENALOG IN ALBINO RABBITS

PURPOSE

To evaluate possible toxicity of intravitreal Kenalog (commercial triamcinolone acetonide) to the retina of albino rabbits.

METHODS

Forty-three albino rabbits were injected intravitreally with 0.1 mL of experimental solution to the right eye and 0.1 mL of saline to the left eye (control). Rabbits in Group A (n=28) were injected with 4 mg/0.1 mL of Kenalog suspension; rabbits in Group B (n=8) were injected with 0.1 mL of Kenalog vehicle; and rabbits in Group C (n=7) were injected with 4 mg/0.1 mL of triamcinolone acetonide. Rabbits were examined ophthalmoscopically and by electroretinogram (ERG) recordings before and at different time intervals after injection. At the end of follow-up, animals were killed and the retinas were prepared for light microscopy.

RESULTS

Thirty-eight rabbits completed 4 weeks of follow-up. Follow-up for 8 and 17 weeks was completed by 29 and 3 rabbits, respectively. Intravitreal commercial Kenalog or its vehicle alone caused approximately 50% reduction in the ERG b-wave amplitude at the end of follow-up. Pure triamcinolone acetonide caused only mild (up to 14%) reduction of the ERG b-wave amplitude. Histologic examination of retinas exposed to Kenalog or its vehicle showed severe damage to all retinal layers in areas close to the site of Kenalog injection.

CONCLUSIONS

Intravitreal injection of 4 mg Kenalog suspension is retinotoxic to albino rabbit eyes. The vehicle of Kenalog is probably the main cause of this toxicity.

Influence of rosuvastatin on the NAD(P)H oxidase activity in the retina and electroretinographic response of spontaneously hypertensive rats

BACKGROUND AND PURPOSE

Retinal complications may be encountered during the development of hypertension as a response to oxidative stress. Statins may reduce the risk of developing hypertension and ocular diseases. We evaluate the effects of rosuvastatin (ROSU) on retinal functionality and oxidative stress levels in normotensive and spontaneously hypertensive rats (SHR).

EXPERIMENTAL APPROACH

Wistar Kyoto (WKY) and SHR were treated for 3 weeks with rosuvastatin (10 mg kg(-1) day(-1)). Electroretinograms (ERG) were recorded before and after rosuvastatin treatment. Reactive oxygen species (ROS) were determined in the retina with dihydroethidium staining and NAD(P)H oxidase activity was evaluated.

KEY RESULTS

Retinal ganglion cell ROS and retinal NAD(P)H oxidase activity were higher in SHR than in WKY rats, respectively (17.1+/-1.1 vs 10.2+/-1.2 AU, P<0.01; 38095+/-8900 vs 14081+/-5820 RLU mg(-1); P<0.05). The ERG b-wave amplitude in SHR was significantly lower than that in WKY rats. Rosuvastatin reduced SBP in SHR but did not change plasma lipid levels. Rosuvastatin treatment in SHR significantly decreased ROS levels (11.2+/-1.3, P<0.01), NAD(P)H activity in retinal ganglion cells (9889+/-4290; P<0.05), and increased retinal plasmalogen content in SHR, but did not modify the ERG response.

CONCLUSIONS AND IMPLICATIONS

Rosuvastatin, beyond lowering cholesterol levels, was able to lower ROS in the retina induced by hypertension, but without improving retinal function in SHR. These findings point to a complex relationship between ROS in the pathogenesis of retinal disease and hypertension.

The Effect of intravitreal N-methyl-DL-aspartic acid on the electroretinogram in Royal College of surgeons rats

PURPOSE

To investigate how the third-order neuronal response contributes to shaping the electroretinogram (ERG) in the Royal College of Surgeons (RCS) rat.

METHODS

Full-field ERGs were recorded from dystrophic RCS rats (n = 30) at 4, 6, 8, 10, 12, or 14 weeks of age in response to different stimulus intensities (maximum intensity, 0.84 log cd-s/m(2)). N-methyl-DL: -aspartic acid (NMDA, 5 mM) was injected into the vitreous cavity of the right eyes to eliminate the third-order neuronal response. The left eyes received the vehicle and served as controls. The third-order neuronal response was isolated by digitally subtracting waveforms of the NMDA-injected eyes from those of the control eyes.

RESULTS

The ERG a- and b-waves deteriorated with the age of the rat. The third-order neuronal response was preserved to a greater degree than the b-wave despite progression of photoreceptor degeneration. Intravitreal injection of NMDA attenuated the a-wave and enhanced the b-wave across the stimulus range from low to middle intensities. This tendency became more pronounced with advancing rat age. In aged dystrophic RCS rats this phenomenon was seen even at maximum intensity. The difference between NMDA-injected and vehicle-injected eyes was larger for the threshold than for the maximum amplitude at each examined time point (P < 0.001). Intravitreal injection of NMDA decreased implicit times of the a- and b-waves after the rats reached 8 weeks of age (P < 0.005 for the a-wave).

CONCLUSION

With advancing photoreceptor degeneration, the third-order neuronal response made a greater contribution to shaping the a- and b-waves in dystrophic RCS rats.

Preclinical safety evaluation of intravitreal injection of full-length humanized vascular endothelial growth factor antibody in rabbit eyes

PURPOSE

To evaluate the preclinical safety of intravitreal bevacizumab, which is a full-length humanized monoclonal antibody against the vascular endothelial growth factor (VEGF), in rabbit eyes over a short-term period.

METHODS

Twenty-four rabbits were divided into two groups, each with two subgroups. The first group (groups 1 and 2) received 1.25 mg (0.05 mL) intravitreal bevacizumab, and the second group (groups 3 and 4) received 3.00 mg (0.12 mL) intravitreal bevacizumab. The right eyes were designated as the study eyes, and the left eyes served as a control and received the same volume of saline intravitreally. Groups 1 and 3 were labeled as early groups and scheduled to be terminated at 14 days. Groups 2 and 4, labeled as late groups, were scheduled to be terminated at 28 days. Besides electroretinography (ERG) and visually evoked potentials (VEP), central corneal thickness, intraocular pressure, fundus photography, and anterior segment imaging were performed at baseline and scheduled time points. Enucleated eyes were preserved for light and electron microscopic investigation.

RESULTS

No anterior segment inflammation was observed, except in one eye in group 1 which showed a uveitic reaction. No evidence of retinal toxicity was seen with intravitreal bevacizumab at doses of 1.25 and 3.00 mg, by either ERG or light microscopy. Electron microscopic assessment revealed mitochondrial damage in the inner segments of photoreceptors. Immunohistochemical staining with bax and caspase-3 and -9 showed intensive apoptotic protein expression in all study sections and minimal expression in the control eyes.

CONCLUSIONS

Although electrophysiologic investigation and light microscopy showed normal retinal function and structure, mitochondrial disruption in the inner segments of photoreceptors was detected by electron microscopy, and apoptotic expression was detected after the injection of intravitreal bevacizumab.

Acute effects of cigarette smoking on multifocal electroretinogram

BACKGROUND

Cigarette smoking was shown to have stimulant effects on pattern visual-evoked potentials. The aim of this study was to investigate the acute effects of cigarette smoking on multifocal electroretinogram (mfERG).

METHODS

This prospective case-control study was held in a tertiary referral centre in Turkish Armed Forces. mfERGs were investigated in a group of habitual smokers (30 right eyes of 30 subjects) in separate real smoking and sham smoking sessions. mfERG responses of the subjects were recorded after overnight abstinence. The responses were averaged over five retinal regions, the central hexagon (CH; central 6 degrees) and four concentric rings (ring 1 [R1; 7-12 degrees], ring 2 [R2; 13-18 degrees], ring 3 [R3; 19-24 degrees], ring 4 [R4; 25-30 degrees]). On each session mfERGs were recorded before (BS) and after smoking (AS) conditions.

RESULTS

Regarding P1 amplitudes (first positive deflection of the mfERG) in the real smoking sessions, the differences were significant in the CH (BS: 66.2 +/- 16.3 microV, AS: 73.3 +/- 19.6 microV, P < 0.001), in R1 (BS: 44.3 +/- 13.0, AS: 48.3 +/- 16.0, P = 0.004) and in R2 (BS: 30.1 +/- 8.3, AS: 33.7 +/- 9.7, P = 0.002). Similar results were found for N1 amplitudes and P1 and N1 (first negative deflection of the mfERG) latencies in the CH, R1 and R2. The differences in outer retinal areas (R3, R4) in the real smoking sessions and in all rings in the sham smoking sessions were not significant.

CONCLUSION

Cigarette smoking may stimulate the central retinal areas in the acute phase. This effect may be related with the stimulant effect of nicotine on neurotransmission, deleterious effects on retinal and/or choroidal circulation, carbon monoxide toxicity and nicotine withdrawal.

Is it possible to predict the long-term response to venlafaxine with the use of biological markers and psychophysiological methods?

INTRODUCTION

The present study investigated whether it is possible to predict the medium term response to venlafaxine using biological markers and psychophysiological methods.

MATERIAL

Fourteen (14) patients aged 21-60 years suffering from Major Depression according to DSM-IV were included in the study.

METHODS

The SCAN v 2.0 and the IPDE were used to assist clinical diagnosis. Patients were investigated with electrooculogram (EOG), Pattern-Reversal Visual Evoked Potentials (PR-VEPs), Dexamethasone Suppression Test (DST), D-fenfluramine Challenge Test, and brain Single Photon Emission Tomography (SPECT). Venlafaxine 150-225 mg per os daily was administered. The follow-up period was 2 years.

STATISTICAL ANALYSIS

Chi-square test and ANOVA were used for the analysis of data.

RESULTS

There was a lower left globus pallidus regional cerebral blood flow in patients with better response. On the contrary, chronic patients were closer to normality.

DISCUSSION

The results of the current study provide preliminary evidence concerning our ability to predict response to venlafaxine and to understand its way of action.

Evaluation of Intravitreal Kenalog Toxicity in Humans

OBJECTIVE

To evaluate possible functional toxicity of intravitreal Kenalog (commercial triamcinolone acetonide) in patients' retinas.

DESIGN

Observational case series.

PARTICIPANTS

Thirty-two phakic eyes of 16 patients who had nonproliferative diabetic retinopathy and bilateral macular edema refractory to laser therapy, which had no other eye disorder and no previous ophthalmic operation.

INTERVENTION

Kenalog (4 mg/0.1 ml) was injected intravitreally to one eye, whereas the second eye served as the control. The experimental eye was chosen as the eye with worse visual acuity (VA).

MAIN OUTCOME MEASURES

Deterioration of electroretinogram parameters of the study eye measured at 3 months of follow-up when compared with the electroretinogram responses of the fellow, control eye and when compared with electroretinogram responses obtained before injection. Visual acuity, intraocular pressure (IOP), and eventual complications were assessed. No improvement or deterioration of VA or any increase in IOP was regarded as a secondary outcome.

RESULTS

Average maximal response amplitude ratios of the dark-adapted b-wave (treated/control eyes) of the electroretinogram were 0.93 before (P = 0.221) and 0.94 (P = 0.387) 3 months after Kenalog injection. Average ratios of the light-adapted b-wave amplitude (treated/control eyes) of the electroretinogram were 1.04 (P = 0.702) before and 0.86 (P = 0.138) 3 months after Kenalog injection. No significant differences (P>0.05) were found between the electroretinogram parameters obtained from all eyes before and 3 months after Kenalog injection. Average VAs in the treated eyes were 1.08, 0.8, and 1.0 logarithm of the minimum angle of resolution units before and 2 and 4 months after injection, respectively. Temporary elevation of IOP was found in 4 treated eyes of 4 patients (25%).

CONCLUSIONS

No electroretinographic evidence of a retinotoxic effect of intravitreal Kenalog was found in our patients.

The effects of the phosphodiesterase type V inhibitor sildenafil on human and bovine retinal function in vitro

BACKGROUND

After the ingestion of sildenafil (Viagra), visual adverse events have been reported, possibly caused by an inhibition of the phototransduction cascade by sildenafil via phosphodiesterase (PDE 6). Therefore, we investigated the effects of sildenafil on photoreceptors and postsynaptic neurons of human and bovine retinas using the isolated superfused vertebrate retina technique.

METHODS

Human and bovine retina preparations were perfused with an oxygen preequilibrated standard solution. The electroretinogram (ERG) was recorded using Ag/AgCl electrodes. After recording stable ERG amplitudes, sildenafil was added to the solution for 45 min. Thereupon, the preparations were reperfused with standard solution for 240 min.

RESULTS

Following the application of sildenafil (3 microMol/l), the b-wave amplitude of bovine and human preparations was reduced continuously and disappeared completely. After reperfusion with the standard solution for 4 h, the b-wave amplitude did not recover completely. Using the same sildenafil concentration (3 microMol/l), the a-wave amplitude of the human retina was not totally abolished, but reduced to 21% of the initial amplitude and remained reduced at washout. For all retinal preparations, the implicit time of the ERG amplitudes remained significantly extended at the end of the washout.

CONCLUSIONS

Strong similarities were detected in the drug-induced changes of the ERG when comparing human and bovine retinas. The results suggest that sildenafil impairs retinal function at not only the level of the photoreceptors, but it also affects the neuronal network of the inner retina at concentrations of approximately 30-fold higher than at therapeutic plasma concentrations.

Differential sensitivity of cones to iron-mediated oxidative damage

PURPOSE

In this study, the hypothesis that increased intraocular levels of iron cause oxidative damage to the retina was tested.

METHODS

Adult C57BL/6 mice were given an intravitreous injection of saline or 0.10, 0.25, or 0.50 mM FeSO(4). Scotopic electroretinograms (ERGs) were performed 3, 7, and 14 days after injection, and photopic ERGs were performed on day 14. Hydroethidine was used to identify superoxide radicals and lipid peroxidation was visualized by staining for hydroxynonenal (HNE). Retinal cell death was evaluated by TUNEL and measurement of inner nuclear layer (INL) and outer nuclear layer (ONL) thickness. Levels of rhodopsin and cone-opsin mRNA were measured by quantitative real time RT-PCR. Cone density was assessed by peanut agglutinin staining and confocal microscopy.

RESULTS

Compared with retinas in saline-injected eyes, retinas from eyes injected with FeSO(4) showed greater fluorescence after intravenous injection of hydroethidine due to superoxide radicals in photoreceptors, greater photoreceptor staining for HNE, a marker of lipid peroxidation, and increased expression of Heme oxygenase 1, an indicator of oxidative stress. ERG b-wave amplitudes were reduced (photopic > scotopic) in FeSO(4)-injected eyes compared with those in saline-injected eyes. Numerous TUNEL-stained nuclei were seen along the outer border of the ONL, the location of cone cell nuclei, at 1 and 2 days after injection of FeSO(4). In FeSO(4)-injected eyes, the thickness of the ONL, but not the INL, was significantly reduced, and 17 days after injection, there were 3.8- and 2.6-fold reductions in the mRNAs for M-cone and S-cone opsin, respectively, whereas there was no significant difference in rhodopsin mRNA. Confocal microscopy of peanut agglutinin-stained sections showed dose-dependent FeSO(4)-induced cone drop out.

CONCLUSIONS

Increased intraocular levels of FeSO(4) cause oxidative damage to photoreceptors with greater damage to cones than rods. This finding suggests that the oxidative defense system of cones differs from that of rods and other retinal cells, and that cones are more susceptible to damage from the type of oxidative stress imposed by iron.